s>EPA
United States
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Response
Publication 9285.7-06FS
July 1992
Understanding
Superfund Risk Assessment
Office of Emergency and Remedial Response
Hazardous Site Evaluation Division (OS-230)
Superfund is the nation's program to clean up un-
controlled hazardous waste sites. Superfund's first
concern is to take action whenever an immediate
threat is discovered. Second, sites that pose the '
greatest potential risk to human health and the en-
vironment are placed on a National Priorities List
(NPL) for long-term cleanup of contamination. Su-
perfund sites are located in every state and poten-
tially affect more than 41 million people who live
within four miles of an NPL Superfund site.
Superfund works to reduce risk:
• Superfund has completed actions to reduce im-
mediate threats at 1,760 NPL and non-NPL sites.
• At the 507 NPL sites where actions have been
completed, the potential risks posed by exposure
to hazardous waste have been reduced for 23.5
million people who live in a four-mile radius.
• A population equivalent to that of Atlanta, Geor-
gia (450,000), has been provided with a safe alter-
native water supply.
• A population equivalent to a near-capacity crowd
at Boston's Fenway Park (30,000) has been relo-
cated from sites posing immediate risks.
People who live near a Superfund site want to know
how it could affect their health. This brochure ex-
plains how the U.S. Environmental Protection
Agency (EPA) examines the potential risks to hu-
man health near Superfund sites. Its purpose is to
help citizens understand the risk assessment process.
WHAT IS RISK ASSESSMENT?
Human health risk is the likelihood that people liv-
ing, working, or playing at or near a Superfund site
could experience health problems as a result of
their contact with, or "exposure" to, chemicals from
the site. The type of health problems an individual
might experience depends on the chemical, how
much of the chemical a person is exposed to, and
how long the exposure lasts. Some chemicals are
harmful in small amounts and other chemicals are
not harmful even in very large amounts.
To evaluate the potential human health risks at a
Superfund site, EPA uses a procedure known as
"risk assessment." (See Highlight 1.) Risk assess-
ment is the scientific estimation of the probability
of harm from exposure to the chemicals found at a
site. It involves identifying what chemicals are at a
site, estimating how and to what extent people
might be exposed to these chemicals, and assessing
the health effects associated with the chemicals.
A Superfund risk assessment estimates the "base-
line risk." This is the potential risk of health prob-
lems occurring if no cleanup action is taken at a
site. The risk estimates are potential risks or pre-
dictions of risk. This is because the risk estimates
are based on mathematical models that make as-
sumptions about how people use the site and how
they might be exposed to chemicals at the site.
EPA collects samples to identify the chemicals
present at a site. The location of the chemicals and
the amounts present at the site are also deter-
mined. Except in rare cases, EPA does not take
samples from humans to determine their exposure
to the chemicals. EPA predicts human exposure
by using models and standardized assumptions
about how people use the site and how chemicals
interact with the human body.
This differs from risk estimates like the chances of
being injured in an automobile accident. Experts
can count the number of automobile accidents that
Printed on Recycled Paper
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HIGHLIGHT 1
The Superfund Process*
Site Discovery
EPA learns of site from reviewing records, reports, receipts and letters
provided by states, hazardous substance handlers, or concerned citizens.
Preliminary Assessment (PA)
Evaluation of existing site-specific data for early determination of need for
further action.
Site Inspection (SI)
Collection of air, soil, and water samples from site and nearby areas.
Information collected about population, weather, and site owner.
Hazard Ranking System (HRS)
Application of a mathematical approach to assessment of relative risks
posed by site.
National Priorities List (NPL)
Lists those sites that are eligible for Superfund-financed remedial action.
Risk
Assessment
Conducted
Remedial Investigation (Rl)
Assessment of the nature and extent of contamination and the associated
health and environmental risks.
Community
Interviews
Risk
Management
Feasibility Study (FS)
Consideration of a range of cleanup options.
T
Proposed Plan
Explanation of cleanup method likely to be chosen and allows for public
comment.
Public
Comment
Record of Decision (ROD)
The official report documenting the background information on the site and
describes the chosen cleanup method and how it was selected.
Remedial Design (RD)/Remedial Action (RA)
Preparation of technical plans. Construction and other work to implement
cleanup.
T
Five-Year Review
Ensures that site is maintained and remains safe.
* At any point in the process, EPA can take immediate action to respond to immediate risks.
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occurred last year to measure the actual risks of driv-
ing a car. There is no similar set of statistics for risks
at Superfund sites, which is why EPA must make
predictions of risk based on models and assumptions.
Because of the uncertainties in using the models to
predict risk at Superfund sites, EPA uses assump-
tions in its models that tend to increase the two fac-
tors that compose risk. These two factors are
exposure to a chemical and the harmfulness, or
"toxicity," of a chemical. By increasing the two fac-
tors that make up the risk, the risk may be overes-
timated. EPA's responsibility is the protection of
human health and the environment. EPA makes its
decisions to protect people based on estimates of risk.
It is important that EPA not underestimate risk to
help ensure the protectiveness of those decisions.
For the most part, when the term "risk" is used at a
Superfund site, it is the baseline risk—the potential
risk of health problems if no cleanup action takes
place. Because EPA uses assumptions that tend to
overestimate the predictions of risk, the actual
number and seriousness of health problems experi-
enced by the community will generally be lower
than predicted by EPA.
RISK MANAGEMENT
HIGHLIGHT 2
Risk Management Questions
Should cleanup be undertaken?
What should the cleanup levels be?
What cleanup method should be used?
The process of using the results of a risk assess-
ment to make decisions at a Superfund site is
known as "risk management." The results of the
baseline risk assessment help EPA to decide
whether to undertake cleanup at the site. EPA uses
risk assessment to help determine what the level of
cleanup should be when legal environmental stan-
dards are not available. Risk assessment is also
used to predict the potential health risks, if any, of
different types of cleanup methods. (See Highlight 2.)
THE FOUR STEPS OF RISK ASSESSMENT
EPA uses a four-step process for risk assessment at
Superfund sites. (See Highlight 3.) It is based on
recommendations made by the National Research
Council in 1983. The National Research Council is
an independent advisor to the government on scien-
tific questions.
STEP 1. DATA COLLECTION AND EVALUATION
In the first step, samples of the air, water, soil,
plants, and animals are taken from locations in and
around the site. These samples are analyzed to de-
termine what chemicals are present and their quanti-
ty and location.
HIGHLIGHTS
Risk Assessment
Data Collection
and Evaluation
Exposure
Assessment
Toxicity
Assessment
Risk
Characterization
STEP 2. EXPOSURE ASSESSMENT
In this step, risk assessors estimate the exposure
that members of the community might have to the
chemicals identified in STEP 1. People may come
in contact with chemicals through the air, water,
soil, food, or other "pathways." For each pathway,
risk assessors estimate the amount of a chemical that
could reach a person's lungs, digestive system, or
skin. Some chemicals are harmful in small amounts
and other chemicals are not harmful even in very
large amounts. The important consideration is peo-
ple's exposure to the chemicals.
In order to estimate through models and standard
assumptions how much of the chemicals people are
likely to be exposed to, risk assessors look at how
people use the site or areas near the site. (See
Highlight 4.) Risk assessors ask questions such as:
Do people live or work on or near the site? Do chil-
dren play on or near the site? Do people drink or
shower in water contaminated with chemicals from
the site? Do people eat fish from or swim in streams
or lakes contaminated by chemicals from the site?
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HIGHLIGHT4
Exposure Pathways
evaporation
Drinking water
. groundwater flow
Eating fish, game, fruit, anH vegetables
Breathing air
INHALATION
Hand-to-mouth contact
DERMAL
Does No Exposure Mean No Risk?
In conducting a risk assessment, EPA may deter-
mine that although there are hazardous chemicals
on a site, there is little chance that people will come
in contact with the chemicals. For example, if there
are no lakes, rivers, or groundwater at the site, and
the chemicals cannot evaporate, or are buried deep
in the ground, then there may be no opportunity for
the chemicals to move from the site to areas where
people would come in contact with them. If there is
no possibility of exposure to the chemicals, and
there is no reason to believe that there will be in
the future, then the chemicals pose no risk.
What about High Exposure Groups?
As a matter of policy, EPA chooses to use estimates of
exposure for individuals in high exposure groups as a
part of a risk assessment done at a Superfund site.
Take, for example, a Superfund site located near a
school playing field. Both children and adults can be
found on the field. However, a typical child in the
neighborhood uses the field more often and in differ-
ent ways than an adult does. In this example, chil-
dren are considered to be the high exposure group
and EPA would use the exposure estimates for chil-
dren in the risk assessment calculations.
The high exposure group is not the absolute worst
case of exposure. EPA recognizes that not everyone
in a community will be part of the high exposure
group. Many people will have less exposure than the
high exposure group. EPA uses the highest exposure
they reasonably expect might happen. This is known
as the "Reasonable Maximum Exposure" or "RME".
This is a term you might hear when the risk assess-
ment for your site is being discussed.
What About the Future?
EPA also considers the potential for future exposures
in this step. A site with little human activity in the
present might be expected to be used for homes and
schools in the future. If this is the case, EPA would
also estimate exposure based on that future use.
STEP 3. TOXICITY ASSESSMENT
To determine if the chemicals found at a site might
cause health problems, risk assessors look at the
results of toxicity studies. Toxicity studies, usually
performed on laboratory animals, examine the
health effects of exposure to measured amounts of
chemicals. There are few human studies on the ef-
fects of chemicals on human health. Instead, EPA
must base its predictions primarily on experiments
that scientists have done using test animals.
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The type of health problem varies depending on the
chemicals and the amount of exposure, or dose.
Health problems can include rashes, trouble with
breathing, damage to vital organs, birth defects,
cancer, or even death. In general, scientists group
these health problems into two types: cancer and all
others (noncancer).
Carcinogens
Chemicals that cause cancer are called carcinogens.
For carcinogens, toxicity studies show that the
number of cases of cancer usually increases as the
dose increases. The reverse is also true. As the dose
decreases, the occurrence of cancer decreases. Any
amount of exposure to a carcinogen carries some
risk of developing cancer. The rate of this increase
or decrease measures the strength of a carcinogen.
The measure of a carcinogen's strength is called a
"slope factor."
To determine the toxicity of a carcinogen, scientists
must rely on animal studies and models. Their
models have built-in assumptions that tend to over-
estimate the harmfulness of the carcinogen.
Noncarcinogens
Chemicals that cause health effects other than cancer
are known as noncarcinogens. For example, lead can
cause anemia and retarded intelligence. Children are
especially affected. Like carcinogens, as exposure to
a noncarcinogen increases, the harmfulness of the
health effect usually increases too.
Scientists believe that there is a certain dose of a
noncarcinogen that the human body can tolerate
without showing signs of illness. For example,
studies seem to show that too much of the chemical
nitrate can cause blood disorders in children. Using
toxicity studies and models, EPA has estimated
that an individual could eat or drink a specific
amount of nitrate each day for 70 years without ex-
periencing a blood disorder. This amount takes into
account that children are especially affected. This
amount is known as the "Reference Dose" for nitrate.
Since the exact amount of a chemical people can tol-
erate depends on the chemical, Reference Doses are
different for different chemicals.
The concept of a Reference Dose is an important dif-
ference between noncarcinogens and carcinogens.
Toxicity studies for carcinogens seem to show that
exposure to any amount of a carcinogen carries
some risk of developing cancer.
The results of animal studies cannot be applied di-
rectly to humans. To take into account this uncer-
tainty, scientists translate the results of animal
studies using theoretical models that take into ac-
count human sensitivity and special populations,
like children. The models have built-in assump-
tions that tend to overestimate the harmfulness of
the chemicals.
STEP 4. RISK CHARACTERIZATION
In this step, the work and results of the three previ-
ous steps are combined, evaluated, and summa-
rized. Here, the risk assessor determines the kinds
of risks and whether the risks are great enough to
cause health problems for people at or near a site.
EPA calculates the risks from carcinogens and non-
carcinogens differently. Risk assessors present their
estimate of carcinogenic risk as a probability (or
chance) that a person would develop cancer over his
or her lifetime due to exposure to a particular carcino-
gen, or carcinogens, at a site. As discussed in STEP
2, risk assessors use the exposure levels of the high-
est exposure groups when calculating the probability.
For example, EPA may estimate that the cancer
risk from a site is "one-in-a-million." This means
that if one million people from the high exposure
group were exposed to chemicals at the site, EPA
estimates that, at the most, one case of cancer could
occur as a result. Most members of a community
are not a part of this high exposure group. An indi-
vidual who experiences less exposure than those in
the high exposure group would have even less of a
chance of developing cancer.
For a noncarcinogen, risk assessors make a compar-
ison between the exposure predicted in Step 2 and
the Reference Dose for the noncarcinogen. The
comparison is expressed as a number, usually close
to the number 1.
RISK MANAGEMENT
The process of using the results of a risk assessment
to make decisions at a Superfund site is known as
"risk management." The results of the baseline risk
assessment help EPA to decide whether to undertake
cleanup at the site. For carcinogens, if the baseline
risk assessment indicates that the risk is greater
than 1-in-10,000, or if Federal or State environmental
standards are exceeded, site managers will generally
begin cleanup activities. If the results of the baseline
risk assessment indicate that the risk is between 1-
in-10,000 and 1-in-1,000,000, cleanup action will gen-
erally not be taken by EPA, unless Federal or State
environmental standards are exceeded.
For a noncarcinogen, if the comparison shows the
exposure predicted in STEP 2 is greater than the
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Reference Dose for the noncarcinogen, cleanup
action will usually take place. When this
comparison number exceeds "1", EPA will generally
take cleanup action. For example, if this
comparison between the Reference Dose for a
noncarcinogen and the predicted exposure in STEP 2
to that noncarcinogen is the number "0.5", cleanup
activities would generally not be undertaken. On the
other hand, if this comparison resulted in the number
"2", cleanup activities would most likely begin.
What about Multiple Chemicals?
Scientists do not yet know how most chemicals inter-
act with one another. One theory is that some chemi-
cals may cancel the effects of another, resulting in
less risk. Another theory is that chemicals may inter-
act to increase harmful health effects, resulting in
even greater risk. Because of this uncertainty, EPA
recommends that the risks from more than one chem-
ical be added together. This means that the risk
number for carcinogens at a site reflects the risks
from all of the carcinogens at the site and that the
risk number for noncarcinogens represents the risk
from all of the noncarcinogens found at a site.
UNCERTAINTY
Risk assessment is not an exact science. While EPA
tries to estimate risk as accurately as possible, there
are many sources of uncertainty in a risk assessment.
Exposure is predicted based on models and assump-
tions about how people living near a Superfund site
might come into contact with the chemicals. How
well the results of animal laboratory studies can
predict the effects of chemicals on humans is also
the subject of controversy among scientists.
EPA must make a choice, or a policy decision, as to
how it will deal with these uncertainties. In gener-
al, EPA uses assumptions and models that may
overestimate risk instead of using assumptions and
models that might underestimate the risk in order
to make sure its decisions protect the health of the
people nearby. As science comes to better under-
stand how chemicals affect human health, EPA will
be better able to estimate risk.
HOW CAN I GET MORE INVOLVED?
A Community Relations Coordinator (CRC) is as-
signed to each Superfund site by EPA The CRC is
an excellent source of information about activities at
a site. Telephone numbers for contacting the CRC for
a particular site are given at the end of this section.
Citizens living or working near a Superfund site can
contribute valuable information for the development
of the baseline risk assessment, particularly if they
get involved early in the assessment process. For ex-
ample, community members can provide information
about pathways of exposure, historical activities, and
future use of the site during community interviews.
EPA's Technical Assistance Grant (TAG) Program
is available to assist with the review of technical in-
formation about the site and promote community
involvement in the decision-making process at Su-
perfund sites. The TAG Program provides an ini-
tial grant of up to $50,000 to community groups
near sites on, or proposed for listing on, the Nation-
al Priorities List. The TAG recipient group is re-
quired to contribute 20% in matching funds toward
the total costs of the program. The matching funds
requirement may be met with cash or through in-
kind administrative services. The community may
use TAG funds to hire a technical advisor to help
them understand information that already exists
about their site or information developed during the
cleanup process. This information may include con-
ditions at the site, the nature of the waste involved,
and the kind of technology available for performing
the necessary cleanup. A TAG award may be re-
newed to facilitate community involvement at all
stages of cleanup. Details about the TAG Program
are provided in the EPA booklet entitled Superfund
Technical Assistance Grants, available free of
charge from EPA's Center for Environmental Re-
search Infomation. The telephone number is (513)
569-7562. The order number for the booklet is
EPA/540/8-90/013.
To find out more about your site, contact the Com-
munity Relations Coordinator in the EPA Regional
Office for your State at the number listed below.
Region 1: Boston, MA (617) 565-3425
(States: CT, ME, MA, NH, RI, VT)
Region 2: New York, NY (212) 264-7054
(States: NJ, NY, PR, VI)
Region 3: Philadelphia, PA (215) 597-9905
(States: DE, DC, MD, PA, WV, VA)
Region 4: Atlanta, GA (404) 347-2643
(States: AL, FL, GA, KY, MS, NC, SC, TN)
Region 5: Chicago, IL (312) 886-6685
(States: IL, IN, MI, MN, OH, WI)
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Region 6: Dallas, TX (214) 655-2240
(States: AR, LA, NM, OK, TX)
Region?: Kansas City, KS (913)551-7003
(States: IA,KS,MO,NE)
RegionS: Denver, CO (303)294-1144
(States: CO, MT, ND, SD, UT, WY)
Region 9: San Francisco, CA (415) 744-2178
(States: AZ, CA, HI, NV)
Region 10: Seattle, WA (206) 553-6901
(States: AK, ID, WA, OR)
FOR FURTHER READING
EPA has prepared Fact Sheets about the Superfund
process. You may request copies from the CRC for
your site. The topics and EPA publication numbers
are listed below.
An Overview 9230.0-05FSh
Identifying Sites 9230.0-05FSk
Exposure Pathways 9230.0-05FSb
The Removal Program 9230.0-05FSg
The Remedial Program 9230.0-05FSm
Community Interviews 9230.0-05FSi
Public Involvement 9230.0-05FSJ
Arsenic 9230.0-05FSa
Benzene 9230.0-05FSd
Trichloroethylene 9230.0-05FSc
PCBs 9230.0-05FSf
Information Repositories 9836.00-02FS
The following publications are available for a fee
from the National Technical Information Service
(NTIS). The telephone number is 1-800-553-NTIS.
U.S. Environmental Protection Agency. Risk As-
sessment Guidance for Superfund, Volume I, Hu-
man Health Evaluation Manual, (Part A).
December 1989. NTIS order number PB 90-155581.
U.S. Environmental Protection Agency. Risk
Assessment Guidance for Superfund, Volume II,
Environmental Evaluation Manual. March 1989.
NTIS order number PB 90-155599.
United States Council on Environmental Quality,
Executive Office of the President. Risk Analysis: A
Guide to Principles and Methods for Analyzing
Health and Environmental Risks. 1989. NTIS or-
der number PB 89-137772.
U.S. Environmental Protection Agency. Hazardous
Substances in Our Environment: A Citizen's Guide
to Understanding Health Risks and Reducing Expo-
sure. September 1990. NTIS order number PB 91-
131987. This publication is also available free of
charge from EPA's Public Information Center.
Phone (202) 260-2080. EPA document number
EPA/230/9-90/081.
U.S. Environmental Protection Agency. The Super-
fund Program: Ten Years of Progress. June 1991.
NTIS order number PB 91-921286.
Publications on related topics are available from
the organizations listed below.
Bureau of Occupational Health, New York State
Health Department. Toxic Substances: How Toxic
is Toxic? (pamphlet). Free of charge. (518) 458-6392.
Institute for Environmental Studies. A Matter of
Chance, A Matter of Choice (magazine). Free of
charge. (608)263-5599.
Institute for Environmental Toxicology, Michigan
State University. Toxicology for the Citizen (book-
let). First copy free of charge, additional copies
$1.00 each. (517) 353-6469.
For technical details and a review of current re-
search on a particular chemical, you may wish to
refer to the Agency for Toxic Substances and Dis-
ease Registry's Toxicological Profile for that chemi-
cal. Information on ordering profiles is available by
calling ATSDR's Toxicology Information Service at
(404) 639-6000 and requesting a "Tox Profile Infor-
mation Sheet." The information service is accessi-
ble 24 hours per day by touchtone phone.
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