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GWERD 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.
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. 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. 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.
- 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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