Last week, EPA added two sites to the National Priorities List (NPL), a list of sites of national priority for known or threatened releases of hazardous substances, solely for the risks posed by vapor intrusion. Vapor intrusion, a topic previously covered on our blog, is the migration of volatile chemicals from soil or groundwater into soil gas and, ultimately, indoor air. These two new NPL sites have vapor intrusion concerns significant enough to, on their own, merit national priority, reflecting the first time EPA has chosen to list sites based solely on this risk.

EPA uses the NPL as a guide for determining which sites warrant further investigation under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as Superfund. EPA uses a Hazard Ranking System (HRS) to assess the potential for sites to pose a threat to human health or the environment. HRS scores have historically been based on other environmental exposure pathways, such as contamination in soil, groundwater, and surface water. But in 2017, EPA added subsurface intrusion as a component of the HRS. This addition allows EPA to consider and score the threat posed by subsurface intrusion in its HRS analysis.

The two newly listed sites are the Rockwell International Wheel & Trim site in Grenada, Mississippi, and the Delfasco Forge site in Grand Prairie, Texas. The Rockwell site is a former chrome plating facility and is currently in use as a metal stamping facility. While EPA identified contamination in other environmental media, such as soil and groundwater, in its HRS analysis, it chose to only score the subsurface intrusion pathway. That score alone was sufficient to result in an NPL listing.

The Delfasco Forge site is a former munitions manufacturing and forge operation. According to EPA, vapor intrusion from this site has resulted in indoor air contamination in the surrounding residential neighborhood. A number of the homes have had systems installed to mitigate vapor intrusion, but EPA still listed this site on the NPL solely for the subsurface intrusion risk.

These listings demonstrate EPA’s continued focus on the Superfund program. Early in his tenure, former Administrator Scott Pruitt signaled his plans to make Superfund a significant agency priority, and it appears that it remains a priority under Acting Administrator Andrew Wheeler. Manufacturers may want to take stock of their current and former facilities to determine whether vapor intrusion may pose a significant risk—either on its own or in combination with risks from other environmental media—to warrant further investigation.

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