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# Overview of the Present Hazard Ranking System

In 1980, Congress enacted the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) establishing the Superfund program to respond to releases an d threatened releases of hazardous substances. CERCLA Section 105 required the U.S. Environmental Protection Agency ( EPA ) to establish criteria for determining priorities among releases or threatened releases of hazardous substances for the purpose of taking remedial action. To meet this requirement, EPA developed the Hazard Ranking System ( HRS ) (47 FR 31180, July 16, 1982) to evaluate sites for the National Priorities List (NPL).

The Hazard Ranking System (HRS) is a screening tool used by the U.S. Enviro nmental Protection Agency (EPA) to assess the relative threat that site s with actual or potential contaminant releases pose to human health or the environment

. The HRS is the primary mechanism EPA uses to place a site on the National Priorities List (NPL)

. Th e sites on the NPL are then further investigated to determine the extent of the threat and whether cleanup of the site under EPA’s Superfund Remedial pro gram is warranted

. Th is information sheet provide s background information on the legal basis for the HRS and a general overview of the HRS evaluation process. 

## What is the Basis for the Hazard Ranking System? The Comprehensive Environmental Response, Compensati on, and Liability Act (CERCLA) , commonly known as Superfund, was passed by Congress in 1980 and amended by the Superfund Amendments and Reauthorization Act (SARA) in 1986

. This law was enacted in response to serious environmental and public health concerns regarding uncontrolled hazardous waste sites, such as Love Canal and Times Beach in the 19 70s. SARA authorized EPA to clean up such sites and to require responsible parties to perform cleanups or reimburse the government for cleanups conducted by EPA. CERCLA, as amended by SARA, required EPA to establish a mechanism for identifying the highes t priority sites – those posing the most immediate and serious potential threats to human health or the environment – and identified criteria that needed to be followed when developing this mechanism. Based on the criteria, EPA created
t he HRS to evaluat e the relative threat of sites with known or potential contaminant releases. The HRS was promulgated in 1982 (47 FR 31180 ) and included three scoring pathways - ground water, surface water, and air. The HRS was amended in 1990 (55 FR 51532 ) to include a di rect exposure pathwa y.

CERCLA also enabled the revision of the National Oil and Hazardous Substances Pollution Contingency Plan, or National Contingency Plan (NCP), which is the regulation that implements CERCLA. The NCP provides the guidelines and proc edures needed to respond to releases and threatened releases of hazardous substances, pollutan ts, or contaminants. Additionally, CERCLA established EPA's N ational Priorities List , which is a list of contaminated sites identified to have known releases or threatened releases of hazardous substances, pollutants, or contaminants throughout the United States and its territories

. The NPL is intended primarily to guide EPA in determining which sites warrant further investigation to ascertain whether remedial act ion is needed to protect human health and the environment affected by releases from those sites

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The HRS is the principal mechanism EPA uses to place hazardous waste sites on the NPL

. It is a numerically based screening system that uses information from initial, limited investigations to assess the relative potential threat that sites pose to human health or the environment due to contaminant releases. The HRS uses data that can be collected relatively quickly and inexpensively, thus allowing most Super fund resources to be directed to site cleanup. It is not a site

- specific risk assessment

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## How D oes the Hazard Ranking System Work?
The HRS score is based on an evaluation of up to four separate pathways: ground water migration , soil exposure, surface wate r migration, and air migration

. Pathways are routes by which exposure to contaminant releases affecting human health or sensitive environments can occur. The ground water migration pathway evaluates the likelihood that hazardous substances will travel through the ground below and contaminate aquifers and drinking water wells that draw on those aquifers. T he surface water migration pathway evaluates the likelihood that hazardous substances can enter surface water and affect people or the environment. Threats to humans from this pathway include drinking water
, the human food chain (i.e.

, contaminants build up in the aquatic organisms that humans in turn consume), and sensitive environment s. The soil exposure pathway evaluates the potential threats to humans and terrestrial environments posed by direct, physical contact with hazardous waste or contaminated soil. This pathway includes threat s to those living on property with hazardous waste or contaminated soils, and those living nearby with access to the prop erty. Finally, t he air migration pathway evaluates the likelihood of release of hazardous substances into the atmosphere and how many people and sensitive environments could be exposed to hazardou s substances carried in the air, including gases and particulates.

The scoring system for each pathway is based on a number of individual factors associated with risk

related conditions at the site. The se factors are grouped into three categories :
1. Likelihood of release/ exposure (i.e., like li hood that a site has released or has the potential to release hazardous substances into the environment , or that targets can come into contact with hazardous substances )

2. Waste characteristics (i.e., inherent toxicity, mobility of the substances and the quantity of the hazar do us substances that has been released )

3. Targets (i.e. , people or sensitive environments actually or potentially exposed to the release )

The HRS site score, which ranges from 0 to 100, is obtained by combining the pathway scores. A site may be scored for one or more of the pathways depending on the nature of the release. Any site scoring 28.50 or greater is eligible for placement on the NPL. Th e HRS score does not represent a specified level of risk but is a cutoff point that serves as a screening

- level i ndicator of the highest priority hazardous releases or potential releases based on the criteria identified in SARA.



## For More Information

**•** For information on the HRS, visit http://www. epa.gov/superfund/programs/npl_hrs/hrsint.htm

**•** F or information on the National Priorities List, visit http://www.epa.gov/superfund/sites/npl/

**•** F or information on Superfund, visit http://www.epa.gov/superfund/index.htm

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