EPA Issues New Vapor Intrusion Guidance
On April 16, the U.S. Environmental Protection Agency ("EPA") released two new draft vapor intrusion guidance documents for public comment. The two documents can be found here and here. The new guidance replaces EPA's draft 2002 policy and sets out significantly expanded investigation and remediation requirements.
"Vapor intrusion" is the general term given to the migration of hazardous gases from subsurface sources, such as contaminated soil or groundwater, into buildings. Vapor intrusion can occur in residential, commercial, and industrial buildings with any foundation type, including basements, crawlspaces, or slabs. The draft EPA guidance focuses on the risk to the health of the occupants, including residents, workers, and visitors in those buildings. EPA has designated vapor intrusion as a potentially significant cause of human exposure to "volatile" (i.e., vapor-forming) hazardous chemicals in indoor spaces. The exposure route of general interest for vapor intrusion is inhalation.
Scope of the New Guidance
The guidance applies to the investigation and remediation at Superfund and Resource Conservation and Recovery Act ("RCRA") sites to address vapor migration into on-site buildings and neighboring structures. Pursuant to the guidance, consideration of the potential for human health risk from vapor intrusion will be evaluated throughout the cleanup process, including the initial site assessment, site investigation, interim response actions, final cleanup actions, and periodic reviews of the selected cleanup plan. The guidance sets out new toxicity values, additional measures for preemptive action, and mitigation system standards. The companion guidance document sets out similar requirements for addressing vapor intrusion associated with petroleum hydrocarbons released from underground tanks.
Complete Pathways, Investigation, Mitigation, and Remediation
According to the EPA guidance, three conditions must exist for hazardous vapors to reach the interior of buildings from the subsurface environment underneath or near a building. First, a source of hazardous vapors must be present in the soil or in groundwater underneath or near a building. Second, vapors must form and have a pathway along which to migrate toward the building. Third, entry routes must exist for the vapors to enter the building, and driving forces must exist to draw the vapors into the building. If these three conditions are present, the vapor intrusion pathway is referred to as "complete." EPA recommends collecting, evaluating, and weighing multiple lines of data to characterize a complete vapor intrusion pathway. Addressing the potential vapor intrusion may be accomplished by removing the contamination or by engineered exposure controls for mitigating vapor intrusion into buildings, as set out in the guidance.
The new guidance will affect ongoing investigation and remedial considerations at many of the country's current Superfund sites. In addition, it is expected that the guidance will prompt EPA to require additional soil and groundwater cleanup at sites where remediation has already been considered complete, as part of the Agency's Five Year Reviews of these sites. One of the more burdensome aspects of the guidance is EPA's recommendation that vapor intrusion risks be evaluated for "reasonably expected future land use conditions including new building construction and new uses and occupants for the uninhabited buildings," thus requiring the need to address potential vapor intrusion at almost any site. An additional consideration is the development of the specific information characterizing the nature and extent of the source, the potential pathways, human health exposure, and risk data that could be used as evidence in legal actions by occupants of the buildings.
Comments on the draft guidance are due May 24, 2013.
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Heidi H. Bumpers
Kevin P. Holewinski
John A. Rego
Charles T. Wehland
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