Last week, we wrote about an audit that MassDEP is conducting of previously closed sites to look for high concentrations of TCE in soils and groundwater. The intent of the audit is to address potential vapor intrusion. The EPA has been paying attention to VI as well, and last Wednesday proposed to add vapor intrusion as a factor to be considered when evaluating the hazards posted by a contaminated site. The rulemaking would make vapor intrusion a component of the Hazard Ranking System (HRS) used to determine if sites are eligible for the Superfund National Priorities List (NPL).
Currently, EPA’s HRS evaluates four exposure pathways: ground water migration, soil exposure, surface water migration, and (outdoor) air migration. EPA’s proposal would restructure the soil exposure pathway and rename it the soil exposure and subsurface intrusion (or SsI) pathway, to include both vapor intrusion and intrusion from contaminated groundwater. Vapor intrusion occurs when volatilized chemicals migrate into structures through cracks in basement slaps, gaps between floors and walls, and space around utility line corridors. Groundwater intrusion might occur when basements flood due to high groundwater levels, leading to contamination of indoor air when contaminants volatilize. Previously, although sites on the NPL might include sites with SsI issues, an SsI pathway alone was not enough to qualify a site for listing in the NPL. EPA’s goal with this proposed revision to the HRS is to facilitate comprehensive remediation of the often extensive subsurface soil and groundwater contamination that is the source of vapor intrusion issues.
EPA has produced a fact sheet on the proposed change. Unlike MassDEP, EPA says it does not intend to “systematically re-evaluate” sites previously deemed not to meet NPL listing criteria under the HRS. However, if new information becomes available for a site or additional sampling is performed due to changing site circumstances, EPA may re-score the site under the new criteria. Once EPA’s proposal is published in the Federal Register, EPA will be taking comment for 60 days.