The U.S. EPA has finalized a proposal to expand the hazards that qualify sites for the Superfund National Priorities List (NPL). The U.S. EPA assesses sites using the Hazard Ranking System (HRS), which quantifies negative impacts to air, groundwater, surface water and soil. The U.S. EPA is adding a subsurface intrusion (SsI) component to the Hazard Ranking System (HRS).
In adding the SsI component to the HRS, sites in the U.S. previously not eligible for the Superfund National Priorities List (NPL) based on other exposure or migration pathways may now be eligible after evaluation of the threat posed by intrusion of contaminants into occupied structures from the subsurface. The subsurface intrusion component will add the subsurface intrusion threat evaluation to a restructured and renamed soil exposure and subsurface intrusion pathway. The previous HRS (40 CFR 300, Appendix A), promulgated December 14, 1990, did not consider the threat posed by subsurface intrusion in its evaluation of relative risk posed by a site. In 1990, the available science and sampling methods were not considered sufficient to evaluate subsurface intrusion threats for scoring purposes. Therefore, the previous HRS did not provide a complete assessment of the relative risk that a site may pose to the public.