EPA Seeks to Add Subsurface Intrusion to CERCLA Hazard Ranking System
The National Priorities List (“NPL”) is EPA’s list of the most contaminated sites in the country that warrant cleanup under the Comprehensive Environmental Response, Compensation and Liability Act of 1980, (“CERCLA” a/k/a “Superfund”). NPL sites usually require extended, extensive and expensive remediation due to the nature of the contamination. To determine if a site should be listed on the NPL, EPA ranks the relative risk of contaminated sites using its Superfund Hazard Ranking System (“HRS”). While rare, when EPA revises the HRS, that change can have a substantial effect on which sites are ranked high enough for inclusion on the NPL. EPA has just proposed such a change by adding subsurface intrusion as a component of the HRS contaminated soil exposure pathway.
Subsurface intrusion (“SI”) typically involves the direct transmission of hazardous substances into a structure, usually through at-grade or below-grade floors and/or through below-grade walls. SI exists in two main forms: vapor intrusion and groundwater intrusion. The concerns presented are largely human health-related, whether by inhalation of volatile compounds entering the structure or by direct contact with contaminated groundwater or residual contaminants left after intruding groundwater evaporates or recedes.
The HRS considers four exposure pathways: groundwater, surface water, air and soil. The HRS has never considered SI separate and apart from these four pathways. The proposed regulation would change that by folding SI risk into the soil exposure pathway – to be renamed the soil exposure and subsurface intrusion pathway – and not change the other existing pathway factors. This change may cause some sites that otherwise would not rank high enough to now be considered for inclusion on the NPL. Due to the nuances of the HRS calculation, this is true even for sites with only a single SI-related soil exposure pathway. EPA says that sites currently listed or proposed to be listed on the NPL would be unaffected by the proposed regulation.
To justify its proposed action, EPA says there has been inconsistent treatment of SI by the states in evaluating site risk. It sees this revision as a model for states to use in their cleanup programs and as something that may lead to a more consistent nationwide approach to SI risk. EPA also believes that hazardous waste regulatory programs under the Resources Conservation and Recovery Act and brownfields program do not always have sufficient legal authority to address all SI risks, especially where SI is the only key exposure pathway. Further, in EPA’s thinking, SI mitigation measures, such as vapor extraction systems, do not necessarily further CERLA’s goal of remediation of “uncontrolled hazardous waste sites” even though they may protect human health. It is also noteworthy that this proposal comes on the heels of revised EPA guidance issued last summer that addresses risk assessment for vapor intrusion.
Clearly, EPA is pressing forward with a more focused and deliberate effort to address SI for NPL ranking and related coordinated federal oversight. Though EPA downplays the scope of the proposed addition of SI into the HRS, the ripple effects of this proposal may be felt more broadly in state brownfield and voluntary remediation programs. Whether contaminated facilities with SI concerns will now face greater scrutiny before being allowed to enroll in these programs is unclear. Regardless, the proposed regulation may create practical hurdles, if not regulatory ones, for property owners and operators if site project delays result from additional HRS consideration. Comments on the proposed regulation must be filed with EPA by April 29, 2016.