What is Vapor Intrusion?
Vapor intrusion occurs when gases enter buildings or subsurface utilities as a result of the presence of volatile chemicals contained within underlying soil or groundwater. Volatile chemicals are most commonly associated with petroleum fuels or solvents. Spills and leaks of petroleum and chemicals from service stations, dry cleaners, and industrial facilities are the cause of the vast majority of vapor intrusion cases.
Why Should I Be Concerned About This Now?
The USEPA and state environmental agencies have recently begun to place a much greater emphasis on the evaluation of vapor intrusion and its potential effect on indoor air when assessing sites with documented soil and/or groundwater contamination. This increased regulatory emphasis has become yet another hurdle to overcome when performing environmental due diligence during property transfers. The 2021 ASTM standard for conducting Phase I Environmental Site Assessments specifically requires the environmental professional to consider the likelihood of subsurface chemical vapors when evaluating a property. In recent instances, the re-opener clause of regulatory “No Further Action” letters in previously closed soil or groundwater contamination cases have been used by regulators in order to address vapor intrusion concerns.
The regulatory concern is primarily related to human health effects of breathing indoor air impacted by toxic volatile chemicals such as benzene at petroleum sites or tetrachloroethylene (a.k.a. PCE or “Perc”) at dry cleaning sites. The regulatory threshold concentrations established for determining potential health concerns related to breathing of these vapors are often well below those that produce odors noticeable to building inhabitants, so laboratory analyses are necessary to evaluate whether problems exist.
How Is Vapor Intrusion Evaluated and Treated?
The presence or likelihood of vapor intrusion into existing or future structures can be evaluated through the collection and laboratory analysis of sub-slab vapor, soil vapor, or indoor air samples. The samples are collected with vacuum canisters or with passive samplers that contain a vapor absorbing material that traps the contaminants. The samples are then submitted for laboratory testing. Lab data is compared to guidance levels established by the USEPA in order to determine if actual concerns exist at levels that require mitigation.
Vapor intrusion mitigation systems are designed to either: 1) block the pathway of vapors into the building through sub-slab ventilation systems in existing buildings or through the placement of vapor barriers installed prior to construction; or 2) actively eliminate the presence of vapors by removing the source of the contaminants in the underlying soil or groundwater. The method of vapor mitigation selected depends upon numerous site-specific factors.
EnviroSouth’s team of professionals is prepared to assist our clients in the evaluation and/or mitigation of vapor intrusion concerns.
Disclaimer: This sheet has been prepared by EnviroSouth, Inc. for general informational purposes only. The contents of this publication shall not be construed as legal or professional advice. Readers should consult an environmental professional before acting on the provided information.