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Research on Vapor Intrusion
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Vapor intrusion is defined as vapor phase migration of volatile organic and/or inorganic compounds into occupied buildings from underlying contaminated ground water and/or soil. Until recently, this transport pathway was not routinely considered in RCRA, CERCLA, or UST investigations. Therefore the number of buildings or homes where vapor intrusion has occurred or is occurring is undefined. However, considering the vast number of current and former industrial, commercial, and waste processing facilities in the United States capable of causing volatile organic or inorganic ground-water or soil contamination, contaminant exposure via vapor intrusion could pose a significant risk to the public. Also, consideration of this transport pathway may necessitate review of remedial decisions at RCRA and CERCLA sites as well as implementation of risk-reduction technologies at Brownsfield sites where future development and subsequent potential exposure may occur.
EPA's Office of Solid Waste and Emergency Response (OSWER) recently (2002) developed guidance to facilitate assessment of vapor intrusion at sites regulated by RCRA and CERCLA where halogenated organic compounds constitute the bulk of risk to human health. EPA's Office of Underground Storage Tanks (OUST) is considering modifying the guidance to include underground storage tank sites where petroleum compounds primarily determine risk and biodegradation in subsurface media can be a dominant fate process. EPA's Office of Research and Development (ORD), specifically, the National Risk Management Research Laboratory (NRMRL) and National Exposure Research Laboratory (NERL) is conducting research and providing technical assistance to EPA program offices, regional offices, and States in the area of vapor intrusion. The following bullets highlight recent accomplishments and areas of research.
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Program Support
- NRMRL and NERL were substantially involved in development of the OSWER guidance. ORD wrote several portions of the guidance pertaining to site characterization and modeling in addition to attending critical meetings, participating in numerous conference calls, and reviewing many drafts of the guidance. ORD's also identified potential deficiencies in the guidance and research necessary to rectify problem areas.
- NRMRL is providing site-specific technical assistance to EPA regional offices and States on vapor intrusion. Site-specific technical assistance has involved document review, attendance at meetings, and formulation of written comments.
- NRMRL funded, organized, and participated in 3 national symposiums and two internet short courses on vapor intrusion. In these symposiums and courses, ORD helped explain the guidance, the science behind vapor intrusion, and need for further research. ORD plans to teach 3 additional courses in 2004.
Research
- NRMRL/GWERD is investigating bias associated with methods commonly used for ground-water sampling (PDF) (1 pg, 503K). Knowledge of the areal and vertical extent of ground-water contamination is helpful in selecting locations for indoor sampling. Ground-water sampling methods typically used by practitioners result in loss of volatile organic compounds (VOCs) and provide little information on the vertical profile of contamination.
- NRMRL/GWERD is investigating bias (loss of VOCs) associated with methods commonly used for soil-gas sampling (PDF) (1 pg, 83K). The reasons for soil-gas sample collection are similar to ground-water sample collection. However, soil-gas sampling can be accomplished at a fraction of the cost of ground-water sampling and much closer to a potentially impacted building thereby minimizing concern over interpolation/extrapolation of data.
- NRMRL/GWERD is currently developing a protocol and supporting data interpretation techniques for sub-slab sampling (PDF) (1 pg, 178K). When used with outdoor air, indoor air, and ground-water or soil-gas measurement, sub-slab sampling provides definitive information necessary to elucidate the source of VOCs in indoor air.
- NERL plans to evaluate the behavior of models used for assessment of vapor intrusion given uncertainty concerning measured inputs and estimated parameters. Mathematical modeling plays a dominant role in decision making in the guidance.
- NRMRL/GWERD is developing a protocol and supporting mathematical modeling to assess gas permeability in sub-slab materials. This will improve the design of sub-slab depressurization systems to mitigate the impact of vapor intrusion.
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EPA/600/R-05/147 March 2006
Assessment of Vapor Intrusion in Homes Near the Raymark Superfund Site Using Basement and Sub-Slab Air Samples.
Document in Sections (PDF) - Full Document (PDF) (131 pp, 7.8MB) - Abstract
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EPA/600/R-06/111 November 2006
Comparison of Geoprobe® PRT and AMS GVP Soil-Gas Sampling Systems with Dedicated Vapor Probes in Sandy Soils at the Raymark Superfund Site
Document in Sections (PDF) - Full Document (PDF) (79 pp, 4.7MB) - Abstract