Seyfarth Synopsis: Under the Trump Administration, the U.S. Environmental Protection Agency (EPA) has fully or partially deleted 22 sites from the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL). This is the largest number of deletions in one year since 2005.

However, the EPA continues to add sites to the NPL, and added five new sites in the Fall of 2018. Two sites are particularly noteworthy as they were added solely due to a subsurface intrusion pathway. Subsurface intrusion is the migration of hazardous substances or pollutants and contaminants from the unsaturated groundwater zone and/or the surficial groundwater into overlying structures. Vapor intrusion is the most common form of subsurface intrusion, but the intrusion also may be in the form of gas or liquid.

The HRS, the principal mechanism EPA uses to determine whether a site should be placed on the NPL, traditionally ranked sites under four pathways: groundwater migration, surface water migration, soil exposure and air migration. In other words, subsurface intrusion historically was not a separate basis for scoring purposes on the HRS, but was instead addressed as part of the remediation of a Superfund site. On January 9, 2017, the rule to add subsurface intrusion as a component to the HRS was published in the Federal Register, and the final rule went into effect on May 22, 2017. See our previous blog about it, EPA Eases Path to Superfund Listing: Vapor Intrusion Component Added to the Hazardous Ranking System.

The first of the two sites listed under the new HRS guidance, the Rockwell International Wheel & Trim site in Mississippi, was a former wheel cover and chrome-plating facility. Although other traditional pathways were present, including soil and groundwater impacts from volatile organic compounds (VOCs), the EPA elected to score the site under the HRS only on the subsurface intrusion component. The EPA determined that there was likely a complete pathway from the subsurface source of VOCs to workers in buildings overlying the soil and groundwater impacts. This assumption was confirmed by indoor air sampling that revealed the presence of trichloroethylene and dichloroethylene in air in the buildings.

The second site, the Delfasco Forge site in Grand Prairie, Texas, is the location of a former munitions and forger operation that operated from the 1950s to 1998. The site is contaminated with trichloroethylene (TCE) both in soil, and groundwater. In 2008, EPA conducted a vapor intrusion investigation that included the sampling of sub-slabs, crawl spaces and indoor air of 16 homes and two commercial structures. Ten of the 18 structures had measurable levels of TCE in indoor air.