Environmental Alert: Vapor Intrusion: EPA is Sharpening Its Focus
On December 8, 2016, the U.S. Environmental Protection Agency (EPA) announced that the ranking system designed to assess potential Superfund sites will now include evaluation criteria related to contamination threats posed by vapor intrusion.
Vapor intrusion occurs when a chemical in vapor-form migrates from a subsurface source into an overlying building. Vapor intrusion can result in exposure to harmful levels of hazardous substances to building occupants. Recognition of vapor intrusion as an exposure pathway presenting risk to human health began with concerns over radon in the 1980s. Since then, awareness has increased that contaminants such as petroleum hydrocarbons and chlorinated solvents in soil, groundwater, and sewer lines may pose threats to indoor air quality.
Vapor migration and intrusion has become a growing concern for property owners and prospective purchasers since it may create significant liability and have a material impact on property value. Screening for vapor intrusion has become a component of environmental site assessments conducted in the course of the purchase and sale of real estate. EPA issued its most recent technical guidance for assessing and mitigating vapor intrusion in 2015. Revision of the Superfund site assessment system to include the vapor pathway is a further indication of the importance of the vapor exposure scenario.
EPA assesses potential Superfund sites using the Hazard Ranking System (HRS), which quantifies impacts to air, groundwater, surface water and soil from hazardous substances releases. Sites receiving HRS scores above a specific threshold can be proposed for placement on the National Priorities List (NPL). EPA targets sites on the NPL for further investigation and possible remediation through the Superfund program.
The modification to the HRS announced by EPA does not affect the status of sites currently on or proposed to be added to the NPL. However, this regulatory change may expand the number of sites that will be placed on the NPL going forward.
Although the HRS modification does not apply directly to sites addressed under other federal or state programs, including brownfield cleanup programs, such as Maine's Voluntary Response Action Program (VRAP), it is an indication that analysis of the vapor intrusion pathway from subsurface to overlying buildings will become an increasingly important element of contaminated site investigations and cleanups.