United States
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Response
Publication 9320.7-01 FS
November 1990
«pPA The Revised Hazard Ranking
System: An Improved Tool for
Screening Superfund Sites
The U.S. Environmental Protection Agency (EPA) has revised the Hazard Ranking System (HRS) in
response to the Superfund Amendments and Reauthorization Act of 1986 (SARA). The HRS is the scoring system
EPA uses to assess the relative threat associated with the release or potential release of hazardous substances from
a waste site. The HRS score is the primary criterion EPA uses to determine whether a site should be placed on
the National Priorities List (NPL). The NPL identifies sites that warrant further investigation to determine if they
pose risks to public health or the environment. Sites on the NPL are eligible for long-term "remedial action"
financed under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA),
as amended by SARA. SARA authorizes a "Hazardous Substances Superfund" totalling $8.5 billion over 5 years
to pay costs not assumed by those responsible for problems at a site. The HRS uses data that can be collected
relatively quickly and inexpensively, thus allowing most Superfund resources to be directed to remedial actions at
sites on the NPL.
Office of Emergency and Remedial Response
Hazardous Site Evaluation Division (OS-230)
Quick Reference Fact Sheet
Original HRS
The original HRS, adopted in 1982,
evaluated the relative threat of a site over five
pathways. The HRS score was based on the
evaluation of the following migration pathways:
ground water, surface water, and air. The two other
pathways, direct contact and fire/explosion, were
evaluated to determine the need for immediate
removal (emergency) action. HRS scores ranged
from 0 to 100. Sites that scored 28.50 and above
on the original HRS were eligible for the NPL.
public. The revised HRS retains the ground water,
surface water, and air pathways, drops the direct
contact and fire/explosion pathways, and adds a
fourth pathway, soil exposure.
Several key provisions of the revised HRS
make it more comprehensive. They:
¦ Evaluate new exposure pathways or
threats that assess direct contact of
people with contaminated soils, and
contamination of the aquatic food chain.
Revised HRS
The revised HRS retains the same cutoff
score and basic approach as the original HRS, while
incorporating SARA requirements as well as
improvements identified as necessary by EPA and the
¦ Expand how toxicity is evaluated,
considering not only acute health effects,
but both carcinogenic and chronic
noncarcinogenic effects.

-------
¦	Increase the sensitive environments
considered from just wetlands and
endangered species to environments
designated by various Federal and
State agencies.
¦	Evaluate the potential for air to be
contaminated and for contaminated
ground water to enter surface water.
Other provisions make the revised HRS
more accurate:
¦	Allow use of concentration data to
determine the quantity of waste at
a site.
¦	Assign higher scores when people
are actually exposed to
contamination than when they are
potentially exposed.
¦	Assign higher scores to potentially
exposed people and sensitive
environments closest to a site, with
scores decreasing as distance from
a site increases.
The complexity and scope of the issues involved in
revising the HRS required EPA to get widespread
input. EPA sought information from a number of
sources such as its Science Advisory Board and, on
three occasions, requested public comment: before
drafting the revisions, after proposing the revisions
in the Federal Register, and after publishing a Field
Test report describing how the revisions scored
actual hazardous waste sites. These procedures
generated over 2,500 comments (from approximately
145 commenters). The majority of the commenters
believed that the revised HRS represented an
improvement over the original HRS. Other
commenters, however, believed that the data required
were too extensive for a screening tool and raised
numerous technical issues. EPA made significant
changes based on these comments, as well as on the
Field Test. The result is a revised HRS that is a
practical and effective tool in identifying the nation's
worst hazardous waste sites.
CERCLA
SITE
ASSESSMENT
PROCESS

-------
THE REVISED HRS...
¦	Adds a fourth pathway, soil exposure, similar to the direct contact
pathway of the original HRS. EPA experience indicates exposure to
contaminated soils or wastes is often important in selecting remedial
action for a site.
¦	Modifies the surface water pathway to:
consider contamination of the aquatic human food chain
consider recreational use
evaluate the potential risk of flooding of the site
add a new ground water to surface water component to permit
scoring of sites where surface water has been contaminated by
ground water.
¦	Modifies the air pathway to include the potential of a site to release
contaminants to the air. In the original HRS, the air pathway was scored
only if an observed release could be documented.
¦	Allows the flexibility to use data on concentrations of hazardous
constituents in wastes, if available, to calculate the hazardous waste
quantity factor. (The original HRS used only the quantity of hazardous
waste as deposited.) A new tiered system uses constituent data, waste
quantity data, volume, and area, providing greater accuracy by allowing
use of the best available data.
¦	Modifies the waste characteristics factor category to multiply the
hazardous waste quantity, toxicity, and other waste characteristics factors,
to make the HRS more consistent with risk assessment principles.
¦	Changes the toxicity factor in all four pathways, basing it not only on
acute toxicity but carcinogenic and chronic noncarcinogenic toxicity as
well.
¦	Adds mobility factors to the ground water and air pathways to evaluate
the ability of specific substances to migrate and reach potential targets.
Mobility, in combination with toxicity, should more accurately assess the
relative risks posed by specific substances.

-------
THE REVISED HRS... (Continued)
¦	More accurately assesses target populations and sensitive
environments by giving greater weight in all pathways to:
those exposed to documented contamination from the site than
those potentially exposed. (The original HRS treated potential
and actual contamination equally.)
and
those exposed to contamination above health-based benchmarks
(for example, Federal drinking water standards) or ecologically-
based benchmarks
¦	Weights target populations and sensitive environments potentially
exposed in the ground water, air, and soil exposure pathways based
on distance, so that the people and environments closest to the site
receive the highest score, with scores decreasing as distance from the
site increases. Dilution weights target populations and sensitive
environments in the surface water pathway.
¦	Increases the number of sensitive environments evaluated and the
weights given them in the surface water, air, and soil exposure
pathways.
¦	Adds specific instructions for scoring radioactive substances.
FOR FURTHER INFORMATION, CONTACT:
Hazardous Site Evaluation Division
Office of Emergency and Remedial Response
Code 0S-230
U.S. Environmental Protection Agency
401 M Street, SW
Washington, DC 20460
or the Superfund Hotline at (800} 424-9346.
(In the Washington, D.C. Metro Area, dial (202) 382-3000.)

-------