IEA Radon_Reporter_April 2025

14 | APRIL 2025 WA MT ME ND SD WY WI ID VT MN OR NH IA MA NE NY PA CT RI NJ IN NV UT CA OH IL DC DE WV MD CO KY KS VA MO AZ OK NC TN TX NM AL MS GA SC AR LA FL MI AK HI VI Guidance Petroleum Hydrocarbons only VIG No VIG VAPOR INTRUSION INTRODUCTION Vapor intrusion (VI) is a potential human exposure pathway where volatile chemicals migrate from soil or groundwater into overlying or nearby buildings. While VI for naturally- occurring radon started being widely addressed relatively quickly after its discovery in the 1980s, VI for volatile organic compounds (VOCs) and other vapor-forming chemicals (e.g., mercury) at contaminated sites has more slowly gotten attention. National guidance has been issued by the USEPA and ITRC, but it has been State agencies that have taken the lead in most jurisdictions. The current state of guidance has been summarized about every five years, including last year (Eklund, et al., 2024). Guidance can take many forms, from comprehensive guidance manuals specific to VI to guidance spread across multiple documents and web pages. Guidance may be specific to a given program (e.g., underground storage tank sites). Some states (e.g., Oklahoma) may have a robust VI oversight program even though they have not formally issued any guidance and, instead, rely primarily on guidance issued by USEPA and/or ITRC. The variety of formats and levels of detail provided by different states pose additional challenges to responsible parties managing sites in multiple regulatory jurisdictions. The number of states with VI guidance has increased from 17 states in 2007 to 35 states in 2012 to 42 states in 2018 and now to 46 states (plus DC). The status of each state is depicted in Figure 1. Statuses continue to change; for example North Dakota issued its first VI guidance document in March 2024. Since the first survey was conducted, there has been some movement towards consensus on certain issues. For example, the use of mathematical modeling to address VI has largely been replaced by reliance on real-world measurements. In addition, states have largely settled upon lateral exclusion distances of 100 ft. for chlorinated solvents and 30 ft. for petroleum hydrocarbons. If buildings fall within those lateral distances of subsurface impacts, further investigation generally is triggered. The distance for State Approaches to Vapor Intrusion FIGURE 1. STATES WITH DRAFT OR FINAL VAPOR INTRUSION GUIDANCE (VIG) OR REGULATION Bart Eklund, Senior Technical Expert, Haley & Aldrich, Inc. Catherine E. Regan, Technical Expert, Haley & Aldrich, Inc. Lila Beckley, Senior Associate Geologist, GSI Environmental Inc.