EPA Issues Long Awaited Updates to its Technical Guidance on Vapor Intrusion
EPA has issued two final guidance documents related to a new human health exposure pathway that is of increasing interest in the environmental arena. The two documents, titled "Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air" and "Technical Guide for Addressing Petroleum Vapor Intrusion at Leaking Underground Storage Tank Sites," provide EPA's current guidance on methods to evaluate and address vapor intrusion - that is, the potential for certain contaminants present in the subsurface to volatilize and migrate upward into residences or other buildings, presenting potential indoor air quality concerns for residents or occupants. EPA's previous draft guidance on this issue dates back to 2002 and did not include the more recent scientific advances in this area.
The first guidance document is applicable to sites that are being evaluated by EPA under CERCLA or RCRA or where EPA Brownfield grants are utilized. It also takes into consideration a wide variety of chemicals in numerous possible settings. The second guidance document primarily addresses releases from leaking petroleum storage tanks sites, such as gasoline stations. Both are likely to be considered by many state regulatory agencies, some of whom do not have any vapor intrusion guidance of their own, and others who refer directly to EPA guidance.
In the documents, EPA has adopted a "multiple lines of evidence" approach to determine whether contaminants have the potential to affect indoor air quality through the presence of a complete exposure pathway. When there is a complete pathway, EPA will determine the need for future action based on the same risk-based approach it uses for setting all cleanup standards, referring remediators to the agency's online "Vapor Intrusion Screening Level" calculator to support the development of site-specific risk-based standards.
Vapor intrusion issues are not confined to new sites or those currently undergoing remediation, and are now frequently being raised during 5-year reviews of completed Superfund remedies if not considered as part of the original remedy. Some state regulatory agencies are also taking a second-look at closed sites to determine whether vapor intrusion is a potential concern that warrants a reopener, and litigation, particularly toxic tort litigation, is also on the rise at these types of sites.
If you have sites that were closed out more than 10 years ago, you may want to consider taking another look at them to determine whether volatile organic compounds were found, and if so, whether there are unaddressed vapor intrusion risks at those sites. Prospective purchasers should also ensure that vapor intrusion issues are evaluated during due diligence, and not rest on the mere fact that the property had previously been closed out.