Hazard Ranking System Scoring. The HRS is a numerical screening system used to prioritize sites for listing on the basis of data from the PA and SI and that is used to decide which sites should be proposed for inclusion on the NPL. Scoring is done using three factors related to risk and four pathways of exposure. The three risk factors are likelihood of release, characteristics of the waste and the people or sensitive environments affected by the release. To determine an HRS score for a site, EPA looks at migration pathways—how contamination moves in the environment. EPA examines four migration pathways: Ground water that may be used for drinking water Surface water (like rivers and lakes) used for drinking water and for plant and animal habitats Soil that people may come in contact with or that can be absorbed lower in the food chain Air that carries contaminants A site can score high on the HRS even if only one pathway score is high. Sites with a preliminary HRS score of 28.50 or greater are eligible for listing on the NPL. EPA may then propose sites that rank high enough on the HRS for listing on the NPL. Each state may also nominate a site for the NPL. Contaminated sites placed on the NPL may require long-term response under the CERCLA Remedial Program. Note that not all sites with a preliminary HRS score of 28.50 or above will be placed on the NPL. HRS scores do not determine the priority for funding of remedial investigations, because the information collected to develop HRS scores is not sufficient to determine either the extent of contamination or the appropriate response (if any) for a site. Moreover, the sites with the highest scores do not necessarily come to EPA’s attention first. EPA relies on more detailed studies in the RI/FS, which typically follows listing. NPL sites may be as small as a few thousand square feet or thousands of acres. Some are complex and highly contaminated, requiring many years to fully study the problem, develop a remedy and complete the cleanup. Once a site is listed on the NPL, the EPA Remedial Program (Figure 2-3) (or the responsible party with oversight by EPA), typically conducts an RI/FS designed to define the extent of contamina- tion, estimate the risk to human health and the environment and evaluate effective remedial alter- natives to address the problem, consistent with the NCP. Federal agencies normally conduct their own RI/FSs at facilities under their jurisdiction, custody or control. A ROD normally is prepared describing the se...
