IEA Radon_Reporter_April 2025

16 | APRIL 2025 VAPOR INTRUSION membrane termination construction (typically per manufacturers recommendations) and/or post-installation quality control testing (i.e., smoke testing) and documentation. Active VI mitigation systems allow soil gas to be vented to the atmosphere. Mitigation systems installed at a given building are often not considered ‘remediation’ systems and states take various positions on if these emissions are significant and should be permitted or if they are de-minimis and/or should be exempt. Guidance on VI mitigation air emissions is often difficult to assess as emission regulations may fall under a separate state division or program. Fifteen states include information or references on emission rate thresholds (e.g., pounds VOCs/day, tons VOCs/year, etc.) that may trigger emission controls and/or permitting. Although some states note that most residential and small commercial systems are unlikely to need emission controls, only 3 states (Michigan, New Jersey, and New York) specifically note that either mitigation systems are exempt or specifically that systems at single family homes or other small residential buildings are exempt. Most states that address mitigation do provide references to documents that can be used to support mitigation design. These documents typically include reference to the 2020 ITRC VI Mitigation Guidance Documents (ITRC, 2020), and several standard guides published and frequently updated by the Indoor Environments Association (formerly American Association of Radon Scientists and Technologists [AARST]) (AARST, 2023a, 2023b, 2023c, 2023d) and/or ASTM (ASTM, 2021a, 2021b). Some states also reference other state’s guidance documents as additional resources for mitigation design. Lastly, mitigation guidance often specifies that designs be completed by experienced professionals. Seventeen states either want to approve proposed designs via state review or want responsible parties to work with experienced professional mitigators. Only seven of these states specifically look for designs to be stamped by professional engineers. TABLE 1. RESIDENTIAL SCREENING LEVEL MINIMUMS AND MAXIMUMS FOR SELECTED VOCS State BENZENE TCE PCE Ground Water Shallow Soil Gas Indoor Air Ground Water Shallow Soil Gas Indoor Air Ground Water Shallow Soil Gas Indoor Air Cal. – DTSC [0.42] [3.2] 0.097 [1.2] [16] [0.48] [0.64] [15] 0.46 Cal. - RWQCB 0.42 3.2 0.097 1.2 16 0.48 0.64 15 0.46 Iowa 1,540 600,000 39.2 -- -- -- -- -- -- Michigan 1.0 110 3.3 0.073 67 2.0 1.5 1,400 41 Missouri 1,000 190,000 4.98 1,600 546,000 12.8 338 200,000 4.27 New Hampshire 2,900 170 3.3 20 20 0.4 240 400 8 New York -- -- -- -- 6 0.2 -- 100 3 Oregon 210 72 0.36 200 95 0.47 3,700 2,200 11 Texas -- -- 11 -- -- 2.1 -- -- 64 Vermont 0.92 4.3 0.13 0.82 6.7 0.2 1.5 21 0.63 Range of Values 6,900x 190,000x 400x 22,000x 91,000x 64x 5,800x 13,000x 140x Notes: (1) Units are μg/L for groundwater and μg/m3 for soil gas and indoor air. (2) The most conservative (i.e., lowest) screening value is shown for each category. See individual state guidance documents for additional information, including limitations and exceptions. (3) Values in brackets are inferred from the guidance but are not found directly in the published guidance. (4) Highest and lowest values for each chemical are color coded. REFERENCES American Association of Radon Scientists and Technologists (AARST). 2023a. Soil Gas Mitigation Standards for Existing Homes. SGM-SF-2023. AARST. 2023b. Soil Gas Mitigation Standards for Existing Multifamily, School, Commercial and Mixed-Use Buildings. SGM-MFLB-2023 AARST. 2023c. Reducing Radon in New Construction of 1 & 2 Family Dwellings and Townhouses - Rev. 5/23. CCAH-2020-0523 AARST. 2024d. Soil Gas Control Systems in New Construction of Multifamily, School, Commercial and Mixed-Use Buildings - Rev. 5/23. CC-1000-2018-0523 ASTM. 2021a. ASTM E2121-21, Standard Practice for Installing Radon Mitigation Systems in Existing Low-Rise Residential Buildings. ASTM. 2021b. ASTM D8408/D8408M-21 Standard Guide for Development of Long-Term Monitoring Plans for Vapor Mitigation Systems Eklund, B., C. Regan, R. Rago, and L. Beckley. 2024. Overview of State Approaches to Vapor Intrusion: 2023. Groundwater Monitoring & Remediation, 44, no. 3 , pp.76-93. Summer 2024. ITRC. Vapor Intrusion Mitigation (VIM) . December 2020. Website accessed on January 6, 2025 at: vim (itrcweb.org )