Overview of the Hazard Ranking System

Overview of the Present
limited Slates Hazard Ranking System
Environmental Protection — *
Agency
In 1980, Congress enacted the Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA) establishing the Superfund program to respond to releases and 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. Environmental Protection
Agency (EPA) to assess the relative threat that sites 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). The 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 program is warranted.
This information sheet provides 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, Compensation, 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 1970s. 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 highest 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
the HRS to evaluate 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 direct exposure pathway.
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 procedures needed to respond to releases and threatened releases of hazardous
substances, pollutants, or contaminants. Additionally, CERCLA established EPA's National 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 action is needed to protect human health and the environment affected by
releases from those sites.
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
Superfund resources to be directed to site cleanup. It is not a site-specific risk assessment.

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How Does 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 water 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.
The 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 environments. 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 threats to those living on property with hazardous waste or contaminated soils, and
those living nearby with access to the property. Finally, the 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 hazardous 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. These factors are grouped into three categories:
1.	Likelihood of release/exposure (i.e., likelihood 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
hazardous 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. The HRS score does not represent a specified level
of risk but is a cutoff point that serves as a screening-level indicator 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/superflmd/programs/npl hrs hrsint.htm
•	For information on the National Priorities List, visit http://www.epa.gov/superfiind/sites/npl/
•	For information on Superfund, visit http://www.epa.gov/superfund/index.htm.
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