Hazardous and Solid Waste

The Inside Scoop on Vapor Intrusion

The EPA suggests that the guides be used to help identify and consider key factors related to VI assessments, risk management decisions, and mitigation. Vapor intrusion is also of particular concern to property owners, municipalities, and real estate developers, especially those involved in revitalization of a perceived brownfield.

Note. While the recommendations in these guides are not, at this point, mandatory, the implications for future liability are important considerations for future development and for past closure actions.

What is vapor intrusion?

Vapor intrusion occurs when contaminants spilled on the ground migrate to the subsurface soils and/or groundwater, move around in the subsurface environment, and eventually enter buildings as a gas or vapor via cracks in the basement or foundation and sewer lines. If the vapors accumulate, residents or workers in the buildings can be at risk.


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Vapor intrusion guide for subsurface soils and groundwater

EPA’s new guide for vapor intrusion from subsurface soils and groundwater provides information on determining if a vapor intrusion pathway is complete, meaning there is an opportunity for human exposure, and if a response action should be taken. If health risks are unacceptable, the guide says that a response action would typically include a combination of:

  • Remediation to reduce or eliminate subsurface vapor sources.
  • Engineered exposure controls for specific buildings to reduce VI or reduce concentrations of vapor-forming chemicals that have already entered the building.
  • Monitoring to assess and verify the performance and effectiveness of the remediation systems and engineered exposure controls.
  • Institutional controls to restrict land use and/or to alert parties (e.g., prospective developers, owners, and municipalities) of the presence of subsurface sources of vapor-forming chemicals and to foster operation, maintenance, and monitoring of the remediation systems and engineered exposure controls.

The guide also includes recommendations on planning, scoping, and conducting investigations; data evaluation and decision making; documentation; community outreach; and other administrative and engineering actions that constitute an effective response.


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Vapor intrusion at LUSTs

EPA’s new guide for vapor intrusion fromLUSTs focuses on “petroleum vapor intrusion” (PVI), defined as the intrusion of vapors from subsurface petroleum hydrocarbons (PHCs) and non-PHC fuel additives into overlying or nearby buildings or structures.  While the guide is based on assessments of “typical underground storage tank (UST) sites,” the EPA says it may also be helpful when addressing petroleum contamination at comparable non-UST sites.

It is important to note that this guide applies to new and existing releases of PHCs and non-PHC fuel additives from leaking USTs and to previously closed sites where there is reason to suspect that there may be potential for PVI.

According to the EPA, petroleum contamination at sites that are not comparable to UST sites—such as refineries, petrochemical plants, terminals, aboveground storage tank farms, pipelines, and large-scale fueling and storage operations at federal facilities—should be assessed under the more general technical guide for subsurface soils and groundwater.

Recommended actions described in the LUST guide include:

  • Assessment and mitigation of immediate threats to safety;
  • Site characterization and development of a conceptual site model;
  • Delineating a lateral inclusion zone;
  • Evaluating the vapor source and attenuation of PHC vapors; and
  • Interrupting the pathway.