For more than two decades, the Environmental Protection Agency (EPA) has considered four exposure pathways in determining whether to list contaminated sites on the Superfund National Priorities List: groundwater, surface water, soil and air. In a Federal Register notice published on January 31 2011, the EPA solicited public comment on the potential addition of a fifth pathway: soil vapour intrusion.

The migration of vapours from sub-surface contamination into overlying buildings, known as vapour intrusion, is a growing concern for federal and state environmental regulators. Vapour intrusion is most common at sites with elevated levels of volatile organic compounds – including chlorinated solvents and sometimes gasoline – which enter indoor air through openings around sewer lines, cracks in a building's foundation or basement, or other preferential pathways.

Under the federal Superfund law, the EPA screens contaminated sites for listing on the National Priorities List through its Hazard Ranking System, assigning each site a score based on its perceived threat to human health and the environment. The risk of vapour intrusion, however, does not currently factor into this determination. A May 2010 Government Accountability Office report found that, given the EPA's inability to designate National Priorities List sites on the basis of vapour intrusion, "[s]tates may be left to remediate those sites without federal assistance, and given states' constrained budgets, some states may not have the ability to clean up these sites on their own".

Until April 16 2011, the EPA will now be collecting public comment on the potential revision of the Hazard Ranking System to account for vapour intrusion. It plans to hold three public listening sessions on the topic. While it has not proposed specific regulatory changes at this point, the EPA "will consider the information gathered from this Notice, listening sessions, and other sources before making a decision to issue a proposed rulemaking to add subsurface contaminant intrusion" to the Hazard Ranking System.

The EPA is also in the process of revising its draft guidance for the evaluation of vapour intrusion risks, which was initially released in 2002 but has yet to be finalised. The EPA outlined a number of likely changes to that document last October and plans to issue updated guidance by November 2012.

Finally, the New York State Department of Environmental Conservation is continuing to re-evaluate vapour intrusion pathways and has reopened several sites that had already been remediated and delisted to require additional monitoring or mitigation measures.

For further information on this topic please contact Christine Leas, Jeffrey Gracer or Michael Bogin at Sive Paget & Riesel PC by telephone (+1 212 421 2150), fax (+1 212 421 2035) or email (, or

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