United States	Office of
Environmental Protection Solid Waste and	Publication 9320.7-02FS
Agency	Emergency Respose	November 1990
&EPA The Revised Hazard
Ranking System:
Qs and As
Office of Emergency and Remedial Response	Quick Reference Fact Sheet
Hazardous Site Evaluation Division (OS-230)
The U.S. Environmental Protection Agency (EPA) revised the Hazard Ranking System (HRS) in response to
the Superfund Amendments and Reauthorization Act (SARA). These revised HRS Qs and As address the SARA
requirements for the revised HRS, specific revisions to the HRS, the impact of the revised HRS on the site
assessment and remedial processes, and selection of the cutoff score.
General
What is the Hazard Ranking System?
The Hazard Ranking System (HRS) is a scoring
system the U.S. Environmental Protection Agency
(EPA) uses to evaluate relative risks to human
health and the environment posed by uncontrolled
hazardous waste sites. The HRS was originally
adopted in 1982 to meet the requirements of the
Comprehensive Environmental Response, Compen-
sation, and Liability Act of 1980 (CERCLA), com-
monly known as Superfund. The HRS is designed to
be a simple, numerically-based scoring system that
uses information obtained from the initial, limited
investigations conducted at a site ~ the preliminary
assessment and the site inspection. Using this infor-
mation, the HRS assigns each site a score ranging
from 0 to 100 based on:
•	The likelihood that a site has released or
has the potential to release contaminants
into the environment.
•	The characteristics of the waste (toxicity
and waste quantity).
•	The people or sensitive environments af-
fected by the release.
How does EPA use the HRS?
EPA uses the HRS as a screening mechanism to
determine whether a site should be placed on the
National Priorities List (NPL). Sites receiving HRS
scores of 28.50 and above are eligible for the NPL.
What is the purpose of the NPL?
The NPL informs the public of sites that EPA has de-
cided require further detailed investigations. These
investigations determine whether the sites represent
a long-term threat to public health or the environ-
ment and, therefore, need remedial action. A site
must be on the NPL to undergo remedial action
financed by CERCLA's Trust Fund. Remedial ac-
tion may involve activities such as containment,
treatment, and disposal of wastes that will bring site
conditions to the point that human health and the
environment are protected.
How does the HRS relate to the National
Contingency Plan (NCP)?
The HRS is Appendix A to the NCP (40 CFR Part
300). The HRS is the mechanism used to evaluate
whether releases should be on the NPL. Sites on the
NPL undergo further investigation and remedial
action if necessary, according to the NCP.
In the near future, tha'Supwfund program wilt fttuo
othar Faot $hMte on technical and policy Isauai that
may aria* during tha Implantation of tha rovfaad
HRS.

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SARA Requirements
Why wasn't the revised HRS completed
by April 1988, as suggested by SARA?
The complexity and scope of the issues involved in
revising the HRS required EPA to get widespread
input to provide a broad spectrum of technical and
policy expertise. EPA sought information from a
number of sources such as EPA's Science Advisory
Board and the public. On three separate occasions,
EPA requested public comment on the revisions, to
permit consideration of public input at various stages
in the development of the revised HRS. The Advance
Notice of Proposed Rulemaking (52 FR 11513, April
9, 1987) gave the public the opportunity to partici-
pate in the design of the revisions. The Proposed
Rule (53 FR 51962, December 23, 1988) requested
comment and input on the proposed revisions. Finally,
the Availability Notice for the Field Test Report on
the HRS Proposed Revisions (54 FR 37949, Septem-
ber 14, 1989) gave the public the opportunity to
reevaluate the proposed rule against its perform-
ance in the field test. EPA received over 2,500
comments (from approximately 145 commenters).
The analysis and careful consideration required to
evaluate all these inputs contributed to the delay in
meeting the SARA-suggested deadline. The Agency
feels, however, that the delay was necessary to satisfy
the SARA requirements in developing a regulation
of such significance.
What specific revisions does SARA re-
quire?
Section 105 requires:
•	EPA to amend the HRS to assure "to the
maximum extent feasible, that the Hazard
Ranking System accurately assesses the
relative degree of risk to human health and
the environment, posed by sites and facili-
ties subject to review."
•	The HRS to assess human health risks
associated with contamination or potential
contamination of surface waters, either
directly or as a result of runoff, taking into
account the use of these waters for recrea-
tion and the potential migration of any
contaminant through surface water to
downstream sources of drinking water.
•	The HRS to take into account:
•	Damage to natural resources that
may affect the aquatic human food
chain.
•	Contamination or potential con-
tamination of ambient air.
Section 118 requires EPA to:
•	Give a high priority to sites where contami-
nation has resulted in the closing of drink-
ing water wells, or has contaminated a prin-
cipal drinking water supply.
Section 125 requires EPA to:
•	Revise the HRS to assure appropriate con-
sideration of sites that contain substantial
volumes of fly ash and other wastes gener-
ated primarily by combustion of coal or
other fossil fuels. The assessment must
consider:
•	Quantity, toxicity, and concentra-
tions of hazardous constituents
present in such wastes.
•	Extent of, and potential for, release
of such constituents into the envi-
ronment.
•	Degree of risk to human health and
the environment posed by such con-
stituents.
Specific Revisions
Is the revised HRS a risk assessment?
No. As required by CERCLA, EPA's Superfund
program focuses its resources on the highest prior-
ity sites. Consequently, initial studies like prelimi-
nary assessments (PAs) and site inspections (Sis)
are modest in scope and performed on a large
number of sites. This has placed certain constraints
on the HRS.
While not a risk assessment, the HRS does pro-
vide a measure of relative risk among the universe of
potential NPL sites. The HRS is used as a screening
tool to identify those sites that represent the highest
priority for further investigation and possible cleanup
2 The Revised HRS: Qs and As

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under CERCLA. Its purpose is not to fully charac-
terize the source and the extent of the contamina-
tion. Rather, its purpose is to evaluate the potential
of uncontrolled hazardous substances to cause damage
to human health or to the environment. Uniform
application of the HRS nationwide enables EPA to
evaluate sites relative to each other with respect to
actual or potential hazards.
EPA uses risk assessments to provide a better
overall indication of potential threats. Such evalu-
ations are performed on NPL sites during the reme-
dial phase of the Superfund program. This evalu-
ation serves to characterize the actual threat posed
by the site in order to plan the appropriate remedial
action to be undertaken at the site.
How extensive are the revisions in the
HRS?
In general, it is fair to say that every factor has
been revised in some way. Some of the most impor-
tant changes are:
•	A fourth pathway, the soil exposure path-
way (named onsite exposure in the pro-
posed HRS), has been added to address
direct contact problems.
•	The food chain threat has been added to the
surface water pathway.
•	Extra emphasis is placed on those sites that
result in actual human exposure, as op-
posed to potential exposure.
•	The toxicity factors have been revised to
include consideration of chronic noncarcino-
genic, carcinogenic, and acute effects. (The
original HRS considered only acute toxic-
ity.)
•	Targets are now weighted according to their
distance from a site or the amount of dilu-
tion likely to occur.
•	Environmental targets are given a more
comprehensive evaluation and greater weight.
•	The air pathway can be scored for potential
release. (The original HRS scored only
observed releases.)
Hew has EPA addressed the requirements
of SARA Section 125?
EPA addressed the requirements as follows:
•	Waste quantity: The revised HRS incorpo-
rates a tiered approach for calculating the
waste quantity factor. This approach uses
the best data available at a site to calculate
waste quantity, including constituent con-
centration data, if adequate.
•	Extent of and potential for release: The
revised HRS provides criteria for determin-
ing when an observed release is signifi-
cantly above background, and adds factors
that improve the way the HRS evaluates the
potential for hazardous substances to be re-
leased.
•	In the ground water pathway, such
factors include the revised depth to
aquifer and mobility factors.
•	In the surface water pathway, po-
tential-to-release by overland flow
and flooding is assessed. In addi-
tion, the persistence factor is re-
vised to include mechanisms for
attenuation other than biodegra-
dation, providing a more accurate
assessment of the potential for
hazardous substances to migrate.
•	In the air pathway, a potential-to-
release mechanism is added, which
takes into account source type,
source size, and mobility.
•	Degree of risk: The revised HRS improves
the toxicity factor, improves calculation of
waste quantity, adds the mobility factor,
revises the potential-to-release criteria, uses
health-based and ecological benchmarks,
and adds dilution and distance weighting.
What pathways does the revised HRS con-
sider?
The revised HRS continues to consider risks in
the ground water, surface water, and air pathways. A
new pathway, soil exposure (called onsite exposure
pathway in the proposed HRS), has been added to
account for ingestion, dermal contact, and other
The Revised HRS: Qs and As 3

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exposures related to materials at the surface that
contain hazardous substances.
Does the revised HRS give more weight to
one pathway (for example, ground water)
than others?
No. The maximum possible number of points is
the same for each of the four pathways.
Does the revised HRS consider hazards to
the environment as well as hazards to
public health?
Yes. The revised HRS takes a more comprehen-
sive approach to evaluate sensitive environments.
The revised HRS expands the list of sensitive envi-
ronments considered to include lands and waters
that have been legally designated as protected areas
by either the Federal government or the States.
Potentially contaminated sensitive environments
are distance weighted; in the surface water environ-
mental threat, actual contamination of sensitive
environments is evaluated based on ecological bench-
marks. The weight assigned to sensitive environ-
ments has been capped at 60 percent of the weight
assigned to human targets, to reflect that human
health threats receive a higher priority. However,
serious environmental problems can score above the
HRS cutoff.
How does the revised HRS take into ac-
count people who are actually being ex-
posed to contaminants, as opposed to
those potentially exposed?
The target factors for all pathways are assigned a
higher value if contaminants are found in drinking
water wells or intakes, school playgrounds, resi-
dences, etc. For example, if a contaminant's concen-
tration exceeds a health-based benchmark such as a
Federal drinking water standard in a drinking water
well, then greater weight is assigned to those persons
drinking the water, regardless of their distance from
the site. Potentially exposed populations are evalu-
ated based on their distance from the site, or the
dilution expected to occur at the point of exposure
within the target distance limit. This is because,
under most circumstances, the concentration of
hazardous substances declines as contaminants
migrate from a site.
What new types of sites will the revised
HRS add to the NPL?
The revised HRS considers contamination of
natural resources that can affect the aquatic human
food chain, making it likely that sites that may be
contaminating aquatic organisms will be listed. Also,
certain direct contact problems, especially those
involving contamination of residential and school
property, are likely to have higher scores under the
revised HRS. Serious environmental impacts are
likely to score above the cutoff score. Sites that
result in high levels of known exposure, even if only
small populations are involved, should score rela-
tively higher on the revised HRS.
Does the revised HRS consider direction
of ground water flow?
Not directly. The revised HRS considers flow
direction indirectly in the method used to evaluate
target populations. If wells have not been contami-
nated by the site, as might be assumed of upgradient
wells, the wells are scored for potential contamina-
tion, rather than actual contamination, and the
population drawing from those wells is distance
weighted. Conversely, if wells have been contami-
nated, as might be assumed of downgradient wells,
the wells are scored for actual contamination and
receive the higher observed contamination score.
Under this scoring scenario, the populations draw-
ing from the upgradient wells would receive a lower
score than those with observed contamination down-
gradient of the site, and with target distance weight-
ing, the upgradient population would have to be sub-
stantial before it could receive a large number of
scoring points.
Site Assessment Process
Does the revised HRS affect any sites cur-
rently on the NPL?
No. CERCLA Section 105(c)(3), added by SARA,
specifically states that it is not necessary for EPA to
rescore sites that were placed on the NPL using the
original HRS.
Will EPA rescore sites that have already
been scored on the original HRS. but did
not meet the 28.50 cutoff?
Not necessarily. Sites scoring below the cutoff
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using the original HRS will not be systematically
evaluated with the revised HRS. However, if either
EPA's Regional Offices or the States receive addi-
tional information, they may elect to rescore sites
that they consider threats to public health and/or
the environment, but that did not qualify for listing
under the original HRS. This may be the situation
with sites that have problems the original HRS did
not address, but which the revised HRS does -- for
example, human food chain impacts or the potential
for contamination of ambient air.
When will the first sites be proposed for the
NPL under the revised HRS?
The first update under the revised HRS is sched-
uled for early 1991.
How will EPA gather information to score a
site using the revised HRS?
In general, EPA will follow the same steps as it did
with the original HRS, although the information
gathered may differ. The site assessment portion of
the Superfund program (the portion before the sites
are proposed for the NPL) is intended to identify
sites representing the highest priority for cleanup.
The process begins with site discovery, or the notifi-
cation of EPA of possible releases of hazardous
substances. These potential sites are then entered
into CERCLIS, EPA's inventory of potential hazard-
ous waste sites.
A preliminary assessment (PA) is performed on
all sites entered into CERCLIS to determine whether
a site merits further action. The PA identifies
hazardous substances related to the site, potential
pathways (ground water, surface water, air, and soil
exposure), the likelihood of release, target popula-
tions, and sensitive environments. The PA is a low-
cost review of existing reports and documentation
about the site to determine whether the site poten-
tially poses a problem.
If the site warrants further investigation, a site in-
spection (SI) is performed. The SI involves collect-
ing additional information to better understand the
extent of the problem at the site, screen out sites that
will not qualify for listing, and obtain data necessary
to calculate an HRS score. The SI usually includes
collection and analysis of environmental and waste
samples to determine what substances are present at
the site and whether they are being released.
How many sites will be added based on re-
visions to the HRS?
The number of sites to be listed is a function of
several variables, such as resources, site character-
istics, and Regional priorities, among others. Some
of these variables are independent of the revisions to
the HRS. Historically, 5-10 percent of the sites
evaluated are eventually placed on the NPL. Cur-
rently, approximately 33,000 sites are included in
CERCLIS, EPA's inventory of potential hazardous
waste sites. To date, approximately 31,000 sites have
received a preliminary assessment. At 19,000 of
these sites, the Agency has decided that further
Federal action is not appropriate. Approximately
12,000 sites are still being evaluated. The Agency has
placed over 1,200 on the NPL and will continue to list
sites expeditiously using the revised HRS. Based on
past rates of listing, the Agency expects to list ap-
proximately 100 sites per year.
Does the revised HRS retain its usefulness
as a screening tool?
Yes. While requiring more data and more calcu-
lations than the original HRS, the revised HRS still
remains within the scope of the site assessment
process. The Agency revised the proposed HRS to
make it simpler. The amount of data and the
number of calculations required to score a site will
vary among sites. Most sites do not require calculat-
ing all factors, because all four pathways are not
always affected. EPA is developing a software pack-
age that will perform these calculations. This pack-
age will not only facilitate scoring sites, but also
significantly lessen the possibility of errors.
Remedial Process
Are sites cleaned up according to their
HRS scores?
No. Hie HRS does not determine whether cleanup
is possible or necessary, or the amount of cleanup
needed; these issues are considered in the more
detailed investigations EPA undertakes to assess the
nature and extent of the public health and environ-
mental risks associated with the site. In planning
these remedial investigations, EPA considers the
HRS score, along with State priorities, further site
data, other response alternatives, and other appro-
priate factors.
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Who pays for cleaning up an NPL site?
Site cleanup can be financed in several ways:
•	The individuals or companies responsible
for the problems can clean up voluntarily
with EPA or State supervision.
•	The responsible party or parties can be
ordered to clean up by Federal or State legal
action.
•	A State or local government can choose to
assume the responsibility to clean up with-
out Federal dollars.
•	The Trust Fund can pay for the cleanup,
then seek to recover the costs later from the
responsible party or parties.
How does the cleanup proceed once a
site is on the NPL?
The cleanup process generally involves these steps:
•	Take any measures necessary to stabilize
conditions, which might involve, for example,
fencing the site or removing aboveground
drums or bulk tanks.
•	Undertake initial planning activities to scope
out a strategy for collecting information
and analyzing alternative cleanup ap-
proaches.
•	Conduct a remedial investigation to char-
acterize the type and extent of contamina-
tion at the site and assess the risks posed by
that contamination.
•	Conduct a feasibility study to analyze vari-
ous cleanup alternatives. The feasibility
study is often conducted concurrently with
the remedial investigation as one project.
•	Recommend a cleanup alternative. The
public is given the opportunity to comment
on the recommended alternative.
•	Design the remedy.
•	Implement the remedy.
Consideration of Removals
If EPA or a private party removes waste
from a site, win EPA include the removed
waste in the waste quantity score?
The Agency will consider response actions done
prior to the site inspection. EPA believes that
considering response actions in HRS scores will
provide increased incentives for rapid response action.
However, where EPA cannot adequately determine
the amount of hazardous constituents remaining
onsite, a minimum value will be assigned to the
hazardous waste quantity factor.
Cutoff Score
How did EPA originally select 28.50 as the
cutoff score for including sites on the NPL?
The HRS score of 28.50 was chosen as a manage-
ment tool because it would yield an initial NPL of at
least 400 sites as suggested by CERCLA.
After analyzing data from 110 sites where the
revised HRS was tested, EPA has decided not to
change the cutoff score at this time.
Why is EPA keeping the same cutoff score
for the revised HRS?
Because the HRS is intended to be a screening
system, the Agency has never attached significance
to the cutoff score as an indicator of a specific level
of risk from a site, nor has the Agency intended the
cutoff to reflect a point below which no risk was
present. EPA does not mean to imply that the score
of 28.50 precisely distinguishes between a "risky"
site and a "nonrisky" site. Nevertheless, the cutoff
score has allowed the Agency to set priorities and to
move forward with studying and, where appropriate,
to clean up hazardous waste sites. The vast majority
of sites scoring above 28.50 in the past have been
shown to present risks.
What kinds of analyses did EPA per-
form to support its cutoff score deci-
sion?
As outlined in the December 1988 proposed HRS,
the following three basic approaches were used to
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For Further Information, Contact
Hazardous Site Evaluation Division
Office of Emergency and Remedial Response
Mall Code OS-230
U.S. Environmental Protection Agency
401 M Street. SW
Washington, DC 20460
OR
The Stiperfund Hotline, (800) 424-9346 In the
continental U.S. or (202) 382-3000 In the
Washington, DC area.
obtain some estimate of equivalence between the
original and revised HRS scores. The approaches
used to define "equivalent to 28.50" included:
•	A statistical analysis to determine what
revised HRS score best correlates to 28.50.
•	A determination of what percentage of po-
tential sites in CERCLIS (EPA's inventory
of potential hazardous waste sites) that
score above 28.50 on the original NPL and
the settting of a cutoff that yields the same
percentage.
•	An examination of the risk levels that corre-
spond to the original HRS score of 28.50
and a determination of what revised HRS
score corresponds to that risk level.
These analyses indicate that there is not suffi-
cient information to conclude that any change in the
current cutoff score of 28.50 is needed at this time.
Will keeping the HRS cutoff score at 28.50
reduce the number of sites added to the
NPL?
NOTICE: The policies set out in this memorandum are
intended solely as guidance. They are not intended,
nor can they be relied upon, to create any rights en-
forceable by any party in litigation with the United
States. EPA officials may decide to follow the guidance
provided in this memorandum, or to act at variance with
the guidance, based on an analysis of specific site
circumstances. The Agency also reserves the right to
change this guidance at any time without public notice.
Historically, the Agency has added 100 to 125
sites per year to the NPL. The Agency expects to list
a similar number of sites each year using the revised
HRS.
Will the HRS cutoff score be re-evaluated
and revised?
EPA will continue to evaluate the effectiveness of
the cutoff score to ensure it is serving its purpose as a
management tool to identify the top priority hazard-
ous waste sites.
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