Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 MEASUREMENT OF 222Rn BY ABSORPTION IN POLYCARBONATES – RESEARCH AND PRACTICE D. Pressyanov, I. Dimitrova, S. Georgiev, K. Mitev Faculty of Physics, St. Kliment Ohridski University of Sofia, Bulgaria Abstract In the last few years, we have gathered experience in measurement of 222Rn in air, water and soil-gas by absorption in polycarbonates. The method employs the remarkable absorption ability to noble gases of some polycarbonates, like Makrolon® (the basic constructive material of CDs/DVDs). This report summarizes the key results of research and practical applications of this method. Calibration procedures, including a posteriori calibration, are described. Comparison between retrospective measurements (by CDs) and estimates based on conventional prospective 222Rn measurements in dwellings are shown. The method is also used for measurement of 222Rn in water and soil-gas. Comparisons with conventional methods for 222Rn measurement in air, water and soil-gas are made and a good agreement is obtained. The sensitivity of the method covers the whole range of concentrations that are of practical interest. The potential for wide scale practical applications of this method and possible directions for further progress are discussed. Introduction The remarkable absorption ability of some polycarbonates like Makrofol®, Makrolon® or equivalents has been employed for quantitative measurements of 222Rn first in 1999 (Pressyanov et al., 1999). Since then several studies were dedicated to the development of practical methods for measurements of radioactive noble gases – mainly 222Rn (Pressyanov et al. 2000; 2004a; 2007), but also 85Kr and 133Xe (Pressyanov et al. 2004b). As a part of the progress in this field a method for precise retrospective 222Rn measurements by CDs/DVDs has been proposed (Pressyanov et al., 2001; 2003). In the last AARST 2007 symposium the performance of this method in laboratory studies has been summarized (Pressyanov, 2007). Herewith, we present results from progress achieved in measurements under real conditions. In the last year, a number of retrospective measurements in dwellings were made. The procedure of a posteriori calibration was tested and utilized. For six of the studied dwellings data from past 222Rn measurements by conventional methods were available. A comparison between CDresults and estimates based on conventional measurements was made and a very good correlation was observed. Acknowledgement: This work has been supported under contracts VUF-08/2005 of Bulgarian Ministry of Education and Science and 08/2008 of the research fund of St. Kliment Ohridski University of Sofia. 1 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Methods based on polycarbonates have also been successfully used for 222Rn measurements in water (Pressyanov et al., 2007) and soil gas. We present pilot results obtained under real conditions. Again, we observe a good correlation with conventional methods. Based on experimental facts we tend to conclude that polycarbonates can be applied for quantitative 222Rn measurements in the three media of interest – air, water and soil gas. The estimated sensitivity suggests that it covers the whole range of 222Rn concentrations in air, water and soil gas that are of practical interest. Materials and Methods In the last decade, we have used different specimens made of Makrofol or Makrolon for 222 Rn measurements. However, the results presented in this report were obtained mainly by measurements with commercial CDs. For retrospective measurements in real dwellings, we have used CDs voluntary provided by homeowners. By interviewing them, the CDs were dated as accurately as possible. In all cases, we managed to date the CDs with accuracy of 1 year or better. This successful dating was possible because of the relatively small size of the study and the possibility for personal communication with the involved inhabitants. From some dwellings more than one CD was obtained, each of different origin and/or age. The CD-specimens used for measurements in water or soil gas were normally exposed for 1-2 weeks. Further, all CDs were treated in the same manner. First, they were left to degas for at least 2 weeks (this is important when CDs are exposed for relatively short time – e.g. in water or soil gas). After that, a surface layer was removed by chemical pre-etching (CPE) at 300C with aqueous solution of 52% KOH (m/v) and 40% methanol (m/v). In the current study a layer with thickness of 80µm was removed (which is just enough to ensure that no tracks from Rn-progeny deposited on the surface are formed), but in order to expand the upper limit of measureable concentrations a thicker layer could be removed. After that pieces of the CDs were etched electrochemically (ECE) at 3.3 kV effective high voltage (6 kHz frequency) at 250 C for 3 hours. A HV generator produced by Ekotronik Ltd. (Prague, Czech Republic, www.ekotronic.cz) was used. The etching solution was mixture of ethanol with 6N KOH solution with 1:4 volume ratio. After ECE the CDs were scanned by a computer scanner and the tracks were counted by dedicated software. The track density at a certain depth (> 80µm) is proportional to 222Rn concentration integrated over the exposure time. The calibration is made by exposing the CD-specimens to controlled 222Rn concentrations. After exposure the CDs must also be left to degas for at least 2 weeks, before CPE and ECE. The calibration factor (CF) is defined as net track density/integrated 222Rn concentration. One feature of the CD method is the possibility for individual a posteriori calibration of each CD. For this purpose the CD taken for analysis is cut in pieces. One is then exposed to controlled 222Rn concentrations and the others not. Further, after etching and counting α-tracks individual a posteriori CF is determined using the difference between the track densities of the exposed for calibration piece of the CD and that of the original piece of the same CD. 2 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 For measurements in soil gas the calibration factor for air was applied. For measurements in water an independent calibration by exposure to controlled 222Rn concentrations in water was made. Results Calibration In this report we emphasize on a posteriori calibration for measurements in air. Pieces of CDs that have already been exposed in dwellings were put in 50 L calibration chamber, where artificial 222Rn concentration was created by a certified 222Rn source. During exposure reference measurements were made by a calibrated radonometer, AlphaGUARD (Genitron GmbH, Germany). In these experiments the individual CF of each CD was obtained. In addition, the results were used to compare the variance in the properties of different CDs as radon detectors. Results are shown in Fig. 1. As seen, the maximum deviation of an individual CF from the average one is about 20%. 0,025 A posteriori individual CF (cm -2 -3 /kBq h m ) 0,030 0,020 0,015 0,010 0,005 0,000 0 2 4 6 8 10 12 14 CD Nr. Fig. 1. Individual a posteriori calibration factors of “old” CDs. The error bars represent counting statistics uncertainty. The horizontal line is a priori CF for a set of new CDs. For calibration in water we used a water sample with high 222Rn concentration (taken from the mineral spa “Momin prohod” in Bulgaria). The reference measurement was done by gamma spectrometer with HPGe detector (relative efficiency 24.9%, 3 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 resolution (FWHM) 1.9 keV at 1332 keV reference gamma line of 60Co). The pieces for calibration were exposed for 48 h in hermetic vessels. During the exposure regular gamma spectrometry measurements confirmed that there was no leakage of radon. The results obtained for CF at 80µm depth in air and in water are: • CD in air, a priori determined CF (for a large group of unused new CDs): 0.021 ± 0.003 cm-2/kBq h m-3. The uncertainty in this and others CFs is due to counting statistics, variation between different CDs and uncertainty in reference concentrations; • CD in air, a posteriori determined CF (for used CDs exposed in dwellings - Fig. 1): 0.0206 ± 0.0027 cm-2/kBq h m-3; • CD in water (for a limited number of CDs): 0.067 ± 0.010 cm-2/kBq h m-3. Notably, the average CF in a posteriori calibration of “old” CDs is the same as the a priori CF obtained for a set of new CDs without previous “radon history”. Real measurements and comparison In real retrospective measurement the following questions were first addressed: a) Whether different CDs taken from the same place give comparable results? b) Will CD results match with independent estimates of retrospective 222Rn concentrations based on past 222Rn measurements by conventional methods? To answer the first question we tried, whenever possible, to obtain more than one CD for analysis. In two dwellings, one with high and another with average 222Rn concentrations we succeeded to obtain four CDs of different origin and age. The results obtained with these CDs are shown in figures 2a and 2b. As can be seen, different CDs give the same retrospective 222Rn concentration within the experimental uncertainty. This conclusion is supported by results from other houses, from which we have obtained two or three different CDs for analysis. 4 50 a Retrospective 222 Rn concentration (Bq m -3 ) Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 45 40 35 30 25 20 15 10 5 0 0 1 2 3 4 5 CD Nr. 400 Retrospective 222 Rn concentration (Bq m -3 ) b 350 300 250 200 150 100 50 0 0 1 2 3 4 5 CD Nr. Fig. 2. Average retrospective 222Rn concentrations measured by different CDs from the same place, a) dwelling with average 222Rn concentration, b) dwelling with elevated 222 Rn concentration. 5 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 In six of the studied houses past 222Rn measurements were available. They were done by conventionally used diffusion chambers with α-track detectors of Kodak-Pathe LR-115 type II. The diffusion chambers used are traceable to a primary international 222Rn standard (Picolo et al., 2000). There is a very good correlation between the results obtained from CDs and those estimated from past measurements by diffusion chambers (Fig. 3). We should note however, that 5 out of the 6 dwellings are from risk areas, without any change and repair for the period of CD storage and therefore great variations in the average annual concentrations are not expected. The remaining one (that at about 20 Bq m-3) is the flat of one of the authors (DP) with well-known radon history. More comparisons will be made in the future, but the pilot results seem very promising. 1000 y = 0,93x + 3,66 2 R = 0,99 900 800 CD (Bq m -3) 700 600 500 400 300 200 100 0 0 200 400 600 800 Past measurements by diffusion chambers (Bq m 1000 -3 ) Fig. 3. Comparison between retrospective 222Rn concentrations measured by CDs and these determined using past measurements with diffusion chambers. Two strategies for measurements in water and soil-gas by polycarbonates are possible, depending on whether a radiometric laboratory capable of measuring beta and gamma radiation is available closely. If it is, the exposed specimens can be used to sample 222Rn and later to be measured for beta or gamma radiation from 222Rn progeny related to radon absorbed in the polycarbonate (Pressyanov et al., 2007). The measurement should start shortly after the specimen is taken (within a few days, but at least 3 h after the end of exposure, so that the 222Rn progeny plate-out decays). The second strategy we consider more promising for the large radon community. In it the tracks formed inside the polycarbonate sample due to absorbed radon and its progeny are developed and counted. After being exposed in water or soil gas, the samples are forwarded to an etching 6 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 laboratory for analysis. This allows measurements in any water supply source (incl. directly in the source – without water sampling) or any terrain where soil gas radon is usable for evaluation of the radon potential. To test this approach for soil-gas, we have exposed four CDs in parallel with conventional diffusion chambers in four points in the region of Sofia, Bulgaria. In order to prevent direct contact with subsoil water the specimens were packed in polyethylene envelopes. The influence of polyethylene packaging had been studied in dedicated laboratory experiments. These studies have demonstrated that 222Rn penetrates by diffusion through the envelopes and that there is no statistically significant difference in the signal from packed and unpacked polycarbonates exposed under the same conditions. The detectors were buried at 60 cm depth and left for two weeks. The results are shown in Fig. 4. Given the small size of this study and the fact that the concentrations are close or slightly above the typical background concentrations of 222Rn in soil-gas, we consider the agreement reasonably good. ) 25 20 15 10 5 222 Rn by exposed CDs (kBq m -3 y = 0,93x 0 0 5 222 10 15 20 Rn by diffusion chambers (kBq m 25 -3 ) Fig. 4. Comparison between 222Rn concentrations in soil gas measured by CDs and diffusion chambers buried at 60 cm depth. For water, we have up to now made a comparison only within the “first strategy” mentioned above (by beta measurements of the sample), following the procedure used in previous laboratory studies (Pressyanov et al., 2007). The results are shown in Table 1. The parallel measurements of water samples were done by gamma-spectrometry with HPGe detector. Again, within the experimental uncertainty we have a good correspondence with parallel conventional measurements, based on water sampling. 7 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Table 1. 222Rn concentration in private water supply sources determined by exposure and measurement of polycarbonate specimens and by laboratory analysis of water samples. Water source Nr. 1 2 3 222 Rn measured by polycarbonates in the source 218 ± 21 Bq L-1 153 ± 17 Bq L-1 126 ± 40 Bq L-1 222 Rn measured by gamma spectrometry of water samples 206 ± 31 Bq L-1 192 ± 29 Bq L-1 130 ± 40 Bq L-1 The evaluation of the sensitivity of the method (applied by α-track etching of exposed CDs) and its usable range are shown in Table 2. As seen, the method appears to cover the whole range of concentrations that are of practical interest in air, water and soil-gas. Table 2. Useful range of concentrations that can be measured by CDs. The lower limit is the minimum detectable concentration. The upper limit corresponds to “saturation” track density of 2000 cm-2. At that level many tracks overlap with others and this hampers track counting. Measurement CD exposed in air for 10y - αtracks at depth 80µm beneath the surface CD exposed in air for 10y - αtracks at depth 200µm beneath the surface CD exposed in water for 1 week α-tracks at 80 µm CD exposed in water for 1 week α-tracks at 200 µm CD exposed in soil-gas for 1 week - α-tracks at 80 µm CD exposed in soil-gas for 1 week - α-tracks at 200 µm Lower limit 3 Bq m-3 Upper limit 3000 Bq m-3 21 Bq m-3 21300 Bq m-3 0.5 Bq L-1 510 Bq L-1 3.3 Bq L-1 3600 Bq L-1 1500 Bq m-3 1.5x106 Bq m-3 10500 Bq m-3 1.05x107 Bq m-3 Conclusions The presented results show the practical performance under real conditions of the method for 222Rn measurements based on absorption in the polycarbonate material of CDs/DVDs. Results from a posteriori calibration and field studies reveal: • The variation in individual CF of different studied CDs is within 20%. If one targets accuracy substantially better than 20% an individual a posteriori calibration can be recommended; 8 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 • • Different CDs from one and the same dwelling give generally similar results. The pilot comparison with independently estimated retrospective 222 Rn concentrations shows a very good correspondence; Quantitative measurements in air, water and soil-gas are possible over practically the whole range of interest. The good performance of the method under real conditions let us strengthen the conclusion that the considered method has a potential for precise measurements and for large-scale practical use. We plan to implement this method in real measuring campaigns and to continue, whenever possible, parallel analysis by conventional methods. 9 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References Picolo J. L., Pressyanov D., Blanchis P., Michielsen N., Grassin D., Voisin V., Turek K. (2000) A radon-222 metrological chain from primary standard to field detectors. Appl. Radiat. & Isot. 52, p. 427. Pressyanov D., Van Deynse A., Buysse J., Poffijn A., Meesen G. (1999) Polycarbonates: a new retrospective radon monitor. Proc. Conf. IRPA’99, Budapest, 23-27 August 1999, p. 716. Pressyanov D., Buysse J., Poffijn A., Meesen G., Van Deynse A. (2000) Polycarbonates: a long-term highly sensitive radon monitor. Nucl. Instrum. Methods Phys. Res. A 447, p. 619. Pressyanov D., Buysse J., Van Deynse A., Poffijn A., Meesen G. (2001) Indoor radon detected by compact discs. Nucl. Instrum. Methods Phys. Res. A 457, p. 665. Pressyanov D., Buysse J., Poffijn A., Meesen G., Van Deynse A. (2003) The compact disk as radon detector-a laboratory study of the method. Health Phys. 84, p. 642. Pressyanov D., Buysse J., Poffijn A., Van Deynse A. , Meesen G. (2004a) Integrated measurements of 222Rn by absorption in Makrofol. Nucl. Instrum. Methods Phys. Res. A 516, p. 203. Pressyanov D. S., Mitev K. K., Stefanov V. H. (2004b) Measurements of 85Kr and 133 Xe by absorption in Makrofol. Nucl. Instrum. Methods Phys. Res. A 527, p. 657. Pressyanov D., Dimitrova I., Georgiev S., Hristova E., Mitev K. (2007) Measurement of radon-222 in water by absorption in Makrofol. Nucl. Instrum Methods. Phys. Res. A 574, p. 202. Pressyanov D. The compact disk as a retrospective radon detector – performance of the method. In: 17th AARST International Radon Symposium, Jacksonville, Florida, 9-12.09.2007. 10 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 ELECTRET ION CHAMBERS (EIC) TO MEASURE RADON EXHALATION RATES FROM BUILDING MATERIALS P. Kotrappa and F. Stieff(1) Rad Elec Inc., 5714-C industry Lane Frederick, MD 21704, USA 301-694-0011 Fax: 301-694-0013 Pkotrappa@aol.com ABSTRACT Electret ion chambers (EIC) have been used for measuring radon in water. This method uses a four liter jar with rubber seals as radon leak tight accumulator. In view of increased interest in measuring radon exhalation rates from building materials, the method is now extended for this purpose. Required equations are derived to compute the exhalation rates for granite samples. As an illustration, a set of granite slabs are characterized by using different accumulation times. Fluxes measured on typical commercially available granites range from 20 to 30 Bq m-2 d-1. These are similar to the published results for granite samples. This is an additional useful application for users of EIC. INTRODUCTION Four liter jars with rubber seals have been used as radon leak tight accumulators. These have been successfully used for measuring radon in water and also for characterizing NIST (National Institute of Standards and Technology) emanation standards. In view of increased interest in measuring radon exhalation rates from building materials, the method is now adapted for this purpose. Required equations are derived to compute the exhalation rates by measuring average radon concentration for a given accumulation period. As an illustration, a set of granite slabs are characterized by using different accumulation times. (1) The authors are developers of, and have a commercial interest in the electret ion chamber featured in this paper. 11 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 MATERIALS AND METHODS An accumulator is simply a container of known volume that can be sealed radon leak tight. The sample and the detectors are enclosed inside the container that serves as an accumulator. Integrating radon detectors such as EIC (electret ion chamber) are used for measuring integrated averages over the accumulation time. See Figure-1. Typical accumulator successfully used for several applications is simply a glass jar with a nominal volume of 4 liters, with a sealable rubber collar (Kotrappa, 1993; Kotrappa, 1994). Radon concentration (Aldenkamp, 1992) at any time T is given by a well known equation (1): C ( Rn) = 0.1814T ( FXA) (1 − e − ) VX 0.1814 Equation (1) When C (Rn) in equation (1) is integrated and divided by the total time, it leads to time averaged radon concentration (Kotrappa, 1994) after accumulation time of T days. This leads to equation (2) ( F × A )   1 − e − 0.1814T 1 −  C ( Rn) Av = V × 0.1814   0.1814T      Equation (2) F is the radon flux in Bq m-2 d-1 A is the area in m2 (F x A) is the exhalation rate in Bq d-1 0.1814 is the decay constant of radon in d-1 C(Rn) is the radon concentration at any accumulation time of T (days) in Bq m-3 C(Rn) Av is the integrated average radon concentration in Bq m-3 T is the accumulation time in days V is the air volume of the accumulator in m3 If we call K as the constant inside the bigger bracket in equation (2), equation (2) can be rewritten as equation (3) and equation (4). 12 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Note K depends only on time of exposure in day units. For those who do not have access to spread sheet, a table can be built to provide K values for different T values. Such table in conjunction with equation (4) is used for hand computation. C ( Rn) Av = (F × A ) V × 0.1814 ×K Equation (3) (F x A)= C ( Rn) Av x V x 0.1814 / K Equation (4) All parameters on right hand side of equation (4) are either measurable or computable. Exhalation rate (FxA) is calculated using equation (4). Further dividing exhalation rate by the area of the sample leads to the flux. Table-1 gives average radon concentration for different accumulation times for exhalation rate (F x A) of 1 Bq d-1. Figure 2 gives a graphical representation of the build up of time averaged concentration for stated accumulation time. PROTOCOLS Accumulator and sample size This protocol describes the method of using sealable jars and EIC radon monitors for measuring radon emanation rates from granite slabs. Sample size of 7.8 cm long, 8.9 cm wide and 3.1 cm thick, or of any other suitable sizes are usable in this method. Sealable glass jars have been used successfully used for measuring radon in water (Kotrappa, 1993) and in using NIST (National Institute of Standards and Technology) sources (Kotrappa, 1994) for calibrating passive detectors. These are of nominal volume of 4 L, with arrangement to seal and suspend an electret ion chamber. Sample is introduced inside the jar, held by small adhesive pivots at the bottom of the jar. Figure 2 gives a sketch of the arrangement. Air Volume of the accumulator One of the parameter needed is the air volume inside the jar. This is obtained by subtracting air volume occupied by the sample and the detector from the volume of the jar. Precisely measured air volume of the jar with one EIC is 3.843 L 9Kotrappa, 1994). The volume of the sample is 0.215 L. Therefore, the net air volume is 3.628L. Time averaged radon concentration 13 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Most suitable EIC is the SST E-PERM® (Kotrappa, 1990). Stick two small adhesive clay (3 mm thick) pieces at the bottom of the sample. This keeps the sample above the bottom of the jar, allowing radon to escape from the bottom part of the sample. Position the sample at the bottom of the jar, suspend a pre-measured EIC, and close the jar and tighten the seal. The measurement has started. At the end of the desired exposure period, remove the EIC, calculate the radon concentration C ( Rn) Av . Set up a similar arrangement without a sample to obtain background radon concentration C ( Rn) Av . The net radon concentration is obtained by subtracting the background concentration from the concentration measured with the sample. Calculation of the exhalation rate and flux Use equation (4) to calculate the exhalation rate from the sample. Divide the exhalation rate by the area of the sample (0.0243 m2) to calculate flux. Error associated with measurement is simply the errors expected in radon measurements. Other errors are negligible. Methods of calculating errors are given in reference (Kotrappa, 1990). ILLUSTRATIVE MEASUREMENTS AND DISCUSSIONS Total of five samples are obtained from commercial granite Supply Company, cut to the required sample size. Results of the measurements done for accumulation time of 2, 3, 5 and 7 days, are given in Table 2. Fluxes measured are in the range of 20 - 30 Bq m-2 d-1. DISCUSSION AND CONCLUSIONS Fluxes measured are in the range of 20 to 30 Bq m-2 d-1. These are similar to the published results for granite samples. Reference [5] gives values from 7 to 29 Bq m-2 d-1 and reference (Hazal-ur-Rehman, 2003) gives an average of 32.4 Bq m-2 d-1. Reproducibility of measurements done on the same sample at different accumulation times, are with in the expected range. Large number of EIC users with E-PERM® system (Kotrappa, 1990) can easily use this method for measuring the required parameters. Being a small accumulator, it is not possible to use larger samples. However the equations given in this note can be used for any other sealable accumulator and other integrating passive or active radon monitors. If sample is likely to leave debris inside the accumulator, it is advisable to enclose the sample in radon transparent bags such as Tyvek bags. Standard EICs do not have significant sensitivity to thoron as such the results are truly for radon. 14 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure -1 Radon Exhalation Measurement 15 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Table-1 Average radon concentration for stated accumulation time for exhalation rate of 1 Bq/day (F X A) -1 Bq d 1 1 1 1 1 1 1 1 1 1 Acc time Days 1 2 3 4 5 6 7 8 9 10 Vol 3 m 0.00363 0.00363 0.00363 0.00363 0.00363 0.00363 0.00363 0.00363 0.00363 0.00363 K 0.08545563 0.16131633 0.22878692 0.28891133 0.34259494 0.39062373 0.43368073 0.4723601 0.50717923 0.53858921 Rn Av. -3 Bq m 129.8 245.1 347.6 439.0 520.5 593.5 658.9 717.7 770.6 818.3 Rn Av. Bq/m3 for Exhalation of 1 Bq/day Rn conc. Bq/m3 1000.0 800.0 600.0 400.0 200.0 0.0 0 5 10 15 Accumulation time in days Figure 2 Build up of time averaged radon concentration for stated accumulation time 16 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Table-2 Results of measurements Acc Time days 3 3 3 5.88 5.88 5.88 Sample # #1 #2 #3 #1 #2 #3 Rn Conc. -1 pCi L 7.61 6.58 5.23 13.06 12.97 9.86 FxA -1 pCi d FxA -1 Bq d F -2 -1 Bq m d F -1 -1 Bqd Kg 21.89 18.93 15.04 22.32 22.16 16.85 0.81 0.70 0.56 0.83 0.82 0.62 33.33 28.82 22.91 33.98 33.75 25.65 1.47 1.27 1.01 1.50 1.49 1.13 17 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 REFERENCES: 1. P.Kotrappa, J.C.Dempsey, R.W.Ramsey, and L.R.Stieff “A practical E-PERM™ (Electret passive environmental system for indoor Rn-222 measurement” Health Physics 58:461-467 (1990) 2. F.J.Aldenkamp, R.J. de Meijer, L.W.Put and P.Stoop “An assessment of in situ radon exhalation measurements and the relations between free and bound exhalation rates” Radiation Protection Dosimetry 45:449453 (1992) 3. P.Kotrappa and W.A Jester “Electret ion chamber radon monitors measure dissolved 222Rn in water” Health Physics 64:397-405 (1993) 4. P.Kotrappa and L.R.Stieff “Application of NIST Rn-222 emanation standards for calibrating Rn-222 monitors” Radiation Protection Dosimetry 55:211-218 (1994) 5. N.W.El-Dine,A.Shershaby, F.Ahmed, and A.S Abdel-Haleem “ Measurement of radioactivity and radon exhalation rate in different kinds of marbles and granites” Appl Radiat. Isot. 55:853-860 (2001) 6. Hazal-ur-Rehman, Al-Jarallah, Musazay, and Abu-Jarad “Application of the can technique and radon gas analyzer for radon exhalation measurements” Appl Radiat Isot. 59:353-358 (2003) 18 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 NATURAL RADIOACTIVITY IN BUILDING MATERIALS - CZECH EXPERIENCE AND EUROPEAN LEGISLATION Jiří Hůlka, Jaroslav Vlček, Jiří Thomas National Radiation Protection Institute, Bartoškova 28, 140 00 Praha Abstract An overview is presented of regulation and control of the natural radioactivity in building material in the Czech Republic (Atomic act 18/1997) and evolution of attitudes in the past 20 years. The sense is explained of regulation based on activity index and Ra-226 concentration, investigation levels and limit values for different materials and radiation protection optimisation process. The results of measurements are summarised. Czech experiences with several thousand houses contaminated by Ra-226 in the past (highly emanated aeratedconcrete houses up 1kBq/kg, slag concrete houses up 3kBq/kg and houses in Joachimstahl up 1MBq/kg ) are summarised. The EU recommendation “Radiological Protection Principles concerning the Natural Radioactivity of Building Materials” is discussed, too. 1. Introduction Historical background: The Czech Republic belongs to countries with highest indoor radon concentration in the world (mean radon value 140 Bq/m3). The primary cause is the high radon concentration in the soil. However, during the seventies and eighties there were found also three groups of houses with significantly elevated radium concentration in the building materials: 1) houses in the small town Jáchymov (Joachimstal) contaminated by residues from uranium paints factory and radium factory, 2) houses from highly emanated autoclaved aerated concrete produced from flying ash, 3) family houses from slag concrete. Some of the important details are summarised. Houses in Jachymov (Joachimstal) Jachymov (Joachimstal), the mining town known from Middle Age thanks to silvermines and coinage (minted coins called Joachims-thalers gave their name to the Thaler and the US dollar), later uranium mining industry and radium producing factory. Due to silver and uranium exploration and factory producing uranium paints and radium before the World War II, the town was locally contaminated in the past. The residues from factories were also used as additive into plaster and mortar in a lot of the Joachimstal´s houses, with 226Ra mass activity up to 1 MBq/kg in extreme cases and indoor gamma dose rates in the range of 10-100 µGy/h. The contamination was not uniform. The case was revealed in the seventies, but that time there was no national legislation concerning indoor radon and indoor radioactivity. The remedy measures carried out in the seventies were drastic - the worst houses were demolished and material taken away and processed in uranium ore mills. Most remaining contaminated houses were mitigated later in the nineties. Remedial measures were based on detailed radon and gamma diagnostic and targeted removal of plasters and mortar, if there was only local contamination. 19 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Family houses from autoclaved aerated concrete In the 1980 there was found the group of family houses built from autoclaved aerated concrete (226Ra mass activity up 1 kBq/kg). Because of high emanation coefficient of this materials (range 15- 30 %), the indoor radon concentration was up to 1000 Bq/m3 in extreme cases. The indoor gamma dose rates were in the range of 0.1-0.3 µGy/h, what is the upper level of normal outside dose rate background in Bohemia. Some 20 000 houses from this material were built in the period 1963-1980. Fortunately, the aerated concrete was used in most of them only as the minor part of building material and hence indoor radon concentrations exceeded the intervention level only in about 1-2 % of these houses. Forced central or local ventilation systems were used for effective mitigation . Different radon barriers (special painting and special wallpapers) were tested but without good results. Family houses from slag concrete The last group was discovered in the 1987. There were found some 3000 factory-made family houses from slag concrete panels (226Ra mass activity in the range 1-10 kBq/kg). The source of the activity was slag from a small power plant burning high radioactive local coal from a mine near Prague. The first Producer Company knew the radioactive danger of the slag from the fifties. After changes in the factory ownership the new management took no care of this danger and more than 2000 family houses were built in the period of 1972-1983 distributed all over the country, most of them in Central Bohemia around Prague. All the peripheral and supporting walls were made from this material, while some partition walls were from bricks. Because of small emanation coefficient of the material (only 1-5%) the indoor radon concentration was only in the range of 200-800 Bq/m3. The indoor gamma dose rates in this group of houses were in the range of 0.5-2 µGy/h; the spatial variation in rooms was characterised by a factor of 2, with highest values in the corner of peripheral walls. The owners of these houses were aware of the cause of their trouble and applied for remedial measures or the possibility to buy up these houses by the government. The government has agreed after great struggle in 1991. Most of the owners have accepted remedial measures; only 4 % owners have sold their house. After some experiments, it was clear that radon removal by forced ventilation was the only effective and reasonable mitigation measure. The ventilation system with heat recovery, controlled by a central computer, was found to be most effective countermeasure and was used in practice. Radon level was reduced to 30% of the former values on average. Other remedial measures (gamma shielding, removal of building material, wall covering by special radon proof materials, etc.) were tested in some cases but were rejected as noneffective. This case revealed the differences in risk perception. As it turned out: - despite the effective doses were the same, the fear of gamma exposure was generally much higher than that of radon exposure (radon exposure was supposed to be easily mitigated), - the human exposure in houses built from man-made “radioactive” building materials (caused by failure of governmental supervision), was perceived worse compare to exposure from natural soil radon, - while at the beginning nearly all owner called for buy-up of their radioactive houses by the government, only about 4 % really decided to sell it. 20 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 2. Development of regulation in the Czech Republic after 1987 It was the mentioned experiences from the past which lead to strict regulation of natural radioactivity. The first regulation was prepared in 1987 for indoor radon a gamma exposure in existing houses and at the same time for natural radioactivity in building materials. 2.1. Interventional levels for existing houses The first recommendation on limitation of both indoor exposures (gamma and radon) in the houses was prepared in 1987. Recommended value for remediation of indoor radon exposure in existing building was set to 400 Bq/m3. Recommended value for indoor gamma dose-rate was set to 2 µGy/h. Having in mind both radon and gamma exposures, the special intervention level that summed both exposures was defined by index S: C Rn D S= + 2 µGy / h 400 Bq / m3 where D is the gamma dose rate (µGy/h) and CRn is the long-term radon concentration (Bq/m3). This sum rule (used only if D > 0.5 µGy/h) and value S = 1 were used for decision making on remedial measures with governmental support. 2.2. Regulation concerning the natural radioactivity of building materials The limit value 226Ra was set to 120 Bq/kg. This value was derived from model room calculation so that the building material will contribute to indoor radon limit value (200 Bq/m3) in new houses not more than 30% (under conservative conditions), having in mind that the underlying soil is the most important source of indoor radon. The other systems of regulation based on limitation of radon exhalation rate or emanation coefficient were discussed but rejected at the end because of sophisticated measurements of exhalation, long term changes and complicated system of limitation (YU 1997, Roelofs 1994, Petropoulos 2001). 3. The European regulation 3.1. Philosophy The radiological protection principles concerning the natural radioactivity of building materials were developed in the second half of the nineties in the Europe. The European Commission (EU Recommendation no.112, 1999, Mustonen 1997, Markkanen 2001)) formulated philosophy, which could be summarised as follows: - Building materials cause exposure by direct gamma radiation and by radon Rn released from the materials into indoor air. Their relative importance varies considerably, but both pathways should be considered when establishing radiological criteria for building materials. - When limits are set for exposure to natural radiation from building materials it must be clearly defined as to what extent the exposure caused by ‘normal’ background is included. The dose criteria used for controls should, therefore, be defined as the excess exposure caused by building materials, i.e. the background dose from natural radionuclides in ‘normal’ Earth’s crust need to be subtracted - The doses to the members of the public should be kept as low as reasonably achievable. However, since small exposures from building materials are ubiquitous, controls should be based on exposure levels which are above typical levels of exposures and their normal 21 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 - - - variations. All building materials contain some natural radioactivity. Small, unavoidable exposures need to be exempted from all possible controls to allow free movement of most building materials within the EU. The concentrations of natural radionuclides in building materials vary significantly between and within the Member States. Restricting the use of certain building materials might have significant economical, environmental or social consequences locally and nationally. Such consequences, together with the national levels of radioactivity in building materials, should be assessed and considered when establishing binding regulations. The amount of radium in building materials should be restricted at least to a level where it is unlikely that it could be a major cause for exceeding the design level for indoor radon introduced in the Commission Recommendation (200 Bq m-3) or - better - some fraction of it in order to allow some contribution from other sources, especially from the underlying soil, without exceeding the design level. Exceptionally high individual doses should be restricted. Within the European Union, gamma doses due to building materials exceeding 1 mSv a-1 are very exceptional and can hardly be disregarded from the radiation protection point of view. When gamma annual doses are limited to levels below 1 mSv, the 226Ra concentrations in the materials are limited, in practice, to levels which are unlikely to cause indoor radon concentrations exceeding the design level of the Commission Recommendation (200 Bq m-3). Controls on the radioactivity of building materials can be based on the following radiological criteria and principles: a) Dose criterion for controls Controls should be based on a dose criterion which is established considering overall national circumstances. Within the European Union, doses exceeding 1 mSv a-1 should be taken into account from the radiation protection point of view. Higher doses should be accepted only in some very exceptional cases were materials are used locally. Controls can be based on a lower dose criterion if it is judged that this is desirable and will not lead to impractical controls. It is therefore recommended that controls should be based on an annual dose in the range 0.3 – 1 mSv. This is the excess gamma dose to that received outdoors. b) Exemption level Building materials should be exempted from all restrictions concerning their radioactivity if the excess gamma radiation originating from them increases the annual effective dose of a member of the public by 0.3 mSv at the most. This is the excess gamma dose to that received outdoors. Separate limitations for radon or thoron exhaling from building materials should be considered where previous evaluations show that building materials may be a significant source of indoor radon or thoron and restrictions put on this source is found to be an efficient and a cost effective way to limit exposures to indoor radon or thoron. Investigation levels can be derived for practical monitoring purposes. Because more than one radionuclide contribute to the dose, it is practical to present investigation levels in the form of an activity concentration index. The activity concentration index should also take into account typical ways and amounts in which the material is used in a building. 22 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The activity concentration index (I) is derived for identifying whether a dose criterion is met: C Ra CTh CK I= + + 300 Bq / kg 200 Bq / kg 3000 Bq / kg where CRa, CTh, CK are the radium, thorium and potassium activity concentrations (Bq/kg) in the building material. The activity concentration index shall not exceed the following values depending on the dose criterion and the way and the amount the material is used in a building: Dose criterion Materials used in bulk amounts, e.g. concrete Superficial and other materials with restricted use: tiles, boards, etc 0.3 mSv (annually) I < 0.5 1 mSv (annually) I<1 I<2 I< 6 The activity concentration index should be used only as a screening tool for identifying materials which might be of concern. Any actual decision on restricting the use of a material should be based on a separate dose assessment. Such assessment should be based on scenarios where the material is used in a typical way for the type of material in question. Scenarios resulting in theoretical, most unlikely maximum doses should be avoided. For the radon pathway, the evaluation of the excess dose caused by building materials is more complicated and the contribution of building materials must be evaluated by using theoretical model and general assumptions on the parameter values. However, it is very difficult to take into account all parameters, e.g. surface-volume ratio, the effect of surface treating done at the building site, and the ventilation rate. The reasonable approach for considering the radon pathway is to limit the amount of 226Ra in the building material so that the indoor radon concentration cannot rise above some pre-set level even under unfavourable conditions. 3.2. Application The dose criterion used for national controls should be chosen in a way that the majority of normal building materials on the market fulfil the requirements. Usually measurements of activity concentrations are needed only in case where there is a specific reason to suspect that the dose criterion for controls might be exceeded. The Member States should require, as a minimum, the measurement of types of materials which are generically suspected. Appropriate dose assessments should be performed if it is discovered that the reference value of the activity concentration index is exceeded. Normally the producer or dealer would be responsible for ensuring and showing that a material put on the market fulfils the radiological requirements set by the Member State. However, other approaches might also be applied according to national circumstances and administrative practices, e.g. the builder or designer of the building could be the responsible party for ensuring that a new building complies with the radiological requirements. The disadvantage of this approach is that appropriate training in radiological modelling should be arranged to all designers and builders. Materials should be exempted from all controls concerning their radioactivity if it is shown that the dose criterion for exemption is not exceeded. This can be done by comparing results of activity concentration measurements with the activity concentration index, or as appropriate, by means of a material-specific dose assessment. An exempted material should 23 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 be allowed to enter the market and to be used for building purposes without any restrictions related to its radioactivity. In the case of export within the EU, it is understood that the value of the activity concentration index or a declaration of exemption should be included in the technical specifications of the material. When industrial by-products are incorporated in building materials and there is reason to suspect that these contain enhanced levels of natural radionuclides, the activity concentrations of these nuclides in the final product should be measured or assessed reliably from the activities of all component materials. Where necessary, also other nuclides than 226Ra, 232Th and 40K shall be considered. The dose criterion should be applied to the final product. Some traditionally used natural building materials contain natural radionuclides at levels such that the annual dose of 1 mSv might be exceeded. Some of such materials may have been used already for decades or centuries. In these cases, the detriments and costs of giving up the use of such materials should be analysed and should include financial and social costs. 4. CONTEMPORARY REGULATION IN THE CZECH REPUBLIC Contemporary Czech legislation concerning indoor natural radioactivity and remedial measures is based on the Atomic Act No.18/1997 and Decree No. 307/2002. The producers and importers of building materials are obliged to ensure systematic measurement of the natural radionuclides in the building materials and to submit results to the State Office for Nuclear Safety. It affords unique opportunity to get nearly complete data set of natural radioactivity in the building material in the Czech market. The central database was prepared at the beginning of 1998 and more than 5000 results of measurements were obtained up to now (Vlcek 2007, SURO 2005). The results of measurements were obtained from 20 laboratories from the Czech Republic. The laboratories are periodically tested and they take part in the comparison organized by National Radiation Protection Institute. The framework of regulation in Czech Republic is based on two-step system: 1 step: screening (exemption) level for activity concentration index (I), based on gamma dose-rate estimation I= C Ra CTh CK + + 300 Bq / kg 200 Bq / kg 3000 Bq / kg 2 step: limit levels for 226Ra mass activity. The sense - limitations of radon exhaling from building materials under unfavourable conditions Table 1: screening levels (activity concentration index I) Index I Type of building material 0,5 Material used in bulk amount (e.g. brick, concrete, gypsum) 1 Raw material (e.g. sand) 2 Material used in „small“ amount (e.g. tiles) Table 2: limit levels for 226Ra type of building material Limit value Ra (Bq/kg) Buildings with 226 Limit value Ra (Bq/kg) Other construction 226 24 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Material used in bulk amount (e.g. brick, concrete, gypsum) Other material used in small amount (e.g. tile..) and raw material (sand, building stone, gravel aggregate, bottom ash..) stay of person 150 without stay of person 500 300 1000 The activity concentration index is used as a screening tool for identifying materials which might be of concern. The index mean values in Czech Republic market are (Vlček 2007): natural building stones 0.4, clay bricks 0.6, concrete 0.3, aerated concrete 0.53, slag concrete 0.69, coal ash and slag 0.63, gypsum 0.17. It was shown that for concrete, aerated and lightweight concrete, clay bricks, natural building stones exposure above 0,3 mSv is possible almost anywhere bulk amounts of material are used. Exposure above 1 mSv is possible if bulk amounts of the concrete contain slag, fly ash or natural sand or rock rich in natural radionuclides If activity concentration index I is above exemption level, the producer of building material is obliged to perform the cost-benefit analysis (the process of the optimisation of radiation protection). The producers need not carry out intervention if the costs are higher than the benefits of such remedial measures. In other word, the costs related to reduction of radionuclide concentration in building materials (namely by a change of raw materials or their origin, by sorting raw materials, by a change of technology and other suitable intervention), would be demonstrably higher than the risks in health detriment. The benefits of remedial measures is calculated in such a way that a reduction of collective effective dose for a group of individuals being assessed is multiplied by a factor of 0.5 million CZK/Sv for the exposure to natural radionuclides. The aim is to reduce the public doses to level as low as reasonably achievable. 5. Conclusion There are several challenges in the possible harmonisation of controls on the radioactivity of building materials. It would be desirable that controls would be sufficiently uniform to allow movement of building materials within the EU. The levels of natural radionuclides in building materials vary significantly between countries and areas and the recommendations for harmonising controls should provide certain flexibility for taking into account specific national circumstances. The Czech experience after 20 years of application of regulation shows that it is possible to regulate all important exposures caused by natural radionuclides in building materials. It is obvious that high indoor gamma dose-rate can be hard to reduce post facto in the existing house. The aim of regulation is to restrict exposure in new buildings especially the highest individual doses. One must also have in mind decreasing ventilation rate (even below 0,1 h-1) in new energy-saving building can lead to problems with indoor air quality. The doses to the members of the public should be kept as low as reasonably achievable, but the dose criterion used for controls is chosen in a way that the majority of normal building materials on the market fulfil the requirements. If aim of regulation would be decrease future collective dose however, the low activity materials should be recommended and public awareness on this issue should be fostered. 25 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 REFERENCES 1. Act No. 18/1997 Coll., On peaceful utilization of nuclear energy and ionizing radiation (Atomic Act) 2. Markkanen M., Challenges in harmonising controls on the radioactivity of building materials within the European Union, The Science of the Total Environment 272, 2001 3. Mustonen R., Pennanen M., Annanmäki M. and Oksanen E. Enhanced Radioactivity of Building Materials. Final report of the contract No 96-ET-003 for the European Commission. Radiation and Nuclear Safety Authority – STUK, Finland, 1997. 4. Petropoulos N.P., Anagnostakis M.J., Simopoulos S.E., Building materials radon exhalation rate: ERRICCA intercomparison exercise results, The Science of the Total Environment 272, 2001.109-118 5. Radiological Protection Principles concerning the Natural Radioactivity of Building Materials, European Commission, Radiation protection No.112, 1999 6. Report SURO, Public Exposure to Natural Radiation in the Czech Republic, National Radiation Protection Institute Prague, 2005 7. Roelofs L. M. M. and Scholten L. C., The Effect of Aging, Humidity and Fly-ash Additive on the Radon Exhalation from Concrete, Health Phys. 67(3):266-271; 1994 8. YU K. N. YOUNG I, E, STOKES K. N., KWAN M.K., and BALENDRAN R. V., Radon Emanation from Concrete Surfaces and the Effect of the Curing Period, Pulverized Fuel Ash (PFA) Substitution and Age, Appl. Radiat, lsot. Vol. 48, No. 7, pp. 1003-1007, 1997 9. Vlček J, Hůlka J., Natural radionuclides in building materials, Bezpečnost jaderné energie, 15 (53), 3/4 2007 p.80-85, ISSN 1210-7085 26 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 AN UPDATE ON THE NEW CANADIAN RADON GUIDELINE AND ITS I MPLEMENTATION Naureen M. Rahman, Renato Falcomer, Jing Chen and Deborah Moir Radiation Protection Bureau, Health Canada, Ottawa, Ontario K1A 1C1, Canada Abstract The first Canadian residential radon guideline of 800 Bq/m3 was set in 1988 and remained unchanged until 2007. Based on new scientific information, Health Canada lowered the radon guideline from 800 to 200 Bq/m3. For the implementation of the guideline, Health Canada has developed a National Radon Strategy in collaboration with other departments, provinces and territories, as well as health professional organizations and private industry. Since the publication of the guideline, significant progress has been made in the implementation of this Strategy. At this meeting, we will give an update on the progress made in the development and implementation of the National Canadian Radon Strategy and discuss its future goals. Introduction/Background Radon is a significant contaminant that affects indoor air quality and is considered to be a health hazard. Radon is recognized as the second leading cause of lung cancer after tobacco smoking. Recent estimates of the proportion of lung cancers attributable to radon range from 6 to 15% (WHO, 2005). The lung cancer burden due to indoor radon exposure is the largest effect of environmental radiation. To effectively reduce radoninduced lung cancer, the World Health Organization (WHO) and many countries have established radon control strategies for dealing with radon reduction in new and existing construction. Current estimates suggest that radon in homes is responsible for approximately 10% of all lung cancer deaths in Canada (Tracy, 2006). New Radon guideline for Canada Health Canada collaborated with the Federal Provincial Territorial Radiation Protection Committee (FPTRPC) to review the health risk from exposure to radon and to revise the Canadian Radon Guideline. This committee supports Canadian federal, provincial and territorial radiation protection agencies by co-ordinating their activities and developing recommendations.The risk assessment was based on new scientific information (Darby, 2004, Krewski,2005 ) and was the subject of a broad Canadian public consultation in 2006. Based on the assessment and feedback from the consultation , the Government of Canada updated its guideline for exposure to radon in indoor air from 800 Bq/m3 to 200 Bq/m3. This updated guideline provides advice that is more broadly applicable and more protective than the 1988 guideline (Health Canada, 2007). 27 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The updated Canadian radon guideline recommends: • Remedial measures should be undertaken in a dwelling whenever the average annual radon concentration exceeds 200 Bq/m3 in the normal occupancy area. • The higher the radon concentration, the sooner remedial measures should be undertaken. • When remedial action is taken, the radon level should be reduced to a value as low as practicable. • The construction of new dwellings should employ techniques that will minimize radon entry and will facilitate post-construction radon removal, should this subsequently prove necessary This Guideline applies to dwellings including residential homes and public buildings such as schools, hospitals, long-term care residences and correctional facilities. Development and Implementation of the National Radon Strategy Following the revision of the Canadian Radon Guideline, Health Canada and the FPTRPC worked collaboratively to develop a strategy for the effective implementation of the revised guideline. The National Radon Strategy led by the Radiation Protection Bureau at Health Canada consists of five basic parts. • • • • • Establishment of a National Radon Laboratory Radon testing projects Development of a radon potential map of Canada Radon research and development Development and implementation of a public education and awareness strategy Establishment of a National Radon Laboratory The National Radon Laboratory was established in 2007 and is situated within the Radiation Protection Bureau in Ottawa and comprises laboratories for assembly, shipping and reading of radon detectors and for the housing of a radon test chamber for calibrations and testing. The Laboratory possesses a variety of radon detectors including E-PeRM, alpha track and continuous radon and radon progeny monitors. The primary function of the Laboratory is to provide testing and analysis support to Health Canada’s radon projects as well as technical advice to other departments, provinces and territories, industry and members of the public.  Radon Certification Program: Increasing public awareness of the risks from radon exposure has created a need for radon testing as well as standards or means by which to ensure the competency of providers of these services to the public. As a result, Health Canada decided to include, as a component of the National Radon Laboratory function, the development of a certification program for service providers offering radon testing in Canada. Health Canada considered two options for the certification program: a government operated program and a program operated by private industry but approved by the federal 28 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 government. Ultimately, based on cost and time for the development of a federally operated program, Canada has decided to pursue the second option of having a private organisation(s) operate the program. In February 2008, the Radiation Protection Bureau began discussions with the National Environmental Health Association (NEHA) and the National Radon Safety Board (NRSB) to expand their current radon proficiency programs to include a Canadian component. These discussions are currently ongoing. Radon Testing Projects  The Federal Government Building Radon Survey: In order to minimize health risks to federal employees due to radon exposure, the Government of Canada decided in 2007 to launch an initiative to measure radon levels in all buildings under its jurisdiction, thereby allowing problems to be identified and addressed through remediation, if necessary. Health Canada is the lead federal department and is coordinating the testing of buildings, with an objective of several thousand buildings to be tested over 4 years.  Residential Cross-Canada Radon Survey: Health Canada intends to perform a survey of residential radon concentrations in a minimum of 15,000 homes randomly selected across Canada beginning in the fall of 2009. The main objectives of the residential radon survey are to: 1. Obtain an estimate of the proportion of the Canadian population living in homes with radon gas levels above the guideline of 200 Bq/m3. 2. Identify previously unknown areas where radon gas exposure constitutes a health problem. 3. Build, over time, a map of indoor radon gas exposure levels. Development of a Radon Potential Map of Canada Health Canada’s radon potential map of Canada is a tool intended for use by various levels of government to identify areas of the country where priority should be given to raise awareness of radon risk and promote testing and remediation. Health Canada does not advocate the use of such a map to determine whether a home should be tested. Health Canada is urging all Canadians to test their homes regardless of location. The map will include data from a number of sources including the radon testing in federal government buildings, the results from the residential cross Canada survey, radon soil permeability and soil gas measurements and aerial and land-based radiation surveys which are currently underway. Radon Research and developments Health Canada’s Radon Strategy also includes a research component, primarily focussed on two areas: radon health effects and the development of new and improved methods for 29 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 detecting and remediating high radon levels in dwellings. The following are some examples of the research activities conducted since the revision of the Canadian Radon Guideline: • • • • Performed a preliminary study on soil-radon gas concentration across southern Ontario, results indicated that radon risk could be high in some areas. (Chen, 2008) Completed a small scale radon/thoron survey in 100 Ottawa homes and another survey of radon, thoron and thoron progeny in 120 Winnipeg homes in order to assess the levels of these radioactive species in indoor air and the need for a strategy for thoron awareness and action similar to radon. (Chen, 2008) Initiated tests of radon emanation rates from a variety of Canadian building materials to assess the potential for contribution to radon levels in homes and public buildings. Performed a pilot study to observe the variations in the equilibrium factor between the concentrations of radon progeny and radon gas. The purpose of this study was to observe the variation in ranges of the radon equilibrium factor “F” in Ottawa dwellings. Development and Implementation of a Public Education and Awareness Strategy Health Canada has developed a social marketing and public outreach strategy. The strategy will focus on homeowners, commercial building owners, the building industry and public health practitioners. The objective of the outreach campaign is to raise awareness of radon, the potential health risks and to encourage testing and action to reduce levels, where necessary. A combination of public service announcements, print materials, web promotions and partnerships with key stakeholders is being used to achieve the goals (Health Canada, 2008). The development of many of these products is being timed to permit roll-out for the fall of 2008 in an effort to coincide with the fall/winter heating season and the optimum time for homeowners to test for radon in their homes. Concluding Remarks Canada’s radon guideline for exposure in indoor air was recently updated from 800 Bq/m3 to 200 Bq/m3. Health Canada, in partnership with our stakeholders, has developed a National Radon Strategy in support of the Guideline. Health Canada is committed to the effective implementation of the Strategy in order to manage the risks posed by radiation exposure in living and working environments. The Strategy incorporates five basic components that should significantly contribute to the reduction of indoor radon exposure levels for Canadians. 30 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References Chen, J., Ly, J., Bergman, L., Wierdsma, J. and Klassen, R. A., 2008, Variation of Soil Radon Concentrations In Southern Ontario, Radiation Protection Dosimetry, Doi:10.1093/Rpd/Ncn192. Chen, J., Tokonami, S., Sorimachi, A., Takahashi, H. and Falcomer, R., 2008, Preliminary Results Of Simultaneous Radon And Thoron Tests In Ottawa Radiation Protection Dosimetry. Darby, S., Hill,D., Auvinen, A., Barros-Dios, J. M., Baysson, F., Bochicchio, H., Deo, H., Falk, R., Forastiere, F., Hakama, M., Heid, I., Kreienbrock, L., Kreuzer, M., Lagarde, F., Mäkeläinen, I., Muirhead, C., Oberaigner, W., Pershagen, G., RuanoRavina, A., Ruosteenoja, E., Schaffrath Rosario, A., Tirmarche, M., TomáBek, L., Whitley, E., Wichmann, H. E. and Doll, R., 2005, Radon in Homes and Risk of Lung Cancer: Collaborative Analysis of Individual Data from 13 European Case-Control Studies, British Medical Journal, Vol. 330, pp. 223-227. . Health Canada 2007, Government of Canada Radon Guideline Available at http://www.hc-sc.gc.ca/ewh-semt/radiation/radon/guidelines_lignes_directrice-eng.php. Health Canada, 2008 Modified, Environmental and Workplace Health web page, Available at: http://www.healthcanada.gc.ca/radon Krewski D., Lubin J. H., Zielinski J. M., Alavanja M., Catalan,V.S., Field, R.W., Klotz, J. B., Le´tourneau, E.G.,Lynch, C. F., Lyon, J. I., Sandler, D. P., Schoenberg, J.B., Steck, D. J., Stolwijk, J.A., Weinberg C. and Wilcox, H.B., 2005, Residential Radon and Risk of Lung Cancer: A Combined Analysis of 7 North American Case-Control Studies, Epidemiology 16: 137–145. Tracy, B.L, Krewski, D., Chen, J., Zielinski, J., Brand, K., Meyerhof, D., 2006, Assessment and Management of Residential Radon Health Risks: A Report from the Health Canada Radon Workshop, Journal of Toxicology and Environmental Health Part A, Vol. 69, Nos 7-8, pp. 735-758. WHO 2005, Radon Fact Sheet, Media Centre, Programmes And Projects, Available at http://www.who.int/mediacentre/factsheets/fs291/en/index.html 31 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 EXPERIMENTAL STUDY ON PASSIVE SUB-SLAB DEPRESSURISATION SYSTEM Bernard Collignan1* Malya Abdelouhab1 Francis Allard2 1 2 CSTB - Centre Scientifique et Technique du Bâtiment. Département Energie Santé Environnement. 84, avenue Jean Jaurès BP 02 77 447 Marne La Vallée Cedex 2 - France LEPTIAB - Université de La Rochelle. Laboratoire d’Étude des Phénomènes de Transfert et de l’Instantanéité : Agro-industrie et Bâtiment Avenue Michel CREPEAU. 17042 La Rochelle. Cedex 1 - France Topic: Radon, prevention in new buildings, experimental study, natural soil depressurisation System. Abstract It appears that Soil Depressurisation System (S.D.S.) is one of the most efficient solutions to prevent buildings against radon from ground. Currently theses systems are mainly used with a fan which enables to extract mechanically air from basement to under pressurise it. On the principle, other way to obtain a depressurisation is to use natural thermal forces and wind effect. But the ability and the efficiency of this technique is not properly characterised. In an experimental house, a one year follow up of a passive sub-slab depressurisation system has been carried out in order to analyse the natural running of such a system during time. A specific sump has been installed under basement and different parameters have been measured: wind (velocity and direction), external temperature, extract flow from basement, basement depressurisation, internal temperature and ground air temperature. An alternative have also been tested using a more efficient static extractor than basic one, to extract flow naturally from basement. This paper presents first experimental results an analysis of the one year follow up. It appears that such a passive system could run efficiently a significant part of the year if it is properly dimensioned, and mainly during cold conditions, where it is more necessary to have a good protection against radon. * Corresponding author bernard.collignan@cstb.fr 32 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Introduction Radon is a radioactive gas which comes from the degradation of uranium and radium present in variable quantity in the earth crust and whose solid descendants can settle in the lung. Radon is one of the pathogenic agents of the lung cancer. It tends to accumulate in closed spaces, which justifies vigilance in the buildings. In France, few thousands of annual cases of lung cancer are thus attributed by the epidemiologists to radon exposure into buildings. In these conditions, it is necessary to maintain As Low As Reasonable Achievable the radon concentration into indoor environment. The presence of radon into buildings results from many parameters. The main source of radon in building is generally the ground under basement. Its entry into building is mainly due to convective forces due to pressure difference between the soil beneath the ground floor and the inhabited volume. This pressure difference is due to temperature difference between indoors and outdoors. It induces an air flow from ground porosity to the indoor environment via basement air leakages. So that, the intensity of radon source in a building is generally growing up with temperature difference. The principles developed on different techniques consist in diluting the radon concentration in inhabited volume and to prevent radon incoming from the ground. In practice, from the various possible configurations for existing buildings, many alternatives techniques calling upon these two combined principles are used. The taking into account of these techniques for the new buildings, as of the design of the building, makes it possible to ensure good system effectiveness with a marginal cost. The principle of reduction of the entry of radon in the buildings the most effective is the Soil Depressurisation System (S.D.S.) under the building in order to prevent the convective air flow from the ground and loaded with radon towards the building (EPA, 1993; Scivyer, 1993 2001 and 2007; Collignan & al, 2003; Allison & al, 2008). However, this system is generally installed with an extract fan which enables to maintain a constant depressurisation beneath building. It is sometimes mentioned that this depressurisation could be obtained naturally using natural thermal forces and wind effect. But the ability and the efficiency of this technique is not properly characterised and needs to be tested. In this context, the aim of this study is to test in an experimental dwelling the ability of a natural sub-slab depressurisation system to maintain depressurisation along the year. Description of the experimental dwelling An experimental dwelling called MARIA (Riberon, 2002) has recently been built in order to study indoor air quality in housing sector. It is a dwelling with one living room and four bedrooms on two levels. Photo 1: Experimental dwelling MARIA During its construction, basement has been prepared to be depressurised. For that purpose, a 40 centimetre thick gravel layer with a membrane under a concrete ground floor have been installed. Two sumps, one centred and one decentred have been put on gravel layer to have the ability to test these two configurations (figure 1). Surface of soil is around 80 m². 33 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 1: Soil Depressurisation System (S.D.S.) installed on basement of MARIA dwelling. Ten different holes have been managed through concrete floor to measure pressure difference between gravel layer and the inhabited volume. In previous works undertaken, basement permeability characterisation has been realised with a variable velocity fan enabling to exhaust air from the gravel layer via the sump. Pressure differences induced were measured with manometer at the ten different holes. It is worth noting that pressure field into basement generated by the exhaust flow is homogeneous on the gravel layer (figure 2). Basement exhaust flow (m3/h) 100 10 10 point 1 point 3 point 2 point 4 point 5 point 7 point 9 point 6 point 8 point 10 Basement depressurisation (Pa) 100 Figure 2: Basement permeability characterisation Other study previously undertaken have shown the ability of a mechanical ventilation exhaust system commonly used in France to generate air renewal into dwelling, to be connected to the S.D.S. to generate sufficient depressurisation in the basement and to ensure simultaneously adequate exhaust flow in the dwelling (Collignan & al, 2004). For the present study it has been needed to create a specific sump with a larger diameter of 200 mm for the extraction in order to be able to used natural forces for the extraction reducing linear pressure losses along duct (photo 2). Photo 2: Installing new sump for natural depressurisation 34 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Protocol A one year follow up of the passive sub-slab depressurisation system has been carried out in order to analyse the natural running of such a system during time. Different parameters have been measured each minute along the year: wind (velocity and direction), external temperature, extract flow from basement measuring duct air velocity, basement depressurisation, internal temperature and duct air temperature (figure 3). - W ind ( ve locity a nd d ire ction) - E xte rna l temp er atur e - Duct a ir velo city - Duct te mpe ra ture - Inter nal te mpe ra ture B ase ment de pr essur isatio n: !P Figure 3: Parameters measured during follow up An alternative have also been tested using a more efficient static extractor than basic one, to extract flow naturally from basement. Specific shape of this static extractor enables to enhance depressurisation at the exhaust of the duct, ameliorating extract flow from basement in wind presence. Basic extractor had been installed from July 2007 until February 2008 and static extractor from March 2008 until June 2008. Photo 3: Basic extractor and static extractor Results Results obtained consist on an important data base of different parameters measured each minute along the year. At first, data have been averaged with a time step of 15 minutes. Figure 4 shows an example of results obtained referring to the evolution of basement extract flow and basement depressurisation along time during a month. 35 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Pa 3 m /h 60 basement extract flow basement depressurisation 50 30 25 40 20 30 15 20 10 10 5 0 05/03/08 0 10/03/08 15/03/08 20/03/08 25/03/08 30/03/08 Figure 4: Evolution of basement extract flow and basement depressurisation during time Figure 5 shows characterisation of basement permeability obtained naturally with natural S.D.S. and compared with characterisation obtained mechanically. m 3/h 1000 Natural extraction 100 Mechanical extraction 10 1 0 1 10 Pa 100 Figure 5: Comparison of basement depressurisation function of basement extract flow for natural and mechanical extraction Based on these results, running of natural S.D.S. has been studied along the year. Figure 6 shows percentage of running time of the system along year above three thresholds of extract flow from basement: 13.5 m3/h, 19 m3/h and 23 m3/h which correspond respectively to around 1 Pa, 2 Pa and 3 Pa of basement depressurisation. Figure 7 shows Monthly averaged temperature difference between air duct and external air and monthly averaged wind force along year. Installing static extractor % Qextr. > 13,5 m3/h (1 Pa) 100 90 Qextr. > 19 m3/h (2 Pa) 80 70 Qextr. > 23 m3/h (3 Pa) 60 50 40 30 20 10 0 juil.-07 août-07 sept.-07 oct.-07 nov.-07 déc.-07 janv.-08 févr.-08 mars-08 avr.-08 mai-08 juin-08 Figure 6: Percentage of running time of the system along year above three thresholds. 36 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 14 °C m/s 4,0 12 3,5 10 3,0 2,5 8 2,0 6 4 Monthly averaged (Tduct-Text) 1,5 Monthly averaged wind force 1,0 2 0,5 0 0,0 juil.-07 août-07 sept.-07 oct.-07 nov.-07 déc.-07 janv.-08 févr.-08 mars-08 avr.-08 mai-08 juin-08 Figure 7: Monthly averaged temperature difference between air duct and external air and monthly averaged wind force along year. In order to analyse the impact of static extractor, figure 8 shows a comparison of extract flow from basement function of wind velocity for natural S.D.S. with static extractor and with basic extractor. To isolate the impact of wind, these running points are considered when temperature difference between air duct and external air is below 4°C. 3 50 m /h with static extractor with basic extractor 45 y = 0,96x 1,99 power (with static extractor) 40 power (with basic extractor) 35 30 25 20 15 y = 0,43x 10 2,08 5 0 0 1 2 3 4 5 6 7 m/s 8 Figure 8: Comparison of extract flow from basement function of wind velocity for system with static extractor and with basic extractor (temperature difference < 4°C). Analysis At first, a high variability of running is observed along the year and even during a day. This is due to the fact that natural forces which make possible the extraction of air from basement are highly variables: temperature difference between air duct and external air and wind force. However, it is seen on figure 6 that percentage of running along year could be significant and mainly in winter season. This is an interesting result because the main cause of radon entrance in a dwelling without prevention against radon is the convective flux due to pressure difference between the dwelling and ground below, which is due to stack effect and this effect is stronger in winter season. In summer season, natural S.D.S. running is very weak but radon convective source is also weak. It is seen in figure 6 that running is better in March than in February. This could be explained by the installation of the static extractor at the beginning of March. Figure 8 shows the impact of this static extractor on extract flow from basement in comparison to basic extractor. At first, it is noted, that for each extractor, a relative dispersion of experimental points is 37 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 observed. This could be due to the fact that wind measurements are made with meteorological station installed on CSTB site but wind “seen” by extractor at roof level of the dwelling could be different and more fluctuant due to obstacles around the dwelling (trees, other buildings). These obstacles could modify wind velocity at roof level in comparison with wind velocity at meteorological station. However, positive impact of static extractor on extract flow from basement is clearly seen on this figure. It can be noted, that for significant wind forces (above 3 m/s) extract flow with static extractor is twice the value of extract flow with basic extractor. Conclusion A one year follow up of a Natural Soil Depressurisation System has been undertaken in an experimental dwelling on CSTB site. The experimental dwelling has been adapted in order to conduct this experimental study. This paper shows a first analysis of results obtained. It appears that natural running of S.D.S. is highly variable along the year but percentage of running could be significant and mainly during winter season. This is an interesting result because preventive solution is mainly needed during this period to fight against radon entrance due to convective fluxes between ground and inhabited volume. During this follow up, two different static extractors have been used: a basic one and other with shape optimised to benefit of the impact of wind on extraction flow. It has been seen that with optimised static extractor, flow from basement is around twice the value than flow obtained with basic extractor. In perspective, it is planed to study hybrid solutions for basement depressurisation using a stato mechanical extractor, which means to use natural forces when sufficient and fan assistance when needed in order to have sufficient basement depressurisation along the year. Acknowledgments This study was partly funded by French Nuclear Safety Authority (A.S.N.). 38 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References Allison C.C., Denman A.R., Groves-Kirkby C.J., Phillips P.S., Tornberg R. Radon remediation of a two storey UK dwelling by active sub-slab depressurisation: Effects and health implications of radon concentration distributions. Environment International. Accepted on 12 march 2008. Collignan B., O’Kelly P. Pilch E. Basement depressurisation using dwelling mechanical ventilation system. 4th European Conference on Protection against radon at home and at work. Praha, 28th june – 2nd july 2004 Collignan B., O’Kelly P. Dimensioning of Soil Depressurisation System for Radon Remediation in Existing Building. Proceedings of Healthy Building 2003, Singapore, vol. 1, pp 517, 523. EPA. Radon Reduction Techniques for Existing Detached Houses. Technical Guidance (third edition) for Active Soil Depressurization Systems. EPA/625/R-93/011. October 1993. Riberon J., O’Kelly P. Maria: an Experimental Tool at the Service of Indoor Air Quality in Housing Sector. Proceedings of Indoor Air 2002. pp 191-195 Scivyer C. Surveying dwellings with high indoor radon levels: a BRE guide to radon remedial measures in existing dwellings. London: Construction Research Publications. 085125-582-5; 1993. Scivyer C. Radon protection for new buildings: a practical solution from the UK. Sci; Total Environ 2001;272:91–6. Scivyer C. Radon: guidance on protective measures for new buildings (BR211). Garston: BRE Press. ISBN 978-1-84806-013-5; 2007. 39 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 COMPLEX SYSTEM OF RADON DIAGNOSIS METHODS AND SPECIFIC EXPERIMENTAL AND THEORETICAL PROCEDURES APPLIED IN THE INDOOR BUILDING ENVIRONMENT Aleš Froňka1, Ladislav Moučka1 1 National Radiation Protection Institute, Bartoškova 28, 140 00 Praha 4, Czech Republic ABSTRACT The paper is aimed at different measuring techniques and methods practically used for a classification of buildings in the context of radiation protection requirements. Specific experimental and theoretical diagnostic procedures designed for identification and quantification of indoor radon entry characteristics are proposed and discussed in detail (continuous simultaneous radon concentration monitoring, blower door technique, infrared Thermography imaging system, continuous soil gas radon measurement, air-exchange rate assessment – tracer gas measurement, visual inspections of buildings, build-up curve numerical analysis, air infiltration parameters assessment etc.). The given system of radon diagnosis was applied and verified on a set of dwellings, covering practically all types of family houses with regards to different types and quality of radon protection measures. INTRODUCTION Instantaneous values of indoor radon concentration fluctuate in time and simultaneously feature the significant space variations within the individual compartments of buildings. Generally, the indoor radon concentration is a result of two competing driving processes, the radon entry rate (Bq.s-1) respectively air-exchange rate (s-1). For the purpose of the individual dose estimation due to radon and its decay products exposure, the annual mean indoor radon concentration assessments derived from the solid-state nuclear track detectors measurements are generally provided. The weather conditions and residential habits, including a habitual behavior of occupants, staying time, number of inhabitants, ventilation and heating regime, ventilation and an air-conditioning systems operation etc., are considered as the most significant influencing factors for the indoor radon measurements and radon exposure assessment. In respect of buildings classification related to preventive and remedial measures efficiency against the radon entry from the subsoil, short-term radon concentration measurements under conservative exposure conditions are usually applied. The measurement conditions are set-up to minimize the false positive results and to avoid misinterpretation accordingly. In this context, a defined range of temperature and pressure field gradient during the measurement is required. The summary overview of radon diagnosis results focused on the ineffective preventive measures against radon penetration has been presented (Neznal, 2006). 40 ACKNOWLEDGEMENT The reported research activities were supported by the research project No. 10/2006 “A development and an application of measuring and diagnostic methods and methodologies for an exposure evaluation to natural radiation in buildings”. Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 RADON DIAGNOSIS PROCEDURES Different measurement techniques and procedures designed for localization and quantification of indoor radon entry characteristics have been tested and applied in respect of primary causes of ineffective preventive and remedial measures identification. Presented modern and sophisticated radon technologies (continuous simultaneous radon concentration monitoring, blower door technique, infrared Thermography imaging system, continuous soil gas radon measurement, airexchange rate assessment – tracer gas measurement, visual inspections of buildings, build up curve numerical analysis, air infiltration parameters assessment, air pressure differences measurement) have been selected as fundamental elements of a complex radon diagnosis system. The artificially produced pressure difference levels enable to identify and localize the most important convective component of the radon entry into the building environment. In order to monitor a distinctive dynamic behavior of indoor radon concentration for specific blower door measurements, a unique continuous radon monitor characterized by a very fast detection response has been designed and applied. Generalized outputs based on qualitative and quantitative analysis of the continuous radon concentration measurements, recorded during the blower door tests, will be performed in detail further in this section. SIMULTANEOUS INDOOR RADON MEASUREMENT A simultaneous continuous indoor radon monitoring within the building, including uninhabited areas, can be considered as a primary method of radon diagnosis. The radon transport from the subsoil and indoor radon distribution including appropriate radon infiltration characteristics of individual rooms can be assessed from results of continuous indoor and soil-gas radon measurements. The single room intrinsic properties, the radon entry rate and the air-exchange rate, can be estimated from the appropriate radon concentration build-up curve numerical analysis. In this context, the constant radon entry rate and ventilation rate approximation has been applied (NRPI, 2005). Several difficulties and limitations can occur during the data processing. The major problem of given approach in real conditions is related to the model assumptions concerning the time dependence of entry parameters represented by constant coefficients in the appropriate differential equation (1). In addition, both quantitative parameters depend on pressure field propagation within the building. The pressure difference variations are closely related to the weather condition, the indoor microclimate, height of the building and residential habits. Due to the fact that the infiltration of the radon is driven by the indoor - outdoor pressure difference (a stack effect) the idea of the artificially produced pressure difference is obvious. dcRn (t ) = # Rn ! (ë + k ) " cRn (t ) dt # Rn cRn (t ) = " (1 ! e !( $ + k )t ) ($ + k )"V Equation (1) Where cRn is a measured indoor radon concentration, ΦRn (Bq.s-1) is the radon entry rate; k (s-1) is the ventilation rate and λ (s-1) represents the radon decay constant. 41 ACKNOWLEDGEMENT The reported research activities were supported by the research project No. 10/2006 “A development and an application of measuring and diagnostic methods and methodologies for an exposure evaluation to natural radiation in buildings”. Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 DEPRESSURIZATION METHOD – BLOWER DOOR DIAGNOSTIC SYSTEM APPLICATION A designed approach is principally based on the combination of a standard BD measurement technique application, commonly used for energy loss studies and air leakages quantification in civil engineering, with a continuous indoor radon concentration monitoring (Froňka, 2005). The different bulk infiltration parameters under defined BD pressure modes for a single room can be assessed independently on human activities and weather conditions. The convective component of characteristic value of radon entry can be significantly enhanced by the artificially produced pressure difference application. Under given pressure conditions, individual radon pathways can be identified and subsequently quantified as well. With regard to the experimental room volume and overall air tightness, the pressure difference for each single BD test can occur within the interval from approximately 5Pa up to 100Pa. In addition, the BD pressure difference over the whole room envelope is managed to be constant for each single BD measuring mode. Under these circumstances, a characteristic height dependence of naturally ventilated buildings is effectively suppressed. For subsequent quantitative analysis, the artificial ventilation rate kBD can be calculated from the BD fan pressure difference record and the radon entry rate can be assessed from the appropriate radon concentration equilibrium state or by the radon build up curve numerical analysis, described above in detail. The most important BD quantitative characteristics, artificial ventilation rate (standard BD characteristic) and the radon entry rate (radon BD characteristic) as a function of the BD pressure difference, can be derived from the BD experimental results using the appropriate air leakage and infiltration approximations (Cavallo, 1992), (Froňka, 2008). At first approximation, the BD artificial ventilation rate Q can be expressed as a power function of the BD pressure difference (2). BD Q(!p ) = f BD " (!p ) n BD Equation (2) Where BDQRn (m3.s-1) is the constant ventilation rate for a defined BD pressure difference Δp (Pa); fBD is the flow coefficient and nBD is the flow exponent. Analogically, identical regression analysis has been applied for the radon BD characteristic evaluation related to the air infiltration from the subsoil into the indoor environment (3). BD # Rn = f Rn " (!p ) n Rn Equation (3) Where BDΦRn (Bq.s-1) is the constant radon entry rate for a defined BD pressure difference Δp (Pa); fRn is the flow coefficient and nRn is the flow exponent. The true value of radon entry rate for natural pressure and temperature field gradients can be estimated from the extrapolation of radon BD characteristic into the low pressure differences region. In respect to individual building component classification, several quantitative infiltration parameters, e.g. the effective leakage area (Froňka, 2005), can be derived from proposed fundamental BD characteristics. BD infiltration parameters The quality of radon-proof preventive and remedial measures for separate building compartments can be expressed as a ratio represented by equation (4). The given ratio, BD radon transfer factor, enables to quantify the contribution of air infiltration from the subsoil relatively to overall air infiltration for the single room. 42 ACKNOWLEDGEMENT The reported research activities were supported by the research project No. 10/2006 “A development and an application of measuring and diagnostic methods and methodologies for an exposure evaluation to natural radiation in buildings”. Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 T!p = BD " Rn ( !p ) csoil (4) Where csoil (Bq.m-3) is the characteristic value of soil gas radon concentration The expression (5) represents a specific value of indoor radon concentration established during the BD depressurization test. The predominant mode of air infiltration phenomenon for a selected BD pressure mode can be determined respectively. cstac = " Rn (!p ) fRn = (!p ) nRn -nBD fBD BD Q ( !p ) BD (5) In order to observe the very fast indoor radon variations due to specific BD experimental conditions, a unique continuous radon monitor characterized by a very fast response was designed and applied (Froňka, 2004). The detection principle of the new device is based on an airflow ionization chamber operating in the current mode. The fast response of the detector vests in the very fast passage (as high as 30 air exchanges) of the filtered air sample through the detector sensitive volume. This arrangement prevents creation of the radon daughters I the sensitive volume and the signal corresponds namely to the pure radon concentration. The details concerning the RADONIC 01 device can be found at www.radon.eu/radonic.html. The characteristic radon buildup curve for the constant BD pressure difference (40 Pa) is illustrated in figure 1. The steady state of radon concentration under such pressure field conditions is established within the time period of 45 minutes. In view of these unique measurement properties, in particular the prominent detection response, the application of the continuous radon monitor is evident. In addition, the described device due to the given detection feature can be routinely used for indoor radon specific behavior monitoring with regard to human activities in the building. The characteristic result of such a type of measurement is given in figure 2. In this case, extremely fast indoor radon variations correspond to a cellar door opening, which is responsible for the dominant component of radon entry into the building environment. Figure 1 Build up curve numerical analysis for the radon diagnostic BD test (40Pa) 3000 2500 c V (Bq.m -3) -3 A = 4516 Bq.m h -1 k = 1,6 h 2000 -1 1500 1000 500 0 10:40 10:52 11:03 11:15 11:26 11:38 11:49 12:01 12:12 time (hh:mm) 43 ACKNOWLEDGEMENT The reported research activities were supported by the research project No. 10/2006 “A development and an application of measuring and diagnostic methods and methodologies for an exposure evaluation to natural radiation in buildings”. Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 2 Indoor radon dynamics study using the continuous monitor with fast detection response 5000 4500 4000 c V (Bq.m -3) 3500 3000 2500 2000 1500 1000 500 0 28.3.2006 12:00 29.3.2006 12:00 30.3.2006 12:00 31.3.2006 12:00 1.4.2006 12:00 2.4.2006 12:00 3.4.2006 12:00 4.4.2006 12:00 time (dd:hh:mm) INFRARED IMAGING SYSTEM For the purpose of radon infiltration pathways localization, the infrared imaging system has been tested as a specific radon diagnostic tool. The standard infrared thermography provides the noncontact surface temperature distribution measurements. In fact, the new approach is in particular focused on an identification of cool soil gas penetrating into the indoor environment. Generally, the diagnostic procedure is based on the simultaneous BD diagnostic measurement and the infrared thermography scanning of individual building structures and elements that are in a direct contact with the subsoil. The cold soil gas is driven by the artificial BD pressure gradient into the indoor environment and causes a drop in temperature in the defined leakage area. Characteristic outputs of infrared imaging system application, a set of normalized infrared images for different BD pressure modes, can be seen in the figure 3. The application of the presented diagnostic method has been experimentally verified for radon entry qualitative analysis purposes. On the other hand, the specific method of semi-quantitative thermograms analysis, a defined area integral delineated by an exact isotherm within the leakage area dependence on applied BD pressure level, can be provided as well. Figure 3 Comparison of normalized infrared images of the defined leakage area for natural pressure field conditions respectively the defined BD pressure modes (17Pa, 32Pa, 50Pa) 15,0°C 15,0°C 14 AR01 14 AR01 SP01: 14,2°C SP01: 13,9°C 13 LI01 13 LI01 12 12 11,5°C 11,5°C 44 ACKNOWLEDGEMENT The reported research activities were supported by the research project No. 10/2006 “A development and an application of measuring and diagnostic methods and methodologies for an exposure evaluation to natural radiation in buildings”. Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 CONTINUOUS SOIL GAS RADON MONITORING In view of design of radon-proof preventive and remedial measures, the radon potential assessment has to be involved into the radon diagnostic system. The knowledge of soil gas radon concentration and soil permeability depth profiles in the vicinity of investigated buildings is essential (Neznal, 2004) due to the subsoil physical properties modification related to a terrain adjustment of the former building site. For the purpose of instantaneous soil gas radon time variations measurement, the new continuous radon monitor has been developed and tested (Froňka, 2008). Simultaneous indoor radon concentration measurement and soil gas radon monitoring enables the instantaneous values of radon transfer factor assessment. In this context, specific human indoor activities resulting in indoor and soil gas radon fluctuations can be observed and investigated in connection with pressure and temperature field gradients. The unique experimental result, a chart of indoor and soil 15,0°C 14 AR01 SP01: 14,3°C 13 LI01 12 11,5°C gas simultaneous continuous measurement in a typical family house with ineffective radon-proof measure, is given in figure 4. 3000 2750 indoor measurement below foil insulation 2500 -3 c V - indoor (Bq.m ) 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 2250 2000 1750 1500 1250 1000 750 500 250 0 3.4.07 6:00 4.4.07 6:00 5.4.07 6:00 6.4.07 6:00 7.4.07 6:00 8.4.07 6:00 cV - below the membrane (kBq.m -3) Figure 4 Result of simultaneous continuous soil-gas and indoor radon concentration measurements – soil gas sampling probe placed in the gap at joint (air filled layer) between the subsoil and a damp-proof membrane 9.4.07 10.4.07 6:00 6:00 time (hh:mm) 45 ACKNOWLEDGEMENT The reported research activities were supported by the research project No. 10/2006 “A development and an application of measuring and diagnostic methods and methodologies for an exposure evaluation to natural radiation in buildings”. Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 TRACER GAS MEASUREMENT For the purpose of an independent air-exchange rate estimation and related radon entry rate analysis, the common tracer gas method using the carbon monoxide as a primary tracer gas has been applied. In addition, a specific mathematical approach based on a state-space dynamic statistical model has been used for experimental data analysis (Jílek, 2007). A simultaneous monitoring of indoor radon concentration and carbon monoxide concentration enables the radon entry rate and the ventilation rate separate assessment for the assumed single zone approximation. Results of tracer gas measurement can be compared with outputs of radon build up curve numerical analysis. Described diagnostic procedure can be routinely applied for the individual room airexchange rate enhancement related to active depressurization system operation providing an effective radon removal from the subsoil. In addition, the method of the independent air-exchange rate assessment has been applied to reliably reveal the main cause of high level of indoor radon occurrence in new buildings or building under construction. In several cases of radon diagnosis measurements, the extremely low air-exchange rate, below the level of 0.05h-1, has been identified as the major cause of high radon concentration presence in the building environment. CONCLUSIONS A complex set of radon diagnostic procedures, including a unique detection system development and specific theoretical approaches for experimental data analysis application, has been proposed and tested in the field under various experimental conditions. The special blower door diagnostic method, pointed out in this paper, provides the stable experimental conditions for the indoor radon concentration measurement independent on weather conditions and human activities in the building. 46 ACKNOWLEDGEMENT The reported research activities were supported by the research project No. 10/2006 “A development and an application of measuring and diagnostic methods and methodologies for an exposure evaluation to natural radiation in buildings”. Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 REFERENCES 1. Neznal M., Neznal M., Jiránek M., Froňka A.: Failure of Preventive Measures against Radon in a New Built Family House – a Case Study. In: Proceedings of Full Papers CD-Rom from the 2nd European IRPA Congress on Radiation Protection. Paris (2006). 2. Public Exposure to Natural Radiation in the Czech Republic. In: Report SURO. National Radiation Protection Institute Prague (2005). 3. Froňka A., Moučka L.: Blower door method and measurement technology in radon diagnosis. In: High Levels of Natural Radiation and Radon Areas: Radiation Dose and Health Effects 06-10 September 2004, Elsevier B.V. International Congress Series, Vol.1276, pp.377-378 (2005). 4. Cavallo A., Gadsby K., Reddy T.A.and Socolow R.: The effect of natural ventilation on radon and radon progeny levels in houses. In: Radiation Protection Dosimetry, Vol.45, No. ¼, pp. 569574 (1992). 5. Froňka A., Moučka L., Čechák T.: Application of the Advanced Radon Diagnosis Methods in the Indoor Building Environment. In: Radiation Protection Dosimetry (in press, 2008). 6. Froňka O., Froňka A., Moučka L., Knapp K.: Device for measurement fast changes of the radon volume activity based on an ionization chamber detector. Patent No. 293111, Industrial Property Office of the Czech Republic, Prague (2004). 7. Neznal M., Neznal M., Matolín M., Barnet I., Mikšová J.: The New Method for Assessing the Radon Risk of Building Sites. In: Czech Geological Survey Special Papers, Prague (2004). 8. Froňka A., Moučka L., Jeřábek M.: Detection properties of a Measuring System for a Continuous Soil Radon Concentrations Monitoring. In: Radiation Protection Dosimetry (in press, 2008). 9. Brabec M., Jílek K.: State Space Dynamic Model for Estimation of Radon Entry Rate Based on Kalman Filtering. In: Journal of Environmental Radioactivity, Vol.98, No.3 (2007). 47 ACKNOWLEDGEMENT The reported research activities were supported by the research project No. 10/2006 “A development and an application of measuring and diagnostic methods and methodologies for an exposure evaluation to natural radiation in buildings”. Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 CONCLUSION OF A MULTI-YEAR STUDY ON THE ELEVATION EFFECTS ON SCINTILLATION CELL COUNTING EFFICIENCY FOCUSING ON THE PYLON™ MODEL 300 James F. Burkhart and Benjamin Abrams Physics Department University of Colorado-Colorado Springs 80918 Phillip H. Jenkins Bowser-Morner, Inc. Dayton, Ohio 45424 Abstract This is a continuation of a study begun in 2005 when the authors first reported on the theoretical possibility of a non-trivial error in calibration of radon chambers caused by the current use of scintillation cells. The ramifications of this error are just now being felt by the radon industry as experts around the world attempt to better define radon concentration standards and insist upon measurement results more accurate than the traditional 25 %. In this report, the authors conclude their study by comparing the theoretical error and the actual experimental error of using a certain popular scintillation cell made by Pylon™(1) with a volume of 271 ml. A graph is presented which predicts the cell calibration error, as a function of the difference in elevation of any secondary chamber and the primary calibration facility, which would be introduced using this Pylon™ cell. The authors summarize their study by presenting a second graph that predicts the cell calibration error introduced by using any right cylinder scintillation cell of any dimensions that can be modeled as a scaled-up or scaled-down version of the popular Rocky Mountain Glassworks cell. Background Both theoretical and experimental investigations indicate that the performance of scintillation cells varies when filled at different elevations, as a result of the dependency of alpha particle range on air density (George, 1983;Eberline 1987; Burkhart, 2005). In fact, it has previously been shown that this discrepancy in cell counting efficiency for the popular Rocky Mountain scintillation cell(2) (a right cylinder cell, 7 cm in diameter and 9.7 cm long, 360 ml in volume) can cause calibration errors between different elevations in the U.S. as large as 9.1% (Burkhart, 2006). As the specific cell geometry influences the magnitude of this error, correction factors must be determined for other cells, cells that are not simply scaled-up or scaled-down versions of the Rocky Mountain cell. This study investigates, therefore, the error in cell counting efficiency at different elevations for the Pylon™ Model 300 scintillation cell, using the same apparatus as was used in the earlier Rocky Mountain cell study. (1) Pylon Electronic Development Company, Ltd., 147 Colonnade Road, Ottawa, Ontario, Canada. (2) Rocky Mountain Scientific Glass Blowing Co., 4900 Asbury Ave., Denver, CO 80222 48 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Theoretical Considerations Alpha particles are the type of radiation emitted from 222Rn and two of its decay products: 218Po and 214Po. It is well understood that the range (R) of an alpha particle traveling in air is inversely proportional to the air density (ρ): ρlRl = ρhRh , (Equation 1) which means that alpha particles travel further at higher elevations (denoted by an “h” subscript) where the air is “thinner” (Lapp, 1963). For example, the alpha particles that are emitted by 222Rn, 218Po and 214Po travel more than 20% further in Colorado Springs, Colorado, which is at 6000 feet elevation, than they do at sea level. Alpha particles that are traveling within a scintillation cell may, therefore, strike the interior of a cell which is filled at a high elevation when they would be quenched within the cell air volume, not striking the scintillator, when the same cell is filled at a low elevation. However, despite having such a significant impact on alpha particle path length, the influence of differing air densities due to elevation has on alpha particle path is not incorporated into current scintillation cell calibration techniques. An important example of why this cell calibration error is commonly ignored can be best understood by following the process by which secondary laboratories calibrate their chambers to the U.S. EPA’s primary facility in Las Vegas, Nevada (elevation of approximately 2,200 feet). Briefly, the EPA sends a sample of radon from their chamber (using a standard grab sampling method with a scintillation cell) to one of the secondary locations for analysis. After analyzing the sample, the secondary location can then adjust its calibration factor for the cell/counting system such that their equipment will report the same radon concentration as the EPA. Indeed, this technique has proven very effective, as it allows the secondary locations to read subsequent cell samples from Las Vegas to within a few percent of the target value. In addition, as long as cells that are filled by a secondary chamber (subsequent to calibration) are sent only to other secondary chambers that have also calibrated with the EPA with a cell with identical geometry, all such secondary chambers will agree on the radon concentration within the cell. Thus, any intercomparison between secondary chambers (which are all calibrated with the EPA chamber using this cell geometry) will not uncover any underlying problems attributable to the air density within the cell. The authors are convinced that this is the reason that the problems caused by using grab cells as an intercomparison have not received much attention in the past. Nonetheless, problems do exist and will show up under some circumstances, causing as much as a 9 % to 10 % error. Specifically, the resultant calibration factors (counts per minute divided by decays per minute; cpm/dpm) that the secondary facilities force onto their systems are dependent upon the radon/air mixture and the difference in air pressure between the Las Vegas chamber and the location of the secondary chamber. Errors will become evident when the cell is refilled at the secondary location (if it is at a different elevation than Las Vegas), and is subsequently used to calibrate a radon instrument or a tertiary chamber because the number of decays per minute necessary to achieve a desired counts per 49 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 minute will change from the earlier calibration, depending upon the difference in elevation between Las Vegas and the secondary chamber. In other words, the cell calibration, cpm/dpm, will be incorrect for the subsequent fill. Clearly, secondary chambers at a high elevation will require less radon (smaller dpm) to achieve the same cpm compared to a chamber at lower elevation. Experimental Procedure In order to fill scintillation cells in a way which duplicated the elevations of Las Vegas and other locations (from sea level to 6000 feet), a 25-liter tedlar(3) bag that is typically used for transporting radon was filled over a 12-minute interval from a commercial radon source manufactured by PylonTM. The bag was placed in a large metal cylinder (40 cm diameter and 150 cm length), which was then sealed for a pressure tight fit. The chamber, with the radon bag inside of it, was then brought to one of four pressures by pumping in outside air. The pressure was read by a digital gauge and maintained to within 0.01 pounds per square inch (psi) of the desired value through the use of a pressure regulator. While held at the desired pressure, radon was extracted from the bag at a rate of 5 SCFH (2.4 L/min), and passed through the scintillation cell for four minutes. Before entering the cell, the decay products that had accumulated in the radon bag were filtered out. The valve located at the exhaust port of the cell was then closed, and the cell was allowed to equilibrate with the pressure of the chamber/bag for one minute. See figure1: Air Back into Room Air Pressure Gauge Pressure Regulator Fill Pump Valves Filter Radon bag Cell Air compresso Air Compressor r Figure (1): An air compressor brings the chamber to a desired pressure. The pressure is maintained to within 0.01 pounds per square inch with a gauge and a regulator. Using a second, independent pump, the radon is extracted from the bag (under pressure), filtered, and passed through the Pylon™ cell. (3) Tedlar bags purchased from Environmental Measurements, Inc. 215 Leidesdorff St., San Francisco, CA 94111 and SKC Inc., 863 Valley View Road, Eighty Four, PA 15330-9613, www.skcinc.com. 50 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The same cell was filled sequentially at ambient pressure (820 hPa) in Colorado Springs (6,000 feet above sea level), an over-pressure of 1 psi (888 hPa, equivalent to 4,000 feet above sea level), an over-pressure of 2 psi (957 hPa, equivalent to 2,000 feet above sea level), and an over-pressure of 3 psi (1026 hPa, roughly equivalent to sea level). The cell was flushed between samples, and the background was re-established for each run. Two correction factors were incorporated into the calculations in order to eliminate confounding errors. Specifically, the loss of radon due to radioactive decay during the time between filling the bag and taking samples was accounted for. Also, when sampling at higher pressures, the increased density of air/radon that entered the cell was corrected for by multiplying by the ratio of the ambient pressure divided by the chamber pressure (according to the ideal gas law). Results Each “run” is defined as a minimum of two fills of a cell: the first fill was done under one of the three over-pressures and the second fill, using the same cell and the same radon in the bag, was done at ambient pressure. A minimum of five runs was completed at each “elevation” below 6000 feet and at ambient pressure (6000 feet elevation), so that a percent error in counting efficiency could be calculated. Considerable difficulty was encountered because of frequent small holes occurring in the tedlar bags causing leaks, especially when the bag was under pressure; many runs had to be repeated. In addition, the bag only held enough radon to measure the error at two or three “elevations” per run. As a consequence, missing values are represented by “X’s” in table 1, below. Run Number Error at Sea Level 1 X 2 X 3 0.08 4 X 5 X 6 X 7 0.04 8 0.09 9 0.04 10 0.11 11 X 12 X 13 X 14 X 15 X 16 X Average +/- σ 0.072 +/- .031 Renormalized 0.00 +/- 0.00 Error at 2000’ 0.05 0.03 0.07 X 0.00 0.08 X 0.07 X X X X X X X X 0.050 +/- .030 0.025 +/- .030 Error at 4000’ X -.02 X .04 -.05 .08 X X 0.07 0.03 0.04 0.03 0.04 0.02 0.02 0.03 0.027 +/- .037 0.050 +/- .037 Error at 6000’ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.078 +/- .031 Table (1): Chart of errors in counting efficiency at different elevations found experimentally for the Pylon™ Model 300 scintillation cell. The errors were calculated using Equation 2, found below. The final row shows the renormalized errors calculated using an error of zero for sea level. See comments section. 51 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The errors in table 1 were initially calculated by defining the error on the counting efficiency at 6000 feet elevation as zero error where cell counting efficiency is here defined as cpm/dpm and the number of decays per minute was held constant for any one run (shown as one row in table 1). Radon was held constant by using radon from the same bag, hence, once corrected for half-life decay, the radon was identical for each run. Since the dpm/cell volume was, thereby, held constant (after correcting for the air volume changes at different pressures) the dpm term in the cell calibration cancels out for each run and only the cpm needed to be compared. Therefore, after counting for 60 minutes, the number of counts (corrected for decay and pressure) at 6000 feet (Nh) was compared to the number of counts (corrected for decay and pressure) at the respective lower N ! Nl elevations (Nl). Thus: Error = h . (Equation 2) Nh These are the values shown in the second to the last row in table 1. In the previously published theoretical model (Burkhart, 2005), however, the error was calculated by dividing by Nl instead of Nh as is done in equation 2 above. However, to minimize incidents of tedlar bags leaking, it was experimentally adventitious to always perform a run at ambient pressure (6000 feet) and finding Nh instead of an over-pressure of 3 psi (sea level) which would have allowed us to find Nl. Therefore, we were able to ascertain a value of Nh for each and every run, making division by Nh more practical than division by Nl, which was frequently not available. Then, in order to more easily compare to previous theoretical and experimental results, all of the error values were renormalized by forcing the error at sea level to be 0 % and correcting the other errors accordingly. These are the values shown in the last row of table 1. (See the simple equation used for renormalization in the comments section at the end of this paper). Discussion of Results There is an error, linear with elevation, when comparing cells filled at sea level with cells filled at other elevations, with the error maximizing at .078 (7.8 %) for cells filled at 6000 feet elevation. This latter result agrees reasonably well with the theoretical prediction(4) shown for the Pylon™ cell in table 2, below. Cell Manufacturer Cell diameter Cell length EDA PylonTM Rocky Mountain 5.3 cm 5.3 cm 7.0 cm 7.5 cm 13 cm 9.7 cm Theoretical Error 8.0 % 8.8 % 9.8 % Table (2): Chart of theoretical differences in counting efficiency between cells used at sea level and at 6000 feet of elevation. The theoretical errors are defined as the Error = 1 – (Nh-Nl)/Nl. In addition, the results confirm the qualitative expected dependence of this error on cell geometry: the error found here for the Pylon™ Model 300 cell is less than that of the (4) The numerical analysis leading to this theoretical prediction, done by Robert E. Camley at the University of Colorado-Colorado Springs, can be found in our earlier work (Burkhart, 2005). 52 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Rocky Mountain cell. We believe this smaller error arises from the relative dimensions between the two types. Specifically, the Pylon™ Model 300 has a relatively smaller diameter compared to its length than the Rocky Mountain. (The ratio of the diameter to the lengths for the PylonTM Model 300 is 0.41, while that of the Rocky Mountain is 0.72.) As previously discussed (Burkhart, 2005), the narrow profile of the Pylon™ Model 300 lessens the extent to which the difference in alpha particle range at different air densities affects counting efficiency. 0.00 0.01 E r r o r Pylon Cell 0.02 0.03 0.04 0.05 0.06 0.07 0.08 Rocky Mountain Cell 0.09 0.10 0 Ft. 2000 Ft. 4000 Ft. 6000 Ft. Elevation above sea level Figure (2) This graph shows the error introduced by using the PylonTM cell for calibration of secondary chambers. The maximum error between two chambers occurs when both chambers calibrate to the Las Vegas U.S. EPA radon chamber while one chamber is at sea level and the second is at 6000 feet above sea level. That error is 0.078, or 7.8 %. With the Rocky Mountain cell, that same maximum error was found to be around 9.1 %, once renormalized to sea level (Burkhart 2006). Secondary chambers, which used either the Pylon™ cell or the Rocky Mountain cell for their calibration with the U.S. EPA, can use figure 2 in order to correct their reported radon to represent the “true” radon in their chamber when exposing a radon instrument or when calibrating a tertiary chamber. By “true” radon, we mean the actual radon in the Las Vegas chamber. 53 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 In order to use figure 2 to calculate the “true” radon in the secondary chamber, find the elevation of the secondary chamber and determine the error of its cell calibration by using figure 2 and the correct curve (either a Pylon™ cell or a Rocky Mountain cell). Then subtract the error for the elevation of the primary calibration chamber. This difference is the net error that should be applied to the secondary chamber’s reported radon value. As the first example, let us take a chamber in Colorado Springs, elevation 6000 feet using a Pylon™ cell. Reading from figure 2, we see the error is 0.078. Assuming that the chamber was calibrated by the U.S. EPA chamber in Las Vegas, we use figure 2 to find an error of about .03 for Las Vegas, which is at 2000 feet. Subtracting the Las Vegas error from the secondary chamber error, (0.078-0.030), we end up with a net error of 0.048. Thus, in order to find the “true” radon from the reported radon, using the original calibration factors, it is necessary to reduce the reported radon of the secondary chamber by .048, or 4.8 %. In other words, because Colorado Springs is at such a high elevation, it took about 5 % less radon to produce the same number of counts per second as the U.S. EPA used during its intercomparison with the Colorado Springs chamber. Also, any device which the Colorado Springs chamber exposes should use the chamber radon value reduced by about 5 %, assuming that the owner of the device wants to be calibrated or compared to the “true” radon value. As a second example, let us take a chamber at sea level. Reading from figure 2, we see that error is 0 for the Pylon™ cell. Using the Las Vegas chamber for calibration gives us the .03 error again. Subtracting the Las Vegas error from the former, (0-.03), we get - .03 which means that the sea level chamber needs to raise its reported radon by about 3 % in order to reflect the “true” Las Vegas value. Failure to make these corrections among secondary chambers could result in an accumulated error as much as 7.8 % if, for example, a radon device is calibrated in a secondary chamber at sea level and is subsequently sent to a chamber at 6000 feet for an intercomparison. If, on the other hand, the Rocky Mountain cell was used in the initial calibration with the EPA chamber and the secondary chambers, the maximum error between chambers could, as seen in figure 2, be as high as 9.1 %. Finally, for cells that have not been specifically studied, one can use a general theoretical predictive model introduced in an earlier paper (Burkhart, 2005). The graph, table 3, shows the maximum error between a chamber at sea level and a second chamber at 6000 Percent Error 12 10 8 6 4 2 0 0 2 4 6 8 10 Scale Factor Table (3): This graph shows the predicted maximum error caused by using a cell that can be modeled as a Rocky Mountain cell scaled up to 9 times larger or down to 1/3 of its manufactured size. The arrows on the graph are used in a simple example that follows below which shows how to apply the graph to other cells. 54 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 feet. The Rocky Mountain cell is 9.7 cm in length and 7.0 cm in diameter. As an example, then, a cell which is two times as large, say, about 20 cm in length and 14 cm in diameter, would be expected to have a maximum error, from table 3, of around 9.5 %, distributed linearly from sea level to 6000 feet. Comments As was discussed in the above paper, it was necessary, for practical reasons, to experimentally calculate the error by counting each cell at one of the over-pressures and at ambient (6000 feet) and calculating the error by dividing by the ambient counts, i.e., N ! Nl Error = h . (Equation 2) Nh However, in order to compare with previous theoretical work, it was necessary to convert this equation to one in which the error was determined by dividing by Nl, i.e.: Nl ! N h . (Equation 3) Nl This was done by taking the error in each row of table 1, which is a fractional error compared to 6000 feet (ambient) and changing it to a fractional error compared to sea level: N ! Nl Start with Error = h . Nh Subtract both sides from 1 and divide both sides by the error Error = N h ! Nl )/Error . Nh Substituting the value for the error from equation 2 into the right hand side, we get: (1 - Error)/Error = (1 - N h ! Nl N ! Nl )/( h ). Nh Nh Taking the reciprocal of both sides and dividing through by the denominator on the right, we get: N ! Nl Error/(1-Error) =1/ (1 /( h - 1 )), which, after multiplying Nh and dividing the right hand side by Nh-Nl gives: (1 - Error)/Error = (1 - Error/(1-Error) = (Nh – Nl)/(Nh-Nh-Nl) And canceling the Nh’s in the denominator and multiplying and dividing the right hand side by -1, gives: Error/(1 – Error) = (Nl – Nh)/Nl, 55 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 which is equation 3, the definition of the error as measured from the lower elevation. References Burkhart, J.F., Jenkins, P.H. and Camley, R.E., “Elevation Effects on Radon Cell Counting Efficiency”, American Association of Radon Scientists and Technologists, Proceedings of the 2005 International Radon Symposium, San Diego, CA, September, 2005. Volume 9-27-1:15, Pages 1-9. Burkhart, J.F., Jenkins, P.H. and Moreland, E.L., Using a Radon Pressure Chamber to Determine Cell Counting Efficiencies as a Function of Elevation”, American Association of Radon Scientists and Technologists, Proceedings of the 2006 International Radon Symposium, Kansas City, MO, September, 2006. Volume 1, Pages 67-75. George, J.L., 1983. “Procedures Manual for the Estimation of Average Indoor Radon Daughter Concentrations by the Radon Grab Sampling Method”, Bendix Field Engineering Corp., Grand Junction, Colorado, GJ/TMC-11 (83) UC 70A, as referenced in the “Indoor Radon and Radon Decay Product Measurement Device Protocols”, U.S. Environmental Protection Agency, Office of Air and Radiation (6604J), EPA 402-R-92004, July 1992 (revised). Page 2-38. Eberline-A Subsidiary of Thermo Instrument Systems, Inc., “RGM-3 Radon Gas Monitor Technical Manual”, Santa Fe, NM 87504, March 1989. Pages 25 and 26. Lapp, Ralph E. and Andrews, Howard, L., Nuclear Radiation Physics, Third Edition, Prentice-Hall Inc., Englewood Cliffs, NJ, 1963, pages 117-119. 56 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 CREATIVITY APPLIED TO A HARD TO SOLVE RADON PROBLEM: A RESIDENCE ON MINING TAILINGS L. Moorman, Ph.D. Radon Home Measurement and Mitigation, Inc. Fort Collins, CO Abstract A residence built in an area with known previous mining activity had reportedly original radon levels of 275 pCi/L. A radon system was installed and intermittently improved during a period of 18 months by a third party certified radon company. After these original mitigation attempts by others, including the use of a four branch system employing seven radon fans and a double membrane barrier, that were tested to be insufficient, an alternative strategy was devised with continuing testing to reduce the radon level. We will discuss attempts, failures and successes of this mitigation which requires creativity on the mitigator’s part to design an efficient system. We will also discuss what was learned about why original mitigation attempts had failed during the first 18 months and will draw conclusions. This talk is aimed to show that certified mitigators must have a certain freedom and must apply creative solutions or else extreme problem situations like this residence may not be able to be mitigated using a simple approach of standard mitigation methods. Introduction This is a case study of the radon mitigation performed on a single residence. The house was originally mitigated by another certified company. We became involved in spring 2006 because of a request for a second opinion by the home owner after the first mitigator had tried to mitigate this home intermittently during a period of 18 months. Concerns were voiced by home owner whether it could be that there was something inherently anomalous about constructing a house in this area that allowed a normal radon vent system not to be able to bring the radon concentration level down to below 4.0 pCi/L. Our pre-investigation showed several aspects of the existing system that were not following applicable guidelines and we recommended appropriate changes, and determined their priority in order to bring radon levels down. A few simple but relevant changes were immediately implemented which seemed to solve the high radon problem. However when winter winds that are characteristic for the area returned, the radon level increased significantly again. Next a more rigorous overhaul of the system was to be implemented as an extension of the work done before. 57 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Status of existing system and early Investigations (Phase 1) A wood framed ranch style residence, with a crawlspace of 2500 sf and a 300 sf media room in basement to the side of the crawlspace on a slab, was built in the late 1980’s in an area that has a history of gold mining. Original radon concentration values of the house were reportedly 275 pCi/L. A third party mitigation company was asked to mitigate it. The company installed, during a period of 18 months, five independent radon vent pipes using seven ventilators with a double membrane in the crawlspace with two connection points under the media room/office slab. Some of the characteristics of the pre-existing system are in Table 1. Table 1: Some characteristics of pre-existing system A RP265 B FR250 C 2xRP265 D 2xRP265 E RP265 Ventilator Location Boiler Room Boiler Room Boiler Room Attic Attic Pipe End Discharge point Evacuation location Size 4" Original through roof South end crawl space, pipe to Geo-mat. 4" Garage attic Wall Drain tile pipe in center of crawl space. 4" Garage attic Wall Under slab of Office 6" Garage attic Wall Drain tile pipe for West side crawl space. 4" Garage attic Wall Slab of small storage crawl space. Four ventilators were located in the boiler room which is located immediately above the small section of crawlspace over the slab immediately next to the media room. Three ventilators were placed in the attic of the garage. Fig. 1 gives an indication of the layout of drain tile pipe and geo mat (A) that was used in the crawl space. Fig 1: Layout of existing system during first visit. Straight pipe lines are solid PVC pipe. curved lines are drain tile pipe. Pipe A marks the Geo-mat. 58 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 After these five active systems were installed Radon levels in downstairs media room had varied between 6 pCi/L and 8 pCi/L as measured with a Safety Siren Pro II radon detector. The first pipe (A) was discharging the radon above the roof through the attic above the media room. All others terminated through a side wall of a garage attic in the same general area immediately above this roof and near the discharge of pipe A. All additional termination points through side wall were within a foot of each other and within five feet of a dryer and furnace vent. Despite the number of ventilators, ballooning of the radon membrane in Southeast side of crawl space was reported at certain times with strong winds. Several tests were performed during the visit. Pressure tests through slab of crawl space near the east wall of storage space with the fan on and off resulted in pressure difference across a slab thickness measured to be +0.001”W.C., independent of whether the fan was on or off. Radon survey test screenings in various areas of the house, in the test hole through the slab and in wall cavities are indicated in figure 1. As part of an initial visit, we performed relative screening flow measurements in various parts of the house. Short three minute test screenings were performed with a femto-Tech CRM410-RS survey instrument capable of taking active air samples with an internal pump. From these screenings we deduced that there are six high radon concentration areas measured as indicated in Fig 2. Radon Screenings 120 survey samples Radon Activity Conc. (pCi/L) 100 minutes 80 60 40 20 0 LR - SH MBR O O SCC CS US GBR EW SH OL CS BoilRM LR O EW SH SCC OL US BoilRM LR - DP D DP DP DP Fig 2; Resulting Test survey screenings. Vertical scale in pCi/L 59 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The following table, table 2, explains the acronyms used in the horizontal axis of the figure: - Changed Location, counts not settled to new value CS Crawl Space D Inside Dryer DP Dryer Drain pipe penetration through drywall EW East Wall in Office LR On table of living room O Office in center 14" off floor OL Outlet SCC Slab Crawl space Center SH Hole in slab of crawl space US Under Stairway Table 2: Acronyms for horizontal axis of Figure 2. Based on manufacturers information of the ventilators we calculated that a maximum air flow can be accomplished by all fans of 1957 cfm, but from an analysis of the vacuum pressures measured below the ventilators in each individual pipe the operational air flow of the combined ventilators in their configuration is 1365 cfm. This actual airflow is still much larger than the airflow normally needed for a house with a footprint of 2500 sf. Normally such a house with a crawl space can be mitigated with a single ventilator and an operation point between 150 and 250 cfm. Suggested solutions (Phase 1), radon activity concentrations in the spring Many suggestions were made to decrease the radon levels based on improving the original system. In the boiler room a 10 inch rubber connector above the FR250 ventilator had the wrong diameter, was loose and attached with black duct tape instead of a hose clamp. A fitting rubber clamp was to be arranged. Vent pipe C was simply placed in a hole under the footer to subslab material from the crawlspace and since this hole was open to the crawlspace no effective removal of air from the sub-slab in media room could be expected. Similarly, vent pipe E from the crawl space with slab section under the boiler room was too close to the footer of crawl space. The small crawl space under stairway was not completely sealed and no air was removed from the single barrier layer under this part of the crawlspace. The distribution of the drain tile pipe over the area of the crawlspace was not even and the ends of the drain tile pipe were found not capped off. The radon discharge points above the roof were found to be close to re-entry points. In the main crawlspace the radon barrier was attached to concrete walls with insulating foam instead of caulk. EPA, 60 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 AARST, ASTM standards all require ventilators not be placed in finished living areas. Placement in a finished boiler room adjoining garage may be useful only if proper year around radon level monitoring is part of the system. Additional two day measurements with the Safety Siren in the utility room showed 68 pCi/L (with door to garage open!) before the rubber coupler was exchanged. After the new fitting rubber coupler was installed in the spring radon levels decreased to acceptable levels in boiler room and adjoining utility and media room, a radon concentration of 1.6 pCi/L was reported in the boiler room, and 3 pCi/L in the media room. This may have been a limited success because there was not much wind and the temperatures were warmer. Thus it was not clear whether low radon levels would be found during unfavorable wind conditions. Thus it was decided to continue to monitor the radon levels with the Safety Siren detectors. Radon concentrations the following winter with high winds (Phase 2) Additional high levels were reported starting next winter (October 2007) when high winds occurred. Values went gradually up to 40 pCi/L in the crawlspace. We continued simultaneous monitoring with Safety Siren detectors that were manually recorded for both crawlspace and basement media room. Repair and modifications of existing system (Phase 2) During our visit in the beginning of the winter we chose to compartmentalize the lower section into three compartments in order to better distribute the air removal rate over the entire area. We also decided to remove and reseal the entire upper section of the 24500 sf barrier material. In the process we found a large hole in the lower barrier (3x4 sf), and the perforated drain tile pipe pulling air from the soil was also crossing the lower barrier and was thus communicating to the air gap between the two barriers. (From now on we will refer to this air gap between the two radon barriers by the name “inter-barrier”.) We also built a separate passive venting system for radon from the inter-barrier to the outside with later options for between the two layers, with options for activation if needed later. In addition, we drilled a new radon extraction hole through the slab of the basement on the far end of crawlspace near the footer to maximize the distance it is removed from the crawlspace in an attempt to prevent a path-way of airflow from the crawlspace. Depressurization tests showed no depressurization even as close as 2 ft away from the hole. This work was completed in a single four day work session, 14 hours per day with two experienced radon mitigators, during the first heavy snow storm of that winter in the area. Thus, because of the weather conditions, no changes were made to the roof exhaust situation. However, the ventilators were installed in a different configuration to optimize evacuation from the various compartments. Continued high radon levels: tests and modifications. 61 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Active removal of radon between barriers did not alleviate high radon levels after phase 2 was completed and monitoring was continued. A modification where active flushing was applied to the small inter-barrier volume showed an asymmetry for the direction of the flow in the inter-barrier volume. A 1 ft long rip in the barrier material was found and repaired. Some ice built up near the Tee of the injection intake inside crawlspace was a concern. Further experimenting in which we verified the working of the monitors continued. Ballooning of membrane still occurred at times, which threatened to damage some of the barrier material. Counteracting this force we proposed a pressurization of the crawlspace. From these experiments we also learned that radon concentrations could be reduced in the media room by diluting the air under the slab by the continual injection of air into the radon extraction hole instead of trying to depressurize the sub-slab material. These experiments are shown in Fig. 3 before day number 134. Adding a third mitigation system in series To counteract the ballooning of the plastic we brought air from the hobby area continually into the crawlspace in order to pressurize it. The hobby area is a separate room but is Fig. 3: A series of experiments with the residence using two and later three simultaneous safety siren test devices. The horizontal axis scale is referenced to Oct. 1, 2007. 62 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 built against the garage and is referred to as the third bay of the garage. Radon concentrations dropped to low levels in the crawlspace and in the media room in the basement next to the crawlspace, as is shown by the radon concentrations below the reference line at 4.0 pCi/L after day number 134 in Fig. 3. The final configuration of the radon mitigation system is effectively summarized in Table 3: The pipe letter names (A through E) were the same as before, although ventilators in pipes may have been exchanged and vent pipes F and G were added. The order of the vent pipes is here rearranged to group individually related radon reduction mechanisms together as can be seen in the last column. Pipe Branch # Ventilator Model Ventilator Location Pipe Diam eter End Discharge/I ntake Location South gable end garage. Area affected Radon Reduction Mechanism D 2 2xRP265 Attic 6” Removes air from below both barriers in Area I Removes air from below both barriers in Area II Removes air from below both barriers in Area III Area I exhaust crawl space and building bypass Area II exhaust crawl space and building bypass Area III exhaust; crawl space and building bypass Interface fresh air dilution and crawl space bypass Interface fresh air dilution and crawl space bypass Sub-slab air dilution (Not pressurization) Crawl space air dilution, and pressurization C 1 RP265 Boiler Rm 4” South gable end garage. B 1 RP250 Boiler Rm 4” South gable end garage. F North 1 HP2133 Crawl space 4” North Rim joist at floor level. Injects fresh air in between two layers. A South 1 RP265 Boiler Rm 4” Through roof above media room. E 1 RP265 Attic 4” South gable end garage. Removes air from between two radon barriers in crawl space. Injects fresh air under slab of media room G 1 RP265 3rd Car Garage 4” Third car garage Injects fresh air to above both layers into crawl space. Table 3: Final Configuration in place since 2/10/08 (#133) Other than the vertical 7 vent pipes and 8 radon ventilators with their characterization and functional details indicated in the table, the system includes the following characteristic elements: 1) two layers of radon barrier material fully sealed in 2500 sf, 6 ft (high) crawl space over a boulder area. 63 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 2) three flexible drain tile pipe loops below both layers of radon barrier material. (I: nearest to the entry into crawlspace under boiler room into crawlspace (north); II: mid section; III: far end section from entry (south)) 3) two banana shaped sections of flexible drain tile pipe (Approx. 60 ft long), one on the north side and one on the south side of the crawl space. Fig 4: Three independent sub-membrane loops of drain tile pipe under both membranes. Straight pipe lines are solid PVC pipe. Curved lines are perforated drain tile pipe. Fig 5: Drain tile pipe layout to dilute and remove radon that makes it past the lower barrier and the corresponding air flow. Through vent pipe A the air is removed. Straight pipe lines are solid PVC pipe. Curved lines are perforated drain tile pipe. 64 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Experiments with this showed that airflow from north to south between the two layers of radon barrier could be increased by adding a few short sections (5 ft) of drain tile pipe in certain areas in the inter-barrier in order to help separate the top and bottom layers of the barrier material at those locations History of area and cause of the problem This wood framed home was built in the late 1980’s in an area that is known for previous extensive gold mining activities. When in 1859 the first prospector found gold (worth $0.13), the gold rush in this area started. Manmade extensive gold mining activity, with dredging, from 1898 to 1942 using 9 dredge boats on the Swan River, French Creek and Blue River were responsible for 50 feet deep piles of dredge tailings. The residence stands over the physical area where dredge tailings of the gold mining industry in Swan River Valley near Breckenridge were located. An aerial photo taken in the early 80”s, before the house was built, showed the dredge tailings in piles of an estimated 100 ft by 40 ft. size. The dredging process has removed the fine materials out of the sub-soil and transformed the sub-soil of the riverbed, making it into a geological structure that most resembles “a bathtub with marbles”. This causes the river for large parts of the year to stream entirely under ground, according to a former City Engineer of Breckenridge, and before 1984 the river could only been seen in the town above the dredge tailings after mountain snow runoff. The fact that a large volume of underground air connects to the interior air of the house is corroborated by three facts: First, the owner of the construction company that built the house said that tremendous winds could be felt through the crawlspace access opening into the house during construction. Second, even with seven fans and a total calculated operational air removal rate of 815 cfm for the combined operating flow of B, C, and D in the final configuration, the system was not always able to overpower the rate with which air rushed into the building from under the barrier. This was simply proven by observing that the radon barrier at times during our work was ballooning when the mitigation system was operating and the lower radon barrier layer was already completely sealed. Third, vacuum pressure tests conducted as close as 2 feet away from the suction hole through the slab part of this house were not able to detect a measurable negative pressure meaning that vacuum pressures at this close distance were smaller than -0.001” W.C. This is a different manmade radon problem than that which has been identified in the prior literature. It is different from the processing of uranium mill tailings into building materials. Instead it is caused by continuing excavation of the land, processing 1 million troy ounces of gold (31,000 kg) from this area. This mining activity over a period of 44 years has sifted all small materials out of the ground, forming lakes and river beds that were refilled with head size boulders which were the tailing products disposed of by the industrialized gold mine dredging process. The last major gold mining operation in Breckenridge operated sporadically until 1973. Since 1984 reworking of the area into a natural landscape has returned the dredges but not the finer particulates of the sub-soil. 65 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Houses are now standing on areas that for a radon problem should be treated with the similar methods for testing and mitigation as karst areas, where radon can be moved into a house via air movement through large and small caves over long distances and the residential radon levels can be strongly dependent on factors as wind and season. For these areas it is advisable that repeated tests throughout the year or long term tests should be conducted as valid tests. The same recommendation should be observed in this area. In other words a radon system working at a given time may not be working at a different time, and only a year long test will tell what the yearly average radon level in a particular house will be. This case shows that, when confronted with this type of manmade radon problem, in order to remove air at a sufficient rate from under the barrier (or slab) multiple depressurization systems may be needed; in this case up to three systems in series. The decisions how to proceed in this research were based on an existing system and may have been different if we had been confronted with the problem as a first mitigator. Fig. 6: Final configuration of the radon system in this residence on dredge tailings that even during unfavorably weather conditions maintained a radon level below EPA’s guideline. The configuration of four radon reduction mechanisms is given in table 3 and the sub-membrane drain tile pipe layout is shown in Fig. 4 and 5. 66 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Conclusions for future radon systems in this or a similar area With the knowledge acquired about the manmade substrate and when working from the start on mitigating a house in this area we could have started with the installation of a single layer hermetically sealed radon barrier with an energy (or heat) recovery system above it in the crawlspace. This latter method may also be the appropriate method when working with a slab in an existing home. In new home construction in this area it is advisable, in my opinion, to have a radon mitigation company with experience placing a hermetically sealed double-layer of radon barrier material under a slab with a layer of sand or gravel immediately above it, before the slab is poured. In addition, all slab openings should be sealed on expansion joints grooves and penetrations, in which case a slight pressurization of this well-sealed layer of material that resides between slab and barriers can be sufficiently pressurized with a smaller air volume rate (possibly accomplished by a single fan.) Such a system accomplished an air shield against the radon otherwise dragged up by air convection. It does not protect against pure diffusive infiltration, unless also a small relief valve is built in at an appropriate location opposite to the pressurization point in order to take advantage of dilution of the air under the slab. 67 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Disposal of Granular Activated Charcoal used for the Treatment of Radon-222 in Well Water. By Robert K. Lewis PA Department of Environmental Protection Bureau of Radiation Protection Radon Division And Paul Houle, PhD, East Stroudsburg University Professor of Physics, Emeritus Abstract Though not yet a major issue, the disposal of spent granular activated charcoal (GAC) filters used in the application of residential radon reduction from well water may one day become a concern. Residual radioactivity collected on the filter media, such as natural uranium, radium, and lead need to be accounted for in order to minimize problems at the disposal site. Well water is known to contain small quantities of uranium, radium, and radon, and the GAC filter has varying collection efficiencies for each. Lead, a decay product of radon will also build up on the filter. Various disposal concerns need to be considered such as, U.S. DOT transportation issues, U.S. NRC regulations, and state TENORM guidance. This paper addresses these issues, in particular as they relate to Pennsylvania. Thesis Can a granular activated charcoal (GAC) filter used for the treatment of radon-222 (radon) in residential well water be legally disposed of in a municipal waste landfill? Introduction The current use of GAC filters in the Commonwealth to treat elevated radon in public well water is very limited, with the number of systems unknown. Additional GAC filters are in use for the treatment of various chemical contamination problems associated with well water, such as for the treatment of trichloroethylene. However, it would be expected that with the final determination of the maximum contaminant level (MCL) by the U.S. Environmental Protection Agency (EPA) for radon-222, the use of the GAC filters would 68 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 increase both in the public water systems and in private wells. This increased use would obviously necessitate the increased demand for disposal of these filters, and would exacerbate issues associated with said disposal. After reviewing the available literature, no definitive study could be found that actually looked at the disposal issue from cradle to grave. Numerous authors (Martin, 1990, Kiner, 1993 , Lowry, 1987a , Lowry, 1987b, Graves (ed.), 1987, Cothern, 1990 (ed), and Reid, 1985) mention the fact the disposal could be a problem, but none investigate the actual state and federal regulations in place to prohibit or allow GAC disposal. Marc J Parrotta (Parrotta, 1991) of the U.S. EPA Office of Drinking Water does provide a good EPA perspective on radioactivity in water treatment wastes; however, the emphasis of the paper is on public drinking water supplies. The primary issue at hand is that the GAC bed will accumulate, over time, various radioactive materials, Rn-222 and its decay products, Natural Uranium, Natural Thorium and Ra-226/228. Hess et al (Hess, 2000) observed Pb-214, Bi-214, Pb-210, Ra-226, U235, Th-234, Th-231, Tl-208, and Ac-228 on carbon filters in use for reducing radon in water. However, some of these filters were in use for up to 10 years, and in a very high radon in water area, Maine. Each of these radioactive species has different adsorptive properties toward the GAC bed, some with high affinity and some with very low affinity. Additionally, all of these radioactive substances are found in ground water in varying concentrations. One author (Martin, 1990) calculated that if the influent radon concentration was 10,000 pCi/L it would take in excess of 12 years for the GAC bed to be considered low level radioactive waste, with the presumption that it would the need to be disposed of in a low level radioactive waste site, of which there are only three in the country, Richland, WA., Clive, UT., and Barnwell, SC. This author’s (Martin) definition of low-level radioactive waste used the 2000 pCi/g (Pb-210) limit which is now outdated. A material that contains radionuclides that are present naturally in rocks, soils, water, and minerals and that have become concentrated as a result of human activities such as manufacturing, water treatment, or mining operations, is known as Technologically Enhanced Naturally Occurring Radioactive Material (TENORM). The uranium, radium, and radon that accumulate on a GAC bed are an example of TENORM (US EPA, 2000). Regulation It is not unreasonable to think that the regulations that cover hazardous and radioactive waste can be overwhelming (See Table 2). For instance the disposal of a GAC bed contaminated with radioactive isotopes could be covered under regulation by the U.S. EPA and the Resource Conservation and Recovery Act (RCRA), the Nuclear Regulatory Commission (NRC) and the Atomic Energy Act (AEA) of 1954, the U.S. Department of Transportation regulations for shipment of radioactive materials, and finally Commonwealth of Pennsylvania regulations on Municipal Waste Landfills (Comm. of PA., 1988). 69 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 U.S. EPA The Resource Conservation and Recovery Act (40 CFR 239 to 282) establishes programs for regulating non-hazardous solid waste (Subtitle D), hazardous waste (Subtitle C), and underground storage tanks (Subtitle I). There are now two aspects to consider, is the GAC bed considered hazardous or non-hazardous waste, and is it considered a mixed waste? Mixed wastes are wastes that contain a hazardous waste component, regulated under RCRA, and a radioactive component, regulated under the NRC. According to 40 CFR 261.4(b)(1) The following solid wastes are not hazardous wastes: Household waste, including waste that has been collected, transported, stored, treated, disposed, recovered or reused. “Household waste” means any material (including garbage, trash, and sanitary wastes from septic tanks) derived from households. According to a letter of February 28, 1995 by Michael Petruska (US EPA, 1995), Chief Regulatory Development Branch, U.S. EPA, household waste must fulfill two criteria to be considered exempt from regulation under RCRA: first, household waste has to be generated by individuals on the premises of a household and, second, “the waste stream must be composed primarily of materials found in waste generated by consumers in their homes.” The waste on the GAC filter is generated by the homeowners on the premises of the household, and the waste stream is via the well water used by the consumers in the home. From this we come to the conclusion that the GAC filter would not be considered hazardous waste and is exempt from regulation under RCRA. We now turn to the consideration of a mixed waste, from which we have already eliminated the hazardous aspect. Since the TENORM on the GAC filter is not regulated under the Atomic Energy Act of 1954, and since we have already concluded that it is not a hazardous waste, it is therefore not considered a mixed waste either. U.S. NRC We now deal with the radioactive part. The NRC is authorized to license and regulate the receipt, possession, use, and transfer of “byproduct material,” “source material,” and “special nuclear material”. The NRC regulations are found in 10 CFR 1-199. Title 10 CFR Part 20 Subpart K deals with radioactive waste disposal, Title 10 CFR Part 61 deals specifically with land disposal of licensed radioactive material. GAC filters are not licensed material nor are TENORM on the filter licensed material. Title 10 CFR 40 deals with the disposal of byproduct material. Byproduct material is material made radioactive by exposure to the radiation incident to the process of producing special nuclear material and the tailings or wastes produced by the extraction or concentration of uranium or thorium from ore processed primarily for its source material content. GAC filters are not byproduct material. Title 10 CFR 61.1 deals with the land disposal of byproduct, source and special nuclear material. GAC filters are also not special nuclear material (Plutonium, U-233, and U-235). Source material is uranium or thorium or any combination of uranium or thorium in any physical or chemical form or ores that contain by weight, 0.05% or more of uranium or thorium or any combination of uranium and thorium (10 CFR 20.1003). By this definition the uranium or thorium on a GAC filter could be considered source material. However, it is considered an “unimportant quantity of source material” (10 CFR 40.13(a)) if the uranium or thorium, or any combination of 70 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 uranium or thorium is by weight less than 0.05% of the mixture. Therefore, the uranium or thorium on a GAC filter would be exempt from regulation if it can be determined that the uranium or thorium concentration on the filter is less than 0.05% by weight or about 335 pCi natural uranium per gram of material or 110 pCi natural thorium per gram of material. This final caveat is yet to be determined. It will be examined in the modeling part of this paper. Three other radioactive isotopes to consider are Ra-226, Ra-228, and Pb-210. There should be very little radium collecting on the GAC filter material. Kinner et al (Kinner, 1993) showed that very little radium adsorbs to the GAC bed due to its extremely hydrophilic nature. Additionally, a cationic ion exchange unit prior to the GAC bed would remove greater than 99% of the radium in the influent stream before it even reached the GAC bed. Neither the Radium-226, Radium-228, nor the Lead-210 is regulated by the NRC since they are not source material, byproduct material, or special nuclear material. (And while these constraints are for licensed materials it is prudent to recognize that agencies such as the NRC, etc. may act on GAC filters as they discover the limits to which GAC filters can become radioactive.) U.S. DOT From a U.S. Department of Transportation point of view the main concern for GAC filters is the transportation of radioactive materials over the highways. Fortunately, there are exempt quantities of radioactive material for DOT purposes. The 2000 version of 49 CFR defined radioactive material as “any material having a specific activity greater than 70 Bq per gram (0.002 microcurie per gram).” This equates to 2000 pCi/g, which is the value found in the US EPA Carbdose (US EPA, 2001) program for disposal issues. However, the DOT regulations changed concerning the definition of radioactive material. The 2006 version of 49 CFR 173.436 now provides isotope specific values for exempt quantities of radioactive material, see Table 1 below. The exempt activity concentrations for natural uranium, uranium-238, radium-226, and lead-210 are 27 pCi/g, 270 pCi/g, 270 pCi/g, and 270 pCi/g respectively. The limits for radium-226, natural uranium, and lead210 are for the parent and assumes their progeny are in secular equilibrium. If it could be determined that the GAC filters have quantities less than the above values then DOT regulations would not apply. This is difficult, short of very expensive laboratory analysis of the GAC material. One paper by (Kinner, 1993) presented data of uranium-238, radium-226, and lead-210 coring data from GAC filters taken out of service after about one year. The GAC filter had received about 100,740 gallons of water over the year-long study. The average radon-222 concentration of influent water was 35,000 pCi/L. One GAC filter was preceded by an ion exchange filter for pre-treatment. The GAC was analyzed using high-resolution gamma spectrometry. Only the maximum values are presented here for comparison with the DOT exempt quantities. The uranium-238 concentration was 178 pCi/g, radium-226 was 0.7 pCi/g, and lead-210 was 246 pCi/g. In this case the analyzed isotopes all are considered exempt from DOT transportation regulation. The unknown in this study was the influent uranium and radium concentrations in the well water. Additionally, had the GAC filter been left in place for 71 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 more than the one year period the exempt activity concentrations may have been exceeded. We have another method of relief from DOT regulation of GAC filters. In a letter from Edward T. Mazzullo (US DOT, 2004), the Director of DOT Office of Hazardous Materials Standards to David J. Allard, Director, PA DEP, Bureau of Radiation Protection, October 8, 2004. Mr. Mazzullo writes “Household wastes, including household wastes contaminated with short-lived radionuclides, are not subject to Hazardous Materials Regulation.” This DOT “Special Permit” would then allow GAC filters (household waste) contaminated with radionuclides, even above 49 CFR 173.436 exempt limits to be transported over the highways. There are two caveats to observe for Table 1 below; one is that the columns with the SI units are the columns to use, and second, in order for a shipment to be exempt from DOT regulation it needs only to be below the activity concentration value or the consignment activity value. This was done so that NORM could be transported on the highways without regulation. As one could imagine, there would be many cases where a truck load of soil would have a consignment activity well above 10,000 Bq (270,000 pCi), but it would be extremely unlikely that the soils specific activity would be greater than 10 Bq/g (270 pCi/g). Typical soil has a radium activity of about 1 pCi/g, well below the activity concentration limit. Table 1 173.436 U.S. DOT Exempt Material Activity Concentrations and Exempt Consignment Activity Limits for Radionuclides. Radionuclide (b) Activity Concentration Bq/g pCi/g Consignment Activity Bq pCi Pb-210 (b) 10 270 10,000 270,000 Ra-226 (b) 10 270 10,000 270,000 Th nat (b) 1.0 27 1,000 27,000 U nat (b) 1.0 27 1,000 27,000 U-238 10 270 10,000 270,000 Limits are on the parent nuclides but assumes their progeny are in secular equilibrium. Several definitions from Table 1 above are given below: 72 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Consignment: A package or group of packages or load of radioactive material offered by a person for transport in the same shipment. Natural thorium means thorium with the naturally occurring distribution of thorium isotopes (essentially 100% by weight Th-232). Natural uranium means chemically separated uranium containing the naturally occurring distribution of isotopes ( approx. 99.28% U-238 and 0.72% U-235 by mass). Radioactive material means any material containing radionuclides where both the activity concentration and the total activity in the consignment exceed the values specified in the table in US DOT 49 CFR 173.436 or values derived according to the instructions in US DOT 49 CFR 173.433. We will discover that since we need to stay below either the activity concentration limits, or the consignment activity limits, and not both, it is easier to stay below the activity limits alone. We will therefore use activity concentration limits when considering U.S. DOT limits in our modeling section of the paper. PA DEP Naturally occurring radioactive materials (NORM) are not specifically regulated in Pennsylvania. TENORM is not regulated unless resulting radiation doses exceed the limits set forth in Title 25, Chapter 219 of Pennsylvania Code (Comm. of PA., 1997). Chapter 219 deals with Standards for Protection against Radiation. As found in 219.51 the dose limit for members of the general public is 100 mrem/yr, and the dose limit in an unrestricted area is 2 mrem/hr, if the individual were continuously present in the area (PA Code 219.51). NCRP Report No. 116 (NCRP, 1993) also recommends a general public dose limit of 100 mrem/yr for man-made sources other than medical and natural background, for continuous exposure. For the specific case of a spent GAC filter disposed of in a solid waste land fill containing TENORM, dose modeling must show that the general public would be exposed to no more than 25 mrem/yr, a fraction of the total dose limit. The Commonwealth can and does regulate discrete sources of radium-226, where the activity is above that stipulated in Chapter 217. The Appendix B Chapter 217, Exempt Quantities has an exempt quantity for radium-226 at 0.1 microcuries (100,000 pCi), and the exempt quantity for lead-210 is also 0.1 microcuries. Chapter 217 deals with the Licensing of Radioactive Material. For the specific case of land disposal of TENORM 73 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 material that exceeds Chapter 217 exempt quantity limits, dose modeling must show that radiation dose is maintained as low as reasonably achievable (PA Code 219.182). Municipal waste landfill disposal of TENORM is specified in Chapter 273 (Municipal Waste Landfills) of Pennsylvania Code (Comm. of PA., 1988). Paragraph 273.201(m) says that TENORM may not be disposed of in a municipal waste landfill, “unless approved in writing by the Department, and the disposal does not endanger the environment, facility staff or public health and safety.” Where the problem arises is at the disposal facility. Though the radioactive material may be exempt from both Federal and State regulation, it may still cause a solid waste facility radiation monitor to alarm. Portal monitors are set to alarm at about 10 microR/hour above background, where background in PA is about 10 microR/hour. This is a most undesirable event, if not previously planned for. The truck must be surveyed, the radioactive material identified and a half-life determined, a DEP regional health physicist may need to be on site, the contents may be accepted or rejected, and the facility records of the incident must be logged. If the contents are rejected by the disposal facility the hauler must obtain a DOT Exemption Form prior to going back on the road (e.g. back to the originator of the waste.) However, if the incoming material that causes the alarm is determined to be NORM, then there are no disposal restrictions and the material can be accepted at the solid waste facility for final disposal. In the case where any available information would indicate that the suspect material is TENORM, as would be the case with a GAC filter, then the DEP Area Health Physicist may authorize immediate disposal. For small quantities the following conditions must be met: the volume of the waste must not exceed one cubic meter, the gamma radiation level at a distance of 5 cm from any source surface does not exceed 50 microR/hour, and the concentration of combined radium isotopes (226/228) does not exceed 5.0 pCi/g. Disposal of higher volumes, surface radiation values greater than 50 microR/hr, and higher radium concentrations may still be disposed of, however, with DEP approval, and environmental assessment and pathway analysis to demonstrate that the annual dose to any member of the general public is unlikely to exceed 25 mrem/yr (PA DEP , 2004). This analysis in fact has already been performed for the case of higher concentrations of radium. In our Pathway Analysis section we actually use 270 pCi/g of radium-226 as one of our inputs for the model. That model result showed a maximum dose of 4.62 mrem/yr, well below the 25 mrem/yr limit. This therefore shows that concentrations of radium-226 higher than 5 pCi/g can safely be disposed of. This also shows that we can exceed the Appendix B Chapter 217 exempt quantity of radium226 of 100,000 pCi, since our GAC charcoal mass is 25,143 grams and we accumulate 0.01 pCi/g/day. After 399 days we have 100,149 pCi on the GAC filter assuming 100% removal efficiency. It is our desire to be able to keep the GAC filters in place for about two years. After two years the GAC filter would have about 100,149 pCi times two years or 200,298 pCi on GAC bed, well above the 100,000 exempt limit, but still acceptable based on pathway analysis. 74 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Table 2, Federal and State Regulatory Limits Agency Uranium Nat Thorium Nat Radium Lead EPA No Reg. No Reg. No Reg. No Reg. NRC ~335 pCi/g ~110 pCi/g No Reg. No Reg. DOT See table 1 See table 1 See table 1 See table 1 DEP <5 pCi/g (Ra-226/228) DEP GAC Volume < 1 m3 DEP <50 µR/hr at 5 cm from surface DEP Annual does to Gen. Public < 25mrem/yr These criteria must be met for disposal and/or transportation. An important note about Table 2 above. As published in the Federal Register on July 2, 1979, “On December 3, 1979, the NRC amended its regulations in 10 CFR 71 to require that all shipments of radioactive material by NRC licensees be made in accordance with DOT requirements.” This would imply that for our purposes of this paper we should ignore the NRC limits and use DOT limits as found in Table 1which are more restrictive. The GAC Filter From a disposal point of view we need to know what would collect on the filter media over its time of use in the home. We certainly know its intended function is to reduce well water radon concentrations, thus it will collect radon-222 and its decay progeny up to and including lead-210. We will know the influent radon concentration and with several other assumptions can use Carbdose version 5.0 to calculate the build-up of lead210 over time. We should try to assure that the lead-210 on the GAC bed does not exceed 0.1 microcuries, (Which turns out to be approximately 4 pCi/g in our GAC filter) the DEP Chapter 217 Appendix B Exempt Quantity limit for Pb-210. We can also calculate the gamma dose rate from the GAC tank. For dose rates we would like to be below 50 µR/hr, and preferably below twice background levels (~20 µR/hr), so as not to alarm portal monitors. The other more difficult disposal issue to consider is the Ra-226/228 and uranium concentrations on the GAC bed. More difficult because, short of running a gamma spectrum on the GAC we can not predict how much radium or uranium will be on the 75 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 GAC. It is also very unlikely that any homeowner would have determined the radium or uranium concentrations in their private well water. And finally, we do know that both radium and uranium occur in all ground water. The one good thing about this fact is that their concentrations in ground water are generally very low. Data supplied by the PA DEP, Bureau of Water Standards and Facility Regulation (PA DEP, 2008) showed a three year (2005, 2006, 2007) average for natural uranium, radium-226 and radium-228 of 1.57, 0.15, and 0.27 pCi/L, respectively. These values represent samples at entry points (finished water) for public water systems within the Commonwealth. Private well water may show higher values. Through a literature search and several personal communications we have been able to determine some approximate efficiencies for the removal of uranium and radium from water by a GAC filter. This will be important to know when we try to calculate how much uranium and radium will accumulate on the GAC bed based on an assumed influent concentration of the two radioisotopes. Karadeniz et. al. (Karadeniz, 2000) found a uranium recovery efficiency for charcoal of 97%. However, this was under specific water quality conditions of 150 ppm uranium, 50 degrees Fahrenheit, and pH of 3. Phillip Egidi (Egidi, 2008) of the Colorado Department of Public Health claims that GAC is about 35% effective for removal of radium, and very effective (>90%) for uranium removal. Finally, Zakutevskii et. al. (Zakutevskii, 2007) conclude that carbon materials as sorbents have fairly high rate of uranium adsorption from a solution and sorption capacity of 1.5-2 mg-equiv g-1 (161 – 214 pCi U/g carbon, or 4,714,312 pCi/GAC unit.) There are also various published values for radon-222 occurrence in the commonwealth, Jerry Rupert (Rupert, 1993) of the PA DEP, Bureau of Drinking Water Management, reported a population-weighted mean of 1,299 pCi/l with a median of 588 pCi/L, for community ground water system entry points. A U.S. EPA study found a mean of 756 pCi/l for finished water from public groundwater, and Dixon and Lee (Dixon and Lee, 1988) found a mean of 1,570 pCi/L. 76 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 MODELING From Table 2 above, there are four areas of concern: Uranium, Thorium, Radium and Lead, all which may accumulate on the GAC bed. Uranium We will consider each in turn beginning with Uranium. There are two regulations of concern, one established by the DOT (27pCi/g.) and the other by the NRC (335pCi/g.). The quantities in parenthesis are the levels below which each of these agencies considers the material exempt from their regulations and rules. As established by the U.S. EPA the best available technology(s) (BAT) for the removal of uranium from public drinking water is via anion exchange, lime softening, enhanced coagulation/filtration, or reverse osmosis, and not GAC. Nevertheless it was decided that it’s likely some of the Uranium will be filtered out by the GAC unit, though the efficiency of removal is somewhat convoluted. In particular various references have tended to support a uranium removal efficiency by GAC in the 90 to 99% range, though this may be for a limited time after which breakthrough (the condition at which the uranium concentration on the GAC begins desorbing from the charcoal, causing the outflow water to have a higher uranium concentration than the inflow water) occurs. This time is reported to be between 3 and 6 months (Sorg, 1988, and Lowry, 1988). The worst possible case is if the GAC unit was 100% efficient in removing the Uranium which would lead to the highest Uranium concentration in the charcoal. In the first few months of use we do find the efficiency of uranium removal by GAC to be almost 100%, and it is somewhat enlightening to investigate that case over a lengthy period. During the balance of this work we make the following assumptions: The volume of the charcoal is 2.0 ft3, the charcoal density is 0.44 gm/cm3, a typical household uses 300 gallons (1134 liters) of water/day. This leads us to recognize that there is 25,143 grams of charcoal in the tank. We will also use a natural uranium concentration in the water as 1.72pCi/l (PA DEP, 2008) (ground water sources only). This is a value in agreement with work done by Cothern and Lappenbusch (Cothern and Lappenbusch, 1983). From these values we find 1950 pCi are added to the GAC filter each day (1.72pCi/l x 1134 l/day) or 0.078pCi/g/day (1950pCi/day / 25143g) which would result in the GAC filter reaching the DOT exemption limit of 27 pCi/g in 346 days or just about one year. If we consider only the NRC limit of 335 pCi/g, this would allow 4295 days, or 11.8 years before the GAC unit arrives at the NRC exemption limit and this seems to be a respectable time period. 77 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Naturally as the Uranium concentration in the water increases, the time to arrive at exempt values will decrease and this prompts us to consider under these conditions (100% removal efficiency) what the maximum natural uranium concentration would be that would lower the time to two years to arrive at the NRC exemption value of 335 pCi/g. One can easily show that the value is 10.2pCi/l, which is well above median uranium in ground water values. It is interesting here to note that according to the PA DEP the range of natural uranium concentrations found in ground water in PA is as high as 57 pCi/l. and as low as equipment detection limits (~0.03 pCi/L). So it appears that under the worst possible conditions (Without breakthrough), a natural uranium concentration of 10.2 pCi/l will require removal of the charcoal every two years, or probably slightly less. At least for the case of a continuous uranium removal efficiency of 100%. In fact under these conditions it’s simple to produce a graph of the time needed to arrive at the NRC exempt limit versus the natural uranium concentration in the water, leading to Figure 1. Figure 1 natural uranium concentration in water pCi/l natural uranium conc. vs. years to NRC exempt limit at 100% efficiency removal 12 10 8 6 4 2 0 0 5 10 15 years to NRC limit of 335pCi/g 78 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Two studies, one performed by (Lowry, 1988), the other by (Sorg, 1988) have shown that Uranium collects in the GAC filter at almost 100% removal efficiency but only for a period of 3 to 6 months after which breakthrough occurs. Another analysis using alpha spectrometry of a uranium in well water sample performed by the PA DEP Bureau of Laboratories in 2008 showed an influent natural uranium concentration of 3.635 pCi/l and an outflow natural uranium concentration of .017 pCi/l, leading us to a 95% reduction for a GAC unit that was in use for approximately only one month. This tempers the analysis of Figure 1, since those results are based on 100% removal efficiency continuously over the time periods mentioned. This underlines the result that the analysis above is clearly leading to maxima which are very conservative. We may also consider the case where the uranium removal efficiency is 100% but for a period of only six months at which point the uranium concentration on the GAC bed will be a maximum because of breakthrough. For these conditions we can then calculate the uranium in water concentration in the influent water that will produce a uranium concentration on the GAC bed of 335 pCi/g. The result is 41pCi/l and this concentration would be an anomalously high value. This suggests that in almost all cases the uranium concentration will not be a disposal issue. If the GAC filter is to be transported, then the 27pCi/g limit is the constraint. In this case, using a 100% uranium removal efficiency for six months we easily show from: 27 pCi l = conc.ofU ( pCi / l ) ! 1134 ! 180d / 25143 g g d Which leads us to the maximum allowed uranium in water concentration to be 3.3pCi/l Lead We’ll now consider the Pb210 problem. This comes in two parts. First is the issue of how much radioactivity (pCi/g) will collect in the GAC tank, and second is the dose that radioactivity provides to its surrounding. We deal with the first part of this problem here. As Radon decays the only daughters which produce a problem are those with half lives at least a few days or longer which lead us to the Pb210, Bi210 and Po210 with corresponding half lives of 22.3y, 5.01d, and 138.4d. EPA has created a computer program titled “CARBDOSE” which is ideally suited to the calculation needed to answer the question, “How many years must pass for a given radon in water concentration to deposit 270 pCi/g of radioactivity from Pb210 in the GAC tank?” The results are the same if we include the daughter concentrations of Bi210 and Po210 since they are presumed to be in secular equilibrium with the Pb210. 79 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Again the assumptions of 300 gallons/day, 100% efficiency for the removal of radon by the GAC, 2 ft3 of charcoal and a density of 0.45g/cc. (This last value for the density of the carbon is approximately 2% higher than that used earlier. It is the value used by the CARBDOSE program. This last value is slightly different than what was used in the above calculations but the difference is negligible.) Running the program for different radon concentrations in the water yields Figure 2 below. Figure 2 radon conc. vs. time to DOT exempt value of 270pCi/g for Pb 210 radon conc. pCi/l 30000 25000 20000 15000 10000 5000 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 time in years to exempt value 210 Figure 2: A graph of the time it takes to accumulate 270 pCi/g of Pb on the GAC filter as a function of the influent radon in water concentration. We’ll note that a GAC unit may have a radon concentration flowing into it as high as 25000pCi/l and it will arrive at the DOT exempt value of 270 pCi/g in 2.5 years. This should give guidance for how frequently the GAC needs to be changed out to avoid having radioactivity above the DOT exempt value of 270 pCi/g for Pb210 Radium We now consider the issue of radium. There are two radium isotopes of concern for our purposes, radium-226 with a half-life of 1600 years and radium-228 with a half-life of 5.84 years. The U.S. EPA MCL for radium is 5 pCi/L for the combined two isotopes. The EPA MCL applies to public water systems and not private wells; however, we will consider the question of how long radium in water takes to accumulate on the GAC cylinder in a private residence, to a concentration of 5 pCi/g. The 5 pCi/g value is a 80 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 disposal limit as defined by the PA DEP beyond which disposal will be problematic. So we consider an influent concentration of Ra 226 and 228 at the EPA MCL of 5 pCi/l, and we ignore the fact that some Ra 228 will decay during the calculated time period. This will be justified by our results and in any case will provide us with a conservative result. The initial approach used is to assume a 100% removal rate to identify the time to 5pCi/g on the charcoal bed assuming a homogeneous distribution of the isotope throughout the bed. With these assumptions we find it would take only 22 days for a GAC unit to reach the 5pCi/g limit. Turning this around we can ask what efficiency of Radium removal is needed by the GAC unit to take 2 years to reach the 5pCi/g limit when the influent concentration is 5 pCi/l, and find this to be 3%. Next we consider data provided by the PA DEP, Bureau of Water Standards and Facility Regulation. They collected data that showed an average radium-226 concentration of 0.15 pCi/L and an average radium-228 concentration of 0.27 pCi/L in public drinking water supplies, for a sum of radium-226/228 of 0.42 pCi/l. Other information (Egidi, 2008 ) suggests that GAC may have a removal efficiency of about 35% or less for radium. Again assuming none of the radium decays, we find (0.42 pCi/l x 1134 liters/day x .35 / 25143 g.) equals 0.007 pCi/g/day deposited onto the GAC bed. This leads us to a time of 2.1 years to reach the 5 pCi/g. limit. Thorium Next, we look at thorium. Ninety nine percent of thorium is Th-232 which has a half life of 14 billion years. Thorium is not regulated by EPA in public drinking water. However, since EPA has an MCL of 15 pCi/l for gross alpha activity, the maximum thorium activity would be 15pCi/l. (This assumes the water is treated to this limit of course.) We can again assume a 100% removal efficiency. We have found no references to describe the removal efficiency of thorium in ground water by the GAC column. Using 15pCi/l, we find the number of days to the U.S. DOT limit of 27 pCi/g (The smaller of the two exemption limits, DOT and NRC ) is 40 days at 100% efficiency. Lowry (Lowry, 1988) points out that “Thorium levels…containing more than 0.1 pCi/l would be unusual, and one with more than 1.0 pCi/l would be extremely rare in ground water. Another group ( Jia, 2008) have measured the concentration of three thorium isotopes (232, 230, and 228) in drinking water in Rome, Italy and found their concentrations to range from 1.9 x 10-5 pCi/l to 3.6 x 10-2 pCi/l. 81 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Using the largest of these values, 1.0 pCi/l as the thorium concentration in the water, we find that the time to reach the exempt limit of 27 pCi/g becomes 1.6 years. And this would be an extremely rare case. Of course if the value of 0.1 pCi/l is used this time to the exempt limit rises to 16 years, and this is the more likely case. Thorium is not considered a disposal issue due to its extremely low concentration in ground water. GAC Dose Rate We now consider the issue of the gamma exposure rate and its limits as given by the PA DEP, Bureaus of Radiation Protection and Land Recyling and Waste Management, which requires that the exposure rate be below 50 uR/hr at 5 cm (see Table 2) from the surface of the GAC tank for the purposes of disposal. Only gamma emissions penetrate the tank so we don’t need to consider the issues of betas and alphas. It is interesting to note that for waste disposal, twice the background level of 10uR/hr, or 20 uR/hr is used to set off the alarms at the waste disposal site. In those cases, then the 50 uR/hr at 2 inches from the surface of the tank is applied. The computer program CARBDOSE is the tool of choice to perform this calculation. We make the very good approximation that the daughters, namely Bi214 and Pb214 are in secular equilibrium with the radon as the radon decays CARBDOSE allows us to calculate the gamma exposure rate verse the influent radon concentration, see Table 3. Table 3 Influent Rn Conc. Vs. Gamma Exposure rate Inflow Rn conc. (pCi/l) Exposure 2in. from tank Time for exposure to wall decrease to 50 uR/hr. uR/hr (days) 1000 244 8.8 5000 1220 17.7 10000 2440 21.4 15000 3660 23.7 20000 4880 25.3 25000 6090 26.5 The last column assumes the daughters decay at the same rate as the radon after the tank is removed from the inflow. Table 3 also assumes that after 30 days of operation the 82 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 GAC has attained almost 100% equilibrium with radon and its daughters, and 30 days is used in the above calculations. From this table we conclude that for those cases where GAC is a viable treatment for radon in water, that is, radon concentrations in water of less than 25,000pCi/l at least as far as exposure concentrations are concerned, setting the tank aside for one month will prevent the exposure from the tank as measured two inches from the tank wall from being greater than 50uR/hr. This Carbdose calculation looks only at the radon daughters. Other isotopes such as Uranium, etc. which may be in the influent water and collect on the GAC filter will also contribute to the gamma exposure rate. The authors’ recommend that all installers of GAC filters purchase and use an appropriate instrument for measuring the gamma exposure rate from the GAC tank and if the exposure rate is greater than 50uR/hr, store the tank at a safe location until such time as the exposure rate is significantly below 50 µR/hr and preferably below 20 µR/hr. Pathway Analysis A solid waste facility must have in place a plan to describe the potential exposure pathway for dealing with radioactive material in the waste stream. One example of this radioactive material for our purposes would be the used GAC filter. One way to model these exposure pathways would be to use basic and conservative regulatory computer codes such as the EPA’s CAP88 or the DOE/NRC’s RESRAD codes. To meet DEP disposal requirements the modeling must show that the annual dose to the general public does not exceed 25 mrem/yr, and for this demonstration we use RESRAD, RESidual RADioactivity (RESRAD, 2001). The input parameters for the model used the maximum values as found in our Table 2 for uranium, thorium, radium, and lead, 335, 110, 270, and 270 pCi/g respectively. Due to the complex nature of the parent-daughter relationship in ground water systems we did not run the dose calculation with all daughters in full equilibrium. If a precise gamma analysis of the GAC material could be run this pathway analysis could be refined with those specific isotopes. It was assumed that 7.4 square meters (80 square feet) of ground was contaminated to a depth of 0.01 meters (0.4 inches). This coverage would be approximately what the 2 cubic feet of GAC material would disperse to. The model then assumes that a farmer lives on top of the contaminated site, raises crops and livestock, and drinks the ground water. There are nine environmental exposure pathways considered in the model. The model calculates doses out to 1000 years. The model also provides for a soil cover over the contaminated area of 0.6 m (24 inches). A maximum dose of 4.62 mrem/yr occurs at 599 years, and this is primarily due to ground shine. Ground shine is radioactivity deposited on the ground that provides a pathway for external exposure. This computer run show’s that this particular GAC filter would not be subject to the 25 mrem/yr limit, and from this aspect would be safe for disposal. 83 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Conclusions It is very possible that the issue of TENORM, i.e. the radionuclides on a GAC filter, will become more of an issue in the near future. We found the EPA does not regulate TENORM, nor does the NRC unless it becomes Source Material. We found that of the three U.S. Government agencies, the U.S. DOT regulations would be the most likely to have an impact on the disposal of spent GAC filters, via transportation of the GAC over the highways. However, with the clarification from the Edward T. Mazzullo letter to the PA Department of Environmental Protection, we see that household waste, which GAC is considered to be, is exempt from the US DOT Hazardous Materials Regulations. We have come to the conclusion that the issue of disposal of TENORM wastes will most likely be handled at the state level, this is certainly the case as it applies to the Commonwealth of PA. In the Commonwealth of PA, waste containing NORM may be disposed of in solid waste disposal facilities with no restrictions. If available information indicates that incoming waste contains TENORM, then various PA DEP criteria must be met before the waste can be accepted for disposal. We researched and found various concentration values for uranium, thorium, radium, and lead in private and public water supplies, and found out how efficient the GAC material is at removing said radioisotopes. We have concluded that any thorium on the GAC bed will not a disposal issue and that uranium, radium, and lead on the GAC can be safely dealt with by disposal approximately every two years. We have not examined the issue of the decreasing efficiency of the GAC bed for radon removal over time. As this issue is clarified the two year disposal recommendation may need adjustment. It is our conclusion that the spent GAC filter will be able to be picked up by curb side waste removal services, transported over the highways and safely disposed of in the local solid waste disposal facility, without encumbering any regulatory oversight, assuming the recommendations of this paper are followed. All mitigators should use appropriate meters for monitoring exposures near the GAC tank and record such information prior to carbon disposal. Influent concentrations of radon as high as 25,000 pCi/l would require the tank be set aside for approximately 30 days. 84 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References 1. Commonwealth of Pennsylvania, Pennsylvania Code. Title 25, Environmental Protection, Chapters 215, 216, 217, 218, 219, 220, 221, Volume 1, Bureau of Radiation Protection, 1997. 2. Commonwealth of Pennsylvania, Pennsylvania Code. Title 25, Environmental Protection, Chapter 273, Bureau of Waste Management, Municipal Waste Landfills, 1988. 3. Cothern, C.R. and Lappenbusch, W.L. Occurrence of Uranium in Drinking Water in the U.S. Health Physics, Vol. 45, No. 1 July 1983, pp. 89-99. 4. Cothern, C.R., and Reber, P.A. (eds). Radon, Radium and Uranium in Drinking Water. Lewis Publishers, Inc. 1990. 5. Dixon, K.L., and Lee, R.G. Occurrence of Radon in Well Supplies. Journal American Water Works Association, July 1988. 6. Egidi, P. Personal Communication. Colorado Department of Public Health, Radiation Management Unit, Hazardous Materials and waste management Division. 7. Graves, B. (ed.). Radon, Radium, and other Radioactivity in Ground Water. Proceedings of the NWWA Conference, April 7-9, 1987. Lewis Publishers, Inc. 8. Hess, C. T., Bernhardt, G.P., Amsden, J.J., Ngue Mba, J., and Jones, R. Radionuclide Accumulation, Radiation Exposure, and Regeneration for Granular Activated Carbon Removing Radon from Drinking Water. Technology, Vol. 7 pp. 431-441, 2000. 9. Jia, G, et.al., Applied Radiation and Isotopes, accepted manuscript, 2008. 10. Karadeniz, M., Eral, M., and Kutahyali, C. Selective Uranium Adsorption on Activated Carbon. Ege University Institute of Nuclear Science, Bornova, IzmirTurkey. Proceedings of Eurasia Conference on Nuclear Sciences and Its Application. October 23-27, 2000. 11. Kinner, N.E., Malley, J.P., Clement, J.A., and Fox, K. R. Using POE Techniques to Remove Radon. Journal American Water Works Association, June 1993. 12. Lowry, J.D., and Lowry, S.B. Modeling Point-of-Entry Radon Removal by GAC. Journal of American Water Works Association, October 1987a. 85 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 13. Lowry, J.D., Brutsaert, W.F., McEnerney, T., and Molk, C. Point-of-Entry Removal of Radon from Drinking Water. Journal American Water Works Association, April 1987b. 14. Lowry, J.D. and Lowry, S.B. Radioniclides in Drinking Water. J. American Water Works Association. Vol. 80, No. 7, July 1988, pp. 50-64 15. Martin, R.D., and Smith, K.A. GAC as a Method for Radon Abatement. Proceedings of the Fourth Annual Radon Conference, October 4-6, 1990. 16. NCRP Report No. 116. Limitation of Exposure to Ionizing Radiation. National Council on Radiation Protection and Measurements, Bethesda, MD. March 31, 1993. 17. Parrotta, M.J. Radioactivity in Water Treatment Wastes: A USEPA Perspective. Journal Amercian Water Works Association, April 1991. 18. Pennsylvania Department of Environmental Protection (PA DEP), Bureau of Radiation Protection and Bureau of Land Recycling and Waste Management. Final Guidance Document on Radioactivity Monitoring at Solid Waste Processing and Disposal Facilities, Jan. 2, 2004. 19. Pennsylvania Department of Environmental Protection, Bureau of Water Standards and Facility Regulation. Personal communication, Lori Ruesskamp, June 2008. 20. Reid, G.W., Lassovszky, P., and Hathaway, S. Treatment, Waste Management and Cost for Removal of Radioactivity from Drinking Water. Health Physics, Volume 48, No. 5, 1985. 21. RESRAD , Version 6.22, Environmental Assessment Division of Argonne National Laboratory. For the U.S. Department of Energy, 2001. © 22. Ruesskamp, L. Personal Communication. PA DEP, Bureau of Water Standards and Facility Regulation. February 2008. 23. Ruppert, J. The Occurrence of Radon in Pennsylvania Community Groundwater Systems. PA DEP, Bureau of Water Supply and Community Health. May 1993. 24. Sorg, T.J. Methods for Removing Uranium from Drinking Water. J. American Water Works Association. Vol. 80, No.7, July 1988, pp. 105-111. 25. US Department of Transportation, Letter from Edward T Mazzullo, Director of Office of Hazardous materials Standards, US DOT to David J. Allard, Director of Bureau of Radiation Protection, PA DEP. October 8, 2004. 86 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 26. US EPA. RCRA Online. Letter to John McNally, February 28, 1995 from Michael Petruska, Chief Regulatory Development Branch. 27. US EPA. Evaluation of EPA’s Guidelines for Technologically Enhanced Naturally Occurring Radioactive Materials. Report to Congress. EPA 402-R-0001, June 2000. 28. US EPA. Office of Ecosystem Protection, Region 1. Carbdose Version 5.0, 2001. 29. Zakutevskii, O., Psareva, T., Strelko, V., and Kartel N. Sorption of U(VI) from Aqueous Solutions with Carbon Sorbents. Radiochemistry Volume 49, No. 1, 2007. 87 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 ELEVATED RADON LEVELS IN HIGH RISE CONDOMINIUM FROM CONCRETE EMANATION Bill Brodhead WPB Enterprises, Inc., 2844 Slifer Valley Rd., Riegelsville, PA USA wmbrodhead@gmail.com www.wpb-radon.com ABSTRACT The author investigated five residential units of an eight story high rise condominium building that had elevated indoor radon levels on every floor. The building had two levels of ventilated garages under most of the building and only partial ground contact. Each floor was constructed with post stressed concrete floors and ceilings. Blower door and ventilation dilution measurements in the units tested indicated very low air change rates to the exterior of the units. E-PERM’s® were placed under three liter metal accumulator’s over exposed surfaces of the concrete in six locations of the building to determine the emanation rate from the concrete. The measurement results indicated the concrete radon emanation rate along with the low ventilation rates was the cause of the elevated indoor radon levels. GENERAL BUILDING INFORMATION The investigated building was actually two buildings above grade with three levels of open parking garages under most of the building. These garages are mechanically ventilated and open to each other. There is an alley way above the garages that separates the buildings. One side of the building is five stories tall. The other side is eight stories tall. There is a single row of ground contact condominiums and commercial stores surrounding three sides of the buildings. Both buildings are built with post stressed concrete slab floors and ceilings. The exterior and interior walls are metal stud framed except around the stairwell and elevator shafts which are concrete walls. There are multiple concrete beams throughout the building supporting the concrete slabs. See aerial photo of the site in Figure 1 below. 88 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 1 1998 aerial view of the building Figure 1 Aerial Photo of both Buildings Building Radon Measurements Short term radon measurements were made by independent testing contractors in 23 different units mostly in the Fall of 2007. The radon measurements in the units varied from 4.0 pCi/l (150 Bq/m3) to a high of 16.3 pCi/l ( 600 Bq/m3). The average of all the measurements was 7.5 pCi/l ( 278 Bq/m3). Every floor of both buildings had units with radon measurements above the EPA guideline. Radon measurements in five different hallways averaged 6.2 pCi/l (230 Bq/m3). Three of the units had short term tests with the windows open. The radon levels with windows open ranged from 0.6 pCi/l (22 Bq/m3) to 3.0 pCi/l (111 Bq/m3). See the range of radon measurements in Figure 2 below. The parking garage under the building has a large exhaust fan on one side and a supply fan on the other side. There were seven measurements made in the parking garage that ranged from 0.3 pCi/l (11 Bq/m3) in two locations to a high of 2.9 pCi/l (107 Bq/m3). The elevator shaft in one of the buildings measured 3.4 pCi/l (126 Bq/m3) and 4.5 pCi/l (167 Bq/m3). The garage measurements and elevator shaft measurements were all less than the measurements in the units indicated that the source of the radon was not likely to be from the soil. There are no 89 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 other air pathways from the lower level to the upper units other than the elevator shaft, the stairwell and possibly some small unsealed openings around conduit runs that are routed up through the building. There is no central HVAC system in the building. Each of the units has it’s own heat pump air handler. Figure 2 Short term radon levels measured inside units Determining the Source Strength A charcoal canister sealed under a poly sheet against a concrete wall in the parking garage averaged 97.7 pCi/l (3615 Bq/m3). This clearly demonstrated that there is significant radon emanation coming from the concrete at the location tested. This test does not however allow any conclusion about how much radon is emanating from the concrete. Note that it is unclear if charcoal canisters can be used to reliably determine the radon emanation from a building material. In order to quantify the radon emanation out of the concrete and to determine if there was significant variation in emanation rates in different locations, concrete emanation measurements were made of the floor, ceiling and walls as well as the ambient air in three different locations in each building. S chamber E-PERMs with short term electrets were used for these tests because they are true integrating detectors and multiple locations can be tested at the same time. The 90 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 emanation rate was determined by placing an E-PERM inside metal accumulators that were sealed to bare surfaces of the concrete. The accumulator was a stainless steel 3.0 liter mixing bowl that was carefully sealed to the concrete using a putty window sealer (Mortite by Frost King) that was placed on the lip of the bowl to form an air tight seal against the concrete. See the photos in Figure 3, 4 and 5 below. Note that in order to obtain the largest signal from the radon emanation from the concrete it is necessary to have as large a surface area versus free air volume inside the accumulator as possible. The three liter mixing bowls provide 0.13 ft2 of surface area per liter of accumulator. The accumulator test was run from 16 to 23 hours at each location. In each case the emanation tests were made on an exposed concrete floor, ceiling or wall of electrical room, storage room or stairwell. No emanation measurements could be made in a unit because there was no exposed concrete. Figure 3 E-PERM placed inside Emanation Bowl with edge sealing 91 Figure 4 E-PERM Slab Emanation with room air measurement Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 5 E-PERM Emanation of ceiling of electrical room The electret pre-exposure and post exposure voltages were used to obtain the average radon concentration under the accumulator and in the room the accumulator tests was being performed in. Note that it is important to quantify the initial radon concentration when the accumulator is sealed to the concrete, especially if the emanation rate is low. The average radon concentration was determined by exposing an E-PERM in the test location. This average concentration was then assumed to be the concentration in the air when the flux tests were started. A more exact method of obtaining the ambient radon at the beginning of the flux test is to expose an E-PERM inside a sealed glass jar that is available from Rad Elec for making radon in water measurements. The voltage loss of the electret sealed in the jar could be subtracted from each flux measurement voltage loss to subtract out the influence of gamma as well as the ambient radon. Note that there is about a 15% lower voltage loss of an electret starting with 250 initial volts versus an electret with 750 initial volts that will cause a small bias. A Bicron Micro-Rem gamma survey meter was used to determine the gamma levels used in calculating the average radon concentration. The gamma measurements throughout the building varied from a low of 4.0 µR/hr to a high of 10.0 µR/hr. There was not any significant increase of gamma directly adjacent to the concrete which might influence the E-PERM reading. Note that the gamma variation would be more critical if a low emanation rate was being measured. In each case the gamma measurements made at the test locations were used in determining the EPERM radon measurement result. 92 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The E-PERM chambers were closed up immediately after being removed from the accumulator. A small correction factor of an additional 10% was added to the calculated emanation rate to compensate for the additional radon and radon decay products that have entered the chamber but have not had sufficient time to discharge the electrets. This correction is not typically necessary when making longer measurements in a relatively stable radon concentration. An ingrowth measurement produces the highest radon concentration at the end of the measurement with a corresponding greater influence from the final radon and radon decay products left in the chamber from the exposure. WPB obtained this calibration adjustment by carefully measuring E-PERMs exposed to an ingrowth that were closed immediately and some E-PERMs that had the same exposure but were left open in a low radon environment for an additional 3 hours before reading the final voltage. The average radon measurement result from the E-PERM under the accumulator and the room air measurement was used to determine the emanation rate by a simple formulae that did not take into consideration the change in ingrowth rate that happens over a multi-day exposure or because of back diffusion into the concrete that also happens with an increasing influence as the length of the measurement extends greater than a day. The emanation rate was determined by subtracting out the assumed or measured initial radon in air concentration (which is actually decaying away), the number of hours exposed, area the bowl covers and the free air inside the accumulator. The concrete emanation was calculated in units of pCi/ft2/hr. The emanation rate can be converted to Bq/m2/hr by multiplying the pCi/ft2/hr by 0.398. See the results in Table 2 below. The radon emanation out of the concrete did not vary significantly across the building. The lowest result was 26.7 pCi/ft2/hr and the highest was 43.9 pCi/ft2/hr. For detailed information on the calculations to use to determine the emanation rate for different length exposures refer to the authors paper entitled “Measuring radon, thoron and action emanation from concrete and granite with continuous radon monitors and e-perms, 2008”. Location East 5th Floor East 6th Floor East 7th Floor West 3rd Floor West 4th Floor West 5th Floor Average Slab Slab Ceiling Ceiling Walls Walls 2 2 2 2 2 pCi/ft /hr Bq/m /hr pCi/ft /hr Bq/m /hr pCi/ft /hr Bq/m2/hr 33.0 26.7 42.6 38.6 32.0 42.5 35.9 13.1 10.6 17.0 15.4 12.7 16.9 14.3 36.2 43.9 32.2 37.0 40.6 14.4 17.5 12.8 14.7 16.5 31.7 15.2 49.8 19.8 33.8 49.1 34.2 41.7 13.5 19.6 13.6 16.6 Table 2 Concrete Emanation results for both buildings 93 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Although there is some variability in the emanation from the different locations there is actually reasonable consistence between all the measurements. The walls which are thicker did have the highest average radon emanation rate. This indicates that it is likely that all of the concrete used in both building has a similar emanation rate. The builder indicated that the same concrete company was used for the entire project. There were four different locations where the concrete ceiling and the concrete slab floor directly above it were measured. The difference between the measurements in each case is given in Table 3 below. Concrete Ceiling 36.2 43.9 37.0 40.6 Concrete Floor 26.7 42.6 32.0 42.5 Ceiling versus Floor + 35.6 % + 3.1 % + 15.6% - 4.5% Table 3 Variation between ceiling and floor above it emanation rate Cozumuta, Graaf and Maijer in 2003 reported that although radon emanation out of concrete can vary by an order of magnitude depending on the relative humidity, there would typically be only a 10-15% emanation difference in the indoor humidity range of 30% to 70% RH. The floors and ceilings were reported to be 7.5 inches (19 cm) thick. The thickness of the concrete walls could not be determined. The average emanation rate from the walls was 23% greater than the average of the ceilings and slab but there is significantly more floors and ceilings than piers or walls in the building. This paper does not address the difference in emanation rates based on the thickness of the concrete. Note that emanation rate is not influenced by building pressures. Radon emanation can be significantly reduced by vinyl flooring or other dense materials that are sealed to the floor. Carpeting and drywall would likely provide very little reduction in radon emanation rate. A section of concrete wall in the stairwell of the fifth floor was tested over a painted section and an unpainted section. The painted concrete emanation test was 9% lower. This variation is within the error range of the detectors so the conclusion is that the paint used in the stairwell on the concrete did not have a significant impact on reducing radon emanation from the concrete. The ceilings of the units were covered with drywall and the floors had carpeting, vinyl, wood flooring or tile. 94 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 MITIGATION BY ADDITIONAL VENTILATION Although it is easy to say the units simply need more ventilation. The difficult questions are how much ventilation do they need and how can that ventilation be most practically, effectively and consistently introduced into each unit. Increasing the ventilation carries a penalty in energy costs, occupant comfort, increased humidity as well as requiring the HVAC to handle any extra load. There would also be a significant cost to re-work a ventilation change if it was inadequate to reduce the radon levels below the EPA guideline or desired maximum final radon concentration. Discussions with Florida Department of Health officials revealed that there had been cases in Florida were the increased unconditioned ventilation used to reduce the radon levels in similar buildings had produced mold growth inside the dwelling. The ventilation increase therefore needs to be carefully designed and installed based on the exact amount of air each unit needs. Determining the Current Ventilation Rate There are a number of methods used to determine the ventilation rate of a building. Air changes per hour (ACH) is the common unit used to define the amount of building ventilation. ACH is considered to be the amount of air coming into and leaving a building in an hour compared to the total volume of the building. In general it is assumed that a building with 1.0 ACH is a leaky building. A typical home built in the fifties and sixties might have 0.5 or greater ACH. A recently built home would generally be thought to have about 0.3 ACH. A very tight home would have 0.1 ACH. ACH are determined by two methods. One method known as a Blower Door Test has a fan with a calibrated orifice blow air into or out of a building. The pressure increase or decrease compared to the air flow is used in blower door software programs to calculate the total area of openings through the shell of the building. The amount of air flow needed to induce a pressure in the building equal to 50 pascals (0.20” sp) is often divided by 20 to approximate an average residential buildings natural ACH ventilation This ACH rate is just an approximation and the ACH rate will change with outdoor wind speed and Figure 6 Blower door set up 95 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 direction as well as outdoor temperature versus indoor temperature. This method of determining natural ventilation rate is based on a typical home having most of its exterior walls adjacent to the outdoors and it’s entire upper level ceiling adjacent to a ventilated attic. In a condominium there may be only one exterior wall that is adjacent to the outdoors and the ceiling and floor is constructed of concrete. In addition any exterior shell leakage to the hallway would not be adding outdoor ventilation. Therefore blower door determinations of natural ventilation rate of a building similar to this building would need to have a very different calculation than typical single family homes. Infiltec, a manufacturer of blower doors, was consulted and they suggested that the ventilation rate could be approximated by dividing the ACH rate obtained at 50 pascals of pressure by 40 instead of 20 however from the measurements made dividing the ACH rate at 50 pascals by 50 would be closer approximation. See table 4 below. A more accurate method of determining the current ventilation rate is to make a direct measurement of the ventilation rate by releasing a unique stable tracer gas into the air and measuring how long it takes for this tracer gas to be reduced. If there is minimal occupant activity in the building, CO2 is often used because it is easy to measure, available and safe. CO2 is already present in the outdoors and people exhaust it while breathing which complicates the measurement. The condo units however have a constant source of radon that can be used for the tracer gas since the introduction of outdoor air is likely to have very little radon concentration. Measuring the change in radon levels as the ventilation is increased can then be back calculated to determine what the ventilation rate is and how much additional ventilation will reduce the radon concentration. In five separate units the radon levels were measured hour by hour and the ventilation levels were varied. Blower door measurements were also made to determine the leakage area of each of these five units. Condo Unit East 5th Floor East 6th Floor West 3rd floor West 4th floor A West 4th Floor B Leakage area in2 175 117 94 75 100 Typical ACH rate (divide 50 Pa rate/20) 0.24 0.38 0.27 0.28 0.23 More likely ACH (divide 50 Pa rate/50) 0.096 0.15 0.11 0.11 0.09 Actual Measured ACH 0.08 0.10 0.13 0.10 0.035 Table 4 Blower door results Blower Door Measurements Blower door measurements were made in by varying the airflow with an HP220 fan that was exhausting air while measuring the reduction in pressure in the unit compared to the hallway. 96 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Blower door depressurization provides a more realistic measure of leakage than pressurization because it maintains bath fans and dryer exhaust louvers in a closed position. The first and last column in table 4 above has the actual measured leakage area and measured ventilation rate. The blower door results obtained at 50 pascals of pressure divided by 50 appear to be closer to the actual measured value. Note that this is 2 ½ times more air tight than most residential housing. Using standard blower door calculations to determine natural ventilation in condominiums is not recommended. Figure 7 WPB Inter-Comparison of CRM monitors Trace Gas Measurements The continuous radon monitors used in this study were inter-compared against three Femto-Tech 210 monitors that had just been calibrated at the factory. See the results in Figure 7 above. A base line radon measurement of the radon levels with the doors and windows closed is required to measure the effects of ventilation changes.. Unfortunately in the three occupied units there were open windows and doors at the beginning of the measurement period. See the photos in Figure 8 and 9 of the ventilation happening in one of the units to reduce radon levels. In this particular unit the Figure 8 Occupant kept bedroom door to patio open 97 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 radon levels were reduced from 13.2 pCi/L (488 Bq/m3) down to around 1.0 pCi/L (37 Bq/m3) with the screened window and patio door left adjar. The radon levels were measured over the next 24 hours as the radon levels climbed to a typical closed house level. Once the typical closed house radon levels were obtained a known quantity of outdoor air was added to each unit and the change in radon levels was then measured. The change in radon concentration versus the quantity of air being introduced was used to determine the natural ventilation rate that took place during the testing period. This ventilation rate can then be used to predict what the ventilation rate was during the previous testing that produced the elevated radon concentrations. This measurement and back calculation can also be used to determine the amount of additional ventilation of outdoor air that is necessary to maintain radon levels below the EPA action guideline. Figure 9 Occupant placed screen in window opening for ventilation In five units plywood frames were secured in an exterior window. In each frame a small fan was installed that included a heater in case the occupants felt the air was cooling the unit too much. The air flow was carefully measured using a 6” flow grid that had been previously calibrated with a low flow bolometer. See photo in Figure 10 below The windows and exterior doors in all the units were closed during the diagnostic testing period. The windows and exterior doors in the two east units were closed prior to the diagnostic testing because the units were vacant. The following radon graphs in Figure 11 through 15 depict the initial baseline radon levels that were achieved and the levels that were achieved as Figure 10 Combination ventilation fan and heater additional ventilation was added. Note, with calibrated flow grid airflow measuring setup there was a strong rain and wind weather pattern happening during the first 24 hours of the measurement period. 98 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 11 Radon Reduction from Increased Outdoor Air 99 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 12 Radon Reduction from Increased Outdoor Air 100 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 13 Radon Reduction from Increased Outdoor Air 101 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 14 Radon Reduction from Increased Outdoor Air 102 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 15 Radon Reduction from Increased Outdoor Air 103 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 MITIGATION RECOMMENDATIONS The radon reduction achieved by the added ventilation during the diagnostic testing was used to deduce the ventilation rate at the test time. In Table 5 below the ventilation rate is compared to the predicted radon levels inside the unit if 0.015 CFM of outdoor air is added for each ft2 of concrete that is adjacent to the interior area of the building. In four of the five units there was reasonable correlation between the predicted values and the actual radon levels. In unit West 4th Floor B the radon levels were the lowest of all the units and yet this unit had the most square footage of concrete. This unit also backs up to the stairwell which provides more exposed concrete from the stairwell poured concrete walls. There is no explanation why this unit’s radon levels were so low. The reduction in radon achieved by the ventilation fan in unit West 4th Floor B was also the greatest amount which then calculates the units ventilation rate at one third the level of the other units. There is no explanation of why condo unit West 4th Floor B is behaving in this manner. Unit East 5TH Floor East 6th Floor West 3rd Floor West 4th Floor A West 4th Floor B Initial Radon level ACH During Test Prev Radon Test ACH during Prev. Test 5.5 3.5 4.75 3.75 2.5 0.084 0.103 0.132 0.095 0.032 10.9 9.5 13.2 10 10 0.042 0.038 0.048 0.035 0.008 0.015 CFM per ft2. concrete + ACH of prev test 42 43 50 34 52 Radon New w/40 Radon pCi/ft2/hr Levels flux 1.7 1.4 1.7 1.3 0.4 1.5 1.4 1.7 1.6 1.8 2 Table 5 Effect of adding 0.03 CFM/ft of floor area to each unit Table 5 above shows that the ventilation level in four of the condo units was around 0.1 ACH during the diagnostic testing. Unit West 4th Floor B had one third this level. The ventilation rate that occurred during the previous tests that had higher radon levels can be deduced to be around 0.04 ACH. Moderate temperatures and lack of wind during the previous radon measurement can easily explain the ventilation rate being half of the ventilation rate recorded during the diagnostic visit. In the table above the predicted radon levels were determined by adding ventilation equal to 0.015 CFM/Ft2 of exposed concrete plus the natural ventilation that existed during the previous radon test period when the natural ventilation rate was very low. In the last column this amount of added ventilation is used to determine the radon levels based on 40 pCi/SqFt/hr emanations 104 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 from the exposed concrete. The radon levels for both calculations are comparable except for unit West 4th Floor B. Since the radon is coming from the concrete and the emanation rate did not vary significantly, the ventilation added to the building should be proportional to the concrete exposure. The ventilation rate for each unit will need to take into consideration all concrete that the unit is exposed to. Note that the diagnostic testing calculations used the square foot area of the condo and included an approximation for additional concrete walls and beams. It was therefore recommended that a minimum of 0.015 CFM be added to each unit for every square foot of concrete floor, concrete ceiling, concrete wall and concrete support column that is exposed to the unit with no less than 30 CFM per single bedroom unit and 45 CFM for a two bedroom unit. Additional ventilation may be appropriate. POSSIBLE MITIGATION OPTIONS Negative Pressure Ventilation One method of inducing ventilation into a building is to exhaust air out of the building from central locations on each floor. Exhaust ducting could be routed from the hallways of each floor to the roof. This would tend to draw air from any leakage points in the building that have access to the hallway. This method would cause varying amounts of air flow to happen to the individual units. Units that have large gaps under the door way to the hallway would tend to have higher air flows than those that having small gaps due to carpeting or other restrictions. This could be remedied by having a pass through transition grill installed between the inside of each unit and the drop ceiling of the hallway. The ventilation to each unit would then vary depending upon each units openings to the outdoors. A unit without an open window might receive very little ventilation while another unit that typically keeps its windows or doors open would have large ventilation increases. This might require over sizing the exhaust system to compensate. The owners that enjoy having windows or patio doors open might find that this system induces increased moisture gain during humid outdoor conditions. This approach would also have reduced effectiveness on any level that had doors from the hallway to the outside. Hallway areas with doors to the outside would tend to get excessive moisture gain on days of elevated outdoor humidity. Negative pressure ventilation is not recommended as the remediation method. Installation of ERV Another method of increasing the ventilation is to install an Energy Recovery Unit (ERV) either inside or outside every unit. This would require two penetrations of the exterior to allow supply air in and exhaust air out. In some cases it may be possible to use an existing bathroom exhaust duct as the ERV exhaust duct if an adequate backdraft damper exists or is installed to prevent re105 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 circulation of the air exhausted by the ERV. Note that the EPA radon mitigation standard’s recommends that the intake port installed on the exterior of the unit for the ERV be ten feet away from any exhaust ports. The ERV will only partially condition the incoming air with the outflowing air. If the outdoor air is 40 degrees and the indoor air is 70 degrees, the entering air will typically be around 60 to 65 degrees. Ideally this air should be routed to the return side of the air handler to further condition it. Note that the ERV must run continuously unless the owner turns the unit off during periods of open house conditions. In most high rise condominiums there is very limited additional space in the equipment room or closet to install the ERV. It will often be necessary to enclose the ERV and new ductwork with finish materials that allow access to the ERV for maintenance. Figure 16 below is a picture of a FanTech SE704N ERV being pre-tested to determine its effectiveness. This unit moves about 60 CFM. Figure 16 Small ERV being tested for effectiveness 106 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Installation of Conditioned Air The units in this building have floor areas from 650 ft2. to 1450 ft2. with a few larger exceptions. This would require at least 30 to 50 CFM of outdoor air for each unit based on the minimum of 0.015 CFM per square foot of concrete exposure. This could be provided with roof top mounted units that fully condition the air. Using 100% conditioned air would minimize any moisture problems or occupant discomfort. There are mechanical storage rooms on each corner of the buildings that line up above each other that could be used to provide air ducts to each floor. The larger challenge will be routing the air from these mechanical/storage rooms to each unit on each floor while ensuring that each unit gets adequate amount of outdoor air. The hallways in the buildings did have a drop ceiling with fire suppression piping and other mechanical utilities routed through the space already. There might be enough space above the drop ceiling to route some or all of the necessary ducts. Note that all the hallways will also need outdoor air. There are a number of grade level condo units that along with their exposure to concrete also have exposure to soil based radon. These units were not tested for radon and may need duct work that is oversized in case soil base radon is contributing an additional radon load to the unit. BUILDING VENTILATION STANDARDS ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers has been updating ventilation guidelines for commercial buildings for 100 years. The society however has not directed much attention to residential dwellings. Residential ventilation was traditionally not a major concern because it was felt that between operable windows and envelope leakage, occupants were getting adequate air. The latest standard developed by ASHRAE for ventilation of residential buildings is Standard 62.2-2003 which took place after this building was completed. Prior to this in 2001, ASHRAE approved a ventilation standard 622001 but this standard was basically the same standard that was adopted in 1989. Note that both 2001 and 2003 standards were and are intended for single family homes and low rise multifamily structures only. The 2001 standard did include specific ventilation flow rates for kitchen, baths, toilets, garages and common areas as well as air exchange rates for living areas. This included an air exchange rate of 0.35 ACH for the living areas with no less than 15 cfm per person from natural and induced ventilation but the standard did not describe how to accomplish this. It was not however until the 62.2.2003 standard that fan forced ventilation was part of the standard and more explicit ventilation requirements were included in the standard. 107 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References Brodhead B.. Measuring radon and thoron emanation from concrete and granite with continuous radon monitors and e-perms. Proceedings of AARST International Radon Conference; 2008 Chao C., Tung T., Chan D., Burnett J.. Determination of radon emanation and back diffusion characteristics of building materials in small chamber tests. Building and Environ. 32:355-362; 1997 Cozmuta I., Van der Graaf E.R., Meijer R.J.. Moisture dependence of radon transport in concrete: measurements and modeling. Health Phys. 85: 438-456; 2003 Kovler K. Perevalov A., Steiner V., Rabkin E.. Determination of the radon diffusion length in building materials using electrets and activated carbon. Health Phys. 66: 505-516; 2004 Roelofs L.M.M., Scholten L.C.. The effect of aging, humidity, and fly ash additive on the radon exhalation from concrete. Health Phys. 67: 225-230; 1991a Rogers V.C., Nielson K.K., Holt R.B.. Radon diffusion coefficients for aged residential concretes. Health Phys. 68:832-834; 1995 Sun H., Furbish D.J.. Moisture effect on radon emanation in porous media. J. Contam Hydrol 18:239-255; 1995 Yu K.N., Chan T.F., Young E.C.M.. The variation of radon exhalation rates from building materials of different ages. Health Phys. 68:716-718; 1995 108 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 EXPERIENCES IN PROTECTION AND REMEDIATION Martin Neznal, Matej Neznal RADON v.o.s.Novakovych 6, 180 00 Praha 8, Czech Republic Abstract The paper presents an overview of some parts of the Czech Radon Programme - results and experiences resulting from the work of many experts from different institutions (Czech Geological Survey; Charles University of Prague, Faculty of Science; State Office for Nuclear Safety; National Radiation Protection Institute; Czech Technical University, Faculty of Civil Engineering; National Institute for Nuclear, Chemical and Biological Protection; Radon v.o.s. and others). During the last 15 - 20 years. Four main topics are discussed: (i) radon protection of new houses based on an individual approach - a building site characterization; (ii) preventive measures in new houses; (iii) remedial measures in existing buildings; (iv) human factor that may become a weak point of the system in some cases. Introduction The first reference to negative health effects of radon appeared in the 16th century: Paracelsus described a specific “miners disease” that occurred in silver mines in Jachymov (Joachimstahl) and Schneeberg, two towns located near the border between Czech Republic and Germany. The symptoms and the development of the disease differed from those of tuberculosis. But as late as in 1951, W.F. Bale (USA) discovered the reason: inhalation of short-term radon decay products (Bale, 1951). The discovery was followed by first epidemiological studies, in the Czech Republic organized by J. Sevc at al. (Sevc, 1993). In 1956, H. Hultquist observed high indoor radon concentrations in Sweden (Hultquist, 1956). Other papers (Akerblom, 1984) described radon from bedrock as a main source of daughter products in dwellings. In the 80s, high indoor radon concentrations were also observed in Czech houses, at first in houses built from materials with higher content of 226Ra (slag concrete; so-called START houses). The first governmental resolution about radon, as well as the first proposal of the uniform method for radon risk classification of foundation soils appeared in 1990 (Barnet, 1990). The governmental resolution represents the starting point of the Czech Radon Programme. Radon Protection of New Houses in the Czech Republic - Individual Approach In European countries, a decision making in the pre-construction phase is typically based on radon risk mapping, or on modelling. However, since 1991 in the Czech Republic, the radon potential for prospective building sites has been characterizing by performing in-situ measurements in the soil. Based on these measurements, protective measures are then included in the dwelling design. The main advantage of the method is given by the fact that it is a site-specific, individual approach. It should enable to propose an optimal preventive strategy corresponding to local 109 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 conditions. Disadvantages - connected for example with temporal changes of measured parameters - are not critical. In our experience, spatial variations of measured parameters are more important than temporal ones. The soil-gas radon concentrations, as well as soil permeability may vary, often greatly, over a small distance. The occurrence of heterogenities may indicate the presence of faults or tectonic zones or possible kasrst geological formations. Because homogeneous geological structure are rare, any evaluation based on a single measurement would be extermly limited. On the other hand, the occurrence of spatial variations represents a good reason for the protection of a building based on the results of a building site characterization, not on large scale radon risk maps. (Neznal, 1991, Neznal, 1992, Neznal, 1996a, Neznal, 1996b, Neznal, 1996c, Neznal, 1997, Neznal, 2004b). In accordance with the Czech Atomic Law, results of the building site characterization are used for the design of protective measures. If the radon index is other than low (i.e. medium, or high), the building must be protected against radon. Protective measures are designed and installed in accordance with the Czech National Standard (CSN 730601 Protection of houses against radon from the soil; 1995, 2000, 2006). The standard method for the determination of the radon index of prospective building sites has been modified (Barnet, 1994, Neznal, 2004a), but the basic principles have remained the same. The evaluation is based on measurement of soil-gas radon concentration and on in situ measurement, or on expert evaluation of soil permeability. Simple, low-cost sampling and measuring techniques are used. A description of the system for soil-gas sample collection follows as an example (See Fig. 1). The sampling system consists of a small-diameter hollow steel probe with a free, sharpened lower tip. The probe is pounded into the ground to a desired depth below the ground surface using a hammer. A punch wire is then inserted into the probe and the tip is moved a few centimeters lower using a hammer again. This action creates a cavity at the lower end of the probe. A cap containing a rubber stopper and a needle is placed on the open upper end of the probe. The soil-gas is sucked and samples of a controlled volume are collected using a largevolume syringe. To obtain the proper vacuum and to avoid underestimating the soil, gas concenctration, the entire system must be perfectly sealed. More detailed information on sampling and measuring techniques has been published (Barnet, 2008). (a) (b) (c) Fig. 1. Soil-gas sampling: (a) Inserting the sharpened tip into the lower end of the probe. (b) The sharp tip is moved a few centimetres lower - this action creates a cavity at the lower end of the probe. (c) Soil-gas sample collection using a syringe. 110 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Currently, apporximately 100 organizations (mostly private firms) are providing radon index services for prospective building sites. Each technician performing these services has to pass a training course and perform a comparison measurement of soil-gas radon concentration at field radon reference sites (Matolin, 1991, Matolin, 2002). A regular metrological verification of all measurement devices for the determination of soil-gas radon concentration is also required. Only firms that fulfil all above mentioned requirements are authorised by the State Office for Nuclear Safety to perform measurement in this field. Preventive Measures in New Houses - Technical Solutions and Experiences The Czech National Standard CSN 730601 concerns not only preventive measures in new houses, but also remediation of existing buildings. It also contains principles of designing and application of various types of radon reduction techniques, as well as requirements for radonproof insulation (Jiranek, 2000, Jiranek, 2001). Protection of new houses against radon penetration from the ground is based on the use of radon-proof insulation; or in combination with passive, and/or active ventilation systems. The basic principles can be summarized as follows: 1. Only materials with known radon diffusion coefficients can be used. 2. Special attention must be given to jointing and to pipe penetration. 3. The passive ventilation systems must be installed in such a way that they can be easily converted to forced (active) systems. Simple airing of the drainage layer by means of pipes that run from one side of the building to another is not an acceptable solution. The prefered ventilation system consists of several perforated pipes that are connected to one vertical exhaust pipe on which a fan can be installed in the future. Realization of preventive measures against radon started in the Czech Republic more than 15 years ago. Long-term measurements of indoor radon concentration have shown that the protection has failed in a non-negligible number of houses (Jiranek, 2006) with greater failures occuring in homes built before 1995 (ie. before publication of the first version of CSN 730601). The most important factors responsible for failures are: - leakages in joints and around pipe penetration, - partial application - insulation is not applied over the entire surface, - perforation of insulation during construction works, - use of insulating materials that were not tested on radon diffusion, or use of low quality products, and - passive ventilation with inlet and outlet holes in external walls only (without vertical exhaust). Remedial Measures in Existing Buildings - Technical Solutions and Experiences Different types of remedial measures in older buildings had been tested in the past (i.ie. ventilation of indoor air with heat recovery, radon-proof membranes, protective coating of the floors, etc.) However, more recently, sub-slab ventilation has shown to be the most effective and appropriate system to solve problems with radon in existing houses (Jiranek, 1998, Jiranek 2002, Jiranek 2004). Soil ventilation systems used in the Czech Republic are usually formed by: - one, or several perforated tubes drilled beneath existing floors (from the cellar, from an external chase, or from an internal chase), - one, or several radon sumps installed into the sub-floor region of the building, 111 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 - a network of flexible perforated pipes inserted into the drainage layer of coarse gravel placed beneath the floors (reconstruction of floors is necessary in this case), - a combination of the above stated measures. The principles of designing and application of various ventilation systems are published in the Czech National Standard CSN 730601. Becasue of its versatility, sub-slab ventilation can be successfully applied in nearly all types of houses. An example concerning a family house with extremely high indoor radon concentrations is described below. The house is located in Northern part of the Czech Republic, in region of former silver mining. It has a small cellar located under 1/5 of the ground floor area. Two types of floors, i.e. a timber floor and a cracked concrete slab have been found in the ground floor. Very high average indoor radon concentrations (about 20000 Bq.m-3 in some habitable rooms; about 70000 Bq.m-3 in the cellar) were observed in the house during detailed diagnostic measurements performed in 2004 (See Fig. 2):. The indoor radon concentration in the cellar was the same as the soil-gas radon concentration in the surroundings of the building. In addition, very fast changes of indoor radon concentration were also observed. In 2005, remedial measures were performed byfirst replacing the timber floors with a concrete slab fitted with a damp proof membrane, thermal insulation, and floor covering A sub-slab ventilation system consisting of two independent sections was then installed. The effectiveness of remedial measures is illustrated in Fig. 3. 50000 -3 ) cR n (Bq.m 40000 30000 20000 10000 0 7.10.04 8.10.04 9.10.04 10.10.04 11.10.04 12.10.04 13.10.04 14.10.04 15.10.04 12:00 12:00 12:00 12:00 12:00 12:00 12:00 12:00 12:00 Fig. 2. Continual measurement of indoor radon concentration in the living room - before remediation. 112 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 6000 5000 -3 ) cR n (Bq.m 4000 3000 2000 1000 0 4.8.05 6.8.05 8.8.05 10.8.0512.8.05 14.8.0516.8.0518.8.0520.8.0522.8.0524.8.05 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Fig. 3. Continual measurement of indoor radon concentration in the living room - after remediation. Ventilation experiment - 4.8. 8.45 - 11.8. 9.30: gradual start of the 1st section; 11.8. 9.30 - 18.8. 10.15: both sections in operation (maximum power); 18.8. 10.15 - 22.8. 12.00: ventilation switch-off. The Weakest Link- The Human Factor The Radon programme in the Czech Republic has a long and rich history. By using using different remedial measures procedures, we are able to evaluate the risk of radon penetration from the ground, and protect residents of both new and existing buildings from elevated indoor radon levels. These remedial measures and procedures, have been developed, published, field tested and are being applied successfully today. Although, this approach is sound (if it is performed correctly, the odds of a successful radon remediation is very high). Problems do exist because of simple human error, or misperceptions caused by psychological, or sociological reasons (Neznal, 2008). Two examples follow. Example A: It is known that the indoor radon concentration significantly changes in time and that it may be strongly influenced by inhabitant’s behaviour. Therefore radon measurements using intergrating devices are the most common. Unfortunately, and all too often, these devices are placed and retrieved by untrained nonspecialists. In addition, the residents either knowingly, or unknowingly, too often do things out of malice or ignorance that can have a significant impact on the radon measurement. The following lists the spectrum of human related problems: - Poor selection of a testing location: The detectors are located in rooms that are declared as habitable rooms (living rooms), but used for other purposes (as storerooms). - Inappropriate time to test: The testing was being performed during a period of long-term floor reconstruction. 113 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Resident variables such as: - people want „to avoid any problems“ (increased ventilation), - people want to get financial support from the government (reduced ventilation), - people like „experiments“, and - people want „to safe money“ (and switch-off the sub-slab ventilation system). Example B: The radon programme is directed by central institutions with the goal to decrease a collective dose. Therefore, a conflict between the individual and an all-society“ points of view is inevitable. However, in some cases remediation may not be recommended. For example, the benefit of the remediation of homes occupied by the elderly may be off set by the stress and discomfort that remedial actions may cause. Conclusion A summary of experiences resulting from the Czech Radon Programme has been presented. Disscusion and conclusions relating to partial problems are included in separate scientific papers (See References). 114 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References Akerblom, G.V.; Anderson, P.; Clavensjo, B. (1984): Soil gas radon - A source for indoor daughters. - Radiation Protection Dosimetry, 7, 1-4, 49-54. Bale, W.F. (1951): Hazards associated with Radon and Thoron. Memorandum to the files. March 14, 1951. - Health Physics, 38, 1062-1066. Barnet, I.; Kulajta, V.; Matolín, M.; Veselý, V. (1990): A proposal of the radon risk classification of foundation soils. In: Barnet, I. ed. Radon investigations in CS. Vol. 1. Praha Geological Survey, 24-28. Barnet, I. (1994): Radon risk classification for building purposes in the Czech Republic. In: Barnet, I.; Neznal, M., eds. Radon investigations in CR. Vol. 5. Praha - Geological Survey; RADON, corp., 18-24. Barnet, I.; Pacherova, P.; Neznal M.; Neznal M. (2008): Radon in geological environment Czech experience. - Czech Geological Survey Special Papers 19, Praha: Geological Survey. Hultquist, H. (1956): Studies in naturally occuring ionizing radiation. - Kungl. Svenska Vetenskapsakad. Handlingar, 6/3, Almquist and Wiksels, Stockholm. Jiranek, M.; Neznal, M.; Neznal, M. (1998): Czech experience with sub-slab depressurization systems. In: Barnet, I.; Neznal, M., eds. Radon investigations in CR. Vol. 7. Praha Geological Survey; RADON, corp., 119-124. Jiranek, M.; Hulka, J. (2000): Radon diffusion coefficient in radon-proof membranes determination and applicability for the design of radon barriers. - International Journal on Architectural Science 1 (4), 149-155. Jiranek, M.; Hulka, J. (2001): Applicability of various insulating materials for radon barriers. - The Science of the Total Environment 272, 79-84. Jiranek, M. (2002): Efficiency and side effects of sub-slab depressurization systems. In: Barnet, I.; Neznal, M.; Miksova, J., eds. Radon investigations in CR. Vol. 9. Praha Geological Survey; RADON, corp., 87-94. Jiranek, M. (2004): Forms of sub-slab depressurization systems used in the Czech Republic. In: Barnet, I.; Neznal, M.; Pacherova, P., eds. Radon investigations in CR. Vol. 10. Praha Geological Survey; RADON, corp., 119-125. Jiranek, M. (2006): Consequences of incorrect design and unqualified realization on reliability and effectiveness of radon reduction measures. In: Barnet, I.; Neznal, M.; Pacherova, P., eds. Radon investigations in CR. Vol. 11. Praha - Geological Survey; RADON, corp.; Joint Research Center IES REM Ispra, 123-130. Matolin, M.; Prokop, P. (1991): Statistical significance of radon determination in soil air. In: Barnet, I., ed. Radon investigations in CS. Vol. 2. Praha - Geological Survey, 20-24. 115 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Matolin, M. (2002): Radon reference sites in the Czech Republic. In: Barnet, I.; Neznal, M., eds. Radon investigations in CR. Vol. 9. Praha - Geological Survey; RADON, corp., 26-33. Neznal, M.; Neznal, M.; Smarda, J. (1991): Radon infiltration risk from the ground in Chaby, Prague. In: Barnet, I., ed. Radon investigations in CS. Vol. 2. Praha - Geological Survey, 3439. Neznal, M.; Neznal, M.; Smarda, J. (1992): Temporal variation of soil gas radon concentration. In: Barnet, I., ed. Radon investigations in CS. Vol. 3. Praha - Geological Survey, 6-12. Neznal, M.; Neznal, M.; Smarda, J. (1996a): Assessment of radon potential of soils - A fiveyear experience. - Environment International, 22, Suppl. 1, S819-S828. Neznal, M.; Neznal, M.; Smarda, J. (1996b): Comparison between large scale radon risk maps and results of detailed radon surveys. In: Barnet, I.; Neznal, M., eds. Radon investigations in CR. Vol. 6. Praha - Geological Survey; RADON, corp., 16-22. Neznal, M.; Pernicka F. (1996c): Temporal changes of soil-gas radon concentration at a test site - uranium mill taillings. In: Barnet, I.; Neznal, M., eds. Radon investigations in CR. Vol. 6. Praha - Geological Survey; RADON, corp., 79-87. Neznal, M.; Neznal, M.; Smarda, J. (1997): Intercomparison measurement of soil-gas radon concentration. - Radiation Protection Dosimetry, 72, 139-144. Neznal M.; Neznal M.; Matolin M.; Barnet I.; Miksova J. (2004a): The New Method for Assessing the Radon Risk of Building Sites. - Czech Geological Survey Special Papers 16, Praha: Geological Survey. Neznal, M.; Matolín, M.; Just, G.; Turek, K. (2004b): Short-term temporal variations of soil gas radon concentration and comparison of measurement techniques. - Radiation Protection Dosimetry, 108 (1), 55-63. Neznal, M.; Neznal, M. (2008): Human perception of radon risk and radon mitigation: some remarks. - Radiation Protection Dosimetry; doi: 10.1093/rpd/ncn125. Sevc, J.; Tomasek, L.; Kunz, E. (1993): A Survey of the Czechoslovak follou-up of lung cancer mortality in uranium miners. - Health Physics, 64, 355-369. 116 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 A brief history of radon measurements and remediation in Spain C. Sainz-Fernandez, L. S. Quindós-Poncela, I. Fuente-Merino, J.L. Arteche-Garcia, J. L. Matarranz*, L. Quindós Lopez Radon Group. University of Cantabria. C/Cardenal Herrera Oria s/n 39011, Santander, Spain * Nuclear Safety Council. C/Justo Dorado 11 28040, Madrid, Spain Abstract Indoor radon levels usually present highly spatial and temporal variations. Natural daily and seasonal cycles as well as other factors like geology, occupancy or weather conditions make the long term average radon level measurements the most suitable way to draw the radiological situation concerning radon in extensive areas. As the risk of lung cancer increases with the increasing radon exposure, this kind of measurements represents the first step to assess risks in exposed population. During the last 30 years the Medical Physics Group of the University of Cantabria (Spain) have carried out several national campaigns of indoor radon measurements which have provided radon values in more than 5000 dwellings. Complementarily to the measurement campaigns, when high radon levels are found remedial actions have to be taken into consideration. The aim of radon remediation is not only to reduce indoor radon levels but to do so with minimal impact on the building structure and occupants. With regard to this important issue our Radon Group has been testing the effectiveness of several remediation systems in a model house located at a high background radiation area. In this presentation, a summary of the different nationwide measurements is shown. Also some conclusions derived from the essays with different remediation techniques and last news about the future building code to be approved by the authorities during this year will be presented. Introduction Nowadays there is a wide scientific consensus about the role of residential radon as a lung cancer risk factor (Darby, 2004)(Krewski, 2005). Since more than thirty years ago, the interest in this main source of natural radiation have promoted the development of national surveys in order to evaluate the average radon levels in houses and locate the areas with a potential risk derived from radon and radon progeny inhalation. In Spain, the first national radon measurement campaign began in 1988 (Quindós, 1991). The data coming from the 2000 measurements carried out in this survey represented the first step to rise the issue of radon in Spain. In addition since 1991 the Spanish Nuclear Safety Council, together with the National Uranium Company and some Universities have developed the so-called MARNA project (Suarez, 1997)(Quindós, 2004). This project is a nationwide study with the aim of estimating potential radon emission from external gamma dose rates and radium calculations taking into consideration geological parameters and empirical correlations found 117 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 between outdoor external gamma dose rates and 226Ra concentration in soil. As a main result, this project provides useful maps of the country where the zones with different gamma radiation levels are showed (Fig.1). From the information obtained in these two studies, several regional surveys and another national one have been carried out until now. Surveys have usually included a broader approach to exposure to natural sources of radiation to people living in the studied areas by measuring external gamma dose rate and radioactivity in soils together with indoor radon. Indoor radon measurements were performed by using track etched detectors CR39 exposed for a six-month period in order to evaluate average radon concentration values. In all the measurements, a seasonal correction factor was assumed in order to mke the results obtained over a six month period representative of the actual mean annual indoor radon concentration (Miles, 2000). Complementarily to the measurement campaigns, when high radon levels are found remedial actions have to be taken into consideration. The aim of radon remediation is not only to reduce indoor radon levels but to do so with minimal impact on the building structure and occupants. In existing houses, the methods to reduce radon concentration are based on dilution and/or pressure changes by means of a pressure modifying sump, often in conjunction with an extraction fan. On the other hand, for new build houses, the installation of radon proof membrane across the entire footprint of the house seems to be the most useful way to prevent radon entry (Scivyer, 2007). With regard to this important issue our Radon Group has been testing the effectiveness of several remediation systems in a model house located at a high background radiation area. Brief description of surveyed areas and main results Surroundings of the Spanish Nuclear Power Plants During 1998 and 1999, financially supported by the Spanish Nuclear Safety Council, regional surveys were conducted to evaluate natural radiation exposure of the people living in the vicinity of the Spanish nuclear power stations. There are six facilities working in the country and the population of these regions is about 200000. In these surveys, indoor radon, external gamma dose rates outdoors and indoors, and radioactivity in soils were measured. A remarkable result was found in the surroundings of Almaraz nuclear power plant in the province of Caceres where the highest mean annual effective dose to the population was found (Quindós, 2003). The estimated value, of 4.07 mSv y-1, is 1.6 times higher than the national average value. The reason of this significant difference in dose value with the other nuclear power stations was the high radon concentrations found in homes. So, in order to perform a more accurate assessment of the dose coming from radon in this area, a new and more extensive survey on indoor radon was carried out in the named Campo Arañuelo region around the Almaraz nuclear power station. 118 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Furthermore the increase of accuracy in dose assessment, this study revealed the presence of a high radon level area called La Vera in the northern side of the Campo Arañuelo region. It was found in La Vera a 9 % of houses with indoor radon concentrations higher than 400 Bq m-3. In addition, the new dose assessment gave a value of 6 mSv per year in La Vera, with a maximum of 25 mSv per year estimated in Jarandilla, a town belonging to the former area where 30 % of houses had radon concentrations over 400 Bq m-3. Vicinity of the Spanish old Uranium Mines From 2000 to 2001 and under the sponsorship of the Spanish Nuclear Safety Council the surveys in the six uranium-mining areas in the country were carried out. The mines are mainly located in the western part of Spain and their surface area shows prevalence of calcite carbonatite, gramodiorites and methmorphic slate rocks on its composition. The exploitation period ranged from 1950 to 1980, and between 1987 to 1996, a general decommissioning plan was carried out. One of the main objectives of the plan was to reduce and control radon flow and contamination of water. The population of these areas is over 400,000 inhabitants. The highest geometric mean radon concentration and annual effective dose for natural sources, of 111 Bq m-3 and 5.1 mSv y-1 respectively, were found in the surroundings of Albala uranium mine (Quindos, 2004). Estimated mean annual effective doses for the six areas studied ranged between 3.2 to 5.1 mSv per year, which is between 1.2 and 2 times higher than the national average value. A 14 % of houses over 400 Bq m-3 were found in the vicinity of the Albala uranium mine. Sierra de Guadarrama The area called Sierra de Guadarrama situated in the North of the province of Madrid has been subject of another regional survey. The first national study showed high percentages of houses with radon concentrations higher than 200 and 400 Bq m-3 (European Union recommendation concerning radon concentrations in new and old houses, respectively)(EU, 1990). Due to the prevalence of granitic rocks in the soil composition of this area and the considerable residential growth (the population of this region has been increased from about 500,000 people in 1990 to 1.5 million in 2000) a regional survey is now ongoing from 2002. Until now, the indoor radon measurements indicate that the 14 % of houses have levels above 400 Bq m-3 and 30 % above 200 Bq m-3. Also, the geometric mean radon concentration is 180 Bq m-3 which is about 4 times higher than the national average value. Villar de la Yegua town Perhaps the most important high background radiation area in Spain is the Villar de la Yegua town where the highest indoor radon concentration, up to 25,000 Bq m-3, have been found, and effective doses coming from natural sources as high as 40 mSv per year has been estimated. Several surveys have been carried out from 1988 to now, confirming Villar de la Yegua as a high radon level area (ICRP, 1994). The main results concerning radon concentration show a geometric mean of 818 Bq m-3, 18.2 times 119 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 higher than the national value, and percentages of houses with concentrations above 400 and 1000 Bq m-3 , of 75 % and 25 % respectively. For these reasons it is clear the convenience of carrying out epidemiological studies in the health effects of natural radiation exposure to the population living in this town, even bearing in mind its small population, of about 500 people. Effectiveness of different remediation techniques In 2004 a two storied model house was built in a high background radiation area. Entry of radon into a dwelling from the soil gas is influenced by factors like radon concentration in the soil gas itself, ground permeability and meteorological conditions in the vicinity of the dwelling. For this reason, radioactivity in soil together with radon in soil and permeability were measured prior to construction of the house in order to characterize the radon source term. Once the construction was finished, indoor radon concentration as well as meteorological parameters like wind velocity, temperature, pressure and pluviosity were continuously measured for more than one year. Along this measuring period, several remediation techniques were tested. Continuous radon monitoring was done with several devices of type DOSEman and RadonScout (SARAD GmbH, Germany) placed in the first floor and cellar of the building. On the other hand, wind speed and amount of precipitation were provided by a nearby meteorological station whereas temperature and pressure values where continuously recorded throughout a number of sensors placed at different locations inside the house. In a first phase before the test of the remedial actions a study about the influence of meteorological parameters on indoor radon concentration was carried out. This study was done with the dwelling closed for four months. During this time, average radon concentrations were of 7000 Bq m-3 in the first floor and 42000 Bq m-3 in the cellar, reaching maximum values of 40000 and 120000 Bq m-3, respectively. The major influence on radon concentrations was found to be the changes in atmospheric pressure and, in a lesser extent, pluviosity. Atmospheric pressure drops were observed to be inversely correlated with significant increases on indoor radon playing the ultimate role in determining the long-term trend in gas concentration. Pressure changes could be effective in inducing the flow of soil air into the building by leading to a significant difference in pressure between the indoor air and the pore air in the nearby soil. On the other hand, amount of precipitation had a shorter-term influence which could be explained because the permeability of the wet soil surrounding the house in considerably lower than that of the dry soil under the construction. Under the above conditions radon soil gas would be forced to enter the house. In the second phase, the remediation techniques essayed were: - Natural air extraction from soil with lateral or central pipe Forced air extraction from soil with lateral or central pipe Pressurization/depressurization of air within the soil with central pipe Crossed ventilation in cellar 120 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 - Insulation barrier (polyurethane product directly applied in floor and walls of the cellar) Except soil gas depressurization and crossed ventilation, all the above techniques showed efficiency above 90 % in reducing radon concentration in cellar as well as in the first floor. Generally speaking, the applied actions were more efficient when applied in the central pipe rather than in the lateral one. Concerning the suitability, the application of a polyurethane compound directly projected to the floor and walls in the cellar would be the best option avoiding the necessity of forced ventilation systems. By this way, radon concentration was reduced until 300 Bq m-3 in the first floor and 1700 Bq m-3 in the cellar. Although inverse correlation could still be appreciated between radon concentration and atmospheric pressure, the thermal insulating effect of the polyurethane barrier could smooth indoor pressure changes thus collaborating to prevent the entry of radon via pressure difference. Finally, the application of radon proof barriers to the walls could also reduce the baseline level defined by emanation from the structure of the building itself, which can be relatively high depending on the type of materials used in construction. Fig. 1: External gamma radiation map of Spain with the radon prone areas found from the national and regional surveys carried out in the country 121 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References Darby et al., Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case–control studies, Br. Med. J. 330 (2004), pp. 223–227. European Union. Council Directive 90/143/EC of 21 February 1990 on the protection of the public against indoor exposure to radon. (1990). Official Journal of the European Communities International Commission on Radiological Protection. Protection against radon-222 at home and at work. ICRP Publication 65 (1994) Oxford: Pergamon Press. Krewski et al., Residential radon and risk of lung cancer: a combined analysis of 7 North American case–control studies, Epidemiology 16 (2005), pp. 137–145. Miles J., C. Howarth, Memorandum: Validation scheme for laboratories making measurements of radon in dwellings: 2000 revision. National Radiological Protection Board. NRPB-M1140. (2000). Chilton, Didcot, Oxfordshire OX11 ORQ. Quindós L. S., et al., Natural gamma radiation map (MARNA) and indoor radon levels in Spain. Env. Int. 29 (2004) 1091-1096 Quindós L. S., et al., Natural radiation exposure in the vicinity of Spanish nuclear power stations, Health Phys. 85(5) (2003) 594-598 Quindós L. S., et al., Population dose in the vicinity of old Spanish uranium mines, Sci. of the Tot. Env. 329 (2004) 283-288 Quindós L. S., Fernández P. L. and Soto J., National survey on indoor radon in Spain, Env. Int. 17 (1991) 449-453 Scivyer C, Radon: guidance on protective measures for new buildings (BR211), Garnston: BRE Press, 2007 Suarez E., J. A. Fernández, Project MARNA: Natural Gamma Radiation Map. Revista de la Sociedad Nuclear Española (1997) 58-65 122 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 EMISSION OF RADON FROM DECORATIVE STONE Michael E. Kitto1,2, Douglas K. Haines1, and Hernando DiazArauzo3 1 Wadsworth Center, New York State Department of Health, P.O. Box 509, Albany, NY 12201 2 School of Public Health, State University of New York, Albany, NY 12201 3 C&C North America, Inc., Stafford, TX 77477 Abstract Over 35 samples of decorative stone, imported into the United States for use as countertops and mantels, were measured for the emission of radon using electrets and continuous radon monitors. The 14 engineered stones emitted little or no measurable radon (≤2 pCi/lb; <0.2 Bq/kg ), while the natural stones emitted up to 42 pCi/lb (3.4 Bq/kg). Pieces of a granite countertop, removed from a local home, emitted an average 170 pCi/lb (14 Bq/kg) of radon. It is estimated that in most cases the contribution of the decorative stone to the indoor radon concentration will be <1 pCi/L, but may exceed 4 pCi/L in rare cases. Introduction Radon (222Rn) is a gaseous decay product of radium, a naturally occurring radionuclide found in all rocks and soils. Inhalation of radon, a Class A carcinogen, and its radioactive decay products have been linked by epidemiological studies to an increased risk of lung cancer. Most indoor radon typically enters buildings at the soil-foundation interface, and a small amount enters the home by emanation from groundwater use, building materials, and outdoor air. The contribution from these sources to indoor radon levels varies widely, although building materials seldom becoming a significant source. Recently, the use of decorative stone (e.g., granite and marble) as a material for the interior of homes has increased dramatically. Stone-based materials contain widely varying levels of the radionuclides, though igneous rocks, such as granite, are commonly associated with a relatively higher content of radioactivity than sedimentary rock. Studies of radon exhalation from building materials, such as bricks and concrete, have been published, but little information currently exists on the contribution from natural-stone countertops to indoor radon levels. A preliminary study (Kitto and Green, 2005) showed that radon and gamma-rays are emitted from natural stone used in homes, with similar results being reported worldwide (e.g., Anjos et al., 2005; Al-Jarallah et al., 2005; Righi and Bruzzi, 2006). Due to the health implications associated with radon and the lack of radiological data regarding the decorative stone that is imported into the US, the goal of the present study was to measure radon emanation from decorative-stone material using radioanalytical techniques. 123 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Methodology The engineered and natural-stone slab samples analyzed in the study are representative of decorative stone commonly manufactured and imported, respectively, into the US for use as countertops, mantels, and hearths. Most of the samples included in the study had a single polished surface (1 ft2; 930 cm2), similar thickness (~0.75 inches; 2 cm), and densities of 2.5-3.0 g/cm3. A granite countertop, removed from a local home, was trisected and included in the study. Radon emanation from the samples was determine in a laboratory environment containing ~0.3 pCi/L of airborne radon and a radiation background of 7 µR/hr. The indirect determination of radon emanation was accomplished by the encapsulation of each sample and measurement of the radon in the enclosed air. Direct determination of radon flux from a sample can be accomplished through absorption onto activated charcoal, etched alpha-track detectors, or discharged electrets. Direct measurement of radon exhalation from the samples was accomplished using a 960-mL hemispherical device (H-chamber; Rad Elec Inc., Frederick, MD) containing a charged Teflon disc (electret). Radon entered the H-chamber through an attached Tyvek sheet in contact with the surface of the samples. The edge of the chamber was sealed to each sample using putty to eliminate leakage for measurement periods of 24-74 h. The flux of radon from the samples was calculated based on a formula and calibration supplied by the manufacturer (Stieff and Kotrappa, 1996). The voltage reader was calibrated using electrets exposed at an accredited radon chamber. Seven duplicate measurements were conducted using this method. The indirect measurement of radon exhalation was accomplished by sealing the samples inside radon-impermeable bags (Associated Bag Co., Milwaukee, WI) to allow the progeny of the emanating radon to ingrow to a steady state in the enclosed air. An aliquot (125 mL) of radon was transferred from the bag into each of two evacuated “Lucas” cells using a 0.75-inch (2-cm) piece of tubing to connect each evacuated cell to a vent nipple installed in the bag. After >3 h, the cells were measured at least five times with an alpha-scintillation counter (Randam Electronic Inc., Cincinnati, OH) and the radon concentrations determined from an average of the decay-corrected measurements. Background count rates averaged 1.8 cpm and the efficiency of the alpha-scintillation counter was ~2.3 cpm/dpm for 222Rn and its short-lived alpha-emitting progeny. The scintillation counter was calibrated using 226Ra standards traceable to the National Institute of Standards and Technology (NIST). Results and Discussion Radon that entered the H-chamber device through the Tyvek membrane discharged the electrets from 0.2 to 9.5 V/hr, including discharge attributable to background (0.2 V/h) radiation. Over half of the samples had net discharges below 2 V/hr, and only six samples had net discharge rates above 4 V/hr. To determine flux, we used a calibration factor, supplied by the manufacturer, that was not confirmed in this study. Calculated radon fluxes showed that two-thirds of the samples emitted <50 pCi/ft2-hr (<20 Bq/m2-hr) of radon, but the fluxes ranged up to 770 pCi/ft2-hr (310 Bq/m2-hr). Results of duplicate measurements of seven samples agreed well (r2=0.99). For this study, the polished side of the samples were measured. As the unpolished side may emanate 124 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 radon at an increased rate due to the lack of polish resin, the fluxes could be greater than measured. The concentration of radon gas from the samples sealed inside the bags was determined using Lucas cells and was found to range from 0.3 to 480 pCi/L (~10 to 17,800 Bq/m3). Since the volume of air remaining in each bag (typically 2-4 L) was determined after the filling of both scintillation cells, the total activity of radon in the bags could be determined for the samples. The equilibrium activity of radon was <30 pCi (1 Bq) from over half of the samples, and only three samples produced >270 pCi (10 Bq) of radon in the bag. Measurement of the mass of the samples allowed determination of the mass-activity concentration; this ranged from <0.1 to 170 pCi/lb (0.01 to 14 Bq/kg). Results of the duplicate scintillation cells were highly correlated (r2=0.99). Based on the H-chamber measurements, the concentration of radon that would accumulate in a room containing the samples can be estimated using general assumptions. For a 20 m3 (10 ft • 10 ft • 7 ft) room containing 3 m2 (32 ft2) of a granite that emanates 770 pCi/ft2-hr (310 Bq/m2hr), the ingrowth of radon would resemble Fig. 1. Included in the estimate is a 0.5 air change/hr and instant mixing in the room. The granite would continually increase the indoor radon level in the room to 1.2 pCi/L (47 Bq/m3). Based on the Lucas-cell measurements, a 500-lb countertop (32 ft2 at 2.6 g/cm3) emanating 170 pCi/lb (14 Bq/kg) of radon, may produce over 4 pCi/L (148 Bq/m3) in the 20 m3 room. As noted above, the unpolished may emanate a greater amount of radon than the polished side, which would explain the lower radon concentrations associated with the H-chamber in Fig. 1. The alpha-scintillation method measured radon emitted from all sides of the samples. If the radon-laden air is dispersed throughout the entire house, the radon level will decrease, and if the air exchange is less, the radon level will increase. Conclusions Emission of radon from 36 types of countertop material produced for home interiors was determined using direct and indirect radio-analytical methods. The methods demonstrated that radon emanates from the surface of most natural stone, but rarely from engineered stone. The radon emanations measured in this study spanned three orders of magnitude, with fluxes > 300 pCi/ft2-hr (120 Bq/m2-hr). As the samples represent a small fraction of the selection available, decorative stones of greater emanating potential inevitably exist. The contribution from 3 m2 of the granite that emitted the most radon in this study to indoor radon concentrations was estimated to be at or below the EPA recommended-action level. Acknowledgments The flux chambers and electrets were generously contributed by Dr. Paul Kotrappa of Rad Elec Inc. This study was sponsored in part by C&C North America, Inc. 125 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References 150 4 3 100 Alpha scintillation cells H-chamber flux monitor 2 50 1 0 Estimated room radon concentration (Bq/m3) Estimated room radon concentration (pCi/L) Al-Jarallah, M.I., Fazal-ur-Rehman, Musazay, M.S., Aksoy, A., “Correlation between radon exhalation and radium content in granite samples used as construction material in SaudiArabia” Radiation Measurements 40 (2005), 625–629. Anjos R.M., Veiga R., Soares T., Santos A.M.A., Aguiar J.G., Frascá M.H.B.O, Brage J.A.P., Uzêda D., Mangia L., Facure A., Mosquera B., Carvalho C., Gomes P.R.S., “Natural radionuclide distribution in Brazilian commercial granites.” Radiation Measurements 39, 245–253 (2005). Kitto M.E., Green J. "Emissions from Granite Countertops", presented at International Radon Symposium, American Association of Radon Scientists and Technologists, San Diego, CA, Sept. 2005. Righi S., Bruzzi L., “Natural radioactivity and radon exhalation in building materials used in Italian dwellings”. J. Environmental Radioactivity 88, 158-170 (2006). Stieff L., Kotrappa P., “Passive E-perm Radon Flux Monitors for Measuring Undisturbed Radon Flux from the Ground”, Proc. International Radon Symposium, American Assoc. Of Radon Scientists and Technologists, Haines City, FL. Sept. 1996. 0 0 2 4 6 8 10 12 Hours Figure 1. Estimate of radon ingrowth in a 20 m3 room from granite countertop material based on measurements conducted using a H-chamber flux monitor and alpha-scintillation cells. 126 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 LUNG CANCER RISK ATTRIBUTABLE TO INDOOR RADON IN A HIGH RADON POTENTIAL REGION OF FRANCE O. Catelinoisa, F. Clinardb, K. Auryb-c, P. Pirarda, L. Nouryd, A. Hocharde, C. Tillierb a Institut de Veille Sanitaire - Saint Maurice Cire Centre-Est - Dijon c Centre d’Epidémiologie de Population - Registre dijonnais des AVC - Dijon d Direction Régionale des Affaires Sanitaires et Sociales de Franche-Comté - Besançon e Observatoire Régional de la Santé de Franche-Comté - Besançon b Abstract Awareness of the health risks due to exposure to indoor radon has raised concern about its impact in the general population. Using all available epidemiologic results, our goal is to accurately estimate this risk based on data collected in a high radon potential region of France (Franche-Comté). For this study, we considered exposure (response relations derived from cohorts of miners and from joint analyses of residential case) from various control studies. The exposure data come from a representative measurement campaign conducted in Franche-Comté. The estimated number of lung cancer deaths attributable to indoor radon exposure in this region ranges from 72 to 139, depending on the model considered. The attributable risk is higher in granitic area (22 to 39% for 7 to 12 deaths) but the number of deaths is higher in sedimentary area (65 to 127 deaths for 13 to 26%). Although indoor radon concentrations are higher in granitic area, the public health impact is more important in sedimentary area because of higher population density. Introduction The French National Institute of Heath Survey (InVS) recently estimated that 1,000 to 3,000 lung cancer deaths a year may be attributable to radon exposure (Catelinois et al., 2007). In the regions where radon is a potential issue, an accurate assessment of its health impact is important to inform, to sensitize the population and to target actions of risk prevention. According to the French National Radon Measurement Campaign performed between 1984 and 1999, Franche-Comté is a French region particularly concerned with radon. But this nation-wide designed study, relying on measurements realized in volunteers’ houses, may not be the best way to assess with accuracy the number of cancer deaths attributable to radon exposure. In fact, the National Campaign was designed to ensure a homogeneous geographic distribution of the measurements (the country was divided into grids of 40 km2) with at least one measurement per grid. Grids that included municipalities with more than 1,500 inhabitants had a second measurement taken in a different location. Volunteers were mainly recruited through contacts in the local governments, which placed and collected the radon detectors. Therefore, data collected in Franche-Comté during this period were not very numerous and perhaps not representative of the various housing types. A more specific design developed for Franche-Comté could be more efficient to assess indoor radon exposure in the region. Objective The first goal of this study was to assess the lung cancer death risk due to indoor radon exposure in Franche-Comté, using a specific radon exposure assessment. A secondary objective was to 127 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 compare the results of this assessment with those obtained using the French National Radon Measurement Campaign already available for all French regions. Subjects and methods Study setting Franche-Comté is a mountainous region situated in NE France bordered to the East by Switzerland. The 16,202 Km² region has three towns which concentrated 50% of the population in 28% of the surface area with half of the region being wooded. Franche-Comté is divided in 4 administrative areas (departments): Doubs, Jura, Haute-Saône and Territoire de Belfort. Identification of the population According to the 1999 French National Institute of Statistics and Economics (INSEE, 2000) census, the total Franche-Comté population consisted of 1,117,257 people. The sex ratio was close to 1 ; 25% were younger than 20 years, 54% were 20–59 years, 14% were 60–74 years, and 7% were older than 75 years. Of this population, according to the French Institute of Health and Medical Research (INSERM; Paris, France), 512 people died of lung cancer (437 men and 75 women) in 1999. Radon exposure assessment Sample scheme The study aimed to be based on a representative sampling of dwellings of the Franche-Comté region. This was achieve through the database of the French National Telecommunications Operator (France-Telecom) which allowed access to the address of most of the population for constructing the sampling frame (Until 2002, France-Telecom was the only operator in charge of dwelling connections to the telecommunication network in France). The designated sample size was 452 dwellings, equivalent to 1 detector per 1,000 homes. The sample was stratified by the geological structure (defined for each of the 1,786 districts of Franche-Comté according to geological maps – Genay, 2005) and by the type of housing (detached houses or blocks of flats). The distribution of the 452 dwellings selected is shown in Figure 1 Questionnaire development and interviewing procedures Questionnaires were developed by the France-Comté Study staff using the experiences of the National Radon Measurement Campaign (IRSN, 2000) and the French Indoor Air Quality Observatory (OQAI, 2003). Up to 7 attempts were made to obtain an answered call for each sampled telephone number. Data were collected by 3 trained interviewers during face-to-face interviews in October and November 2005. Dwelling and household characteristics were collected using standardized questionnaires. The data provided information about demographic characteristics, residential and smoking habits, and technical characteristics of the dwelling like surface area, number of room, building materials and ventilation. Indoor radon measurements were carried out using 2 Kodalpha LR 115 detectors placed in a randomly selected bedroom and in the living-room for 2 months. Statistical analysis The number of lung cancer deaths due to indoor radon exposure was estimated in a four-stage process: identification of the population, choice of the exposure-response relations, radon exposure assessment, and characterization of lung cancer risk. As described above, data on population and lung cancer deaths were provided respectively by the French National Institute of Statistics and 128 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Economics and the French Institute of Health and Medical Research. Concerning the choice of exposure-response relations, we used results obtain through two major epidemiologic studies: the joint analysis of 11 cohorts of miners (BEIR 1999) and the joint analysis of 13 European case– control studies (Darby et al. 2005). They have been resumed in a recent paper (Catelinois et al., 2006). Because, indoor radon measurements vary with season (they are highest in winter and lowest in summer), corrections for seasonal variation was required for the 2-month measurements in order to estimate annual exposure. To obtain these seasonal correction factors, the model developed by Pinel et al. (1995) was applied to the French database of indoor radon measurements. Application of the exposure–response relations mentioned above necessitates knowledge of the number of spontaneous deaths from lung cancer (i.e., apart from radon exposure). It was assumed that most of the 512 lung cancer deaths observed in 1999 were probably due to smoking, with some attributed to indoor radon alone, while others to the interaction between smoking and indoor radon, and the remainder to such other risk factors as air pollution and occupational exposure (Darby et al. 2001). To estimate the number of lung cancer deaths attributable to indoor radon exposure, we applied the data described above to the following formula: Nr, a, d, s = (RRr,a × Na, d, s)/(1 + RRr,a), where Nr, a, d, s is the number of lung cancer deaths due to indoor radon exposure at age a, in district d and for sex s. RRr,a is the relative risk for age a, and radon exposure r. Na, d, s is the total number of lung cancer deaths at age a in district d and for sex s. Calculations were carried out by age, gender, and administrative areas (departments). Results The Franche-Comté radon measurement campaign A total of 907 households were invited to participate. About 50% of those accepted with minor differences between strata (54.2% for the granitic dwelling stratum, 49.8% for detached houses and 47.7% for flats established on sedimentary geology). Few variables, both available in the FrancheComté study and in the 1999 National French Census (INSEE, 1999), have been used to search a possible selection bias. Participants did not differ from the inhabitants of Franche-Comté in term of age, gender, social and occupational group (data not shown). The dwellings of the participant households were also comparable to the Franche-Comté dwelling park in term of age of construction, number of rooms in the dwellings and renter / landlord status of the occupants. Therefore, a post-stratification strategy, initially considered, was not performed. Comparison between the National Radon Measurement Campaign and the Franche-Comté Study Table 1 lists a comparison between Franche-Comté measurements extracted from the National Radon Measurement Campaign in France and the present Franche-Comté Study. In the former study, measurements were performed in three different types of room with a majority in the livingroom. Although the place of measurement and the period of measurement differ in the two studies, distributions of radon concentration were quite similar. Indoor radon measurements were slightly lower in the Franche-Comté Study: arithmetic means were 138.2 and 134.0 Bq/m3 respectively for the National Campaign and for the Franche-Comté Study, and geometric means were 88.3 and 79.6 Bq/m3. Estimates of lung cancer deaths attributable to indoor radon exposure in Franche-Comté Table 2 shows the estimated number of lung cancer deaths attributable to indoor radon exposure using 2 datasets of indoor radon measurements (the French National Radon Measurement Campaign and the Franche-Comté Study) and 3 exposure-response relationships. Depending on the risk model used, the total number of lung cancer deaths ranged from 72 to 174. The calculations 129 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 suggest that of the 512 lung cancer deaths in 1999 in Franche-Comté, 8% to 34% may be attributed to indoor radon exposure. The model obtain from the joint analysis of the European case-control studies (Darby, 2005), produced the fewest attributable deaths, the age-duration BEIR VI model the most. Although the proportion of lung cancer deaths varied from 13% to 26% in sedimentary areas (vs. 23% to 40% in granitic areas) depending to the risk model, 65 to 127 lung cancer deaths were expected vs. only 7 to 12 in granitic areas. Discussion This is the first study in France providing radon concentration measurements based on a representative sampling of dwellings. This particular design allowed us to calculate with accuracy the number of lung cancer deaths attributable to indoor exposure in a high level indoor radon area. The results indicate that Franche-Comté is a high radon-emission area, even in the sedimentary zone. Using the risk assessment method proposed by the NRC (Covello and Merkho, 1993 ; NRC, 1983) we estimated the number of lung cancer deaths in France in 1999 attributable to indoor radon exposure. The consideration of several different exposure-response relations, which come from either cohorts of miners or residential case-control studies, allowed us to compare estimates of attributable deaths based on various exposure-response relations. We also considered the variability of indoor radon exposure between and within sedimentary and granitic areas of Franche-Comté. Over the past two decades, many epidemiologic studies, mainly cohorts of miners and case–control studies in the general population, have estimated the lung cancer risk associated with radon exposure. Because miners are generally exposed to higher levels than the general population, using miners’ data for assessing risks in general population clearly raises methodological issues, especially those related to the extrapolation of risk from high to low exposure and the transposition of risk estimates from miners to the general population (BEIR 1999). Although the radon hazard is no longer subject to debate, the use of risk models based on occupational exposure to assess the lung cancer risk attributable to indoor radon exposure is rightfully still considered a problem. In this risk assessment, the number of lung cancer deaths due to indoor radon exposure is relatively stables regardless the exposure-response relation used. Nevertheless, as in the risk assessment performed for the entire of France, risk estimates obtained from miner studies appear conservative. Lung cancer deaths due to indoor radon exposure can be considered premature because approximately half occur before the age of 70 years. We did not calculate the number of years of lost life, but given the long life expectancy in France, this figure may be quite high; management of the risk due to radon is clearly a major public health issue in France. Of the 512 lung cancer deaths in Franche-Comté during 1999, indoor radon probably caused 1326% whereas 5-12% of lung cancer deaths were attributable to radon exposure in all of France. Our results must be interpreted according to the number of people in each geological category. Although 23 to 40% of lung cancer deaths were attributable to radon in granitic areas, granitic areas represent only 5% of the population and 9% of lung cancer deaths: most of lung cancer deaths attributable to radon will occur in sedimentary areas. Actions of risk prevention should not be only focused on granitic territories. Conclusion This study is the first lung cancer risk assessment associated with residential radon exposure in Franche-Comté. When we consider uncertainties related to the exposure–response relation and geographic variations in radon exposure, we find that the total number of lung cancer deaths in 130 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 1999 attributable to indoor radon exposure ranges from 72 to 140. Most of them will occur in sedimentary areas sometimes regarded as zones of low radon risk. Awareness and risk prevention campaigns against radon hazard could not be turn only to the most exposed people in granitic areas, but should rather concern the overall population of the Region. References Améon R., Dupuis M., Diez O . (2004) House effect study – experimental site of KersaintPlabennec. (in French) . Rapport DEI/SARG n°04-05 – Fev 2004 - IRSN BEIR (1999). Health Effects of Exposure to Radon. BEIR VI. Washington, DC:National Academy Press. Catelinois O. et al. (2007) Assessment of the health impact related to indoor exposure to radon in France. BEH n°18-19 155-158. Available at http://www.invs.sante.fr/beh/2007/18_19/index.htm (in French) Covello V., Merkhofer M. (1993) Risk Assessment Methods. Approaches for Assessing Health and Environmental Risks. New York/London:Plenum Press. Darby S., Hill D., Doll R. (2001) Radon: a likely carcinogen at all exposures. Ann Oncol 12(10):1341–1351. Darby S., Hill D., Auvinen A., Barros-Dios J.M., et al. (2005) Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies. BMJ 330(7485):223 Genay Y. (2005) Identification of potentially high radon exhalation in Franche-Comté. Besançon. Drass de Franche-Comté. - in French – INSEE (2000) Recensement INSEE de 1999 de la Population Française, par Commune, Age et Sexe. Paris : Institut National de la Statistique et des Etudes Economiques. http://www.insee.fr/ IRSN (2000). National Radon Measurement Campaign of natural radioactivity in France. Available at http://www.irsn.org/index.php?position=radon_5 (in French) National Research Council. (1983) Risk Assessment in the Federal Government : Managing the Process. Washington DC: National Academy Press. OQAI (2003) Enquête Nationale Logements. http://www.air-interieur.org . (in French) OQAI (2008) Ventilation in French dwellings and schools (in French) – OQAI workshop – June 2008 - Paris. http://www.air-interieur.org . Pinel J., Fearn T., Darby S.C., Miles J.C.H. (1995) Seasonal correction factors for indoor radon measurements in the United Kingdom. Radiat Prot Dosimetry 58(2):127–132. Tirmarche M, Laurier D, Bergot D, Billon S, et al. (2003) Quantification of Lung Cancer Risk after Low Radon Exposure and Low Exposure Rate: Synthesis from Epidemiological and Experimental Data. Contract FIGHCT1999-00013. Brussels: European Commission. 131 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 1: Sampling scheme of the Franche-Comté Study 452,124 dwellings in the Franche-Comté area 19,005 dwellings established on granitic geology 433,119 dwellings established on sedimentary geology 254,376 detached houses 178,743 blocks of flats Random selection 120 dwellings (65 participations) 659 houses (328 participations) 128 flats (61 participations) 132 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Table 1: Comparison of Franche-Comté measurements extracted from the National Radon Measurement Campaign and the Franche-Comté Study. National Radon Measurement Campaign (1984 – 1999) (oct. & nov. 2005) (volunteers) (random selection of dwellings) N 249 318 27 202 88 (%) or [95%CI] No. of administrative areas No. of measurements No. of m. in a bedroom No. of m. in a living-room No. of m. in an other room Arithmetic mean [ 95%CI ] Geometric mean [ 95%CI ] No. of m. upper than 200 Bq/m3 No. of m. upper than 400 Bq/m3 No. of m. upper than 1000 Bq/m3 Franche-Comté Study (%) or [95%CI] (8.5%) (63.5%) (27.7%) N 306 869 436 433 0 138.2 88.3 [121.2 - 155.2] [81.0 - 96.2] 134.0 79.6 [121.3 - 146.7] [74.7 - 84.8] 52 20 3 (16.3%) (6.3%) (0.9%) 203 79 12 (23.4%) (9.1%) (1.4%) (50.2%) (49.8%) (0.0%) N: number of dwellings 95% CI: 95% confidence interval of the mean 133 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Table 2: Comparison of the estimates of lung cancer deaths attributable to indoor exposure in Franche-Comté in the French National Radon Measurement Campaign and the Franche-Comté Study French National Radon Measurement Campaign Male Female Total Male Female Total 437 75 512 437 75 512 147 126 27 23 174 149 93 118 17 21 110 139 61 11 72 21% 27% 23% 29% 21% 27% 14% 14% 14% Franche-Comté Study No of total lung cancer deaths (1999) No of total lung cancers attributable to indoor radon exposure Study of miners EAD EAC Indoor study Darby Proportion of lung cancers attributable to indoor radon exposure Study of miners EAD EAC Indoor study Darby 34% 29% 36% 31% 34% 29% EAD: Exposure-age-duration model BEIR VI (BEIR, 1999) EAC: Exposure-age-concentration model BEIR VI (BEIR, 1999) Darby: Raw risk model from the joint analysis of the13 European case-control studies (Darby, 2005) 134 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Table 3: Estimates of lung cancer deaths attributable to indoor exposure in sedimentary and granitic areas of Franche-Comté. (Indoor radon measurements from the Franche-Comté study) Sedimentary structure Granitic structure Total 482 30 512 100 127 10 12 110 139 65 7 72 21% 26% 33% 40% 21% 27% 13% 23% 14% No of total lung cancer deaths (1999) No of total lung cancers attributable to indoor radon exposure Study of miners EAD EAC Indoor study Darby Proportion of lung cancers attributable to indoor radon exposure Study of miners EAD EAC Indoor study Darby EAD : Exposure-age-duration model BEIR VI (BEIR, 1999) EAC : Exposure-age-concentration model BEIR VI (BEIR, 1999) Darby : Raw risk model from the joint analysis of the13 European case-control studies (Darby, 2005) 135 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 NATURAL RADIOACTIVITY IN BUILDING MATERIALS - CZECH EXPERIENCE AND EUROPEAN LEGISLATION Jiří Hůlka, Jaroslav Vlček, Jiří Thomas National Radiation Protection Institute, Bartoškova 28, 140 00 Praha Abstract An overview is presented of regulation and control of the natural radioactivity in building material in the Czech Republic (Atomic act 18/1997) and evolution of attitudes in the past 20 years. The sense is explained of regulation based on activity index and Ra-226 concentration, investigation levels and limit values for different materials and radiation protection optimisation process. The results of measurements are summarised. Czech experiences with several thousand houses contaminated by Ra-226 in the past (highly emanated aeratedconcrete houses up 1kBq/kg, slag concrete houses up 3kBq/kg and houses in Joachimstahl up 1MBq/kg ) are summarised. The EU recommendation “Radiological Protection Principles concerning the Natural Radioactivity of Building Materials” is discussed, too. 1. Introduction Historical background. The Czech Republic belongs to countries with highest indoor radon concentration in the world (mean radon value 140 Bq/m3). The primary cause is the high radon concentration in the soil. However, during the seventies and eighties there were found also three groups of houses with significantly elevated radium concentration in the building materials: 1) houses in the small town Jáchymov (Joachimstal) contaminated by residues from uranium paints factory and radium factory, 2) houses from highly emanated autoclaved aerated concrete produced from flying ash, 3) family houses from slag concrete. Some of the important details are summarised. Houses in Jachymov (Joachimstal) Jachymov (Joachimstal), the mining town known from Middle Age thanks to silvermines and coinage (minted coins called Joachims-thalers gave their name to the Thaler and the US dollar), later uranium mining industry and radium producing factory. Due to silver and uranium exploration and factory producing uranium paints and radium before the World War II, the town was locally contaminated in the past. The residues from factories were also used as additive into plaster and mortar in a lot of the Joachimstal´s houses, with 226Ra mass activity up to 1 MBq/kg in extreme cases and indoor gamma dose rates in the range of 10-100 µGy/h. The contamination was not uniform. The case was revealed in the seventies, but that time there was no national legislation concerning indoor radon and indoor radioactivity. The remedy measures carried out in the seventies were drastic - the worst houses were demolished and material taken away and processed in uranium ore mills. Most remaining contaminated houses were mitigated later in the nineties. Remedial measures were based on detailed radon and gamma diagnostic and targeted removal of plasters and mortar, if there was only local contamination. Family houses from autoclaved aerated concrete In the 1980 there was found the group of family houses built from autoclaved aerated concrete (226Ra mass activity up 1 kBq/kg). Because of high emanation coefficient of this materials (range 15- 30 %), the indoor radon concentration was up to 1000 Bq/m3 in extreme 136 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 cases. The indoor gamma dose rates were in the range of 0.1-0.3 µGy/h, what is the upper level of normal outside dose rate background in Bohemia. Some 20 000 houses from this material were built in the period 1963-1980. Fortunately, the aerated concrete was used in most of them only as the minor part of building material and hence indoor radon concentrations exceeded the intervention level only in about 1-2 % of these houses. Forced central or local ventilation systems were used for effective mitigation . Different radon barriers (special painting and special wallpapers) were tested but without good results. Family houses from slag concrete The last group was discovered in the 1987. There were found some 3000 factory-made family houses from slag concrete panels (226Ra mass activity in the range 1-10 kBq/kg). The source of the activity was slag from a small power plant burning high radioactive local coal from a mine near Prague. The first Producer Company knew the radioactive danger of the slag from the fifties. After changes in the factory ownership the new management took no care of this danger and more than 2000 family houses were built in the period of 1972-1983 distributed all over the country, most of them in Central Bohemia around Prague. All the peripheral and supporting walls were made from this material, while some partition walls were from bricks. Because of small emanation coefficient of the material (only 1-5%) the indoor radon concentration was only in the range of 200-800 Bq/m3. The indoor gamma dose rates in this group of houses were in the range of 0.5-2 µGy/h; the spatial variation in rooms was characterised by a factor of 2, with highest values in the corner of peripheral walls. The owners of these houses were aware of the cause of their trouble and apply for remedial measures or the possibility to buy up these houses by the government. The government has agreed after great struggle in 1991. Most of the owners have accepted remedial measures; only 4 % owners have sold their house. After some experiments, it was clear that radon removal by forced ventilation was the only effective and reasonable mitigation measure. The ventilation system with heat recovery, controlled by a central computer, was found to be most effective countermeasure and was used in practice. Radon level was reduced to 30% of the former values on average. Other remedial measures (gamma shielding, removal of building material, wall covering by special radon proof materials, etc.) were tested in some cases but were rejected as noneffective. This case revealed the problem of risk perception. 2. Development of regulation in the Czech Republic after 1987 It was the mentioned experiences from the past which lead to strict regulation of natural radioactivity. The first regulation was prepared in 1987 for indoor radon a gamma exposure in existing houses and at the same time for natural radioactivity in building materials. 2.1. Interventional levels for existing houses The first recommendation on limitation of both indoor exposures (gamma and radon) in the houses was prepared in 1987. Recommended value for remediation of indoor radon exposure in existing building was set to 400 Bq/m3. Recommended value for indoor gamma dose-rate was set to 2 µGy/h. Having in mind both radon and gamma exposures, the special intervention level that summed both exposures was defined by index S: C Rn D S= + 2 µGy / h 400 Bq / m3 where D is the gamma dose rate (µGy/h) and CRn is the long-term radon concentration 137 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 (Bq/m3). This sum rule (used only if D > 0.5 µGy/h) and value S = 1 were used for decision making on remedial measures with governmental support. 2.2. Regulation concerning the natural radioactivity of building materials The limit value 226Ra was set to 120 Bq/kg. This value was derived from model room calculation so that the building material will contribute to indoor radon limit value (200 Bq/m3) in new houses not more than 30% (under conservative conditions), having in mind that the underlying soil is the most important source of indoor radon. The other systems of regulation based on limitation of radon exhalation rate or emanation coefficient were discussed but rejected at the end because of sophisticated measurements of exhalation, long term changes and complicated system of limitation (YU 1997, Roelofs 1994, Petropoulos 2001). 3. The European regulation 3.1. Philosophy The radiological protection principles concerning the natural radioactivity of building materials were developed in the second half of the nineties in the Europe. The European Commission (EU Recommendation no.112, 1999, Mustonen 1997, Markkanen 2001)) formulated philosophy, which could be summarised as follows: - Building materials cause exposure by direct gamma radiation and by radon Rn released from the materials into indoor air. Their relative importance varies considerably, but both pathways should be considered when establishing radiological criteria for building materials. - When limits are set for exposure to natural radiation from building materials it must be clearly defined as to what extent the exposure caused by ‘normal’ background is included. The dose criteria used for controls should, therefore, be defined as the excess exposure caused by building materials, i.e. the background dose from natural radionuclides in ‘normal’ Earth’s crust need to be subtracted - The doses to the members of the public should be kept as low as reasonably achievable. However, since small exposures from building materials are ubiquitous, controls should be based on exposure levels which are above typical levels of exposures and their normal variations. - All building materials contain some natural radioactivity. Small, unavoidable exposures need to be exempted from all possible controls to allow free movement of most building materials within the EU. The concentrations of natural radionuclides in building materials vary significantly between and within the Member States. Restricting the use of certain building materials might have significant economical, environmental or social consequences locally and nationally. Such consequences, together with the national levels of radioactivity in building materials, should be assessed and considered when establishing binding regulations. - The amount of radium in building materials should be restricted at least to a level where it is unlikely that it could be a major cause for exceeding the design level for indoor radon introduced in the Commission Recommendation (200 Bq m-3) or - better - some fraction of it in order to allow some contribution from other sources, especially from the underlying soil, without exceeding the design level. - Exceptionally high individual doses should be restricted. Within the European Union, gamma doses due to building materials exceeding 1 mSv a-1 are very exceptional and can 138 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 hardly be disregarded from the radiation protection point of view. When gamma annual doses are limited to levels below 1 mSv, the 226Ra concentrations in the materials are limited, in practice, to levels which are unlikely to cause indoor radon concentrations exceeding the design level of the Commission Recommendation (200 Bq m-3). Controls on the radioactivity of building materials can be based on the following radiological criteria and principles: a) Dose criterion for controls Controls should be based on a dose criterion which is established considering overall national circumstances. Within the European Union, doses exceeding 1 mSv a-1 should be taken into account from the radiation protection point of view. Higher doses should be accepted only in some very exceptional cases were materials are used locally. Controls can be based on a lower dose criterion if it is judged that this is desirable and will not lead to impractical controls. It is therefore recommended that controls should be based on an annual dose in the range 0.3 – 1 mSv. This is the excess gamma dose to that received outdoors. b) Exemption level Building materials should be exempted from all restrictions concerning their radioactivity if the excess gamma radiation originating from them increases the annual effective dose of a member of the public by 0.3 mSv at the most. This is the excess gamma dose to that received outdoors. Separate limitations for radon or thoron exhaling from building materials should be considered where previous evaluations show that building materials may be a significant source of indoor radon or thoron and restrictions put on this source is found to be an efficient and a cost effective way to limit exposures to indoor radon or thoron. Investigation levels can be derived for practical monitoring purposes. Because more than one radionuclide contribute to the dose, it is practical to present investigation levels in the form of an activity concentration index. The activity concentration index should also take into account typical ways and amounts in which the material is used in a building. The activity concentration index (I) is derived for identifying whether a dose criterion is met: C Ra CTh CK I= + + 300 Bq / kg 200 Bq / kg 3000 Bq / kg where CRa, CTh, CK are the radium, thorium and potassium activity concentrations (Bq/kg) in the building material. The activity concentration index shall not exceed the following values depending on the dose criterion and the way and the amount the material is used in a building: Dose criterion Materials used in bulk amounts, e.g. concrete Superficial and other materials with restricted use: tiles, boards, etc 0.3 mSv (annually) I < 0.5 1 mSv (annually) I<1 I<2 I< 6 The activity concentration index should be used only as a screening tool for identifying materials which might be of concern. Any actual decision on restricting the use of a material should be based on a separate dose assessment. Such assessment should be based on scenarios 139 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 where the material is used in a typical way for the type of material in question. Scenarios resulting in theoretical, most unlikely maximum doses should be avoided. For the radon pathway, the evaluation of the excess dose caused by building materials is more complicated and the contribution of building materials must be evaluated by using theoretical model and general assumptions on the parameter values. However, it is very difficult to take into account all parameters, e.g. surface-volume ratio, the effect of surface treating done at the building site, and the ventilation rate. The reasonable approach for considering the radon pathway is to limit the amount of 226Ra in the building material so that the indoor radon concentration cannot rise above some pre-set level even under unfavourable conditions. 3.2. Application The dose criterion used for national controls should be chosen in a way that the majority of normal building materials on the market fulfil the requirements. Usually measurements of activity concentrations are needed only in case where there is a specific reason to suspect that the dose criterion for controls might be exceeded. The Member States should require, as a minimum, the measurement of types of materials which are generically suspected. Appropriate dose assessments should be performed if it is discovered that the reference value of the activity concentration index is exceeded. Normally the producer or dealer would be responsible for ensuring and showing that a material put on the market fulfils the radiological requirements set by the Member State. However, other approaches might also be applied according to national circumstances and administrative practices, e.g. the builder or designer of the building could be the responsible party for ensuring that a new building complies with the radiological requirements. The disadvantage of this approach is that appropriate training in radiological modelling should be arranged to all designers and builders. Materials should be exempted from all controls concerning their radioactivity if it is shown that the dose criterion for exemption is not exceeded. This can be done by comparing results of activity concentration measurements with the activity concentration index, or as appropriate, by means of a material-specific dose assessment. An exempted material should be allowed to enter the market and to be used for building purposes without any restrictions related to its radioactivity. In the case of export within the EU, it is understood that the value of the activity concentration index or a declaration of exemption should be included in the technical specifications of the material. When industrial by-products are incorporated in building materials and there is reason to suspect that these contain enhanced levels of natural radionuclides, the activity concentrations of these nuclides in the final product should be measured or assessed reliably from the activities of all component materials. Where necessary, also other nuclides than 226Ra, 232Th and 40K shall be considered. The dose criterion should be applied to the final product. Some traditionally used natural building materials contain natural radionuclides at levels such that the annual dose of 1 mSv might be exceeded. Some of such materials may have been used already for decades or centuries. In these cases, the detriments and costs of giving up the use of such materials should be analysed and should include financial and social costs. 4. CONTEMPORARY REGULATION IN THE CZECH REPUBLIC Contemporary Czech legislation concerning indoor natural radioactivity and remedial measures is based on the Atomic Act No.18/1997 and Decree No. 307/2002. The producers and importers of building materials are obliged to ensure systematic 140 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 measurement of the natural radionuclides in the building materials and to submit results to the State Office for Nuclear Safety. It affords unique opportunity to get nearly complete data set of natural radioactivity in the building material in the Czech market. The central database was prepared at the beginning of 1998 and more than 5000 results of measurements were obtained up to now (Vlcek 2007, SURO 2005). The results of measurements were obtained from 20 laboratories from the Czech Republic. The laboratories are periodically tested and they take part in the comparison organized by National Radiation Protection Institute. The framework of regulation in Czech Republic is based on two-step system: 1 step: screening (exemption) level for activity concentration index (I), based on gamma dose-rate estimation I= C Ra CTh CK + + 300 Bq / kg 200 Bq / kg 3000 Bq / kg 2 step: limit levels for 226Ra mass activity. The sense - limitations of radon exhaling from building materials under unfavourable conditions Table 1: screening levels (activity concentration index I) Index I Type of building material 0,5 Material used in bulk amount (e.g. brick, concrete, gypsum) 1 Raw material (e.g. sand) 2 Material used in „small“ amount (e.g. tiles) Table 2: limit levels for 226Ra type of building material Limit value Ra (Bq/kg) Buildings with stay of person 150 Limit value Ra (Bq/kg) Other construction without stay of person 500 300 1000 226 Material used in bulk amount (e.g. brick, concrete, gypsum) Other material used in small amount (e.g. tile..) and raw material (sand, building stone, gravel aggregate, bottom ash..) 226 The activity concentration index is used as a screening tool for identifying materials which might be of concern. The index mean values in Czech Republic market are (Vlček 2007): natural building stones 0.4, clay bricks 0.6, concrete 0.3, aerated concrete 0.53, slag concrete 0.69, coal ash and slag 0.63, gypsum 0.17 3,10. It was shown that for concrete, aerated and light-weight concrete, clay bricks, natural building stones exposure above 0,3 mSv is possible almost anywhere bulk amounts of material are used. Exposure above 1 mSv is possible if bulk amounts of the concrete contain slag, fly ash or natural sand or rock rich in natural radionuclides If activity concentration index I is above exemption level, the producer of building material is obliged to perform the cost-benefit analysis (the process of the optimisation of radiation protection). The producers need not carry out intervention if the costs are higher than the benefits of such remedial measures. In other word, the costs related to reduction of radionuclide concentration in building materials (namely by a change of raw materials or their origin, by sorting raw materials, by a change of technology and other suitable intervention), 141 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 would be demonstrably higher than the risks in health detriment. The benefits of remedial measures is calculated in such a way that a reduction of collective effective dose for a group of individuals being assessed is multiplied by a factor of 0.5 million CZK/Sv for the exposure to natural radionuclides. The aim is to reduce the public doses to level as low as reasonably achievable. 5. Conclusion There are several challenges in the possible harmonisation of controls on the radioactivity of building materials. It would be desirable that controls would be sufficiently uniform to allow movement of building materials within the EU. The levels of natural radionuclides in building materials vary significantly between countries and areas and the recommendations for harmonising controls should provide certain flexibility for taking into account specific national circumstances. The Czech experience after 20 years of application of regulation shows that it is possible to regulate all important exposures caused by natural radionuclides in building materials. It is obvious that high indoor gamma dose-rate can be hard to reduce post facto in the existing house. The aim of regulation is to restrict exposure in new buildings especially the highest individual doses. One must also have in mind decreasing ventilation rate (even below 0,1 h-1) in new energy-saving building can lead to problems with indoor air quality. The doses to the members of the public should be kept as low as reasonably achievable, but the dose criterion used for controls is chosen in a way that the majority of normal building materials on the market fulfil the requirements. If aim of regulation would be decrease future collective dose however, the low activity materials should be recommended and public awareness on this issue should be fostered. FUNDING This work was funded by the SONS (State Office for Nuclear Safety, Czech Republic), contract SUJB 9/2006. 1. 2. 3. 4. 5. 6. 7. 8. 9. REFERENCES Act No. 18/1997 Coll., On peaceful utilization of nuclear energy and ionizing radiation (Atomic Act) Radiological Protection Principles concerning the Natural Radioactivity of Building Materials, European Commission, Radiation protection No.112, 1999 Mustonen R., Pennanen M., Annanmäki M. and Oksanen E. Enhanced Radioactivity of Building Materials. Final report of the contract No 96-ET-003 for the European Commission. Radiation and Nuclear Safety Authority – STUK, Finland, 1997. Markkanen M., Challenges in harmonising controls on the radioactivity of building materials within the European Union, The Science of the Total Environment 272, 2001 Vlček J, Hůlka J., Natural radionuclides in building materials, Bezpečnost jaderné energie, 15 (53), 3/4 2007 p.80-85, ISSN 1210-7085 Report SURO, Public Exposure to Natural Radiation in the Czech Republic... National Radiation Protection Institute Prague, 2005 YU K. N. YOUNG I, E, STOKES K. N., KWAN M.K., and BALENDRAN R. V., Radon Emanation from Concrete Surfaces and the Effect of the Curing Period, Pulverized Fuel Ash (PFA) Substitution and Age, Appl. Radiat, lsot. Vol. 48, No. 7, pp. 1003-1007, 1997 Roelofs L. M. M. and Scholten L. C., THE EFFECT OF AGING, HUMIDITY, AND FLYASH ADDITIVE ON THE RADON EXHALATION FROM CONCRETE, Health Phys. 67(3):266-271; 1994 Petropoulos N.P., Anagnostakis M.J., Simopoulos S.E., Building materials radon exhalation rate: ERRICCA intercomparison exercise results, The Science of the Total Environment 272, 2001.109-118 142 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 RADON DIFFUSION COPEFFICIENT – A MATERIAL PROPERTY DETERMINING THE APPLICABILITY OF WATERPROOF MEMBRANES AS RADON BARRIERS Martin Jiránek1, Kateřina Rovenská2,3 and Aleš Froňka3 Czech Technical University, Faculty of Civil Engineering, Thákurova 7, 166 29 Praha 6, Czech Republic 2 Czech Technical University, Faculty of Nuclear Sciences and Physical Engineering. Břehová 7, 115 19 Praha 1, Czech Republic 3 National Radiation Protection Institute, Bartoškova 28, 140 00 Praha 4, Czech Republic 1 ABSTRACT Barrier properties of various waterproofing materials against radon were studied by means of the radon diffusion coefficient. Method for the determination of this material property used in the Czech Republic is presented. Results of radon diffusion coefficients measurements in more than 300 insulating materials are summarized. We have found out that great differences exist in diffusion properties because the diffusion coefficients vary within eight orders from 10-15 m2/s to 10-8 m2/s. Various possibilities of application of the radon diffusion coefficient for the design of radon barrier materials are discussed. Setting strict limits for maximal radon diffusion coefficient or minimal thickness of membranes results in significant reduction of the amount of materials that can be used for protection against radon. Calculation of the membrane thickness based on the radon diffusion coefficient and particular soil conditions and building characteristics seems to be the most effective and convenient approach. INTRODUCTION Some damp-proof or waterproof membranes placed over the entire surface of the house substructure can prevent radon from entering buildings from the soil. However the selection of effective radon barriers from the total amount of tanking materials is very difficult due to the lack of information about radon diffusion through these materials. Radon diffusion coefficient is a material property that determines this transport and therefore it can be used for the proper selection of radon-proof membranes based on a quantitative parameter assessment. Testing of barrier properties of tanking materials against radon by means of the radon diffusion coefficient started in the Czech Republic in 1995 according to the method introduced by the Faculty of Civil Engineering of the Czech Technical University in Prague in cooperation with the National Radiation Protection Institute in Prague. Up to now a quite excellent database of results is available (more than 300 materials obtained throughout Europe and Canada, have been measured). This enables to make some general requirements considering the applicability of the radon diffusion coefficient for the design of radon-proof membranes. DETERMINATION OF THE RADON DIFFUSION COEFFICIENT The Czech test method, which is accredited by the Czech Accreditation Institute, is based on the determination of the radon flux through the tested material placed between two cylindrical containers. Radon diffuses from the lower container, which is connected to the radon source, through the sample to the upper container. From the known time dependent curves of the radon concentration in both containers the radon diffusion coefficient can be calculated. Radon concentration in both containers that serve as ionisation chambers operating in current mode is measured continuously by fully automatic measuring device enabling monitoring in 143 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 very short time intervals (from 1 minute). Detailed description of the measuring technique, which schematic drawing is presented in Fig. 1, can be found in (Jiránek, 2008). Figure 1: Schematic drawing of the new device (1.1, 1.2 – upper (receiver) containers, 2 – lower (source) container, 3 - pressure difference sensor, 4 - pump, 5 – control and operation unit, 6 – radon source, 7 – tested sample). In order to obtain reliable values of the radon diffusion coefficient from the measured data, the calculation must be based on an appropriate mathematical model reflecting the time dependent radon concentration curves not only in the source and receiver containers, but also in the membrane itself. For the analysis of the radon concentration curve measured in the upper container we use the time dependent numerical modelling of the non-steady state radon diffusion through the membrane. Applied numerical model simulating the whole measuring process solves the one-dimensional diffusion equation: #C (x,t) #t = D. # 2C (x,t) #x2 " !.C (x,t) (1) where D is the radon diffusion coefficient [m2/s], λ is the radon decay constant (2.1 X 10-6 s-1 ) and C(x,t) is the radon concentration [Bq/m3]. 144 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 2: Fitting the numerical solution to the measured concentration in the receiver container. Radon diffusion coefficient is derived from the process of fitting the numerical solution to the measured curve of radon concentration in the receiver container (Fig. 2). The great advantage of the applied mathematical solution is that it enables to determine the radon diffusion coefficient from data obtained by all known measuring modes used throughout Europe. This is very helpful, especially in the situation when no uniform measuring method exists within Europe. VALUES OF THE RADON DIFFUSION COEFFICIENT 7.3E-09 2.5E-10 8.1E-11 3.6E-11 2.3E-11 Na bentonite paper/geotextile EPDM polymer cement coatings PO recycled PVC-P polymer midified bitumen compositions LDPE modified bitumen ECB PVC-P PP HDPE chlorinated PE PU coatings 1.0E-14 1.0E-15 2.2E-11 1.9E-11 1.5E-11 1.4E-11 1.3E-11 1.0E-11 Measured by the Czech Technical University and National Radiation Protection Institute 1.0E-13 oxidised bitumen 1.0E-12 3.9E-14 1.0E-11 5.8E-12 2.3E-12 1.0E-10 3.5E-12 1.0E-09 oxidised/modified bitumen with Al sheet Radon diffusion coefficient D2/ s(m ) 1.0E-08 1.2E-10 Results of the radon diffusion coefficient measurements are summarized in Fig. 3. On x-axis materials are grouped into categories according to the chemical composition. Fig. 3: Summary of the radon diffusion coefficient measurements realized in various waterproofing materials. On x-axis materials are registered with respect to rising order of their diffusion coefficients (HDPE - high density polyethylene, LDPE low density polyethylene, PVC-P - flexible polyvinyl chloride, PP - polypropylene, PO – polyolefin, PU – polyurethane, ECB ethylene copolymer bitumen, EPDM - ethylene propylene dien monomer). 145 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Fig. 3 shows very clearly that in common insulating materials used for protection of houses against radon the diffusion coefficients vary within eight orders from 10-15 m2/s to 10-8 m2/s. The lowest values were obtained for bitumen membranes with Al foils no matter whether the bitumen was modified or not. On the other hand the highest values of the radon diffusion coefficient were discovered for sodium bentonite placed between paper or geotextile sheets, rubber membranes made of EPDM, polymer cement coatings and polyolefin membranes. Radon diffusion coefficient for the majority of materials varies in the range 3 X 10-12 and 3 X 10-11 m2/s. From Fig.3 it is also evident that relatively long scatter lines were obtained for two material categories – for bitumen membranes with Al foils and for polymer modified bitumen compositions. In case of membranes with Al foils it is caused by different thickness of Al foils. However in the category of bitumen compositions it is a result of different chemical composition of each material. It means that on the lower end of the scatter line materials with very good barrier properties can be found, but on the upper end there are materials, which could be hardly considered as radon-proof. Since the mean value lies close to the upper end, we can assume that majority of these materials will not work satisfactorily. DESIGN OF RADON-PROOF MEMBRANES Radon diffusion coefficient has been adopted in several countries (Czech Republic, Germany, Spain, Netherlands, Ireland, etc.) as a suitable parameter for the design of radon-proof membranes. However the application of this parameter differs from country to country. In general we can find three different approaches how to use the diffusion coefficient for the design of membranes: 1. the radon diffusion coefficient D of the radon-proof membrane must be below the strict limit value, 2. the thickness d of the radon-proof membrane must be at least three times greater than the radon diffusion length l (Keller) calculated as l = (D/λ)1/2, 3. the thickness of the membrane is calculated for each house (Jiránek, Hůlka, 2000, Jiránek, Hůlka, 2001, Jiránek, 2004, CTS, 2006) according to the radon diffusion coefficient in the membrane, radon concentration in the soil on the building site and house parameters (ventilation rate, area in contact with the soil). Limit for the maximal value of the radon diffusion coefficient The main problem connected with this approach is how to choose correctly the limit value. To be safe and reliable under all circumstances (for all types of houses and radon concentrations in the soil) it should be rather lower than higher. However the lower the limit will be, the more materials will be of no use. For a typical single-family house, typical soil gas radon concentration and typical thickness of the membrane the maximum value of the radon diffusion coefficient should be 1 X 10-11 m2/s. As a consequence of this the protection against radon will be solved preferably by materials with Al foils, which is from the technical point of view meaningless, because membranes with Al foils feature very low elongation and therefore they can very easily loose their barrier properties by destroying of the Al foil. Limit for the minimal thickness of the membrane Limits for the minimal thickness of membranes are derived from the assumption that most radon atoms will decay before they pass through the insulation, if the thickness of the insulation is greater than the diffusion length. However the condition that the insulation thickness should be at least three times greater than the diffusion length that is applied in 146 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 some countries (Keller) leads to the enormous thickness of membranes. The required thickness exceeds the production thickness, if the radon diffusion coefficient is higher than 1 X 10-12 m2/s in case of plastic membranes or 4 X10-12 m2/s in case of bitumen membranes. This simply leads to the conclusion that the requirement d ≥ 3l is stricter than the previously described limit for D and will be met by a considerably smaller group of materials. CALCULATION OF THE MEMBRANE THICKNESS Under the conditions that the insulation is placed over the entire area of structures in direct contact with the soil, all joints between sheets are airtight and any penetration of utility entries through the insulation is properly sealed, we can consider the convective transport of radon to be negligible. Therefore it is possible to assume that the radon supply rate into the house with continuous tanking is created only by the diffusion through the insulation. Based on this simplification the highest permissible radon exhalation rate into the house, Elim, can be expressed by equation (2): Elim = Cdif .V . n A f + Aw (Bq/m2h) (2) where V is the interior air volume (m3), n is the air exchange rate (h-1), Af is the floor area in direct contact with the soil (m2), Aw is the area of the basement walls in direct contact with the soil (m2) and Cdif is a fraction of the reference level for indoor radon concentration Cref caused by diffusion. The value of Cdif can be estimated, for example according to the Czech standard ČSN 730601 as 10% (CTS, 2006). This means that the importance of the diffusion is reduced to 10 % of Cref and the remaining 90 % of Cref is reserved for the accidentally occurring convection. In this context, the thickness of the radon-proof insulation can be derived with respect to real geological and building characteristics from the condition that the radon exhalation rate E from the real insulation in a real house calculated according to equation (3) must be less or equal to the highest permissible radon exhalation rate Elim calculated for that house, i.e. E ≤ Elim. E = !1 . l . ". CS 1 sinh( d / l ) (Bq/m2h) (3) where Cs is the radon concentration in the soil gas (Bq/m3) measured on the building site, λ is the radon decay constant (0,00756 h-1), d is the thickness of the radon-proof insulation (m), l is the radon diffusion length in the insulation l = (D/λ)1/2 (m), D is the radon diffusion coefficient in the insulation (m2/h) and α1 is the safety factor that should eliminate the inaccuracies arising during the soil gas radon concentration measurements. Values of α1 can be estimated according to the soil permeability (for highly permeable soils α1 = 7, for soils with medium permeability α1 = 3 and for low permeable soils α1 = 2,1). On the assumption that the insulation is homogeneous, its minimal thickness can be calculated from equation (4) obtained after the replacement of E in the equation (3) by Elim from equation (2). # 1.l .".C s .(Af + Aw ) d ! l .arcsinh C dif .n.V (m) (4) The great advantage of this approach is that the design of the radon-proof membrane can be fitted according to particular conditions (soil and building characteristics). The possibility of 147 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Thickness of insulation (mm) under- or over-dimensioning is thus strongly reduced. This method of the radon-proof insulation design was thoroughly verified in practice because it has been used in the Czech Republic since 1996. 100 3 Cs = 200 kBq/m + low permeability or 3 Cs = 60 kBq/m + high permeability 10 1 0,1 3 Cs = 100 kBq/m + low permeability or 3 Cs = 30 kBq/m + high permeability 0,01 3 Cs = 30 kBq/m + low permeability or 3 Cs = 10 kBq/m + high permeability 0,001 1,00E-13 1,00E-12 1,00E-11 1,00E-10 1,00E-09 Radon diffusion coefficient2/ D s ) (m Fig. 4; Thickness of the insulation calculated according to the equation (6) for different values of D and various combinations of soil gas radon concentration and soil permeability. The influence of the soil permeability is introduced by the safety factor α1 that increases proportionally with the permeability. Chart is valid for the house with habitable rooms in the basement. The principle of designing according to this method can be identified from Fig. 4 in which the thickness of the insulation is plotted as a function of the radon diffusion coefficient and various combinations of soil gas radon concentration and soil permeability. It is clear that the thickness of the insulation with D lower than 10-12 m2/s can be only several tenths of one millimetre, even in the areas with high radon concentration in the soil. Such small thickness is hardly producible and applicable due to sensitivity to puncturing and thus thicker insulation must be in practice used. On the other hand, the applicability of the insulation with D of order of 10-10 m2/s will be very strongly dependent on building characteristics and the radon concentration in the soil. Membranes with D above 1.10-10 m2/s are too permeable to be used for radon-proof insulation. This clearly leads to the conclusion that the optimal value of the diffusion coefficient can be found within the interval 5.10-12 to 5.10-11 m2/s. This interval corresponds with the production thickness of the most frequently used insulating materials, that is 1 or 2 mm for plastic foils and 3 or 4 mm for bitumen membranes (which in addition can be applied in two or three layers). CONCLUSIONS Radon diffusion coefficient seems to be a convenient parameter for testing of radon-proof membranes and thus measurement of this parameter should be required for all insulating materials designated as a radon barrier. 148 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Time dependent numerical modelling of the radon diffusion through membranes under the non-steady state conditions that simulates the whole measuring process provides evaluation of the radon diffusion coefficient with the highest accuracy. Based on the experience from the Czech Republic controlling applicability of membranes by setting strict limits for the maximal value of the radon diffusion coefficient or the minimal thickness of the membrane is not a convenient approach. It seems to be reasonable to replace strict limits by the real design of the insulation in dependence on particular building and soil characteristics. Radon diffusion coefficient plays a crucial role in this design, because it enables to calculate the membrane thickness and the radon exhalation rate from the membrane. In countries, where radon prone areas are classified according to indoor radon data and where measurements of the radon concentration in the soil gas are not so common, evaluation of Cs can be a problem. However it can be overcome, if we realize that in fact radon prone areas substitute real soil gas concentrations. Therefore an appropriate value of the radon concentration in the soil can be added to the each type of the radon prone area. The uncertainty of this procedure can be covered by the safety factor α1. Design of radon resisting membranes should be more complex. It should be stressed that barrier properties of membranes should be in balance with other very important properties such as durability, flexibility, buildability, chemical resistance, etc. ACKNOWLEDGEMENT Presented work has been supported by the research project MSM 6840770005. 149 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 REFERENCES 1. Jiránek M., Hůlka J.: Radon Diffusion Coefficient in Radon-proof Membranes – Determination and Applicability for the Design of Radon Barriers. In: International Journal on Architectural Science, Vol. 1, No. 4, p. 149 – 155, 2000 2. Jiránek M., Hůlka J.: Applicability of various insulating materials for radon barriers. In: The Science of the Total Environment 272 (2001), pp. 79-84 3. Jiránek M.: Testing and Design of Radon Resisting Membranes Based on the Experience from the Czech Republic. In: Proceedings from the 4th European Conference on Protection against Radon at Home and at Work. Praha 28.6.-2.7.2004 4. Jiránek M., Froňka A.: New Technique for the Determination of Radon Diffusion Coefficient in Radon-proof Membranes. In: Radiation Protection Dosimetry, 2008, doi:10.1093/rpd/ncn121 5. Fernández P.L., Quindós L.S., Sainz C., Gómez J.: A Theoretical Approach to the Measurement of Radon Diffusion and Adsorption Coefficients in Radonproof Membranes. In: Nucl. Instr. and Meth. in Phys. Res. B, 2003 6. Keller G.: “Radonisolierte Häuser“ – Bautechnische Vorschläge für den Neubau und für Sanierungsmaßnahmen. Universität des Saarlandes, Homburg 7. Labed V., Rannou A., Tymen G.: Study of 222Rn Permeation through Polymer membranes: Application to Continuous Measurement of 222Rn in Water. In: Health Physics 1992, Vol. 63, N.2, pp.172-178 8. Spoel W.H.: Radon Transport in Sand. A Laboratory Study. Technische Universiteit Eindhoven, 1998 9. Czech Technical Standard ČSN 73 0601 “Protection of Buildings against Radon from the Soil”. Czech Standards Institute, Praha, 2006 150 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 WORKING WITH PARTNERS TO MAKE THE MOST OF NATIONAL RADON ACTION MONTH By Cindy Ladage, Nuclear Policy Analyst & Patrick Daniels, Health Physicist of the Illinois Emergency Management Agency Radon Program Abstract Grabbing the attention of the public is not an easy thing to do, especially when conveying the risk of a colorless, odorless, radioactive gas that consumers can only detect by testing. Sharing information about lung cancer, the devastating health effect from radon can be daunting. By pairing with partners, National Radon Action Month can be a marketing opportunity that should not be missed. In January of 2008, the Illinois Emergency Management Agency teamed with the Respiratory Health Association of Metropolitan Chicago, the American Lung Association of Illinois, Cook County Environmental, Chicago Department of Public Health and the United States Environmental Protection Agency Region V office as well as the University of Illinois Extension office and Illinois State University’s Radon Awareness program to create events to reach the public. The combined efforts made each partner reach its maximum results with minimal input. Working together can work for any group to create an event that will spur radon outreach. Introduction USEPA has designated the month of January as National Radon Action Month. Fondly known as NRAM, the USEPA website states “The aim of National Radon Action Month is to increase the public's awareness of radon, promote radon testing and mitigation, and advance the use of radon-resistant new construction practices.” While those of us who work in the radon industry promote radon year round, for thirty days, you have the opportunity to reach out and grab the attention of the media and the citizens of your state, county, or municipality. Competing with New Years and other first of the year activities can be daunting, so what can be done to obtain the maximum effort with minimal cost and input? Partnering is the answer. By working with others you may convey the message that radon is a colorless, odorless, radioactive gas that is the leading cause of lung cancer among nonsmokers. Sharing the message that radon can only be detected by testing, radon can easily be reduced through mitigation and when building a new home radon resistant you can reduce the radon potential and ease the cost of mitigation along with making it more aesthetically acceptable. When these messages play during NRAM you can take advantage of a oncea-year mega-marketing opportunity. 151 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Combine forces with those with similar interests, your radon partners. Although this comes from a governmental perspective, the radon industry can use American Association of Radon Scientists and Technologists (AARST) and other professional organizations like American Society of Home Inspectors (ASHI), National Environmental Health Association (NEHA) etc. to achieve the same type of results. By using a professional organization or working with your state, county, nonprofit or extension counterpart, the message gains credibility and appears as more than a business promo. Methodology In 2008, the Illinois Emergency Management Agency (IEMA) Radon Program joined forces to display and present in Chicago. We teamed with the American Lung Association of Illinois, Respiratory Health Association of Metropolitan Chicago, Cook County Environmental, Department of Chicago Public Health and University of Illinois Chicago, as well as Illinois State University and the University of Illinois Extension office for different activities. We kicked off our radon poster contest during radon action week with the University of Illinois Extension office at the helm. Why work together? Why not just go it alone? Eileen Lowery of the Respiratory Health Association stated, “I was inspired to work with radon colleagues from throughout the state as we had the opportunity to bring the radon message to so many people in a variety of activities. It would have been impossible to get the message out to so many people without our partnership.” Some of the activities that Ms. Lowery refers to include radon displays in Chicago at the Cook County Building which was secured by Martha Jones of Cook County Environmental, the American Lung Association Building which Angela Tin and other ALA staff secured and the USEPA Region V office where radon presentations were also made to USEPA staff. Mike Murphy and Jeanette Marrero set up this event. What did it accomplish? Over a three-day period, over 600 radon test kits (or coupons) and radon information were distributed. Statewide about 33% of residents use the radon test kits (ALA has had a usage rate of 34%). Recently IEMA sent out a follow-up survey. Many that did not initially test are now testing, so this percentage should increase in the future. 152 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Eileen Lowery, Cindy Ladage, Tony Amatto, Sherrill Keefe and Martha Jones at the Cook County Building Setting up in public areas and in places of employment worked well allowing us to share the radon message in a nonthreatening way. By including local experts and nonprofits the radon message gained credibility that state program, federal agencies or a business may not garner alone. Wikipedia defines a nonprofit organization as one that “is a legally constituted organization whose objective is to support or engage in activities of public or private interest without any commercial or monetary profit.” Together we had fact sheets, displays, and material and a variety of expertise that included a nurse and an environmental educator who could answer questions on lung cancer, and locals who knew radon levels in the vicinity. Angela Tin, Director of Environmental Services for the ALA shared, “The American Lung Association of Illinois is a proud partner with the Illinois Emergency Management Agency (IEMA) in educating the public on the principles of radon testing and mitigation to reduce exposure to this known health hazard.” Reducing exposure, lowering the risk of lung cancer, is everyone’s goal and the exhibits provided risk-reduction information to a cross section of the Chicago urban population. Along with the exhibits, which can work for anyone anywhere, press coverage can provide extended coverage long after the event is over. This is the case for the Radon Networking Day that also takes place during National Radon Action Month. Ruth Ann Lipic of Illinois State University’s Radon Awareness Program coordinates with IEMA to create a learning opportunity for radon partners. This event promotes sharing ideas and emphasizes how to maximize results with minimal input by working together. Ruth Ann Lipic shared, “By planning together for a Radon Networking Day, we have been able to 153 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 invite and educate new radon partners and grantees from across the state. It is a formula of 1+1=3.” How does this same type of event work for those in the radon industry? You can work with home inspectors, real estate agents, bankers, mortgage lenders and builders and share what is new in the industry. Together you can share resources to spread the word about radon locally. A press release can make a meeting a media event. At Radon Networking Day Gloria Linnertz received the second annual Radon in Excellence Award. Ruth Ann Lipic was the first deserving recipient. Combining the award with the networking day created an event that some media willingly covered. A picture taken at an event can also serve as part of a follow-up article in your newsletter, professional publication, or local newspaper. Joe Klinger the Illinois Emergency Management Agency Assistant Director hands out the award to the 2008 winner Gloria Linnertz. 154 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Spreading the word about radon through publications during NRAM is another successful way to spread information about radon. This year, Barb Sorgatz, a lung-cancer survivor was willing to share her story with several media outlets, and the press listened. Articles from Barb’s story appeared in Chicago papers as well as the Illinois Public Health Association Newsletter. IEMA also had several publications that picked up articles about radon and the importance of testing. All these combined with the fact that the new Radon Awareness Act went into affect during NRAM brought a lot of attention to the radon subject. The attendance of Barb Sorgatz and Gloria Linnertz at Radon Networking Days increased attention to this subject. Seventy-five attendees, a record, attended this oneday event. Conclusion- Documenting Results By tracking calls, website hits, and other numbers you can measure the impact of an outreach effort. Again, when partnering their efforts count also as your own. Here are the radon document requests over a two-year period (see the January 2008 spike). Keep in mind that the new Act does account for a lot of the numbers being reported. Document Totals 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 Jan-06 Apr-06 Jul-06 Oct-06 Jan-07 Apr-07 Document Totals Jul-07 Oct-07 Jan-08 Apr-08 155 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 As you can see below, the test-kit requests parallel this chart. Test-Kit Totals 10,000 100000 9,000 90000 8,000 80000 7,000 70000 6,000 60000 5,000 50000 4,000 40000 3,000 30000 2,000 20000 1,000 10000 This0 increased interest in radon has also created a jump in radon professional licensees. 0 Jan-06graph Apr-06 Jan-07 years. Apr-07 Jul-07 Oct-07 Jan-08 Apr-08 Jul-08 See the below Jul-06 over theOct-06 past two Monthly Totals Total Since Jan 2006 Licensed Professionals Number of Licensees 350 325 324 311 303 300 296 275 272 274 272 276 278 276 269 267 266 264 261 250 Jan-07 Apr-07 Jul-07 Oct-07 Jan-08 Apr-08 Number of Licensees 156 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Media coverage can create sparks of interest that go on long after the event. In many cases where spikes are shown for requests for extra documents and test kits, this was not always from the result of a national newspaper. Many times the spike was from some of the local weekly papers that picked up a story. Those living in the vicinity reacted from the story up to a month or two after the story hit the paper. This can be especially seen in the spike from January to February 2008. You can’t be everywhere during NRAM, but you can promote your radon activities through a variety of ways such as your website, radio shows, press releases and other means that don’t always require you to be there. Additional Resources What other resources can help maximize your marketing efforts during NRAM? There are several sources that can provide you with the assistance you need to share your message. Most state-agency radon programs offer free radon publications. USEPA has a variety of publications as well. See the USEPA website at http://www.epa.gov/radon/pubs. The University of Illinois Extension Office also created a website with IEMA that answers general questions about radon that you might find useful. See www.takeactiononradon.uiuc.edu. The American Association of Radon Scientists and Technologists, AARST, also has resources available on its website as well. See http://www.aarst.org/radon_info.shtml. Both the American Lung Association http://www.lungil.org/ and the Respiratory Health Association of Metropolitan Chicago http://www.lungchicago.org can also provide information about radon and lung cancer. The American Lung Association’s toll free line, 1-800-LUNG-USA, offers one-on-one telephone assistance with nurses and medical personnel who can answer questions pertaining to lung cancer. 157 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References http://iaq.custhelp.com/ “Frequently Asked Questions” Eileen Lowery of the Respiratory Health Association Ruth Ann Lipic, Illinois State University Radon Awareness Program Angela Tin, American Lung Association of Illinois http://en.wikipedia.org/wiki/Non-profit_group “Not for Profit Organizations” IEMA’s “Radon Outreach” power point presentation presented at 2008 Region V meeting in Cleveland, Ohio. http://www.epa.gov/radon/pubs “How to Order” http://www.aarst.org/radon_info.shtml “What is Radon” www.takeactiononradon.uiuc.edu http://www.lungil.org/search “radon query” http://www.aarst.org/radon_info.shtml. http://www.lungil.org/ http://www.lungchicago.org 158 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 POST-MITIGATION RADON CONCENTRATIONS IN MINNESOTA HOMES Daniel J. Steck1 Physics Department, St. John’s University Collegeville, MN 56321 ABSTRACT Real radon risk reduction requires that mitigation systems maintain low radon concentrations for years. In most states, the actual radon reductions are not known since systematic or representative sampling of post mitigation radon is not routinely done or archived. Uncertainty about the accuracy of post-mitigation screening tests, aging effects on system performance and follow-up testing maintenance plague calculations of the long-term effectiveness of current mitigation techniques. Effectiveness calculations usually assume an average post-mitigation concentration of 2 pCi/L; an assumption that is unconvincing to some public policy makers. To investigate mitigation system performance in Minnesota, 150 homeowners, selected from the clients of six professional mitigators, were sent detectors for one screening test and two long-term tests. These homeowners reported an average pre-mitigation radon concentration of 10.3 pCi/L (380 Bq m-3). Long-term radon concentrations measured during the winter and spring of 2008, six months to 7 years post-mitigation, averaged 0.8 pCi/L. A model calculation suggests that if this kind of effective mitigation were applied across the state, tens of thousands of Minnesotans could be spared lung cancer mortality. The cost per life saved by mitigation would be less than the comparable cost of medical treatment alone. INTRODUCTION Long-term exposure to elevated radon (222Rn) concentrations has been linked to increased lung cancer risk. When radon concentrations in a home exceed 4 pCi/L (150 Bq m-3), the USEPA recommends that the house be mitigated. Real radon risk reduction requires that mitigation systems maintain low radon concentrations for years. The most common mitigation system, particularly in the Upper Midwest, is active soil depressurization (ASD). This method relies on a pressure difference between the soil gas underneath the house and the atmosphere to remove the radon-laden soil gas. To be effective, an ASSD system needs to maintain a substantial pressure difference with a fan and well-sealed suction piping. The performance of a system is usually tested shortly after installation, often with a short-term test left with the homeowner at when the system is installed. Mitigation system performance can change through fan failure, blockages, and leaks. Follow-up radon measurements by the homeowner are recommended by the EPA, but in most states, the actual radon reductions are not known since systematic or representative sampling of post mitigation radon is not routinely done or archived. 1 This work was supported, in part, by a St. John’s University Faculty Development grant. 159 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Uncertainty about the accuracy of post-mitigation screening tests, aging effects on system performance and follow-up testing maintenance plague calculations of the long-term effectiveness of current mitigation techniques. Yet, the long-term post-mitigation radon concentrations play a pivotal role in estimates of the lives saved by radon reduction programs. There is little published data on the performance of professionally-installed mitigation systems. Early unpublished reports of systems installed by research and development teams in a limited number of houses suggested that 2 pCi/L might be achievable in many homes (USEPA 1992). Two studies done in the early 1990’s suggested that most mitigation systems could lower radon concentrations to below 2 pCi/L (Brodhead et al. 1993, Brodhead 1995). In the years since, mitigation system effectiveness calculations usually assume an average post-mitigation concentration of 2 pCi/L; an assumption that is not well supported by a representative sample of radon measurements in houses from all regions that have been mitigated by current practioners using modern techniques. Public policy makers who are contemplating new laws and regulations for radon risk reduction prefer data from systematic and unbiased samples rather than self-reported data from mitigators or radon detector manufacturers. In an earlier radon survey, 18 mitigated houses were measured, by chance, during a general survey (Steck 2005). This group of houses had an average radon concentration of 2.9 pCi/L in their living spaces and 28% of them exceeding the USEPA 4 pCi/L action level. However, the 12 houses that had been professionally mitigated had an average radon concentration of 1.7 pCi/L and only 8% exceeded the action level. The present study aims to assess the performance of professionally-installed mitigation systems in a radon-prone state. The assessment is based on long term radon measurements from an unbiased sample of single family homes whose mitigation system is more than 6 months old. These results, when combined with radon measurements from unmitigated homes, can be used to estimate the potential that mitigation has for saving lives in existing Minnesota homes. METHODS Research funds for this study were obtained from a private source to provide privacy for the data of both the professional contractors and homeowners who participated. Ten professional mitigation contractors, selected from the list that the Minnesota Department of Health maintains (MDH 2008) were sent enrollment letters requesting their cooperation in this research project. The ten were selected to have a good sample of experienced and new mitigators with both urban and rural clients. Five agreed to provide client contacts for systems that were installed in single family homes during the period from 6 months to 7 years prior to January 2008. From these client lists, invitations were sent to 300 homeowners who were selected to reflect a good mixture of new and older systems in urban and rural locations. Sixty-seven invitations were returned as undeliverable. One hundred sixty six homeowners agreed to participate by returning the post card questionnaire (3 returned the card but declined measurements). The questionnaire contained questions about the operating status of the system, pre and post mitigation radon measurements and practices. 160 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 1 shows the locations of these homes and the county average radon concentration measured during an earlier study (Steck 2005).Each home received a radon detector packet that contained an Air Check short-term detector (AC) for a short-term, screening measurement (ST) and two Landauer RADTRAK® alpha track detectors (ATD) for longterm measurements (LT). Detector packets were sent between 1 February and 15 March 2008. The homeowners were instructed to perform a screening measurement as soon as possible at the location where they had made an earlier pre-mitigation screening measurement. An ATD was also to be placed at this location, referred to as the Primary site. An additional ATD was to be placed in a frequently occupied room usually on another level which was referred to as the Secondary site. If possible, the Secondary site was to be a bedroom. The ATDs were returned after mid June 2008. Hence the measurements spanned one half of the winter season (closed house) and the spring (mixed open and closed). Average Rn in Lowest Living Space 0 pCi/L - 1 pCi/L 1 pCi/L - 2 pCi/L 2 pCi/L - 3 pCi/L 3 pCi/L - 4 pCi/L 4 pCi/L - 8 pCi/L 8 pCi/L - 16 pCi/L Figure 1 Measurement locations and county average radon concentrations A quality assurance program using duplicates (10%), spikes (8%), and blanks (5%) was followed to characterize the AC and ATD detector performance. RESULTS One hundred and sixty-six homeowners returned questionnaires describing their home, mitigation system status, and radon measurement practices. The median age of the mitigation systems was 2 years (average age 2.3 years) and they ranged 0.5 to 7 years. Homeowners reported pre-mitigation average radon of 380 Bq m-3(10.3 pCi/L) and a 161 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 post-mitigation average radon of 44 Bqm-3 (1.2 pCi/L). Table 1 summarizes the selfreported radon distribution statistics. Table 1 Self reported pre- and post mitigation radon concentrations at the primary site Pre mitigation Rn Post mitigation Rn Post mitigation Rn: Screen Post mitigation Rn: Long term Number 128 104 88 8 Median Bq m-3 (pCi/L) 300 (8.0) 35 (1.0) 33 (0.9) 46 (1.3) Average Bq m-3(pCi/L) 380 (10.3) 45 (1.2) 44 (1.2) 44 (1.2) Seventy-six percent of the respondents did a post-mitigation measurement. Ninety-two percent of those measurements were short-term. For the 40 systems that were more than 2 years old, the average number of years since the last post-mitigation radon measurement is 2.6 years and median is 3 years. Ninety-one percent of the homes had a living space in the basement. That location was used as the primary measurement site in this survey. The other 9% used the first floor as their primary measurement site. Secondary measurement sites were primarily on the first floor with only 6% on the second floor or higher. Complete radon measurement results are available for 129 homes. Both types of detectors met the QA performance standards. The pertinent radon measurement distribution statistics are given in Table 2. The average of the long-term radon measurements at the primary and secondary sites is used as the statistic to assess mitigation effectiveness. Since many of the individual radon results were reported to be less than the instrumental lower level of detection (LLD), Figure 2 shows that the radon concentration distributions were neither strictly normal nor lognormal. However, above the LLDs the radon results were better described by a lognormal distribution than a normal distribution. Table 2 Radon concentration measurement statistics Screen at primary site Long term at primary site Long term at secondary site Long term house average a Number 137 132 126 133 Median a Bq m-3 (pCi/L) 28 (0.75) 11 (0.30) 13 (0.35) 15 (0.40) Average Bq m-3(pCi/L) 52 (1.42) 31 (0.84) 30 (0.80) 31 (0.83) Distributions were lognormal above the instrumental LLD 162 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 100 0.7 90 80 t n u o C 0.6 70 0.5 60 0.4 50 40 0.3 30 0.2 20 0.1 10 0 0 1 2 3 4 5 6 Long term house average Rn pCi/L 0.0 7 P r o p o r t i o n p e r Figure 2 A histogram of the long-term average radon concentrations. B a r Figure 2 shows the post-mitigation radon distribution for the average long-term radon concentration measured in each house. Only 3% of the houses still had home average radon concentrations above the USEPA reference level, 150 Bq m-3(4 pCi/L), while 6% had at least one of the measurement results above that reference value. The fraction of homes with average radon above 110 Bq m-3(3 pCi/L) and 75 Bq m-3(2 pCi/L) were 6% and 9% respectively; while 8% and 16% had at least one of the measurements that exceeded those lower reference values. DISCUSSION The post-mitigation radon concentrations observed in the present work are in general agreement with the early 1990’s studies in New Jersey and nationwide (Brodhead et al. 1993, Brodhead 1995). The nationwide survey, conducted for AARST included 86 mitigators mostly from the east (Brodhead 1995). He measured the long-term radon concentrations in 226 houses which had been professionally-mitigated within the past year or so. He found that 70% of the houses had post-mitigation radon concentrations less than 2 pCi/L and 94% had concentrations less than 4 pCi/L. Even though the Minnesota mitigation systems had been operating longer (average age 2.3 years) their performance was slightly better than the 1995 nationwide sample, with 90% less than 2 pCi/L and 97% less than 4 pCi/L. In fact, the median radon concentration in these mitigated houses is about the same as the regional outdoor concentration (Steck et al. 1999). The post-mitigation radon concentration was not strongly correlated with the self-reported pre-mitigation (R2 ~0.1). The post-mitigation concentration did not significantly differ from mitigator-to-mitigator nor depend strongly on the age of the system. Only about 60% of the homeowners did their own follow-up measurement. Short-term measurements accounted for 90% of these homeowner post-mitigation tests. The correlation between short-term measurements and long term average in the house in this 163 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 study was similar to the correlation in unmitigated Minnesota homes R2 ~0.4 to 0.6 (Steck 2005). A single screening test correctly classified the true living space radon 92% of the time. The predictive value of a positive test screen was 20% and a negative screen was 98%. These performance figures were substantially better than observed in unmitigated Minnesota homes (Steck 2005). Had the screening measurement been used to assess the success of the mitigation system, 8% of the measurements would have reported concentrations above 150 Bq m-3(4 pCi/L) which is quite similar the national results. Two of those homes had long-term home average radon above the reference value and 8 did not (false positive). Two of the homes with long-term home average radon above the reference value had screening results below the reference value (false negative). As long as the possibility for occasional false readings is kept in mind, shortterm measurements appear to be adequate for post-mitigation assessment. Responsible mitigators perform one or more post-mitigation tests shortly after the system is installed. Most of these measurements are short-term. Informal reports and online discussions of mitigator or agency follow-up tests suggest that the effective performance observed in the present study is not unusual. To see if that was the case for a specific mitigator, 200 job sheets from one of the experience mitigators (RW) were analyzed. The randomly selected job sheets contained handwritten pre- and post-mitigation radon results. The short-term radon concentration distribution of the 20 mitigator’s clients who participated in the current study was virtually identical to the distribution of the 200 from the mitigator’s records. To estimate the risk reduction that is possible through mitigation, the results of this study were coupled with the results from a random sample of radon concentrations in living spaces of unmitigated houses from across Minnesota. See Figure 1 (Steck 2005). Since both radon and population are highly spatially varied, the analysis was carried out on a county-basis. Bayesian estimated geometric means and standard deviations were calculated for each county. A Monte Carlo simulation which used the 4 pCi/L action level was used to generate the average radon reduction if mitigation systems achieved and sustained an average radon concentration of 1 pCi/L. This simple model assumes a static population and sustained mitigation performance over a 74 year lifetime. The risk reduction was calculated by multiplying the population in single family homes, extracted from the 2000 census data, with the radon reduction and the EPA lifetime risk estimates (USEPA 2003). The estimated potential lives saved by mitigation are roughly 50,000 in Minnesota. The potential lives saved by county are shown in Figure 3. Many public health policy decisions hinge on the cost-effectiveness of the proposed action. For some rule-making, the EPA uses a value of a statistical life saved based on the willingness of individuals to pay for protection (EPA reference SLA). Recently, that the reduction of that value to $6.9 million per life saved was lamented in media reports. This value might serve as a reasonable benchmark as the upper limit of expenditures for avoiding radon-related lung cancer through mitigation systems. The cost per life saved by medical treatment alone can provide a lowest reference value for expenditures. Using the American Cancer Society’s lung cancer incidence and survival data and the National 164 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Cancer Institutes’ cost for medical treatment, the cost per life saved by medical treatment in the first year post-diagnosis is estimated to be approximately $150,000. Potential for lives saved by mitigating single family homes from above 4 pCi/L to 1 pCi/L 0 - 100 100 - 250 250 - 500 500 - 1000 1000 - 10000 Total potential current residents lives saved ~ 50,000 Figure 3 The spatial distribution by county of potential lives saved by mitigating existing single family houses. The cost per life saved by mitigation systems can be estimated from costs required to identify homes above the action level, the costs to install the system, the costs to operate the system, the maintenance costs and the lives saved per installed mitigation system. The costs and lives saved will have a range of variation and uncertainty that depend on the region. If all current Minnesota single family homes (2.5 residents per house) above the action level where mitigated to a 1 pCi/L, then the cost per life saved by mitigation would be less than or comparable to the cost per life saved using medical treatment during the first year post-diagnosis. This conclusion was based on the following assumptions: each measurement costs roughly three times the wholesale cost of a longterm detector ($35) and installation costs are in the range from $1000-$1800. Six replacement fans ($120) were believed to be needed over the 70 year operational period. Annual operating costs based on fan wattages (20 to 80W) and annual heat penalty ($100) ranged from $120 to $170. The heat penalty was based on the leakage air rate from the recent EPA soil moisture and ASD study (Turk and Hughes 2007) along with local heating loads. A more sophisticated analysis of the annual energy costs for central Minnesota (Mooreman 2008) suggest a wider range ($70 to $500) and higher central estimate ($300). Using the central cost estimate, the cost per life saved is then roughly the same for mitigation or medical treatment. Even at the high end of the operating costs, mitigation costs per life saved are still less than 1% of the EPA’s value of a statistical life saved. In addition, if mitigation fails to prevent the cancer, the medical treatment option 165 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 is still available. Even if the action level were lowered to 3 pCi/L, mitigation is still a cost-effective preventive measure. CONCLUSIONS Like most studies, this one could have been improved with a wider sample of houses and mitigators. Nevertheless, it shows that dramatic radon reductions are possible in many Minnesota homes using current practices and technologies. If the kind of effective mitigation encountered in this study were widely implemented throughout the state, tens of thousands of Minnesotans could be spared lung cancer mortality. Since the cost per life saved by mitigation would be less than the comparable cost of medical treatment, it would be wise public health policy to support radon mitigation for homes. ACKNOWLEDGMENTS Special thanks goes to these community-minded and courageous mitigators who shared their client lists, thus making this project possible: William and Robert Carlson, Healthy Homes LLC; Randy Weestrand, Radon Removal Inc.; Jack Bartholomew, Radon, Energy and Ventilation Services; Will Rogers, Radon Relief; and Gary Vaness, Radon Reduction Inc.,. I also wish to thank Brendon Murn for assistance with the mitigation effectiveness model and Leo Moorman for helpful discussions about operating costs in our region. 166 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 REFERENCES American Cancer Society http://www.cancer.org/docroot/STT/stt_0_2006.asp?sitearea=STT&level=1 Accessed 6/21/2008 Brodhead B, Clarkin M, Brennan T. Initial results from follow-up measurements of New Jersey homes mitigated for radon. Proceedings of the 1993 International Radon Symposium, Denver, CO available at http://aarst.org/radon_research_papers.shtml Brodhead B. Nationwide survey of RCP listed mitigation contractors. Proceedings of the 1995 International Radon Symposium, Nashville, TN available at http://aarst.org/radon_research_papers.shtml Minnesota Department of Health. List of Minnesota Radon Mitigation Service Providers: http://www.health.state.mn.us/divs/eh/indoorair/radon/mitigation.html ; Accessed 12 January 2008 Mooreman L. Yearly Energy Losses of Leaky Radon Mitigation Systems. Proceedings of the 18th Annual International Radon Symposium, Las Vegas, NV. September 2008 National Cancer Institute Table L2. Estimates of National Expenditures for Medical Treatment for the 15 Most Common Cancers http://www.cancer.gov/search/results.aspx?keyword=medical+cost+estimates+for+comm on+cancers&old_keyword=medical+cost+estimates+for+common+cancers&pageunit=10 &type=rp&first=11&page=2 Accessed 7/29/2008 Steck DJ. Spatial and temporal indoor radon variations. Health Phys 62:351–355; 1992. Steck DJ, Field RW, and Lynch CF. Exposure to atmospheric radon. Environmental Health Perspectives; 107: 123-127; 1999 Steck DJ. Residential Radon Risk Assessment: How well is it working in a high radon region? Proceedings of the 15th Annual International Radon Symposium, San Diego CA. September 2005 Turk B and Hughes J. Exploratory Study of Basement Moisture During Operation of ASD Radon Control Systems Contractor Report to: U.S. Environmental Protection Agency, 2007 http://www.epa.gov/radon/pdfs/moisturestudy/study_main.pdf Accessed 7/29/2008 U.S. Environmental Protection Agency . Technical support document for the 1992 Citizen’s guide to radon. Washington D.C.; U.S. Government Printing Office; 400-K92011; May 1992 167 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 U.S. Environmental Protection Agency. Assessment of Risks from Radon in Homes EPA 402-R-03-003; 2003 http://www.epa.gov/radon/risk_assessment.html Accessed 7/29/2008. 168 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 SEASONAL RADON VARIATIONS IN UTAH TESTING RESULTS: SHORT TERM TEST RESULTS WITHIN 10% OF THE EPA THRESHOLD (4.0 PCI/L) SHOULD BE REPEATED IN A DIFFERENT SEASON David Joseph Neville, Radon Program Coordinator1 John Douglas Hultquist, Radon Program Manager Division of Radiation Control, 168 North 1950 West, Salt Lake City, UT 84114-4850. Email at davidneville@utah.gov & jhultquist@utah.gov Phone 1 (801) 536-4250. ABSTRACT Investigators in the Utah Indoor Radon Program conducted a study to observe the potential variations in seasonal radon measurement tests. Data from Utah’s Newborn Test Kit database was utilized. Initial contact letters and email reminders were sent to participating home owners, who were mailed activated charcoal detectors on 28 January 2008. The data suggests that homes where radon test results fall within 10% the U.S. Environmental Protection Agency (EPA) action level of 148 Bq m-3 (4.0 pCi/L) should be retested during a different season, before mitigation actions are recommended. Key words: radon; 222Rn; indoor levels; seasonal variations; radiation protection. INTRODUCTION Lung cancer is one of the deadliest forms of cancer. Recent articles reported that 13% of all lung cancers do not have a direct connection to smoking (Cowley and Kalb, 2005). Lung cancer is cited as the cause of death in 160,000 Americans a year—more than breast cancer, colon cancer, and prostate cancer combined. The Environmental Protection Agency (EPA) estimates that indoor radon is responsible for 1 Note: Funding was provided by the EPA’s State Indoor Radon Grant (SIRG) and the Utah Division of Radiation Control. 169 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 approximately 21,000 of these deaths (EPA, 2005). In 2007 surveys were conducted in Utah of radon mitigators certified by the National Environmental Health Association’s National Radon Proficiency Program (NEHA-NRPP) regarding radon mitigation system installations. The survey found that 80% of home owners who choose to install radon mitigation systems did so as the direct result of an indoor radon test, conducted as the result of a real estate transaction, which indicated levels above the Environmental Protection Agency’s (EPA) action level of 148 Bq m-3 (4.0 pCi/L). The Utah Department of Environmental Quality supports an Indoor Radon Program which encourages potential home buyers or sellers to “…include Radon testing as part of the home inspection process” (DEQ, 2007). Seasonal variations of indoor radon levels have been noted in climates ranging from Alabama to Canada with humidity and precipitation being the primary cause (see McNees and Roberts, 2007; Chen, 2003; Steck, 1992; Zhang, et al 2007). We seek to further explore seasonal indoor radon testing variations obtained in homes built in dry climates that have snow capped mountains throughout the winter months. We affirm the statement of the Conference of Radiation Control Program Directors (CRCPD) and the Alabama Radon Program that “…suggests that other State radon programs should retest their known summertime negative radon tests during subsequent wintertime heating seasons to determine the extent of this problem in their State” (CRCPD, 2007). The EPA recommends long-term (greater than 90 days) and short-term (less than 90 days) tests to determine indoor radon levels (EPA, 2005). Ford and Eheman (1997) remark “…a minority of people are retesting in accordance with current EPA recommendations.” Most residential real estate transactions provide a short amount of time to allow a buyer to conduct home inspections and tests. This includes testing for indoor radon levels. Continuous Radon Monitors (CRM) may be utilized because of this shortened time frame. Data provided by the National Association of REALTORS® for Utah 170 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 (Figure 1), show that home sales increase as temperature levels increase and decrease as temperature levels decrease (NAR, 2008). Figure 1. Homes sold by month in Utah CLIMATE, GEOLOGY AND SNOW CAPPED MOUNTAINS Soil gas movement is characterized by two mechanisms: plain diffusion and pressure differentials. During winter months, the presence of homes can extend pressure differentials in the soil away from foundations with the effect of radon gas being drawn up into the structure. This will, naturally, increase indoor radon levels within homes during winter months. The United States Geological Survey (USGS) asserts that “…the soil and climatic factors controlling soil-gas radon must be understood adequately…” 171 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 (Gunderson and Wanty, 1993; see also Zhang 2007) in order to predict the seasonal variation of soil and indoor radon values obtained from short-term sampling. Utah receives less than 10 inches of precipitation annually and is the second driest state in the union (Precipitation, 2008). This lack of moisture contributes to the porous geology commonly found throughout Utah. During the winter months, water from melting snow packs seeps into the top-soil and will refreeze creating an ice cap in the top-soil. This ice cap decreases the flow of radon gas into the atmosphere and, combined with the frequent basement construction in Utah homes, increases indoor radon concentrations. During the summer months a similar effect can be seen in Utah homes as porous soils fill with water, lowering radon gas permeability (Figure 2). Figure 2: Monthly averages of pCi/L levels in Utah homes 172 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The effect of water frozen within the top-soil during winter months produces a more effective cap that retards radon flux to the atmosphere and potentially increases in residential soil-gas radon concentration results. Kovach (1945) found that the highest soil-gas radon concentrations of the year occur when the ground is frozen, an example of the increased radon gas trapping in the upper layers of the soil (see also Gunderson and Wanty, 1993). Consideration must also be given to cold air being heavier than warm air. This creates a cap on the soil that, along with frozen moisture, tends to inhibit radon gas from entering into the atmosphere. When combined with low barometric pressures associated with wintertime storms, ice caps hold more radon in the soil so it can then diffuse into structures. Seasons Redefined For the purposes of this study, we defined two seasons. First, "summertime" as months when the ground is not likely covered with snow (April through September) and second, "wintertime" as months when the ground is likely covered with snow (November through February). Indoor radon tests were conducted in January and February 2008 when Utah snow levels were significantly higher than in previous years. For 2008, reported snow levels were 118% and 171% of normal (Snowfall, 2008). By chance, 6-8 inches of snow fell on the day test kits were mailed to participants. This snowfall could be a factor in the accompanying results, though it should be noted that a snowcap effect was assumed during the wintertime. MATERIALS AND METHODS In 2004 the Utah Radon Program established a cooperative agreement with a local private health care provider, named Intermountain Health Care (IHC), to provide free indoor radon test kit coupons to parents of each newborn child. Approximately 6,815 test kits have been distributed with the intent to increase radon awareness and testing in Utah. 173 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 In November of 2007, the Utah Radon Program mailed 453 letters to potential participants (individuals who had previously tested their homes for indoor radon in the summertime). A follow-up reminder in mid-December of 2007 was also sent. 181 individuals responded affirmatively to the letter and agreed to participate in the study by conducting a second indoor radon test. Participants were mailed test kits during the week of 28 January 2008. Of the initial 181 volunteers, 132 (73%) completed the wintertime follow-up test. Chen states “…this sample size can serve the survey purpose well” (Chen et al. 2008). Twelve of the original volunteers were sent quality control duplicates and asked to perform those tests side by side with identical opening and closing times. Ten of the twelve quality control duplicate tests came back within the quality control standards or coefficient of variation (COV) suggested by the EPA (EPA, 1993). 2 Participation and Response 126 of the 132 wintertime produced acceptable indoor radon test results, e.g. sealed properly, correct start and end times listed, mailed within suggested timeframe, etc. These wintertime tests were used for statistical comparison with previous summertime levels. Information was collected regarding in home placement of the test kits. As a result, 1 test kit result was removed due to the summertime test kit being hung from the ceiling while the wintertime test kit was placed on a folding chair. RESULTS Comparisons showed that 62% of the wintertime tests were higher than their summertime tests, 15% were lower and 23% were the same. ("Same" meaning within 14% relative difference, a range of the general level of precision attributed to activated charcoal adsorption tests (EPA, 1993)). 48 (38.1%) of 2 Initial summertime indoor radon test kits were purchased from the provider "Air Chek, Inc." Follow-up wintertime indoor radon test kits were purchased from "Alpha Energy Laboratories." Both companies manufacture EPA approved activated charcoal adsorption tests. 174 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 the 126 wintertime tests results were above the 148 Bq m-3 threshold established by the EPA for mitigation, while 36 (19.9%) of the original 181 summertime tests were above the same 148 Bq m-3 threshold. Similarly, 41 of the 126 (32.54%) tests, when averaged according to EPA recommendations, were above the 148 Bq m-3 threshold (Figures 3 and 4). These results suggest that nearly 13% of all summertime indoor radon tests may result in a false negative reading, providing homeowners, REALTORS®, and relocation companies' with incorrect information. As noted by White (1994), “The chance of making the wrong mitigation decision increases as the mean of the two measurements approaches 148 Bq m-3 from either direction….” Performing a Student t-test (assuming equal variances) resulted in the two-tailed results being statistically significant at the 0.0001 level. Figure 3: Seasonal averages of pCi/L levels in Utah homes 175 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 4: Comparisons between tests in different seasons DISCUSSION In Utah, wintertime indoor radon levels are expected to be higher based on the following factors: (1) ground surface soil moisture and snow cover, which inhibit radon gas movement into the atmosphere; (2) Pressure differentials between the interior of a home (due to heating the interior air) and the soil surrounding the home. Air pressure in homes tends to be lower than the soil surrounding them. This results in radon gas seeping through foundation openings into the home directly. Our study suggests that indoor radon level testing during the summertime months should be followed by a wintertime test if the measured summertime radon values are above 3.5 pCi/L and that a wintertime test of 4.5 pCi/L should be retested in summertime to better understand the yearlong averages. A long term alpha-track detector placed inside the residence for one year would be the best solution. 176 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 CONCLUSIONS Since real estate transactions occur more often in summertime months, the authors suggest conducting an additional indoor radon test in the wintertime in order to gather complete information on average radon concentrations in a particular home. Concerns associated with seasonal variations can be allayed by utilizing a long term test to measure yearlong averages in indoor radon gas concentrations of a particular home. In areas where the snow cover may increase indoor radon gas levels, the authors suggest an addendum to real estate transactions, escrowing the funds necessary to mitigate possible wintertime levels. Acknowledgments The author wishes to extend special thanks to Mario Bettolo of the Utah Division of Radiation Control. His substantive assistance in editing and organization cannot be quantified. Nevertheless, any errors are solely the authors’ responsibility. 177 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 REFERENCES Chen, J. Estimate of annual average radon concentrations in the normal living area from short-term tests, Health Phys, 85:740-744; 2003. Chen, J, Tracy, BL, Zielinski, JM, and Moir, D. Determining the sample size required for a community radon survey. Health Phys, 94:362-365; 2008. Climate data. Available at: http://lwf.ncdc.noaa.gov/oa/climate/research/cag3/cag3.html. Accessed . 19 March 2008. Conference of Radiation Control Program Directors (CRCPD). Radon Bulletin, 3, pp. 2-3; 2007. Cowley, G. and Kalb, C. (2005). The deadliest cancer, Newsweek, Available at: http://www.newsweek.com/id/56500. Accessed 12 March 2008. Ford, ES and Eheman, CR. Radon retesting and mitigation behavior among the U.S. population, Health Phys, 72:611-614; 1997. Gundersen, LCS and Wanty, RB. Field studies of radon in rocks, soils, and water—U.S. Geological Survey research on the geology, geophysics, and geochemistry of radon in rocks, soils, and water. 1993. Kovach, EM. Meteorological Influences upon the Radon Content of Soil-gas, Transactions, American Geophysical Union, 26, 241-248; 1945. McNees, JL and Roberts, SH. Summertime short-term negative radon tests need to be retested in winter, Health Phys, 93:74-77; 2007. Precipitation data. Available at http://climvis.ncdc.noaa.gov/cgi-bin/cag3/state-map-display.pl. Accessed 19 March 2008. Snowfall report data. Available at: http://www.crh.noaa.gov/product.php?site=NWS&issuedby=SLC&product=CLM&format=CI&version =4&glossary=0 . Accessed 26 March 2008. Steck, DJ. Spatial and temporal indoor radon variations, Health Phys, 62:351-355; 1992. U.S. Environmental Protection Agency. A citizen’s guide to radon. Washington, DC: U.S. EPA; 402-K00-006; 2004. U.S. Environmental Protection Agency. Indoor radon and radon decay product measurement device protocols. Washington, D.C.; U.S. EPA; 520-402-R-92-004; 1992c. 178 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 U.S. Environmental Protection Agency. Protocols for radon and radon decay product measurements in homes. Washington, DC: U.S. EPA; 402-R-93-003; 1993. White, SB. Making mitigation decisions based on short-term tests of 222Rn, Health Phys, 67:180-182; 1994. Zhang, Z, Smith, B, Steck, DJ, Guo, Q, and Field, W. Variation in yearly residential radon concentrations in the upper Midwest, Health Phys, 83:288-297; 2007. 179 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 RADON, THORON AND THEIR PROGENY IN LANCASTER PA HOMES Henry Stewart Penn Manor High School, Millersville, PA 720 Rohrer Road, Lancaster, PA 17603 Daniel J. Steck1 Physics Department, St. John’s University Collegeville, MN 56321 Two radon isotopes are commonly found in US homes. Conventional wisdom holds that 220 Rn (thoron) concentrations are lower than 222Rn (radon) concentrations and pose a smaller health risk in most living spaces. An earlier survey of radon and thoron gas in 30 Lancaster, PA homes found some with elevated concentrations of both isotopes. That survey found some living spaces with higher short-term concentrations of thoron than radon. To improve the estimate of the long-term risk from exposure to these gases, we took both short and long-term measurements in 20 homes. In addition to grab samples of radon and thoron progeny in two different seasons, we measured the long-term gas concentrations and surface deposited activity to estimate contributions to the potential airborne dose from radon and thoron progeny. The following averages were found: longterm average radon concentration 395 Bq m-3 (10.7 pCi/L) with an estimated radon progeny equilibrium ratio 0.24; long-term thoron concentration 120 Bq m-3 (3.2 pCi/L) and progeny equilibrium ratio 0.02. Estimated average effective doses calculated from long-term gas measurements and short-term progeny measurements are: radon progeny 7.3 mSv yr-1 and thoron progeny 0.6 mSv yr-1. INTRODUCTION Residential radiation measurements in the US taken during the 1980’s occasionally included both 222Rn and 220Rn (Schery 1985, 1990). To distinguish these two isotopes we will follow the common practice of using the nicknames radon for the former and thoron for the latter. Thoron, like radon, can pose a health risk because its progeny can deliver radiation dose to lung and other tissues. However, the short half-life of thoron limits its transport from sources like soil and building materials to indoor living spaces. Thus, it was generally believed that thoron concentrations indoors would be low and have large spatial variation making thoron exposures difficult to assess (Nero 1988). Significant potential alpha energy concentrations (PAEC) can accumulate indoors even at low thoron concentrations because one of its decay products, 212Pb, has a long half life. Early surveys concentrated on thoron progeny measurements rather than thoron measurements to better quantify the potential environmental radiation doses. They found that thoron can generate a significant fraction of the total PAEC in homes and can be an 1 This work was supported, in part, by a St. John’s University Faculty Development grant. 180 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 important fraction of the dose delivered to the lungs (Schery 1985, 1990, Dudney et al. 1990, Martz et al.1990, Tu et al. 1992). However, since few measurements of thoron or its progeny have been made in homes since the early 1990s, its spatial and temporal distribution indoors is largely unknown. Interest in thoron has been revived with the discovery of elevated thoron indoors in China. An earlier study of the radon and thoron in Lancaster suggested that there might be high thoron homes there (Stewart 2007). These cases raise the question of the effects of thoron on the potential dose to individuals and on “radon” measurement technologies used in risk assessment. (Shang et al. 1997, Wiegand et al. 2000, Tokonami et al. 2004, Yamada et al. 2005, Steck 2006). While the dose is primarily delivered by the progeny for both radon isotopes, measurements of radon gas are most common in residential risk assessment since they are easier to make, especially over extended periods of time. While gas measurements in homes typically average over days to months, typical progeny measurements are grab samples that collect the radionuclides over brief periods of time (5 to 10 minutes). This practice introduces substantial uncertainty in exposure assessment because both gas and progeny have strong temporal variation on diurnal to seasonal scales. Integrating passive progeny measurement technologies show promise for improving radiation risk assessment in homes (Steck et al. 2007). The primary goals of this study were to measure the long term average concentrations of radon and thoron gas, to take grab samples of their progeny in two seasons in order to estimate the doses available in select Lancaster PA homes, and to test the field performance of passive progeny dosimeters. METHODS To estimate the long-term airborne radon and thoron progeny in the living spaces, we placed track-etch gas and progeny detectors for 90 day exposures. Grab samples were taken of the gas and airborne progeny upon placement of these detectors, and then again upon retrieval. Estimates of the long-term equilibrium ratios (FR, FT) were based on the averages of measurements from these grab samples. Finally, long-term radon progeny PAEC and dose were estimated from the long-term gas concentrations and the average grab sampled F’s. Twenty homes, located in Lancaster County, PA, were measured for radon, thoron and their progenies. The locations were selected from a prior study (Stewart 2007) to ensure measurable results. The sites in the houses were selected based on the lowest lived-in level. An equal number of basements and first floors were sampled. The initial grab samples were taken and the long-term tests were placed between 8/18/2007 and 11/26/2007. The final grab samples were taken and the long term tests were collected between 12/19/2007 and 2/25/2008. 181 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Two types of grab samples were collected for this study, radon and thoron progeny, and radon and thoron gas. The progeny grab samples were measured using the Ludlum Measurements Inc. Model 2000 counter and Model 43-9 alpha scintillation detector, and data were collected to computer storage using DEPOMON interfacing software. The progeny grab sampling equipment was calibrated in the laboratory with a SARAD EQF whose calibration is traceable to PTB. After taking a background count and checking the calibration using a 230Th sealed source, air was pumped through a glass fiber filter for 5 minutes for radon progeny and 10 minutes for thoron progeny respectively. Then counts from the filter were taken every minute for 50 minutes or 325 minutes, for radon progeny and thoron progeny respectively. The progeny activities were calculated using the Tsivoglou method for radon progeny and the Khan-Busigin-Phillips for thoron progeny (Khan et al. 1982) The gas grab samples were taken using the Durridge Co. Inc. RAD7. After lowering the internal relative humidity to 9%, three consecutive 20-minute tests were conducted and the results averaged. Long-term average concentrations were measured with track-etch detectors. Radon and thoron gas detectors, conventional and encapsulated ATD’s, were placed more than one meter from the external walls, and usually about 1.6 meters from the floor, but not less than one meter. The surface alpha activity of radon and thoron progeny (specifically 214 Po and 212Po respectively) were measured using open track registration detectors fitted with several energy absorbing filters. In all but two cases, the surface deposition detectors were placed on a window pane, as close to the center as achievable. In the exceptions, they were placed on a structural steel support beam and a plastic wall fixture. These gas detectors (Steck 2006) and surface progeny detectors have been described elsewhere (Steck 2007 et al.). RESULTS Almost all of the distributions were more lognormal than normal, so geometric mean, geometric standard deviation and average statistics are given for the major results. The grab sample distribution statistics for the progeny measurements are given in Table 1. The spatial and temporal variations are shown in Figure 1 and 2. Table 1: Progeny Grab Sample Measurement Statistics in Lowest Lived-in Sites Radon progeny (All 20 sites) Thoron progeny (All 20 sites) Median(GSD) mWL Average mWL 38 [2.1] 3.8 [1.9] 48 4.7 Equilibrium ratio Median[GSD] 0.22 [1.4] 0.018 [3.4] 182 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 1: Radon progeny PAEC from the initial and final grab samples Figure 2: Thoron progeny PAEC from the initial and final grab samples 183 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The results from the long-term track registration detectors are shown in Tables 2 and 3. Table 2: Long-term gas measurement statistics Radon (All sites) 1st Floors Basements Thoron (All sites) 1st Floors Basements Number 20 10 10 20 10 10 Median [GSD] Bq m-3 325 [1.9] 108 [3.5] Average Bq m-3 (pCi/L) 395(10.7) 289 (7.8) 501(13.5) 121(3.3) 56 (1.5) 185 (5.0) Figure 3: Site-to-site-variation of the radon and thoron gas concentrations A statistical summary of the surface activities of 214 Po and 212Po are given in Table 3. Table 3: Long-term surface activity measurement statistics Median [GSD] Number Bq m-2 214 Radon progeny( Po) 20 28 [2.0] Thoron progeny (212Po) 20 2.6 [2.3] Average Bq m-2 37 3.5 184 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 DISCUSSION Although measurement of radon gas in homes is common today, simultaneous measurements of radon and its progeny are rare. Those kinds of measurements were made occasionally during the early research period of the 80’s and 90’s (Nero 1988). One reason for the rarity is the cost and difficulty of a progeny sampling protocol that would average over the temporal variation to give a representative measure of the available dose. The present work, taking place in select homes in a single locality, should contribute to the data on the relationship between radon and radon progeny, but no claims of representativeness are made for other houses. The radon is considerably elevated in these homes compared to national averages. The average equilibrium ratio (FR), that is the fraction of the airborne Potential Alpha Energy Concentration (PAEC) compared to the maximum possible, is lower than the “rule-of-thumb” value; 0.24 vs. 0.4. Nevertheless, when one calculates the dose rate available from radon progeny using the UNSCEAR approach of Equilibrium Equivalent Concentration (EEC), the effective dose rates average to 7.3 mSv/yr and vary from 1 to 18 mSv/yr (UNSCEAR 2000). Thoron measurements are rare in the US. Few studies report simultaneous radon, radon progeny, thoron and thoron progeny measurements. Schery’s work in the mid 80’s shows a reasonable correlation between radon and thoron gas concentrations; R2~0.5 (Schery 1985, 1990 Li and Schery 1992). Our results (shown in Figure 4(a)) show general agreement with Schery’s results as well as a recent study in the Upper Midwest (Steck 2006). Poorer correlations were found in Gansu Province between the two isotopes in homes where thoron dominated due to building materials (Tokonami et al. 2004, Shang et al. 2005, Yamada et al. 2006). Correlations between thoron, radon and their progenies are not well documented. Figure 4(a) shows the relationship between the gas concentrations alone while Figure 4(b) shows correlations between the EEC values which include gas and progeny. The R2 in both cases is approximately 0.5. (a) 185 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 (b) Figure 4 Correlation between (a) radon and thoron gas concentrations and (b) equilibrium equivalent radon and thoron gas concentrations. Simultaneous measurements of both thoron and its progeny are difficult. Even in locations where thoron gas is higher than normal, thoron progeny concentrations are low. Grab samples taken with modest air flow rates and reasonable times yield progeny concentrations with substantial uncertainties as Figure 2 illustrates. No surveys of correlations between thoron and its progeny in the US have been published. An abstract of recent work suggests that a central estimate of the equilibrium ratio between thoron and its progeny in US homes may be 0.02 (Harley and Chittaporn 2006). This value is similar to one reported for homes in China (Tokonami et al. 2004, Yamada et al. 2006) but much less than the value given in UNSCEAR 2000. We found a median equilibrium ratio for thoron progeny of 0.018 but a variation of a factor of 3 around that median. Some of the variation undoubtedly arises from measurement variation and counting statistics. Nonetheless using the UNSCEAR EEC approach, we estimate that the available effective dose rate from thoron progeny to average 0.6 mSv/yr in this sample of houses. Passive progeny dosimeters based on surface deposition hold the promise to improve risk assessment through integrating the measurement of the progeny. Passive detectors can be left in place for months tracking the average activity of surface-deposited progeny in an efficient, effective manner. New technologies have shown reasonably good results in laboratory and limited field tests (Steck et al. 2007). We deployed surface alpha tracketch detectors in this study. Figure 5 shows that the correlation between the estimated airborne progeny (EEC) and the average surface deposited activity for both the radon and thoron is fairly good (R2 ~0.5). Part of the variability is likely due to the use of grab samples for the F values and partly due to the variation in surface deposition conditions which were not taken into account in this analysis. 186 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 (a) (b) Figure 5 Correlation between estimated airborne progeny and gas concentration for (a) radon and (b) thoron. CONCLUSIONS Elevated radon, thoron and their progenies were found in most of these homes. There was reasonable correlation between radon and thoron gas concentrations as well as the corresponding fractions of airborne progeny. Long-term measurements of activities of surface-deposited progeny show promise for estimating average airborne radon and thoron progeny dose rates in residential settings. 187 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 REFERENCES Dudney CS, Hawthorne AR, Wallace RG, Reed RP. Radon-222, 222Rn Progeny, and 220Rn Progeny Levels in 70 Houses. Health Physics 58:297-311; 1990. Harley N and Chittaporn P. Radon and thoron equilibrium factors: calculation and experimental values. Health Physics 90(Supplement), S103; 2006 Khan A, Busigin A and Philips C. An Optimization Scheme for measurement of the concentration of the decay products of Radon and Thoron. Health Physics 42, 809826; 1982. Li Y, Schery SD, Turk B. Soil as a source of indoor 220Rn. Health Phys. 62:453-457; 1992. Martz D, Falco R, Langner GJ. Time-Averaged Exposures to 220Rn and 222Rn Progeny in Colorado Homes. Health Physics 58:705-713; 1990. Nero AV. Radon and its Decay Products in Indoor Air: An Overview. In: Nazaroff WW, Nero AV, eds. Radon and its Decay Products in Indoor Air. New York, NY: John Wiley & Sons; 1988: 1-53. Schery SD. Measurements of Airborne 212Pb and 220Rn at Varied Indoor Locations within the United States. Health Physics 49:1061-1070; 1985. Schery SD. Thoron in the Environment. Journal of the Air and Waste Management Association 40:493-497; 1990. Shang B, Wang Z, Iida T, Ikebe Y, Yamada K. Influence of 220Rn on 222Rn measurement in Chinese cave dwellings. In Radon and thoron in the human environment, eds. A. Katase, and M. Shimo, pp. 379–384; 1997. Singapore: World Scientific. Shang B, Chen B, Gao Y, Wang Y. Thoron levels in traditional Chinese residential dwellings. Radiat Environ Biophys 44: 193-199; 2005 Steck D. A preliminary thoron survey in the Upper Midwest. Proceedings of the 16th Annual International Radon Symposium, Kansas City September 2006 Steck D, Rahman S, Harrison D and Kotrappa P. Passive radon progeny dosimeters: feasibility studies. Proceedings of the 17th Annual International Radon Symposium, Jacksonville September 2007. Stewart H. A study of the relationship between radon and thoron in houses. Proceedings of the 17th Annual International Radon Symposium, Jacksonville September 2007. Tokonami S, Sanada T, Yang M. Contribution from thoron on the response of passive radon detectors. Health Phys. 80:612–615; 2001 188 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Tokonami S, Sun Q, Akiba S, Zhuo W, Furukawa M, Ishikawa T, Hou C, Zhang S, Narazaki Y, Ohji B, Yonehara H, and Yamada Y. Radon and thoron exposures for cave residents in Shanxi and Shaanxi provinces. Radiat. Res. 162:390–396; 2004 Tu KW, George AC, Lowder WM, Gogolak CV. Indoor Thoron and Radon Progeny Measurements. Radiation Protection Dosimetry 45:557-560; 1992. United Nations Scientific Committee on the Effects of Atomic Radiation. 2000. Sources and Effects of Ionizing radiation, Report to the General Assembly of the United Nations with Scientific Annexes, United Nations sales publication E.00.IX.3, New York. Wiegand J, Feige S, Quingling X, Schreiber U, Wieditz K, Wittmann C, and Xiarong L. Radon and thoron in cave dwellings (Yan’an, China). Health Phys. 78:438–444; 2000. Yamada Y, Sun Q, Tokonami S, Akiba S, Zhuo W, Hou C, Zhang S, Ishikawa T, Furukawa M, Fukutsu K, Yonehara H. Radon–Thoron discriminative measurements in Gansu Province, China, and their implication for dose estimates. Journal of Toxicology and Environmental Health, Part A, 69:723–734; 2006. 189 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 ANALYSIS OF LONG-TERM MEASUREMENTS OF RADON IN A DOLOMITE CAVE Kateřina Rovenská1,2 and Lenka Thinová2 1 National Radiation Protection Institute, Bartoškova 28, 140 00 Praha 4, Czech Republic 2 Czech Technical University, Faculty of Nuclear Sciences and Physical Engineering. Břehová 7, 115 19 Praha 1, Czech Republic Abstract Measurement of the radon concentration has been performed in the Bozkov dolomite cave since 2002. Radon concentration was obtained by two means: continuous measurement by Radim3 monitor in 30-minute interval and 6-month average by LR115 SSNTD in the diffusion chamber placed at 8 points along the cave tour route. The radon concentration shows diurnal, seasonal, and yearly variations. The concentration maximum in the caves, in contrast to the dwellings, is in the summer time. At the same time, high variability of radon concentration occurs. Statistical analysis of the long-time series of radon concentrations was performed; the meteorological data were taken into account. In-situ and laboratory gamma spectrometric measurements are also included in this paper. The annual effective dose from radon for the cave guide (year 2006, working time spent in the cave 414 h) was 3.05 mSv; radon concentration used was obtained by SSNTD as described above. Introduction Public open caves are underground workplaces with a high probability of elevated radon concentration (thousands of Bq/m3). Thus, caves constitute a special case for radiation protection in workplaces. Several papers focusing on the dose assessment for cave guides have been published (Rovenská, 2008). To fulfill the Czech national radiation protection standards and methodology, the radon concentration in the public open cave is measured by SSNTD Kodak LR 115 with the concentration integrated over a6 month time interval. The dose from radon has been evaluated on the basis of SSNTD results. As far as one is interested in the dynamics of radon in the cave, one needs continuous record of radon concentration and other quantities that may influence the concentration. The development of the radon concentration time series is influenced by the temperature difference between the outside and the inside air, changes in pressure, strength of radon source, velocity and direction of air flow and other possible factors (i.e., local releasing of air pockets with high concentration, etc.) Study of the data could help the better understanding of the processes in the cave. Bozkov dolomite caves were chosen for this kind of measurement, which started in 2002. Cave description Bozkov dolomite caves (BDC), originated in Silurian period, are one of 13 of the public open caves in the Czech Republic and the only cave system in the North Bohemia accessible to the public. The BDC are situated on the northern slope of the Bozkov village in the hilly landscape of the Krkonoše foothills. Caves originated in karstic mass in the area of Zelezny Brod crystalline regions. The entrance into the underground space was discovered by dolomite miners in the 1940s. Attractive items of the sightseeing route include underground lakes with crystal-clear blue- 190 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 greenish water. The caves and their surroundings is a protected area; protected both by nature and by landscape protection law. The average temperature in the cave is between 7.5 – 9 °C, the relative humidity is near 100%. The cave tour is 350 m long and takes 45 minutes. Figure 1 shows the map of the cave on which measurement points are depicted with the red points. The BDC has been continually monitored since 2002. Figure 1: Map of the Bozkov dolomite cave, red points are SSNTD measuring points Methods of measurement Radon Radon has been monitored in two ways in the cave. Continuously, by a Radim3 continuous monitor with 30-minute response intervals and as an average for 6 months by SSNTD (also called alpha track detectors). Radim3 consists of a small diffusion chamber and semiconductor detector. Radon concentration is determined by spectrometric measurement of the RaA alpha activity. Statistical error is equal to ± 20%. A power supply is necessary for operating the monitor. Blackouts often stopped the data acquisition and it was necessary to start the device manually. The effect of humidity is compensated up to 90% RH by the device itself. In case of an averaged measurement of radon concentration, the cave has been monitored by SSNTD using Kodak LR115 foil as free detectors and since 2004 enclosed in the plastic diffusion chamber called Ramarn. There are 8 SSNTDs for summer starting on 1st of April and ending on 31st of October and 4 SSNTDs for winter season (lower concentration) placed along the cave tour route. The concentration was integrated per 6 months according to the summer and winter use in the cave. 191 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Meteorological data Meteorological data were obtained from the Liberec meteo-station, which is owned and operated by the Czech Hydro-meteorological Institute. The Liberec station is 20 km, straightline, from the Bozkov village. Results The acquired data are not complete in time because of the power supply blackouts as mentioned above. The most consistent data were obtained from the place called Lake and Hell. The results of analysis of the data from these two places are described in this section. Annual variations The annual variation is demonstrated on the Fig. 2 which compares the daily radon concentration average from the Lake for the years 2002 – 2006. Summer averages measured by SSNTD for these years are shown in the Fig. 3, from which the variation is also visible. Lake - Daily average of radon concentration 10000 2002 2003 2004 2005 2006 9000 8000 End of the Summer season 7000 Beginning of the Summer season CRn (Bq/m3) 6000 5000 4000 3000 2000 1000 0 29.12 7.2 18.3 27.4 6.6 16.7 25.8 4.10 13.11 23.12 time Figure 2: Interannual variation of radon concentration 192 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 SSNTD season average radon concetration 14000 Summer/2001 Summer/2003 Summer/2005 12000 Summer/2002 Summer/2004 Summer/2006 CRn (Bq/m3) 10000 8000 6000 4000 2000 0 Chapel Midnight Crossing Hell Muggy way Helmet November way Lake position Figure 3: Interannual variation measured with SSNTD, circles - free SSNTD, squares - SSNTD in diffusion chamber (Thinová, 2008) Seasonal variations The highest radon concentration in the cave is found in the hot summer time. Assuming that in the lower inaccessible parts of the cave some of the radon sources (sediments and rocks with high content of 226Ra) are present, the increase in concentration is caused by the stack effect1 determined by outside and inside temperature difference. A one-year progress of the radon concentration and temperature difference is shown in the Fig. 4. Figure 4: Seasonal variation of radon concentration corresponding to the temperature difference 1 Stack effect is caused by the cold cave air escaping into the outer atmosphere. 193 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Diurnal variations Equally to the seasonal variations the diurnal ones are influenced mainly by the temperature difference. This dependence is depicted in following six graphs (see Fig. 5 – 10). Table 1 shows the parameters of measured intervals. The temperature difference was obtained as a difference between outside and inside temperature. Table 1: Description of measured intervals in the Lake Season AvgCRn (Bq/m3) AvgTempIn (°C) AvgTempOut (°C) Avg Temp difference Summer 4220 10.7 21 10.0 Autumn 2850 10.8 9.3 -1.5 Winter 1660 9.7 -7.3 -17.0 Lake 2003 - Radon concentration, Outside Pressure C tempOut 4400 25 4100 °C C Rn (Bq/m3) 4200 20 4000 3900 C Rn (Bq/m3) 30 4300 15 3800 3700 6.8.03 12:00 7.8.03 0:00 7.8.03 12:00 8.8.03 0:00 8.8.03 12:00 9.8.03 0:00 C 4500 35 10 9.8.03 12:00 985 980 4200 975 4100 970 4000 965 3900 960 3800 955 3700 6.8.03 12:00 950 7.8.03 0:00 7.8.03 12:00 8.8.03 0:00 8.8.03 12:00 9.8.03 0:00 9.8.03 12:00 tim e Figure 5: Summer season, Temperature difference high Figure 6: Summer season, influence of pressure Lake 2003 - Radon concentration, Outside Temperature C 990 4300 tim e 4000 Tout 4400 hPa Lake 2003 - Radon concentration, Outside Temperature 4500 tempOut Lake 2003 - Radon concentration, Outside Pressure 14 4000 3500 12 3500 3000 10 3000 2500 8 2000 6 1500 4 1500 2 1000 19.11.03 0:00 C pressOut 980 2500 970 °C CRn (Bq/m3) °C CRn (Bq/m3) 975 2000 965 1000 19.11.03 12:00 20.11.03 0:00 20.11.03 12:00 21.11.03 0:00 21.11.03 12:00 22.11.03 0:00 19.11.03 12:00 20.11.03 0:00 20.11.03 12:00 tim e tempOut Lake 2003 - Radon concentration, Outside pressure -2 1500 -6 1400 -8 1300 -10 1200 -12 1100 31.1.03 0:00 31.1.03 12:00 1.2.03 0:00 1.2.03 12:00 2.2.03 0:00 2.2.03 12:00 3.2.03 0:00 -14 3.2.03 12:00 time Figure 9: Winter season, Temperature difference high CRn (Bq/m3) -4 °C CRn (Bq/m3) 1700 1600 C 1900 0 1800 1000 30.1.03 12:00 960 22.11.03 0:00 Figure 8: Autumn season, influence of pressure Lake 2003 - Radon concentration, Outside Temperature C 21.11.03 12:00 time Figure 7: Autumn season, Temperature difference near zero 1900 21.11.03 0:00 pressOut 990 1800 985 1700 980 1600 975 1500 970 1400 965 1300 960 1200 955 1100 1000 30.1.03 12:00 hPa 19.11.03 0:00 950 31.1.03 0:00 31.1.03 12:00 1.2.03 0:00 1.2.03 12:00 2.2.03 0:00 2.2.03 12:00 3.2.03 0:00 3.2.03 12:00 time Figure 10: Winter season, influence of pressure 194 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 These figures show that the time shift between changes in temperature and radon concentration is in the range of 2 – 12 hours with the average of 7 hours. The correlation is strongly dependent on the properties of period for which the correlation is evaluated. Measurement in high relative humidity The following section will show the comparison of measurement with Radim3 placed in a plastic box with desiccant and in the free air in the cave. The data were acquired at the same time and at the same place (Hell). As can be seen from Fig 11, the plastic box caused smoothing of the brief radon peaks. On the other hand, in the period without the sudden concentration peaks, the results from free Radim3 and enclosed Radim3 in the plastic box are in a good agreement (Fig. 12). Comparison of measurement with free Radim3 and Radim3 in plastic box Comparison of measurement with free Radim3 and Radim3 in plastic box 25000 2300 Free Radim3 1900 CRn (Bq/m3) CRn (Bq/m3) 2100 Radim3 in box 20000 15000 10000 1700 1500 1300 1100 900 5000 Free Radim3 700 0 13.2.04 12:00 14.2.04 0:00 14.2.04 12:00 15.2.04 0:00 15.2.04 12:00 16.2.04 0:00 Radim3 in box 500 19.12.03 20.12.03 20.12.03 21.12.03 21.12.03 22.12.03 22.12.03 23.12.03 23.12.03 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 16.2.04 12:00 time time Figure 11: Smoothing of peaks Figure 12: Good agreement of the measured data The average concentration for the period shown in Fig. 11 is 3420 Bq/m3 for the free Radim3 and 3067 Bq/m3 for the enclosed Radim3. The averages for the day after the peak maximum (second day of the interval shown) are 2287 Bq/m3 for the free Radim3 and 3190 Bq/m3 for the enclosed Radim3. Radon is diffusing through the plastic box and the peak is smoothed and delayed. The average concentration for the period shown in Fig. 12 is 1444 Bq/m3 for the free Radim3 and 1384 Bq/m3 for the enclosed Radim3. Comparison of the results of continuous measurement average and SSNTD results Because of the inconsistent variation of the data, it was not possible to substitute for missing data in a reliable way. Therefore, the comparison between the radon concentrations obtained by SSNTDs and from time series of continuous measurements is not relevant. Gamma spectrometry analysis Gamma spectrometry was performed on rock and sediments samples. Table 2 shows the spectrometry results. These values are little higher than the average content in other public open caves. Table 2: Description of measured intervals (Thinová, 2007) Activity (Bq/kg) 40 228 226 K Th Ra Bedrock Phyllite 01 385.0 ± 13.6 2.2 ± 0.6 3.3 ± 0.4 Phyllite 02 261.1 ± 8.2 3.0 ± 0.3 7.7 ± 0.2 Sediments Hell Crossing Lake 468 378 363 15 20 13 51 29 31 195 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Radon concentration in water samples Radon concentration in water was measured by Radim4. The measured activities are 7.6 Bq/l in average. This value is one of the highest among the water samples taken in public open caves. On the other hand, the average concentration in drinkable water in the Czech Republic is 15 Bq/l. Summary The processing of long time series of radon concentration showed the variability of concentration in year, during day and among the years. Therefore, it is not possible to substitute the missing data by the data from other period or other years. The strong correlation between concentration and temperature was shown in summer season when the temperature difference is very high. On the other hand the concentration in the cave is stable during cold months. This study is a preliminary one. It is still necessary to compare the data with the air flow measurement, measurement of the seismicity and other measurable quantities. 196 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References 1. Thinová L: Final report for the project VaV 12/2006: Correction of dose assessment for the underground workers, Praha 2007, in Czech. 2. Rovenská K., Thinová L.: Assessment of the dose from radon and its decay products in the Bozkov dolomite cave, in: Radiation Protection Dosimetry, 2008, doi:10.1093/rpd/ncn114. 3. Thinová L., Burian I.: Effective dose assessment for workers in caves in the Czech Republic – experiments with passive radon detectors, in: Radiation Protection Dosimetry, 2008, doi:10.1093/rpd/ncn118. 197 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 MEASURING RADON AND THORON EMANATION FROM CONCRETE AND GRANITE WITH CONTINUOUS RADON MONITORS AND EPERM’s® Bill Brodhead WPB Enterprises, Inc., 2844 Slifer Valley Rd., Riegelsville, PA USA wmbrodhead@gmail.com www.wpb-radon.com Abstract The author investigated the use of commercially available continuous radon monitors (CRM’s) and S-Chamber E-PERM’s® using short term electrets to measure the radon (222Rn) and thoron (220Rn) emanation from concrete and granite counter tops. The performance of CRM’s and EPERM’s® placed in 3 to 23 liters metal accumulator chambers sealed to a building material were compared to the total emanation rate of the building material when the material was placed in a sealed 122 liter chamber. Concrete slabs were constructed that had radon only versus radon and thoron and actinon(219Rn) to determine the test equipment response to these isotopes. A thoron chamber was constructed to test the detectors response to thoron and the reduction in response to thoron when the detectors were placed in diffusion barriers. Accumulator and sealed chamber tests on three different granites found significant variation in emanation rates depending on what side of the granite was tested. Elevated Indoor Radon Levels due to Building Materials The author investigated a 200 unit seven story tall condominium unit that had elevated radon levels in the hallway and individual units on every floor. This building had two levels of ventilated parking garage under most of the building that precluded ground base soil gas as the source. The building was constructed with post stressed concrete floors and ceilings and concrete support columns. All other walls except those adjacent to stairwells were metal stud and drywall construction. Ventilation measurements indicated the units were typically getting less than 0.1 air changes per hour (ACH). A simple method was used to measure the concrete emanation rate by placing single EPERM’s® inside 3 liter stainless mixing bowls that were sealed against exposed concrete floors, ceilings and walls. The total ingrowth inside the bowl was determined by doubling the E-PERM® average after first subtracting the back ground radon when the unit was first sealed. This total ingrowth is then divided by the hours of exposure and multiplied times the volume of the accumulator and divided by the square feet of exposed concrete to obtain the emanation rate of the concrete. The exposures were approximately 24 hours long to minimize the effect of ingrowth decay. These emanation measurements made on every floor of the condominium indicated that the concrete along with the low ventilation rate was the likely source of the elevated radon. The research presented in this paper was conducted to determine if an accumulator method using continuous radon monitors (CRM’s) or E- 198 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 PERM’s® with ingrowth correction factors would provide a simple method with reasonable accuracy to determine the emanation rate of any building material. Testing Equipment Set Up The author has two AB5 Pylons® with passive radon detector heads (PRD) and a RAD7® radon monitor. These units were cross compared with two similar AB5 Pylons with newer CPRD heads supplied by Pennsylvania DEP Radon Division. In addition the following CRM’s were generously loaned from the manufacturer/suppliers; two Femto-Tech 510’s®, Sun Nuclear 1029®, Rad Elec Scout®, RadonAway RS500® , RadonAway RS800® and the RTCA On Guard. Metal test chambers were constructed varying in size from 38 liters to 129 liter size by using commercially available metal trash cans with removable lids. Each of the cans had all interior seems sealed with urethane caulking and then covered with 17 mil aluminum tape. A power cord was installed in each chamber with the cord penetration carefully sealed in a similar manner. Sampling ports were installed in each of the chambers by mechanically attaching 3/8” ball valves through the side of each chamber and carefully sealing the penetration. See picture in Figure 10. The removable lid for each chamber had pliable plumbers putty placed around the edge. A ball valve would be left open and the lid pressed down on the chamber, compressing the putty and forming an air tight chamber when the ball valve was closed. The tightness of the chamber was tested by flowing radon into a chamber with two CRMs and then closing all the valves to allow the radon to decay. The radon decayed with a normal radon decay rate indicating that there was no radon leakage out of the chamber. See the decay rate chart below in Figure 1. Figure 1 Chamber Tightness test 199 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The author has several radon, thoron and actinon sources that were used to test the performance of the different CRM’s and E-PERMs®. One of the sources is soil. During an investigation of a home in need of a radon mitigation system, a suction point was located where a 300 υR/hr gamma reading was obtained at the slab. The soil excavated from this home produces 0.75 pCi/oz/minute (1.6 Bq/gm/hour). This soil was dried and placed in three 6” by 60” long metal ducts that were carefully sealed and constructed with sampling ports on either end. Initial sniff measurements made of the soil indicated it had a low thoron content. Some of this soil was mixed into a concrete test slab to increase its emanation rate. A more careful grab sample of the soil source was then made with a Pylon AB5® and scintillation cell with the counter set to 20 second count interval. The tubing length from the soil source to the cell was less than a foot long and the air flow was set at 4 lpm flow with a 0.8 µm filter. See the graph in Figure 2 below. The last 20 second cell count while sampling was 661 counts. As soon as the pump was turned off the next 20 second count fell to 328. The next 20 second count dropped to 117. The counts then fell off more gradually, dropping to 91 and then a minute latter to 70 and then a minute or two later to around 55. The sample was aged and counted latter indicating about 140 pCi/l (5,180 Bq/m3) of radon at 4 lpm flow rate. This extreme drop in counts indicates the soil is producing significantly more actinon which has a 4 second half life than radon. The decay also indicates there is some thoron in the soil but it is difficult to measure because of the very high level of actinon in the soil. Figure 2 Soil Source Checked for Thoron & Actinon 200 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Once it was determined that there was significant thoron and actinon being produced by the soil source, a 75 liter decay chamber was constructed that delayed the airflow into the final test chamber by 15 minutes (75 liters / 5 lpm flow) to ensure that both thoron and actinon were decayed out. A 47 millimeter 1 µm filter was installed inline before the final test chamber to collect most decay products produced by the actinon, thoron or radon. 1 to 5 lpm of air was pushed through the soil sources using a small aquarium pump. Dwyer flow gauges were installed before and after the test chamber to monitor the flow rate and ensure there was no leakage out of the chamber. The chamber exhaust air is vented to the outside. A typical flow through chamber set up is illustrated in Figure 3 below. Note that the test chamber had internal power outlets and a small mixing fan to create uniform levels inside the chamber. Each tube produces 125 pC i at 4 lpm flow WPB Test C hamber Exhaust vent to outside 6 " metal ducts w ith 48 " of Soil 1- 5 LPM airflow Sealable 117 liter metal chamber 75 Liter chamber creates at least 15 minute delay 4 3 2 1 Soil CRM Ball Valve sampling ports for grab samples or R AD 7 measurements CRM Valved inlet CRM CRM 4 CRM 3 2 1 Low flow mixing fan inside chamber 1 um filter D w yer airflow meter Gravel bed Aquarium pump 1 -5 LPM flow Figure 3 Soil Source Test Chamber Ingrowth Comparison The CRM’s and E-PERM’s response to ingrowth of radon was tested by sealing the detectors in a 122 liter chamber with a small radium source placed at the inlet to the interior mixing fan. The volume of the fans, CRM’s and chargers placed in the chamber was subtracted from the empty chamber volume. The CRM volume was determined by measuring the components of each unit rather than the outside dimensions to factor in the free air area inside the CRM’s. Table 1 below 201 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 gives a table of the volume size used for each CRM. Note that the CRM volume was not based on the external CRM dimensions but the approximate mass volume of all the components of the CRM. The source of the radon is an antique toy that was manufactured in the 1920’s by the same company in Pittsburgh that produced the gram of radium that was gifted to Marie Curie. The source produces no measurable 220 thoron. The radon levels would then ingrow depending upon the open volume of the chamber and the length of time the chamber was left sealed. RS 800 0.76 liters Scout 0.56 liters EPerms 0.123 liters SN 1029 0.66 liters Pylon AB5 PRD 2.5 liters RS 500 0.70 liters Femto 510 0.61 liters RTCA OnGuard 0.81 liters Table 1 Detector volumes A comparison of CRM measurements to an ingrowth of radon in a sealed chamber in Figure 5 below indicated the RAD7 which pumps air into its chamber every 5 minutes may have been responding to the ingrowth of radon more quickly than the other CRMs. All testing was done with the CRMs set to hourly intervals. A delayed response to an increasing radon concentration would reduce their calculated ingrowth. Figure 4 CRM In-growth versus Grab sample measurements 202 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 A second test was performed using a dozen Pylon 300A scintillation cells that were first measured for background count and then filled with a known radon concentration and then counted at least four hours later in order to calibrate their individual efficiency. Two Pylon AB5’s and other CRM’s were then placed in a sealed chamber with 109 liters of free air and a radium source. The RAD7 was not available for this second test. See the results graphed in Figure 4 above. There were five small mixing fans inside the chamber during the 36 hour exposure. Single grab samples using the calibrated scintillation cells were taken every 2 to 4 hours during the exposure. The plotted ingrowth and the mathematical calculated ingrowth is shown in Figure 4 above along with the Pylon response and its mathematical ingrowth line. Note that the grab sample ingrowth of 510 pCi/hr (18,870 Bq/hr) is 16% greater ingrowth than the Pylon ingrowth of 440 pCi/hr (16,280 Bq/hr). The varying delayed response of different CRMs to increasing radon levels could be due to the different radon progeny each CRM counts to determine the radon levels or to other factors. The table 2 below gives the average amount of additional ingrowth each CRM would require to match the RAD7 and grab sample results based on this single test. Additional testing would be needed to confirm this response. The RadonAway RS800 and FemtoTech data is based only on the initial RAD7 data displayed in Figure 5 because their monitor results during the grab samples were significantly off. Unit Correction % Pylon +15% RTCA +14% Scout +9% SN1029 +9% RS500 +6% RS800 +1% F-510 +10% Table 2 Correction factor for CRM in-growth delay Although Figure 5 is a crowded graph some general CRM performance differences can be seen that repeated in other similar exposures. In general the Pylon AB5 and the RAD7 produced the smoothest line that makes determining ingrowth rate more accurate. The RadonAway RS800 had the next smoothest ingrowth line although the unit tended to under report the radon level increase during the initial 8 to 10 hours of exposure. It appears radon entry into the chamber of the RS800 is delayed thus producing the lag and facilitating the smoother line. This may be why the RS800 also had the least response to thoron. Because the RS800 tends to under respond for the first six hours, this data cannot be used for the ingrowth calculation. The FemtoTech 510 performed well until the radon levels climbed above 80 pCi/l (3000 Bq/m3) when it would bias low. In most cases however the ingrowth measurements will not be above 80 pCi/l. Note that the RTCA On-Guard CRM does not record any results above 100 pCi/l (3700 Bq/m3) and the RS800 does not record results above 200 pCi/l (7400 Bq/m3). The Sun Nuclear 1029, Scout and RadonAway RS500 which are less expensive units had greater variability than the other detectors. Longer exposure period would help minimize the effect of this variability. The small size of the Scout and SunNuclear 1029 if the handle is removed does allow them to be placed under a large metal mixing bowl (7.5 liters) which also has one of the lower liters to 203 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 5 CRM In-growth Performance square foot ratio and thus will produce the most radon increase per hour inside the accumulator. See Table 3 below. Accumulator liters Small mixing bowl 2.95 Large mixing bowl 7.3 2.5 gallon bucket 9.63 Small trash can 8.65 width 8.5” 21.6 cm 12.75” 32.4 cm 10.25” 26 cm 8.375” 21.3 cm ft2 m2 ft2/liter m2/liter 0.39 0.036 0.13 0.012 0.89 0.083 0.12 0.011 0.57 0.053 0.06 0.006 0.38 0.035 0.04 0.004 2 2 Table 3 - Accumulator area to liters – larger ft /l or m /l higher the response CRM Response to Slab with Thoron & Actinon It was not possible to quantify CRM response to actinon because its half life of 4 seconds is too short. All of the CRM’s and E-PERMs were however tested to determine their response to 204 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 thoron. In typical indoor air measurements, a detectors thoron response would not be considered important because it is assumed that thoron’s half life of 55 seconds does not allow enough time for it to reach the breathing or testing zone if the source is the soil. Thoron sources inside the dwelling would be more likely to influence CRMs that were sensitive to thoron levels. Flux measurements made under an accumulator however place a radon detector in very close proximity to the source which might contain thoron. A detector that is very sensitive to thoron could cause a false interpretation of the results if thoron is present in the material. In most cases the diffusion length of the material is long enough to decay out the thoron. Because thoron’s half life is very short it will reach a maximum concentration inside the accumulator during the 1st hour of exposure. Table 4 below is the calculated response that thoron would have if there was equal alpha activity from thoron and radon and the detector only provided an average such as the Pro-Series 3 monitor or an E-PERM. If CRM’s are used under an accumulator the thoron response can be eliminated by using the slope of the ingrowth after 4 hours to determine the emanation rate since the radon will continue to ingrow while the thoron will be steady state. If only average is used for this exposure length 12 hours 24 hours 48 hours E-PERM bias if equal Thoron & Radon Pro-Series 3 bias if equal Thoron & radon + 0.8% + 0.4% + 0.2% + 1.0% Table 4 Effect of thoron on average of detector results All of the CRM’s and EPERMs were tested to determine their response to thoron. A 114 liter chamber was constructed with two computer type fans installed 1/3 up from the bottom of the chamber and two additional computer type fans 2/3 of the way up. The four fans created a counter clockwise air flow with a velocity of 1.3 meters per second or approximately 1 revolution around the chamber per second. Each fan had thorium coated Aladdin lantern mantles suspended in the fan’s airflow. See photo below Figure 6 - 114 liter Thoron Chamber using Aladdin mantles & fans 205 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 in Figure 6. Two sampling ports in the walls of the chamber were used to flow air through a RAD7 that is capable of measuring thoron concentrations. The CRM’s and E-PERMs were exposed in the sealed chamber for 18 to 48 hours. The 4 to 12 Aladdin mantles produced enough thoron to maintain the chamber at 200 to 600 pCi/l of thoron as measured by the RAD7. The thoron concentration was measured by averaging 30 minutes of sampling data taken during two periods during the exposure length. The RAD7, which was located outside the chamber, was set up with short tubing and the small desiccant holder to minimize thoron decay loss. In each exposure outdoor air was blown into the chamber prior to sealing the chamber to minimize radon levels. Any activity above background radon levels that the detectors recorded above the chamber radon background was assumed to be caused by thoron. Table 5 below demonstrates the dramatically different thoron response of the CRM monitors that were tested. The RadonAway RS800 had very little response to thoron. When the RS800 was exposed to 550 pCi/L (20,300 Bq/m3) of thoron it only displayed an average of 3.4 pCi/l (126 Bq/m3). The RadonAway RS500 which has a very similar metal case however responded dramatically to thoron concentrations. It also had an increasing response which may have been due to a response to the decay products of thoron inside the chamber. See Figure 7 below. This increasing response would bias the results if there was significant thoron in the material being flux tested. The Femto-Tech 510 also responded to thoron but did not have an increasing concentration over the exposure. The Scout, Sun Nuclear 1029 and Pylon AB5 PRD had some limited response. The inexpensive Pro-Series 3 radon monitor also responds significantly to thoron. E-PERM S-Chambers with short term electrets had an average response to thoron of 4%. RS 800 0.5% Scout 6.4% EPerms 4.0% SN 1029 5.5% Pylon AB5 PRD 2.8% RS 500 67% Femto 510 17% Pro-Series 3 22% On-Guard 10.9% Table 5 - Detector Response to 220 Thoron 206 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 7 - Detector response to steady state 220 Thoron Reducing Thoron Response Any lengthening of the time it takes for thoron to reach the detectors sensors will reduce the detectors response to thoron. Radon, thoron and actinon will pass through but be slowed down by thin plastic depending on the plastic density and molecular structure. If one is trying to use the E-PERM thoron chambers to measure thoron it is important to know the background radon without having the detector respond to the thoron. Readily available zip lock food storage bags were tested to determine if they could reduce entry of thoron. The data in table 6 below was obtained by exposing different configurations of S-Chamber E-PERMs for one to two days in the thoron chamber at two different concentrations and once to only an ingrowth of radon. In each thoron test all the EPERMs were suspended in the center of the chamber to allow free circulation of thoron enriched air around them. Three different diffusion barriers were tested, Tyvek envelope, Ziploc brand vegetable bag that has pin holes in the plastic every centimeter (3/8”) and double Hefty One Zip brand bags. The thickness of the plastic was not available. In order to induce a longer travel path for the thoron an E-PERM was placed inside an open Hefty bag and both were then placed inside a second open Hefty bag. E-PERMs without any bag covering were also exposed. 207 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 E-PERM setup No covering Inside Tyvek bag Inside Vegetable bag Inside 2 zip-loc bags 550 pCi/l 20.3 kBq/m3 thoron 3.6% N/A 1.7% 0.6% 191 pCi/l 7 kBq/m3 thoron 4.0% 3.7% 2.8% 1.5% Just radon 100.0% 100.0% 97.5% 85.0 % Table 6 – Thoron & Radon Reduction from plastic bags Building Materials Two concrete slabs were hand mixed and poured in forms. Sakrete 5000 plus concrete mix was purchased locally from a building supplier and used for both slabs. This higher strength concrete was used to closer mimic commercial post stressed concrete. Each slab was carefully mixed using the water to concrete ratio specified by the manufacturer. The drying time of the slabs was reduced by keeping the slabs covered and occasional misting them with water for 14 days. The slabs were allowed to dry for at least 60 days before any testing was done on the slabs. One of the slabs referred to hereafter as the “mixed slab” had 9 ounces of high radon/thoron/actinon soil thoroughly mixed in with the cement to raise the radon emanation rates. The mixed slab is 17” by 17” by 3.5” thick (43x43x8.9 cm) (36.7 kg). The 3.5” edge around the perimeter of the slab was covered with 17 mil aluminum tape to allow radon emanation from only the two flat surfaces for a total area of 4 square feet (0.37 m2). See photo of this slab in Figure 19 below. The second slab referred hereafter as the “cold slab” is 16” round by 4.5” thick (40 cm round x 11.4 cm thick)(31.7 kg). The 4.5” perimeter of this slab is also covered with aluminum tape. This slab has 2.8 square feet (0.26 m2) of exposed slab. 208 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 WPB building material emanation test using Flow Through Test Chamber Exhaust vent to outside Sealable metal chamber C R M’s inside chamber 4 3 2 1 CRM CRM Ball Valve sampling ports for grab samples or R AD 7 measurements 4 Building Material In chamber D esiccant column Valved inlet 3 2 1 um filter 0 .1 to 1 .0 LPM airflow 1 Low flow mixing fan inside chamber D w yer airflow meter Granular activated C oconut carbon ( GAC ) Aquarium pump Figure 8 – Slab Flow through Measurement Chamber Testing Cold & Mixed Slab with Ingrowth & Flow through The radon emanation rate for both slabs was determined by placing them individually inside a sealed metal chamber and measuring the ingrowth that takes place. To test the ingrowth method the mixed slab emanation rate was also measured by a flow through method. The cold slab did not have a high enough emanation rate to allow a flow through test. The flow through method eliminates the need to know the exact volume inside the chamber and the determination of the emanation rate is a straight forward calculation but the exact flow rate through the chamber must be known and the radon levels of the inflowing air must also be know. The flow rate was determined by using a Dwyer airflow gauge that was cross compared to a lab research bubble film flow gauge. Note that the authors six flow gauges vary from 8% high to 5% low compared to the cross calibrated unit. Any radon in the inflowing air will bias the reading. Even outdoor air can often exceed 1 pCi/l (37 Bq/m3) at night. In order to eliminate the need to measure the radon levels of the inflowing air a radon filtering method was tested. A 3” PVC pipe, 10 feet long (3.6 cm X 3 meters) was filled with 0.5 cubic feet (14 liters) of granular activated coconut carbon (GAC). To test the effectiveness of the carbon filter, one lpm of desiccant dried air containing 150 pCi/l (5500 Bq/m3) was pushed through the carbon. It took eight days and six hours of continuous steady flow rate of 1 lpm before radon broke through the carbon. This carbon was then replaced with 209 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 fresh carbon. The GAC filled PVC pipe makes an excellent pre-filter to eliminate any need to subtract background radon from the measured radon levels produced inside the chambers. The air entering the carbon tubes should be dried with a desiccant to maintain maximum radon reduction. Figure 8 above illustrates how a flow through chamber for testing building materials can be set up. The mixed slab was tested with a modified flow through setup by adding a second chamber that the CRM’s were placed in to allow thoron to decay out and minimize their influence on the CRM’s. The following three charts represent the three different methods of measuring emanation rate of the slab that had hot soil mixed into it. Figure 9 is the flow through method. Figure 10 is the total slab in a sealed chamber method. Figure 12 is different CRMs sealed under accumulator metal buckets. Note that the ingrowth emanation rate is determined by using the formula in Table 7 below. These methods produced results that varied from a high of 200 pCi/ft2/hr to a low of 150 pCi/ft2/hr or a total variation of about 25%. Figure 9 – Slab Flow through Measurement Chamber The ingrowth of radon into a sealed chamber or accumulator in Figure 10 below is compared to the mathematical ingrowth using the formula in Table 7. Using this formula allows any exposure duration to be used and the initial radon in the chamber to be subtracted from the ingrowth created by the building material. Unless carbon filtered air is used it will be necessary in most cases to approximate this initial radon concentration based on ambient radon measurements or make a grab sample measurement. 210 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The mathematical ingrowth needs to incorporate the free air volume of the accumulator (accumulator volume minus the volume of the detector(s) & building material), the area of the slab that is exposed and the initial radon levels when the detector is sealed in the accumulator. Figure 10 – Slab In-Growth Measurement Chamber The following formula, which can be entered into a spreadsheet program, is repeated each hour to obtain the mathematical radon concentration at each hour during the exposure: SR HR AR = Starting Radon under the accumulator = Exposure hour = Area accumulator covers in square feet (this can be m2 if source strength is changed to Bq/m2/hr) VOL = Free air volume inside accumulator in liters X = Multiplication addition & subtraction symbols CAV = Constant Adjustment Value SS = Source Strength in pCi/sq ft/hr (this can be Bq/m2/hr if area is changed to m2 and Bq units are used) (SR X (exp(-0.1813 X (HR / 24)))) + ((((SS X AR) X 24) / (VOL X 0.1814)) X (1 – (exp(-0.1814 X (HR / 24))))) – CAV Table 7 – CRM Accumulator Source Strength (SS) Formula 211 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Note that the first part of the formula is used to subtract out the diminishing effect of radon trapped under the accumulator at the start of the exposure. The second formula includes a Constant Value Adjustment (CAV) which is used to adjust the mathematical ingrowth line up or down so that it lines up with the CRM data plotted on the chart. The CAV must be a constant value throughout the exposure so that it does not affect the slope of the mathematical ingrowth only it’s placement on the chart. The need to adjust the mathematical ingrowth is due to CRM response delay, thoron, or different detector starting times versus chamber sealing. The CRM data and mathematical ingrowth value from the accumulator formula are both plotted in a spreadsheet. The Source Strength value and Constant Value Adjustment (CAV) of the accumulator formula are varied until the slope of the mathematical ingrowth matches the slope of the CRM data. Flux Testing the Slabs with Accumlator Chambers The emanation rate of both slabs was tested by sealing a metal chamber (accumulator) on top of the slabs with a CRM installed inside. In each case the slab was elevated off the floor to allow open air circulation. The accumulator, which should be made of metal or glass to avoid any diffusion of radon out of the chamber, can be a metal mixing bowl or metal bucket. All seams in the accumulator must be caulked or foil taped diffusion tight. The accumulator should be just large enough for the CRM to fit inside to maximize the radon ingrowth. The volume of the accumulator in liters needs to be obtained by carefully measuring the interior dimensions or by filling the accumulator up with a known quantity of water. The material volume of the CRM or E-PERM needs to be known and subtracted out of the accumulator volume The volume of each CRM was measured and the approximate values are given in Table 1 above. Flexible plumbers putty was used to seal the accumulator with the CRM inside to the slab. The area of exposure needs to include one half of the area the putty covers. Most putty’s have some oil content and will leave a stain if the surface is porous. See photo in Figure 11 below of the RS800 and a 2.5 gallon (9.6 liter) metal bucket. All seams inside the bucket were sealed. Figure 11 – RS800 sealed under 9.6 Liter Accumulator for Mixed Slab 212 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The CRM’s need to be left under the accumulator for 12 to 48 hours. The data is input into a spreadsheet graph and the source strength value of the mathematical ingrowth formula and the Constant Adjustment Value (CRV) are adjusted until the mathematical ingrowth matches the actual CRM ingrowth. The source strength value is the emanation rate of the material in pCi/ft2/hr or Bq/m2/hr. Figure 12 – CRM’s sealed under Accumulator over Mixed Slab Figure 12 shows the difference in CRM performance and the emanation rate based on using the mathematical ingrowth formula as previously discussed. RS 800, which is the least sensitive to thoron lags behind and then over responds by 25% compared to the SN1029 and Femto-Tech 510. The Femto-Tech 510 starts to fall off the ingrowth slope at 85 pCi/l but it responds well up to that point. The RS 500 has a 10% higher ingrowth than the Scout and SN 1029. No EPERMs were exposed under the accumulator with the mixed slab because of a high gamma reading. Emanation from Unaltered Retail Concrete A second slab without any additional soil added was made with “Sakrete 5000 plus” concrete mix obtained from a local building supplier. The emanation rate of radon from this mix is too low to use the flow through method to measure the entire slab (16” round by 4.5” thick - 40 cm round by 11.4 cm thick). Instead the entire slab was sealed inside a chamber with two AB5 Pylons. See the results in Figure 13 below. 213 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 13 – Pylon ingrowth data compared to mathematical ingrowth The mathematical ingrowth is determined by using the formula in Figure 17 above and adjusting the source strength and CAV until the CRM data and the mathematical ingrowth match. A thoron sniff measurement using the RAD7 during the ingrowth did not reveal any significant thoron concentrations coming from the cold slab. The ability to obtain similar results using CRM’s and E-PERMS under smaller accumulators is displayed in the graph in Figure 14. The CRM’s were placed under either a 9.6 liter or 7.4 liter metal bucket that was sealed on top of the slab. Note the variation in measurements when using a less precise Scout, SN1029 or RS500. These monitors need to be exposed for longer periods to improve accuracy. The full slab test in Figure 13 indicated an emanation rate of 8.2 pCi/ft2/hr (28.2 Bq/m2/hr). The SN1029 and RS 500 are within 10% of the total slab measurement while the RS 800 was 27% lower and the FemtoTech 510 is 39% lower. 214 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 14 – CRM compared to mathematical ingrowth E-PERM’s were also exposed a number of times under accumulators. For E-PERM measurements it is important to know the initial radon levels at the start of the measurement and the gamma emanation which might be elevated in some cases above background from the building material. Gamma measurements can be made with a properly calibrated gamma survey instrument or more accurate measurements can be obtained by using 2 mR gamma dosimeters obtainable from Rad Elec Inc that are exposed over a one to two day period and then re-charged with a portable charger. See photo in Figure 15. The ambient radon in air concentration trapped inside the accumulator that is decaying during the exposure period needs to be factored out of the ingrowth measurement. A less precise method is to approximate the initial radon measurement based on average radon in air measurements made in the same location and then use the first part of the formula in Table 8 to determine the Starting Radon Influence (SRI). A more precise method if the initial radon concentration is not known is to seal an E-PERM in a glass jar at the beginning of the measurement. The average radon concentration of the E-PERM in the jar is the SRI value. The SRI value is subtracted from the radon measurement obtained under the accumulator (RUA). The formula for obtaining this Figure 15 – 2 mR Gamma Dosimeter & re-charger 215 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 measurement is given in Table 8. Note that the lower the emanation rate the more critical it is to measure the starting radon concentration. If the E-PERM is immediately closed up at the end of the accumulator exposure the E-PERM’s response delay to the in-growing radon will bias the average reading low. This effect is more pronounce for an in-growth exposure of increasing radon concentration than a steady state exposure because the highest radon concentration happens at the end of the exposure. One method of compensating for the final out-gassing of radon in the chamber after the exposure and the final decay of the radon short lived decay products left in the E-PERM chamber is to leave the E-PERM open an additional 3 hours in a low radon environment. This would be in-practical in most cases because of the availability of a low radon environment and the time constraint of waiting three hours. To test the amount of bias at the end of an ingrowth exposure, 12 E-PERMs were exposed to a radon ingrowth inside a sealed chamber. Six of the E-PERMs were read immediately and 6 were left open in a lower radon environment (outside mid-afternoon) and read three hours later. The difference equaled about 10% higher emanation rate which is added to the formula in Table 8. This is similar to the CRM bias. If the influence of the starting radon concentration is not measured using the E-PERM sealed in a jar method then the starting radon influence (SRI) is determined by the first formula given below which can be entered into a spreadsheet. The SRI is then included in the second formula to determine the emanation rate. RUA = E-PERM average radon under accumulator measured by an E-PERM ARL = Approximate ambient radon level when E-PERM is sealed SRI = Starting Radon influence (use either E-PERM average in sealed jar or 1st part of formula in Figure 24) EXD = Exposure Days AR = Area accumulator covers in square feet (this can be m2 if source strength is changed to Bq/m2/hr) VOL = Free air volume inside accumulator in liters X = Multiplication symbol SS = Source strength in pCi/sq ft/hr SRI = (ARL X (1- exp(-(0.1813 X EXD))) / (0.1814 X EXD)) SS = ((((RUA-SRI) X VOL X 0.1814) / AR) / (1-((1- exp(-0.1814 X EXD)) / (0.1814 X EXD))) / 24) X 1.1 Table 8 – E-PERM Accumulator Source Strength (SS) Formula Note that the first calculation (SRI) determines the diminishing effect of radon trapped under the accumulator at the start of the exposure. Single S-Chamber E-PERM’s were exposed under an accumulator sealed on top of the cold slab. 216 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Pylon average 8.2 pCi/ft2/hr Ingrowth correction 1.15 9.4 pCi/ft2/hr 3.7 Bq/m2/hr E-PERM smooth side 5.5 pCi/ft2/hr Final decay correction 1.1 6.0 pCi/ft2/hr 3.5 Bq/m2/hr E-PERM rough side 6.0 pCi/ft2/hr Final decay correction 1.1 6.6 pCi/ft2/hr 3.6 Bq/m2/hr Table 9 – E-PERM under accumulator versus Pylons with cold slab ingrowth The E-PERM’s were placed under 3 liter accumulator bowls and they calculated emanation rate was 33% lower than the Pylon. It is unclear why they responded so much less. The Pylon exposure with the total concrete slab was not repeated to determine if the total emanation rate out of the concrete was reduced because the summer months had higher outdoor humidity levels that the slab was exposed and there may have been a decreased emanation rate because of humidity being greater than 80%. See paper on radon emanation and moisture content of concrete in references below. Measuring Granite Tiles & Countertops Granite typically contains 238 uranium and 226 radium which decays into 222radon which will escape into the air. There is concern that granite with unusually high levels of radium could significant increase the radon levels if it was installed in an air tight homes or areas of the home that had limited air exchange. Several pieces of granite were obtained that had higher than average emanation rates of radon in order to test the ability to measure the emanation rate using the accumulator method. These pieces of granite were first measured by placing them in a sealed chamber with one or two AB5 Pylons. The graph of 1.25” (3 cm) thick granite in Figure 18 is the highest emanating granite slab that was tested. Granite emanation rate in this study uses units of square feet or square meters of the polished top side but the granite is actually emanating from both sides of the material although not at equal rates. Note that the emanation rate across the granite surface is also likely to vary significantly. 217 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 16 – Granite Emanation Rate in a sealed Chamber The accumulator method was used to measure the emanation rate of the granite samples by sealing a metal trash can (7 to 8 liter size) with a CRM’s inside to either side of the granite. The volume of the CRM is subtracted from the volume of the accumulator to determine the actual free air. It was determined that the granite area the accumulator covered needed to include half the width of the putty placed around the accumulator as additional area emanating into the chamber. Figure 17 – Granite Emanation Rate Variation 218 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Table 10 and 11 below depicts the significant difference between emanation rates of the polished side versus the un-polished side. The JB granite had a plastic fiber re-enforced coating that is apparently stopping 98% of the radon emanation out of the un-polished side. The CB granite was the reverse with almost 8 times more radon emanation from the un-polished side versus the polished side. The NG granite had 40% more emanation from the un-polished side versus the polished side. The difference between emanation rates is due to the increased surface area of the un-polished side and the different sealing methods used on the polished side. Polished granite typically has fillers installed to fill the small indentations in the granite before it is final polished. These results indicate the need to measure both sides of a granite counter top to avoid significant errors. It may be possible to test the underside of a granite kitchen slab by removing a cabinet drawer to gain access for the accumulator. The last three columns in Table 10 gives the radon emanation rate determined by measuring the entire piece in a sealed chamber. The sum of the CRM accumulator measurements versus the total emanation matches within a few percentage points for two of granites. The NG granite has a total emanation rate that is almost 20% less than the sum of measurements of the two sides. Variation between measuring the total granite piece and individual sides could be due to variations in emanation across the surface of the granite. Granite type NG granite JB granite CB granite Polished emanation pCi/ft2/hr 240 120 1.0 Unpolished emanation pCi/ft2/hr 345 2 7.8 Total emanation pCi/ft2/hr 490 125 8.6 Total emanation pCi/m2/hr 5274 1345 92.6 Total emanation Bq/m2/hr 195 50 3.4 Table 10 – Granite Emanation Rate calculated with CRM’s Granite type NG granite JB granite CB granite Polished emanation pCi/ft2/hr 199 107 1.6 Unpolished emanation pCi/ft2/hr 376 1.4 11.9 Table 11 – Granite Emanation Rate calculated with E-PERMs The likely variation across the granite surface and the difference in emanation rate between the polished and un-polished side can easily produce a significant bias in a single accumulator test of only one side of a granite slab. 219 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The gamma rates of the four granite pieces were measured with a Bicron Micro Rem gamma meter that had been recently calibrated as well as with the Rad Elec 2 mR/hr gamma dosimeters. There was only a 10 to 15% difference in measurement results between the two types of gamma measurements. See picture of gamma dosimeters in Figure 15 above. The gamma measurements are compared to the measured radon emanation rate in Table 12 below. In each case the average of the background gamma was subtracted from three gamma dosimeters placed on top of the granite pieces. This small sample of four granite pieces indicates the ratio between the gamma emanation rate and the radon emanation rate varies by a factor of 8. The variation in the ratio between gamma measurements and radon emanation rate will likely indicate which granite pieces are unlikely to increase radon levels but are not likely to be able to indicate how much radon emanation is coming off granite based on gamma measurements. Granite type NG granite FS granite JB granite CB granite Gamma µR/hr above background 99.3 25.0 12.7 3.4 Total emanation pCi/ft2/hr 490 508 125 8.6 pCi/ft2/hr per µR/hr above background 4.9 20.3 9.8 2.5 Table 12 – Gamma emanation rate versus radon emanation Calculating Radon Increase from Building Material Emanation Rates Determining the increase in radon levels from a building material is difficult even if the building material has a uniform emanation rate. Radon emanation from concrete may be reduced by the materials placed over the concrete such as vinyl flooring or ceramic tile although drywall, paint, texture coatings or carpeting may provide very little reduction in emanation rate. This total emanation rate per hour from the material is divided by the liters of outdoor air moving into the structure or room every hour to obtain the radon level increase. The amount of outdoor air entering a building can obviously change hour by hour depending upon wind load, temperature difference inside to outside, exhaust fan operation and window and door position. Any change to this ventilation rate will have a linear effect on the radon levels since the emanation rate from building materials is likely to be fairly consistent. The introduction of outdoor air into the dwelling will likely be well mixed if the unit has an air handling system that is operating. If there is no air handling system or it is not operating then the increased radon in air from the building material will vary from room to room depending on the room’s volume versus exposure to the building material and the natural mixing taking place from room to room. If some assumptions are made, one can calculate the contribution of increased radon in a small home that is very air tight. An air tight home would be most influenced by building material emanation rate. The condominiums the author worked on had air change per hour (ACH) rates less than 0.1 ACH. If we use 0.1 ACH with a 1250 ft2 (116 m2) condominium the ventilation rate would be 28,316 liters per hour. If 40 ft2 (3.72 m2) of granite was installed in this size dwelling assuming even mixing of the air by an operating air handling system the radon levels would be increased by the amounts given in Table 13 below. If the condominium floors and 220 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 ceilings were constructed of concrete, as they typically are, there would be 2500 ft2 of concrete exposure. If the emanation rate of the cold slab (9.4 pCi/ft2/hr) is used, the radon increase will be around 0.8 pCi/l. The cold slab was however only 3.5 inches thick (8.9 cm) while a typical condominium slab is 7 to 8 inches thick (18 to 20 cm). The “diffusion length” of concrete (point where only 37% of the element is escaping) has been measured by other researchers to be around 10 cm (4”). The double thickness of the actual slab versus the tested cold slab will increase the surface radon emanation but it would likely not be linear. Note however that the concrete even using the cold slab emanation rate increases the radon levels a greater amount than the granite having an unusually high emanation rate. CB Granite 0.1 pCi/l 4 Bq/m3 JB Granite 0.2 pCi/l 7 Bq/m3 NG Granite 0.7 pCi/l 26 Bq/m3 Concrete 0.8 pCi/l 30 Bq/m3 2 Table 13 – Radon increase in 1250 ft (116 m2) dwelling with 0.1 ACH 2 2) 2 2 2 from 40 ft (3.7m granite or 2500 ft (232m )concrete at 9.4 pCi/ft /hr emanation Summary In most cases it will not be possible to take a sample of a building material and place it inside a sealed chamber with a radon monitor to measure the emanation rate. This study has demonstrated that placing a continuous radon monitor or E-PERM inside a metal or glass accumulator that is sealed to the emanating material surface is a reasonably reliable method for determining the emanation rate assuming the emanation rate is consistent across the surface of the material. It appears from the small number of granite samples tested that granite can have significant variation in emanation rates between surfaces . Concrete slabs however are likely to have significantly more uniform emanation rates assuming the material came from the same source and if there have been no coatings applied to one side of the concrete. To obtain emanation rates, it is necessary to know the exact volume of the accumulator, the amount of free space taken up by the detector and the area the accumulator is covering. The detector should be in place from 24 to 48 hours. Materials with low emanation rates should have 48 hour exposures. The emanation rate in pCi/sq ft/hr or Bq/m2/hr can be determined by using the formulas given in this paper. The CRM ingrowth rate will need to be matched to a mathematical ingrowth rate obtained from the formulas and adjusted until it matches the ingrowth of the CRM data to determine the emanation rate. This emanation rate times the area of the material exposed inside the dwelling divided by the ventilation rate will give the expected radon increase provided by the material. Changes in the radon concentration will therefore be directly related to the ventilation rate of the dwelling. Acknowledgements This study would not have been possible without the very generous donation of equipment from Rad-Elec, Femto-Tech, RadonAway, Sun Nuclear, RTCA and Pennsylvania DEP Radon Department. In addition the author is very indebted to the following individuals for much needed advice and help: Mike Kitto, Paul Kotrappa, Dan Steck, Phil Jenkins and Al Gerhart. 221 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References Ackers J.G., Den Boer J.F., DeLong P., Wolschrijin R.A., Radioactivity and radon exhalation rates of building materials in the Netherlands. Sci.Total Environ. 45: 151-156; 1985 Chao C., Tung T., Chan D., Burnett J.. Determination of radon emanation and back diffusion characteristics of building materials in small chamber tests. Building and Environ. 32:355-362; 1997 Chyi L.L.. Radon testing of various countertop materials final report. University of Akron, May 2008 Cozmuta I., Van der Graaf E.R.. Methods for measuring diffusion coeffients of radon in building materials. Sci. Total Environ. 272: 323-335; 2001 Cozmuta I., Van der Graaf E.R., Meijer R.J.. Moisture dependence of radon transport in concrete: measurements and modeling. Health Phys. 85: 438-456; 2003 Folkerts K.H., Keller G., Muth H.. An experimental study on diffusion and exhalation of 222Rn and 220Rn from building materials. Rad. Prot. Dosim. 9: 27-34; 1984 Gadd M.S., Borak T.B.. In-situ determination of the diffusion coefficient of 222Rn in concrete. Health Phys. 68: 817-822; 1995 Janga M., Kanga C.S., Moonb J.H.. Estimation of 222Rn release from the phosphogypsum board used in housing panels. J. Envirn. Radioact. 80: 153-160; 2005 Keller G., Hoffman B., Feigenspan T.. Radon permeability and radon exhalation of building materials. Sci.Total Environ. 272:85-89; 2001 Kitto, M., Green J.. Emanation from granite countertops. Proceedings of AARST International Radon Conference; 2005 Kotrappa P., Stieff L.R.. NIST traceable radon calibration system for calibrating true integrating radon monitors – E-PERM . Proceedings of AARST International Radon Conference; 1993 Kotrappa P., Stieff L.R. Volkovitsky P.. Radon monitor calibration using NIST radon emanation standards: steady flow method. Journ. Rad. Protection Dosimetry; 2005 Kovler K. Perevalov A., Steiner V., Rabkin E.. Determination of the radon diffusion length in building materials using electrets and activated carbon. Health Phys. 66: 505-516; 2004 Kovler K.. Radon exhalation of hardening concrete: monitoring cement hydration and prediction of radon concentration in construction site. Journ. Environ. Radioactivity 86: 354-366; 2006 222 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Llope W.J.. Radiation and radon from natural stone. Rice University, 5/7/2008 Misdaq, M.A., Amghar A.. Radon and thoron emanation from various marble materials: impact on the workers. Radiat. Meas. 39: 421-430; 2005 Pavilidou S., Koroneos A., Papastefanou C., Christofides G., Stoulos S., Vavelides M.. Natural radioactivity of granites used as building materials. Journ. Environ. Radioactivity 89: 48-60; 2006 Righi S., Bruzzi L.. Natural radioactivity and radon exhalation in building materials used in Italian dwellings. Journ. Environ. Radioactivity 88: 158-170; 2006 Roelofs L.M.M., Scholten L.C.. The effect of aging, humidity, and fly ash additive on the radon exhalation from concrete. Health Phys. 67: 225-230; 1991a Rogers V.C., Nielson K.K., Holt R.B.. Radon diffusion coefficients for residential concretes. Health Phys. 67:261-265; 1994 Rogers V.C., Nielson K.K., Holt R.B.. Radon diffusion coefficients for aged residential concretes. Health Phys. 68:832-834; 1995 Sahoo B.K., Nathwani D., Eappen K.P., Ramachandran T.V., Gaware J.J., Mayya Y.S.. Estimation of radon emanation in Indian building materials. ScienceDirect 42:1422-1425; 2007 Stoulos S., Manolopoulou M., Papastefanou C.. Assessment of natural radiation exposure and radon exhalation from building materials in Greece. J. Environ. Radioact. 69:225-240; 2003 Stoulos S., Manolopoulou M., Papastefanou C.. Measurement of radon emanation factor from granular samples: effects exposure and radon exhalation from building materials in Greece. J. Environ. Radioact. 69:225-240; 2004 Sun H., Furbish D.J.. Moisture effect on radon emanation in porous media. J. Contam Hydrol 18:239-255; 1995 Yu K.N., Chan T.F., Young E.C.M.. The variation of radon exhalation rates from building materials of different ages. Health Phys. 68:716-718; 1995 223 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 SOLVING TURBULENT FLOW DYNAMICS OF COMPLEX, MULTIPLE BRANCH RADON MITIGATION SYSTEMS L. Moorman, Ph.D. Radon Home Measurement and Mitigation, Inc. Fort Collins, CO ABSTRACT Active radon mitigation systems with a large flexibility in their complexity are simulated via computer calculations assuming incompressible gas flow dynamics. When designing more complex, multiple branch systems, insight into the turbulent flow dynamics inside the systems vent pipes may be of advantage in design and optimization of pipe sizing and radon ventilator characteristics. I will show how their effects can be simulated and assessed during the installation of real systems. For an N-branch, active, non-looped, radon mitigation system I will show how to construct the complete set of non-linear equations with its independent variables and demonstrate how these can be uniquely solved and applied to optimize a system under design. A number of real systems were used to compare with calculations. I will show a number of applications using this program: 1) The effects of sub-slab material and its resistance on the system. 2) The effects of turbulent flow through vent pipes of various diameters. 3) The effects of varying ventilator characteristics. 4) Calculations of multiple pipe branches in real time. INTRODUCTION The equation that governs the pressure distribution for the air in a single branch radon system in its simplest form consists of three components, the pressure loss through the soil and the radon extraction cavity, the pressure loss due to the resistance of the air with the pipe system and the pressure boost by the action of an operating ventilator somewhere in the pipe system. I will first discuss each of these components separately and indicate in each case which theoretical functional behavior approximates the description of the various pressure differences best. After that I will put together the components and describe how the equations for complete radon mitigation systems can be derived for multiple branches. Numerical evaluation of the solutions will result in gaining quantitative insight into the use of the equivalency of pipe sizes in complex radon systems. SUB SLAB MATERIAL AND CAVITY RESISTANCE PARAMETERIZATION. A dimensionless parameter that characterizes the flow for a gas through an opening or capillary is the Knudsen number. This is defined as the ratio of the mean free path of particles in the gas divided by a characteristic dimension such as the diameter of the pipe: ! Kn = (1) d In the movement of atoms or molecules of gas through small capillaries of the sub-slab medium, such as soil, rock or concrete, the flow may be more determined by the 224 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 collisions with the walls of the pores in the porous material than by collisions among the gas particles. In that case, the viscosity of the gas (which is a parameter for the friction inside the gas) does not play a large roll in the dynamics of the system. Therefore, on the one hand, very slow air movement inside a medium when no active soil depressurization exists, direct diffusion of radon gas through small capillaries may be the largest mode of transportation for radon. On the other hand, when enough small cracks and openings exist, or if the pore size in the material is large enough, convective movement of air which drags radon with it through these openings is more likely to dominate the mode of transportation for radon. The sub-slab material plus extraction cavity resistance (friction) for air movement when an active soil depressurization system operates can be measured in situ by placing a fan with relevant power and flow characteristics directly over the final excavated extraction cavity and measuring the pressure across the fan while running the fan at various speeds. When varying pressure differences, ΔPf, and measuring corresponding flow rate s, F, the curve that is generated appears in practice sufficiently linear in the relevant flow range for active mitigation systems. Fig. 1 shows an example of these parameters that were measured in existing homes during mitigations. Fig 1: Flow measured as a function of pressure difference across ventilator in the configuration described in text for various residences and different branches in one residence. 225 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Flows were measured by timing the capture of air from the end of the fan into a well determined size bag of known volume. Accuracy was verified by employing the same method to measure the fan curves as advertised by manufacturers for various fans. Flow measurements were found to be somewhat lower than the manufacturer’s specification, but sufficiently accurate to be able to use this method for this purpose. The resulting slope in Fig 1 is independent of which ventilator is used on a radon extraction cavity for the measurement. The observed linearity allows us to define a (local) linear friction Rg for the combined soil with extraction cavity through the following relationship: !Pf = PFR g (2) This equation can also be understood by interpreting the right hand side as the combined soil pressure drop inside the cavity (ΔPs=PFRg) which must counteract the pressure boost (ΔPf) by the fan in this simple model. The experimental linearity may be related to the fact that air velocities further away from the extraction cavity, representing the majority of the sub-slab material, are small. Deviations from linearity are expected at higher flow rates. By dividing both sides of the Eq. (2) by pressure and flow rate I obtain an equation for the friction: !Pf Rg = (3) PF The unit of resistance is independent of the units used for pressure. If flow is expressed in cubic feet per minute (cfm) this resistance expresses how many minutes it takes for one cubic foot air to move through the extraction cavity (min/cf) [in SI units the flow would be expressed in m3/s and the resistance would be in s/m3]. In Fig. 2 a graph is shown of a number of measured soil resistances graphed against the relative fan depressurization, which is the measured depressurization across the fan compared to the maximum fan depressurization at zero air flow. What can be seen in this “landscape of resistances” is a correlation of low soil resistance with low relative fan depressurization, as in large gravel, and a correlation of high soil resistance with high relative fan depressurization, as is the case in very tight clay. Other sub-slab material types found in between are designated as pea gravel, sand, looser clay, hard sand and clay. It must be emphasized here that the measurement of the resistance is unique to the specific residence and includes not only the sub-slab material type 226 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Fig 2: Resistances measure of excavated radon cavities in existing homes following method of Fig 1. but also any inhomogeneities in the sub-slab material and any leaks due to openings in the slab. The measured resistance defined here is a good quantification of the effective resistance that a radon mitigation system will be subject to via this radon extraction cavity. In this sense, I have found a quantification for the resistance of the extraction cavity with sub-slab material which is also valid when dealing with a multi-branch radon mitigation system. Thus this information can be used in simulations that include the complete system with all branches as will be shown later. VENT PIPE MODELING Laminar, viscous flow is indicated by values of the Knudsen parameter, defined in Eq. (1), smaller than 0.01 indicating that collisions between the particles of the gas are much more abundant and are determining the character of the flow rather than particle-to-wall collisions. This is the situation in air moving through a pipe at small speed and flow rates. At small flow rates, for viscous, laminar flow through a cylindrical tube the velocity of a fluid with viscosity η can be shown to be a parabolic (quadratic) function of the distance from the axis with the largest velocity on the central axis of the tube, and a zero velocity near the wall. The volume rate of fluid crossing any section of the tube with radius r for this flow is given by: #r 4 F= !P (4) 8"L 227 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 This is known as Poiseuille’s formula and is important in medicine since it gives a qualitative understanding of blood flow through our arteries and veins. In addition, by reading Eq. (4) from right to left it can be interpreted that under steady state flow conditions the pressure loss along any section of a cylindrical pipe of length L is a linear function of the flow rate through a cross section of the pipe: 8"L #P = 4 F (5) !r However, when the flow velocity of a fluid becomes sufficiently large, laminar flow breaks down and turbulence sets in. The critical point for the onset of turbulence in a fluid can be characterized by a dimensionless parameter referred to as the Reynolds’ number, which is the ratio of the shear stress in the fluid due to turbulence and the shear stress due to viscosity given by: 2r"v NR = (6) ! In this equation ρ is the density of the fluid and v the velocity. Experiments have shown that the flow will be laminar when the Reynolds’ number is below 2000 and the flow will be turbulent for values above 3000. In between these values the flow can be either laminar or turbulent and can go back and forth. When the air speed increases through a pipe, the same model applies and when the Reynolds’ number increases beyond its critical value the air flow becomes turbulent and the resistance increases. For such situations the linear relationship between pressure loss along the pipe and flow rate is no longer valid and the new relationship is a nonlinear function of flow rate that must go through zero. Thus I can extend the pressure loss behavior to a more general form with two parameters which may be different for each diameter of the pipe: !P( F ) = cF a (7) The variables for the pressure drop along 100 ft of the pipe for different diameters are known from the heating and ventilation industry and values for 2”, 3”, 4” and 6”round tubes are known. The derivative of this pressure loss to flow can be written as: "#P ( F ) = caF a !1 "F The length must be scaled appropriately to the total equivalent length of the pipe where 90 degree elbows and 45 degrees elbows have a certain equivalent length in air resistance to straight section of pipe of the same diameter. This equivalent length approximation is used in the heating and ventilation industry for ducts and assumes that the nonlinearity (power of F) of the components is the same for connections as for straight pipe. If this is not the case a different equivalent length would have to be determined for each component at each air flow rate. In the following I will use the assumption that the equivalent length calculation can be made. VENTILATOR CURVE MODELING 228 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 The modeling of the ventilator curve (fan curve) can be done sufficiently accurate for our goal by three parameters. I assign a new function with three parameters to each ventilator and have verified it can be accurately described for each fan (f) by: (8) g ( f , F ) = q1 + q 2 F b2 This means the derivative to the flow rate of the fan curve is: "g ( f , F ) = q 2 b2 F b2 !1 "F In our model of multiple branch radon mitigation systems I will allow for the possibility that any pipe section between nodes (pipe TEE’s) can have a fan inserted. SINGLE BRANCH RADON MITIGATION SYSTEM For the calculation of a single Branch radon mitigation system, I can now add the individual components keeping in mind that all pressure losses due to sub-slab material and cavity resistance and resistance in pipe system together are counteracted by the pressure boost from the ventilator, resulting in the nonlinear one-dimensional equation: a PF1 R g + c1 F1 ! g ( f , F1 ) = 0 (9) Once the resistance for the sub-slab material (Rg) is measured, it can be shown that a unique solution exists for each fan and pipe diameter. By dividing the equation by pressure and flow I find: a !1 F1 g ( f , F1 ) (10) ! =0 P PF1 This can be employed in a graphic solution even during the mitigation as is shown in the fan resistance response curve in Fig. 3. R g + c1 For any given ventilator, relevant calculations can be made that will give us insight in the flow dynamics of the system by numerically evaluating the solution to Eq. (9) as a function of equivalent length for various cavity resistances. The resulting curves for one commonly used fan are shown in Fig 4. It shows that the relative change of volume rate through the system is very different depending on the resistance. For low cavity resistance the flow rate depends strongly on the equivalent length for short equivalent lengths only whereas for high resistances the flow rate is nearly independent of the equivalent length. 229 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Fig 3: Fan Resistance Response curve: Method of graphically solving Eq. (10). For 4” diameter pipe system and 175 ft equivalent length the red squares indicate the resistance for all flow rates. To solve the equation find the crossing with the fan curve (green and blue squares) indicated by a red circle and shift the circle up by the extraction cavity friction (heavy red solid line) along the fan curve to find the value inside the second circle. The arrow points at a flow rate of approximately 80 cfm which is the steady state flow that this ventilator in this mitigation system will support. For a 3” diameter pipe it is indicated at the second arrow that the flow will go down to approximately 50 cfm., thus loosing 38% of the flow rate through this system. The dashed horizontal line indicates the resistance of a different extraction cavity that was measured with a higher resistance which leads to a flow rate solution even with a 4” pipe of approximately 50 cfm. Similarly I have evaluated this information given in figure 4 for different diameter pipes, which is most relevant for 3” and 2” pipes. I can than evaluate the ratio for flow rate of the 3” pipe with 4” pipe. This ratio is given in Fig. 5 as a function of equivalent length for each cavity resistance. It can be seen that suppression effect of flow for smaller pipe sizes are strongest for low cavity resistances (crawlspace, gravel) and weakest for large cavity resistances (hard sand, or clay). This can be qualitatively reformulated by the statement that high flow rates are easier choked by a smaller diameter pipe than low flow rates, and that when the flow rate is small the effect of pipe diameter is not very important. 230 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Fig4: For a FR150 fan with 4-inch pipe for a single branch system the volume rate is numerically calculated for several extraction cavity resistances as function of equivalent length. The information obtained from these calculations and for similar calculations for 2” diameter vent pipes can be summarized by defining a criterion for flow rate loss. I choose to extract from Fig. 5 a critical equivalent length that corresponds to a flow rate loss of 20% for each resistance. These critical equivalent lengths can be graphed against the sub-slab material and cavity resistance as has been done in figure 6 which in turn allows for the following interpretation. The regions divided by the solid and dashed lines are the regions in which there is a certain equivalence of system. It can be seen that in some cases less than 20% loss is expected by switching to a smaller pipe diameter. This is indicated by the notation: 3” or 4” inside the graph. Similarly, there is a region at large cavity resistances and shorter length systems where the flow dynamics for even 2” pipe would be similar to 3” and 4” pipe diameters. On the other hand it is clear that at small cavity resistances only for very short systems, up to 10 ft equivalent length, the 3” and 4” systems are similar and at 25 ft equivalent lengths one can expect already as much as 30% flow loss when switching to a 3” vent pipe. Nevertheless, the correct interpretation of this graph is that it shows equivalence of systems but does not show whether either of the equivalent systems will work to reduce radon levels. 231 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Fig. 5: For a FR 150 fan for a single branch system the ratio between the volume rate employing 3 inch and 4 inch piping in the system is shown. Fig 6: Equivalent Dynamics Graph (Fan specific, here for FR150). Flow reduction data points for 20% flow loss are connected with straight lines in the graph. The areas in between the lines are marked for which pipe diameters are equivalent within the chosen criterion of the flow loss. The open symbols with dashed lines are for 30% loss. TWO BRANCH RADON MITIGATION SYSTEM 232 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 In deriving the equations for a 2-Branch system I can develop a set of three equations that are similar to the Kirchhoff equations in electronic circuits with the one important difference that the equations here are nonlinear in the flow and that it is not immediately clear that only a single flow solution exists. i) Fan equation: !P2 + !P1 = !Pf ii) iii) Kirchhoff Rule through the two branches: !P2 = !P3 Flow conservation: F1 = F2 + F3 (11) By substituting iii) in i) the set of equations can be written as two nonlinear equations in two independent variables (F2 and F3 ) only: PF2 R g 2 + c 2 F2a 2 + c1 ( F2 + F3 ) a1 ! g ( f , F2 + F3 ) = 0 i’) (12) ii’) PF2 R g 2 + c 2 F2a 2 ! PF3 R g 3 ! c3 F3a3 = 0 The equations can be written in a vector formulation as r r r (13) A( F ) = 0 and solved numerically by finding the root of the two dimensional equation. The solution of Eq. (13) can be found numerically by use of an assumed reasonable r starting value of the flow vector, F0 , and, by iteration, finding the small root deviation vector from the previous approximate solution. For iteration number n I find: "1 ( % r r . /Ai + & # A ( F ) = " L"1 A ( F ) )) d n = "! ,, (14) ! q n pq q n &- /Fk * r # q q &' Ft # $ pq In which I defined the Jacobian matrix: rr & 'A # (15) L = $$ i !! % 'Fk " and the inverse of this matrix is: 1 & L22 ' L12 # $ ! (16) L'1 = det L $% ' L21 L11 !" I than find the next iteration of the solution vector in the two dimensional “flow space” from the previous approximate solution by r addition: r r (17) Fn +1 = Fn + d n r I then choose to continue the iteration until a certain stopping criterion d n " ! , for a sufficiently small value of ε, is reached, at which time the closest approximation to the r solution is Fn for final value of t reached. The method described here to solve Eq. (13) is mathematically known as the Newton–Raphson method of root finding for a nonlinear system of functions with multiple independent variables. N-BRANCH RADON MITIGATION SYSTEM 233 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 More general solutions have been derived for 3- and 4-Branch radon mitigation systems with a possibility of up to 7 ventilators in the various branches of the mitigation system. From this, it is possible to formulate an N-Branch mitigation system with (2N-1) ventilator insertion points. In a non-looped system as is shown schematically in Fig. 7 this would be one ventilator for each of the N branches, one ventilator in the common upper stack of the system (Branch 1) and (N-2) ventilators for the interconnecting pieces between the nodes of the N pipe branches. As an example, when deriving the equation for 4 branches I write down the fan equation, three Kirchhoff equations and the continuity equation. This leads to four non-linear equations with four independent unknown variables. The four independent variables are the flow values in each of the four branches that connect to the ground: & F2 # $ ! r $ F3 ! (18) F =$ ! F4 $ ! $F ! % 5" Fig. 7: Schematics of a 4-branch radon mitigation system with the parameter definitions used in the derivations. and the 4-dimensional mitigation system equation thus is: r r r (19) A( F ) = 0 234 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Similar to Eq. (15) I can derive the 4-dimensional Jacobian matrix: In this: &/ + . rr & *A # $ . $ L = $$ i !! = $ % *Fk " $ 0 $ 0 % / / / # ! '- ' ) ') ' )! ', ' ( ' (! ! 0 , ' + !" (20) ( = a ! f1 ' = b ! f2 & = c ! f3 % = d ! f4 $ = e ! f5 # = A ! FA " = B ! FB in which the flow resistance components of the upper stack are:: a = PF1(2345) = c1 a1 ( F2 + F3 + F4 + F5 ) a1 !1 A = PA(3B) = c A a A ( F3 + F4 + F5 ) a A !1 B = PB(45) = c B a B ( F4 + F5 ) aB !1 and in which the flow resistance components of the branches with sub-slab material connections are: b = RP 2 = PRg 2 + c2 a2 F2a2 !1 c = RP3 = PRg 3 + c3 a3 F3a3 !1 d = RP 4 = PRg 4 + c4 a4 F4a4 !1 e = RP5 = PRg 5 + c5 a 5 F5a5 !1 In addition the active ventilator boost derivatives in the common upper part of the vent stack is given by: f1 = f1 (2345) = q1b1 ( F2 + F3 + F4 + F5 ) b1 !1 and for the individual branches i = 2, 3, 4, or 5 these ventilator boost derivatives are given by: f i = f i (i ) = qi bi Fi bi !1 For the interconnecting sections A and B between the various node points the ventilator boost derivatives are given by: f A = q A b A ( F3 + F4 + F5 ) bA !1 f B = q B bB ( F4 + F5 ) bB !1 Solving the set of equations defined in Eq. (19) is similar to the approach of solving Eq. (13), as was done in Eq. (17) with use of Eq. (14), following the Newton-Raphson 235 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 method for a set of non-linear equations with multiple independent variables. In this case the 4x4 Jacobian matrix In Eq. (20) must be inverted. Although there is an analytical expression for this inversion, the numerical evaluation of this is cumbersome. Instead, a numerical evaluation of the inverted 4x4-matrices was applied directly via the Quattro Pro matrix inversion function and solutions of the set of equations were calculated with an iterative approach by using three embedded macros. Verification of the validity of the inversion process was done by multiplication with the original matrix and by testing the convergence of the solution. With fairly generic starting values of the flows, the four dimensional calculations converged most of the time in less than 8 steps to a result of the final flow that is close to the accuracy of the computer. The equations presented contain all of the physics that was discussed before. Additional physical effects that can be included are gravitational effects which can be responsible for a fan to act differently when moving air horizontally over 25 ft compared to moving air over a vertical lift of 25 ft, as well as the lift due to temperature differences of air inside the pipe compared to outside air (the stack effect for a passive system). Also certain aspects of the Bernoulli effect can be included in these equations, and have not yet been included in the above formulation. Finally I must mention that these equations are for incompressible flow, which in its defense is a sufficiently accurate approximation for the air parameter regime in which radon systems generally operate. In Fig 8 I show an example of a calculation for a house where we installed a three branch system with the HP220 ventilator in the attic of the garage 2 ft under the discharge point. Slab areas were 600, 1050, and 100 sf to be serviced by the three branches 2, 3 and 4, respectively. The lower half of this figure shows the vacuum (negative) pressures that the computer program calculated to solve Eq. (19) for the cavity parameters measured and equivalent lengths of pipes calculated. The horizontal axis gives relevant observation points along the system with the Sky-limit pressure on the right and the Sub-slab limit pressure on the left, which will always be the same and at zero pressure. At the mark “P-hole” the pressures in each of the three extraction cavities is given and “P1-below fan” is the pressure in the top stack of the system immediately below the ventilator in the attic of the garage. The program allows for placing the system at further distances away from the discharge point for instance when installing an outside system.. At the marker P_45B the pressure is given at the node where branches 4 and 5 come together and the air flows into pipe B. The same is the case for the other node points. The top half of the figure shows the flow rates indicated on the right vertical axis of the numerical solution that the computer calculated for each marker along the horizontal axis. In this case an HP220 fan was simulated, the top stack was 45 equivalent feet long and branch 2, 3, and 4 each 65 equivalent feet long with 2, 3, and 4 inch diameter pipe, respectively and branch 5 was 40 equivalent feet long with 3 inch diameter pipe. A and B were 10 and 20 equivalent feet of 4 inch diameter pipe. 236 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Cavity resistances were for cavity 2: 2×10-5 min/cf, for cavity 3: 8×10-5 min/cf and for cavity 4: 1×10-3 min/cf and cavity 5 was essentially deactivated in this calculation by giving it a virtual resistance of 100 min/cf. It is interesting to see that the flows indicated at P_hole through branch 2, even though the vacuum pressure is small, is almost as large as through branch 3, despite the fact that branch 2 only uses 2 inch piping and branch 3 has 3 inch piping. This is due to the fact that the cavity resistance of branch 2 was a factor four lower than the cavity resistance for branch 3. Fig. 8: The numerical program shows the resolution in a graph that can be conveniently read of. The vacuum pressures in the three radon extraction cavities under the slab are given at P_hole, as are the three airflows in the individual branches. When calculating Reynolds numbers the program showed that branch 5 and B were operating in the laminar regime, rather than the turbulent regime as is the case for the other branches as shown in Fig. 9. 237 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Fig. 9: Reynolds numbers in the various pipe branches indicating the flow dynamics applicable. CONCLUSION A theory for single-branch radon mitigation systems was developed in which experimental data were used to support the theory that the sub-slab material and extraction cavity resistance can be sufficiently well described by a single resistance parameter. The differences between laminar and turbulent flow through round pipes were discussed and the roll of the Reynolds’ number as a criterion for the onset of turbulence in the air flow. A method utilizing the Fan Resistance Response graph was developed to aid in graphically solving the 1-branch mitigation system equation. By numerically solving the single branch radon mitigation equation for many different situations I have derived criteria for the equivalence of different size piping under various circumstances, and developed a quantitative insight in those circumstances when pipe sizes cannot be considered equivalent. These insights were graphically summarized in the Equivalent Dynamics Graph which can be helpful during installation of radon mitigation systems possibly leading to more appropriate pipe size choices in the future. As an example of an N-Branch system, for a four-branch, active, non-looped, radon mitigation system I derived the complete set of non-linear equations with its independent variables and demonstrated how these can be solved numerically and applied to optimize a system under design. A three-branch example was discussed in detail showing that this system has simultaneously turbulent and laminar flow in different branches. 238 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 RADON PREVENTION AND MITIGATION IN FINLAND: GUIDANCE AND PRACTICES Hannu Arvela, Heikki Reisbacka and Petteri Keraenen Radiation and Nuclear Safety Authority - STUK PO Box 14, 000881 Helsinki Finland ABSTRACT Two new Finnish mitigation guides have been issued. The first guide gives basic information and practical examples on all mitigation methods and results achieved. The second guide is a detailed guide for design and implementation of sub-slab-depressurization (SSD) in low-rise residential houses. The presentation includes many examples from the guide for SSD and radon well and other methods. The most efficient methods are SSD and radon well, typical radon concentration reduction factors being 70 - 90%. Radon well is effective only on soils where air permeability is high enough; e.g., on gravel and in esker areas. A single radon well can reduce radon concentration in many dwellings at a distance up to 20 - 30 meters. Sealing entry routes and ventilation or pressure-reduction-based measures resulted in lower reduction factors but play an important role in mitigation practices. The national prevention guide and results achieved are presented. The guide is based on the following measures: use of bitumen felt in the joint of foundation wall and floor slab, sealing of penetrations and installation of radon piping. Radon prevention is essential and required in the whole country. 1. Introduction Finland belongs to the countries of high indoor radon concentrations. Cool climate, long heating season with no long-term airing through windows, building soils with high air permeability and foundation structures promoting flow of radon-bearing air from soil to indoor spaces are the main reasons for high indoor radon concentrations. Approximately 50,000 dwellings, 3% of all dwellings, exceed the action limit of 400 Bq/m3. Most of these are low-rise residential buildings. Similar problems are found in flats with the slab of the bottom floor in contact with the ground. The reference limit for design and construction of new buildings is 200 Bq/m3. The number of houses in Finland exceeding this limit is 200,000, which is 18% of single-family houses. Preventive measures should be taken in all buildings in the whole country in order to avoid new dwellings that need mitigation. The first indoor radon mitigation studies were carried out in the mid 1980’s. These studies 239 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 resulted in first mitigation reports which gave basic information of active sub-slab suction installations. Both STUK and the Ministry on Environment published mitigation guides in the 1990’s. The STUK guide gave an overview of all methods and the results achieved. The guide of the Ministry focused on sub-slab depressurization (SSD), design and implementation. Both guides have been revised in 2008 (Arvela and Reisbacka 2008, Ministry of Environment 2008). The ministry guide is a detailed guideline for design. The STUK guide refers to the ministry guide and gives key principles for design and implementation. Table 1 gives the contents of the guides. Table 1 Key contents of the mitigation guides STUK guide Indoor radon mitigation 1. Introduction -Radon entry, ventilation depressurisation 2. Efficiency of mitigation methods 3. House inspection before mitigation 4. Sub-slab depressurization - Principle, design, suction pits, location of pits, exhaust piping and fan, installation - SSD through foundation wall 5. Radon well - Design, results, examples 6. Sealing entry routes - Practical guidance, materials 7. Crawl-space ventilation 8. Ventilation-based methods Mechanical and natural ventilation, examples 9. Cellar ventilation 10. Radon mitigation in blocks of flats -depressurisation problems, ventilation, SSD, radon well 11. Workplaces and large buildings - Brief overview 12. Methods used in house inspection 13. Prices of mitigation 14. Radon prevention in new building SSD guide, Ministry of Environment Indoor radon mitigation in low-rise residential buildings. Sub-slab depressurization. 1. Introduction 2. Overview of mitigation methods 3. Design principles 4. Designing a SSD Foundation and floor construction - Load-bearing walls - Need of sealing work - Number and location of suction pits 5. Practical installation - Normal suction pit and deep suction pit 6. Implementation - Dimensioning of air flows - Improvement of the efficiency 7. Air exchange 240 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 - Brief overview 241 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 2. Results achieved in indoor radon mitigation The STUK guide reports mitigation results in 400 dwellings based on a detailed mitigation questionnaire sent to house owners in 2000-2001. Figure 1 shows a summary of the results. Sub-slab depressurization (SSD) and radon well are the most efficient methods. Typical reduction factors for both methods are 70 - 90%. In difficult cases additional sealing work is needed in order to achieve a low radon concentration. The reduction factors for other passive methods are clearly lower, as shown in Figure 1. SSD can be implemented through both floor slab and foundation wall. The ministry guide focuses on the implementation of SSD through floor slab. The STUK guide gives examples and guidance also for foundation-wall installations. SSD’s have been installed in many cases through foundation wall in terraced houses where the floor slab area is not large. The reduction factors are typically above 80%. Installation of a preparatory radon piping has become increasingly common in houses built during the last ten years. Activation of this piping through an exhaust fan has resulted in high reduction factors typically above 80%. A radon well is constructed outside of the house, and the well sucks air from soil from a depth of 3 - 4 metres. Figure 2 shows the principle of a radon well. This ventilation decreases the radon concentration of soil air below the house foundation efficiently. A single radon well can reduce radon concentration in many dwellings at a distance up to 20 - 30 meters. A radon well is effective only on soils where air permeability is high enough; e.g., on gravel and in esker areas. Radon reduction methods based on ventilation reduce radon concentration either through increased ventilation or lowered house vacuum level. A reduction factor above 50% has been achieved only in cases where the original air exchange rate has been defective or when the house vacuum level has been high. Typical reduction factors have been 10 - 40%. Increasing the operation time or power of mechanical ventilation and opening existing or installing new fresh air vents are typical measures. Installation of new fresh-air vents does not result normally in reduction factors above 50%. Sealing entry routes aims at reduction of leakage flows of radon-bearing soil air into living spaces. Sealing may be very requiring. In many cases the results are qualified only when the entry routes have been sealed almost completely. Best results have been achieved in houses where the foundation wall is of cast concrete. Floor joints with foundation walls of porous light-weight concrete cannot be sealed with normal methods. 242 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 100 Radon reduction % 80 60 40 20 0 ds et w m l ra ve Se nd on m en t ho el l es dr a of g in al Se ill y tr en ve r la el ed ro ut tio ila nt h. ex h. C ec .m pr n nt ve nt ve E S/ ec m Im . pr Im . . nt ve t. h. t en em ov pr Im na h. ex d an ly pp su A ba N ew nt ve ve t us ha ex h. ec m ew N nt l w on ad R ad R ug ro th D SS el ng pi pi on tio h SS fo D un th da ro ug n h w sl al l ab -20 Figure 1. Radon reduction factors achieved using various mitigation methods, minimum, 25th percentile, 75th percentile and maximum. The results are based on a questionnaire study of 400 houses. Well designed and implemented mitigations result in reduction factors which are better than the typical reduction factors in the figure. 243 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 2. Principle of a radon well. A radon well ventilates soil air and decreases radon concentration in soil air in a large area. 3. Radon prevention 3.1 Brief history of radon-resistant construction in Finland In the new (1990- ) housing stock indoor radon concentrations are higher than in older houses. This is due to prevalent use of slab-on-ground foundation. In the 1950’s cellar houses and crawl space were the prevalent foundation types. Today 200,000 single-family houses (18%) exceed the radon concentration limit for new buildings, 200 Bq/m3. Radonresistant new construction is a key issue when aiming at low indoor radon concentration at the national level. The first guide for radon-resistant new construction was published in 1996. The key measures were sealing the gap between the floor slab and foundation wall with elastic sealant and installation of radon piping. However, the sealing practice was too tedious and did not become common. At the same time installation of radon piping has become more common. Sealing practices were studied in a wide joint venture. These studies resulted in a revised guidance published in 2003 (Building Information Ltd). 3.2 Radon prevention guidance The guidance focuses mainly on radon-resistant construction of slab-on-ground foundation which is the big radon challenge in the Finnish foundation construction. The guide gives also basic facts for crawl-space construction: good ventilation and properly sealed floor construction. Use of light-weight concrete blocks makes radon mitigation more difficult. Sealing of the gap between the floor slab and foundation wall is not effective, because leakage flows find an alternative route through the porous foundation wall and wall structures. This emphasizes the need for prevention work. The revised guidance gives three main prevention measures. First, the joint of the foundation wall and floor slab should be sealed using a strip of bitumen felt (Fig 3). Second, all penetrations should be sealed carefully. The third measure is installation of a preparatory radon piping beneath the slab. Figure 3 shows also the recommended sealing practice for cellar walls. Bitumen felt should be used also on the outer surface of the cellar wall in case the foundation wall is of porous light-weight concrete blocks. In case of the cellar wall being of cast concrete, this is needed only on the grounds of moisture prevention. The guidance aims at low indoor radon concentration through qualified sealing work. 3.3 Prevention practices Installation of radon piping has become more common since the mid 1990’s. Since 2003, when the new sealing practice was issued, use of bitumen felt has also become one of the regular practices required in the building permission process especially in southern Finland. Experience from the radon campaigns, which local authorities and the Radiation and Nuclear Safety Authority organise together, show that in many areas the radon piping is installed in more than half of the new buildings. 244 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 245 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 3 Sealing of the joint of the foundation wall and floor slab using a strip of bitumen felt in a slab-onground foundation (left) and in a cellar foundation (right). Figure 4 Preparatory radon piping. An exhaust fan should be installed in case the sealing work is not effective. 246 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 Figure 5 Handling of bitumen felt and seaming of the strips in the corner. 3.4 Tracer-gas studies STUK has carried out tracer-gas studies in houses where preventive measures have been taken. Tracer gas containing 95% of nitrogen and 5% of hydrogen was used. The houses studied were provided with sub-slab piping, and the tracer was led under the slab using a fan which quickened the flow of diluted tracer into piping and sub-slab gravel. The method is very sensitive and finds also leakages of minor importance. The studies showed that the nonseamed bitumen felt strips in corners were leaking. The method does not clearly show the leakage rate and the importance of the finding. However, it shows that the corners should be sealed more carefully by heating the strips and using bitumen glue. The leakage studies also showed that omissions in sealing of the penetrations for electric cables and water pipes were very common. 3.5 Defects in radon piping efficiency The efficiency of radon piping is normally high, typically 70 - 90%, as shown in Figure 1. Use of very coarse crushed masonry materials as filling beneath the floor slab and also beneath foundations has created a new problem. Standard radon piping is no longer capable of creating a good sub-slab vacuum. In a cold climate, the air flow created by the exhaust fan is restricted to the limit of potential substructure and sub-soil temperature problems. This observation emphasizes the need for careful sealing work. 3.6 Summary on prevention The current experience shows the importance of all prevention measures: use of bitumen felt, sealing of penetrations and installation of preparatory radon piping. The key challenge today is the introduction of prevention practices in all building activities and carefulness in sealing work. 247 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 248 Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium Las Vegas NV, September 14-17, 2008. AARST © 2008 References Building Information Ltd. Radon prevention. Building file RT 81-10791. Helsinki 2003. Arvela Hannu ja Reisbacka Heikki. Residential indoor radon mitigation. STUK-A229, Radiation and Nuclear Safety Authority, Helsinki August 2008. Ministry of Environment. Indoor radon mitigation in low rise residential buildings. Sub-slab depressurization. Helsinki 2008. (Autumn 2008) Mitigation publications will be available on website: www.stuk.fi 249