Section 105(a)(8)(B) of CERCLA sets forth the outlines of the scoring system used by the U.S. Environmental Protection Agency (the “EPA”) Superfund program to assess and rank the potential and actual threat associated with sites across the country. The scoring system is known as the Hazard Ranking System (the “HRS”). The HRS was originally adopted in 1982, but was subsequently amended in 1990 in response to the Superfund Amendments and Reauthorization Act.
The HRS groups information obtained by EPA from its Preliminary Assessment and Site Inspection into four predetermined categories or “pathways.” The pathways include: (1) groundwater migration; (2) soil exposure; (3) surface water migration; and (4) air migration. EPA then weighs the four pathways against three individual factors grouped into three categories: (1) the likelihood of a release; (2) waste characteristics; and (3) “targets” or nearby human population and sensitive environments. EPA next assigns numeric values to each pathways and plugs the numbers into a magic formula that spits out a score ranging from 0 to 100. Any site that receives a score of 28.50 or above must be placed on the list of sites that require the most urgent attention, known as the National Priorities List (the “NPL”). Since 1991, EPA has added, on average 30 sites to the NPL each year. That number, however, may begin to rise soon.