Vapor Intrusion Proposed For Superfund Hazard Ranking System

U.S. EPA is proposing to amend the ranking system used to assess potential “Superfund” sites to include potential vapor intrusion. The Hazard Ranking System (HRS), required by the Superfund statute, is the primary mechanism used by EPA to assess the relative threat associated with actual or potential releases of hazardous substances. Sites that score 28.50 or greater under the HRS are eligible for inclusion on the National Priorities List (NPL). The NPL is intended primarily to guide the EPA in determining which sites warrant further investigation. A score of 28.50 does not represent a specified level of risk but is a cutoff point that serves as a screening-level indicator of the highest priority releases or threatened releases.

The HRS includes four scoring pathways - ground water, surface water, air and soil exposure. Additional pathways have been identified by EPA as posing significant threats to human health and the environment, and one such pathway is vapor intrusion. Vapor intrusion occurs when contaminants enter into indoor spaces, generally residences, from environmental sources such as contaminated ground water or contaminated soil.

Historically, EPA's Superfund program has responded to vapor intrusion contamination by two mechanisms: (1) through its emergency response program at sites not on the NPL, or (2) through sites placed on the NPL because of other pathway-related risks. In May 2010, the Government Accountability Office (GAO) issued a report that concluded that if vapor intrusion sites are not assessed and, if needed, listed on the NPL, some seriously contaminated hazardous waste sites with unacceptable human exposure may not otherwise be cleaned up. In response, EPA is proposing to add a new HRS pathway so that sites with vapor intrusion contamination can be evaluated for inclusion on the NPL.

EPA initiated rulemaking in January 2011, and current expects final rules to be completed by January 2012.

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