The D.C. Circuit recently held that EPA was not required to consider mitigation measures taken at a site when determining whether to add the site to the National Priorities List (“NPL”) under CERCLA. Meritor, Inc. v. EPA, No. 18-1325, 2020 WL 4299124 (D.C. Cir. July 28, 2020).

In 2016, the U.S. Environmental Protection Agency (“EPA”) conducted a study of indoor air quality at the Rockwell International Wheel & Trim facility (the “Site”), located in Mississippi, and discovered elevated concentrations of toluene, trichloroethylene (“TCE”), and cis-1,2-dichloroethene (“DCE”) in the main building at the Site. In 2017, Meritor, Inc. (“Meritor”), which inherited liability for contamination at the Site, conducted a subsurface investigation beneath the main building and uncovered elevated levels of toluene and TCE. In that same year, Meritor installed a sub-slab depressurization system designed to mitigate the impacts of vapor intrusion in the main building. In 2018, notwithstanding Meritor’s mitigation efforts, EPA added the Site to the NPL based on vapor intrusion impacts.

When determining whether to add a facility to the NPL, EPA applies the complex Hazard Ranking System found at 40 C.F.R. Part 300, Appendix A. To evaluate whether a particular exposure pathway necessitates adding a particular facility to the NPL, EPA weighs the following factors: (1) the likelihood of release, (2) the waste characteristics, and (3) the targets of the exposure. Meritor filed a petition for review before the D.C. Circuit, challenging EPA’s application of the Hazardous Ranking System to the Site.

First, Meritor argued that EPA failed to account for the sub-slab depressurization system. When evaluating the “likelihood of exposure” factor, EPA found that there was an “observed exposure” based on the indoor air exceedances witnessed before the sub-slab depressurization system was installed and therefore assigned the maximum value. The Court held that EPA is not required to consider the effects of remedial measures in determining the likelihood of exposure when there was an observed exposure, as opposed to a potential exposure.

Second, Meritor argued that EPA, when evaluating the “targets” of the exposure, inappropriately relied on a residential health benchmark which assumed that workers in the main building would be exposed 24 hours per day and 350 days per year for 26 years. Meritor pointed out that the Hazard Ranking System directs EPA to select an “appropriate benchmark” and that therefore EPA should have selected an industrial, rather than a residential, health benchmark. The Court, in rejecting this argument, noted that Table 5-20, which sets forth the health-based benchmarks, does not mention site-specific characteristics and that the Hazard Ranking System already accounts for workers’ relatively lower exposure. For example, EPA is directed to divide the number of full-time workers by three and the number of part-time workers by six to account for their relatively lower exposure.

Finally, the Court rejected Meritor’s arguments that EPA miscalculated the “waste characteristics” factor of the vapor intrusion pathway because Meritor had failed to raise those arguments before EPA before filing its petition for review.

The D.C. Circuit’s decision in Meritor v. EPA is a reminder of the “significant deference” afforded to EPA in its NPL listing decisions and that Courts will tend apply the plain language of the listing criteria, even when subsequent remedial measures have been employed to reduce the likelihood of a release at a site.

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