Role of Background in the CERCLA Cleanup Program
U.S. Environmental Protection Agency
Office of Solid Waste and Emergency Response
Office of Emergency and Remedial Response
April 26, 2002
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Table of Contents
Purpose Page 3 of 13
History Page 4 of 13
Definitions of Terms Page 5 of 13
Consideration of Background in Risk Assessment Page 6 of 13
Consideration of Background in Risk Management Page 7 of 13
Consideration of Background in Risk Communication Page 8 of 13
Hypothetical Case Examples Page 8 of 13
References Page 12 of 13
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Purpose
This document clarifies the U.S. Environmental Protection Agency (EPA) preferred
approach for the consideration of background constituent concentrations of hazardous
substances, pollutants, and contaminants in certain steps of the remedy selection process, such as
risk assessment and risk management, at Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA or "Superfund") sites. To the extent practicable,
this document may also be applicable to sites addressed under removal actions and time-critical
actions. In general, the presence of high background concentrations of hazardous substances,
pollutants, and contaminants found at a site is a factor that should be considered in risk
assessment and risk management.
The primary goal of the CERCLA program is to protect human health and the
environment from current and potential threats posed by uncontrolled releases of hazardous
substances, pollutants, and contaminants. Contamination at a CERCLA site may originate from
releases attributable to the CERCLA site in question, as well as contamination that originated
from other sources, including natural and/or anthropogenic sources not attributable to the
specific site releases under investigation (EPA, 1995a). In some cases, the same hazardous
substance, pollutant, and contaminant associated with a release is also a background constituent.
These constituents should be included in the risk assessment, particularly when their
concentrations exceed risk-based concentrations. In cases where background levels are high or
present health risks, this information may be important to the public. Background information is
important to risk managers because the CERCLA program, generally, does not clean up to
concentrations below natural or anthropogenic background levels.
A comprehensive investigation of all background substances found in the environment
usually will not be necessary at a CERCLA site. For example, radon background samples
normally would not be collected at a chemically contaminated site unless radon, or its precursor
(radium, Ra-226) was part of the CERCLA release. Also, EPA normally would not analyze
background samples for Ra-226 at a cesium (Cs-137) site, or dioxin at a lead site where dioxin
was not the subject of a CERCLA release into the environment.
This document provides guidance to EPA Regions concerning how the Agency intends to
exercise its discretion in implementing one aspect of the CERCLA remedy selection process.
The guidance is designed to implement national policy on these issues.
Some of the statutory provisions described in this document contain legally binding
requirements. However, this document does not substitute for those provisions or regulations,
nor is it a regulation itself. Thus, it cannot impose legally-binding requirements on EPA, States,
or the regulated community, and may not apply to a particular situation based upon the
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circumstances. Any decisions regarding a particular remedy selection decision will be made
based on the statute and regulations, and EPA decision makers retain the discretion to adopt
approaches on a case-by-case basis that differ from this guidance where appropriate. EPA may
change this guidance in the future.
History
Background issues are discussed in a number of EPA documents1. A need for CERCLA-
specific guidance was identified during risk assessment reform discussions with stakeholders in
1997. An issue that is often raised at CERCLA sites is whether a reliable representation of
background is established (EPA, 1989). To assist Regions with this issue, EPA developed a
peer-reviewed practical guide to sampling and statistical analysis of background concentrations
in soil at CERCLA sites (EPA, 200 Ib).
EPA has developed this policy to respond to questions about the general application of
background concentration during the CERCLA remedial investigation process.2 This policy
encourages national consistency and responds to the Agency's goals for risk characterization and
communication of risks to the public as expressed in other EPA policy and guidance, including:
• Policy for Risk Characterization which provides principles for fully, openly, and clearly
characterizing risks (EPA, 1995b); and,
• Cumulative Risk Assessment Guidance which encourages programs to better advise
citizens about the environmental and public health risks they face (EPA, 1997c).
Definitions of Terms
Risk Assessment Guidance for Superfund Volume I, Human Health Evaluation Manual [RAGS] (EPA, 1989).
Preamble to the National Oil and Hazardous Substances Pollution Contingency Plan (NCP, 1990a).
Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions (EPA, 1991).
Determination of Background Concentrations of Inorganics in Soils and Sediments at Hazardous Waste Sites (EPA,
1995a).
Soil Screening Guidance: User's Guide (EPA, 1996).
Ecological Risk Assessment Guidance for Superfund (EPA, 1997a).
Rules of Thumb for Superfund Remedy Selection (EPA, 1997b).
Soil Screening Guidance for Radionuclides: User's Guide (EPA, 2000).
ECO Update. The Role of Screening-Level Risk Assessments and Refining Contaminants of Concern in Baseline
Ecological Risk Assessments (EPA, 200 la).
2The process of determining when risks warrant remedial actions and the degree of cleanup for specific
hazardous substances, pollutants, and contaminants involves many factors that are not addressed in this document.
Additional guidance is provided in the EPA (1991) Role of the Baseline Risk Assessment in Superfund Remedy
Selection Decisions.
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For the purposes of this policy, the following definitions are used.
Background refers to constituents or locations that are not influenced by the releases
from a site, and is usually described as naturally occurring or anthropogenic (EPA, 1989; EPA,
1995a):
1) Anthropogenic - natural and human-made substances present in
the environment as a result of human activities (not specifically
related to the CERCLA release in question); and,
2) Naturally occurring- substances present in the environment in
forms that have not been influenced by human activity.
Chemicals (or constituents) of concern (COCs) are the hazardous substances, pollutants,
and contaminants that, at the end of the risk assessment, are found to be the risk drivers or those
that may actually pose unacceptable human or ecological risks.3 The COCs typically drive the
need for a remedial action (EPA, 1999a).
Chemicals (or constituents) of potential concern (COPCs) generally comprise the
hazardous substances, pollutants, and contaminants that are investigated during the baseline risk
assessment. The list of COPCs may include all of the constituents whose data are of sufficient
quality for use in the quantitative risk assessment, or a subset thereof (EPA, 1989).
Screening is a common approach used by risk assessors to refine the list of COPCs to
those hazardous substances, pollutants, and contaminants that may pose substantial risks to
health and the environment. Screening involves a comparison of site media concentrations with
site-specific risk-based values.4
Consideration of Background in Risk Assessment
Guidance for determining if site risks are unacceptable is discussed in the EPA (1991) Role of the Baseline Risk
Assessment in Super fund Remedy Selection Decisions. As stated in the EPA (1991) memorandum, "EPA uses the
general 10"4 to 10"6 risk range as a "target range" within which the Agency strives to manage risks as part of a
Superfund cleanup." The risk used in this decision generally is the "cumulative site risk" to an individual using
reasonable maximum exposure (RME) assumptions for either current or future land use and includes all exposure
pathways which the same person may consistently face. See also EPA (1989) PxAGS, Section 8.3.
4Risk-based values or concentrations are generally based on a cancer risk of one-in-a-million (IxlO"6) or a hazard
quotient of 1.0 for noncarcinogens (EPA, 1996) or screening-level ecological risk values (EPA, 1997a; EPA, 2001a).
COPCs with concentrations below the screening levels might be excluded from the risk assessment unless there are
other pathways or conditions that are not addressed by the screening values (EPA, 1996).
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A baseline risk assessment generally is conducted to characterize the current and
potential threats to human health and the environment that may be posed by hazardous
substances, pollutants, and contaminants at a site. EPA's 1989 Risk Assessment Guidance for
Superfund (RAGS) provides general guidance for selecting COPCs, and considering background
concentrations. In RAGS, EPA cautioned that eliminating COPCs based on background (either
because concentrations are below background levels or attributable to background sources) could
result in the loss of important risk information for those potentially exposed, even though
cleanup may or may not eliminate a source of risks caused by background levels. In light of
more recent guidance for risk-based screening (EPA, 1996; EPA, 2000) and risk characterization
(EPA, 1995c), this policy recommends a baseline risk assessment approach that retains
constituents that exceed risk-based screening concentrations. This approach involves addressing
site-specific background issues at the end of the risk assessment, in the risk characterization.
Specifically, the COPCs with high background concentrations should be discussed in the risk
characterization, and if data are available, the contribution of background to site concentrations
should be distinguished.5 COPCs that have both release-related and background-related sources
should be included in the risk assessment. When concentrations of naturally occurring elements
at a site exceed risk-based screening levels, that information should be discussed qualitatively in
the risk characterization. To summarize:
• The COPCs retained in the quantitative risk assessment should include
those hazardous substances, pollutants, and contaminants with
concentrations that exceed risk-based screening levels.
The Risk Characterization should include a discussion of elevated
background concentrations of COPCs and their contribution to site risks.
• Naturally occurring elements that are not CERCLA hazardous substances,
pollutants, and contaminants, but exceed risk-based screening levels
should be discussed in the risk characterization.
This general approach is preferred in order to:
Encourage national consistency in this area;
• Present a more thorough picture of risks associated with hazardous substances,
pollutants, and contaminants at a site; and,
Prevent the inadvertent omission of potentially release-related hazardous
technical guidance should be consulted for sampling and analysis of background concentration data (EPA,
200 Ib).
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substances, pollutants, and contaminants from the risk assessment.
This approach is consistent with the Policy for Risk Characterization which provides
principles for fully, openly, and clearly characterizing risks (EPA, 1995b). Risks identified
during the baseline risk assessment should be clearly presented and communicated for risk
managers and for the public. Risk characterization is one of many factors in determining
appropriate CERCLA risk management actions (EPA, 1991; EPA, 1995b).
Consideration of Background in Risk Management
Where background concentrations are high relative to the concentrations of released
hazardous substances, pollutants, and contaminants, a comparison of site and background
concentrations may help risk managers make decisions concerning appropriate remedial actions.
The contribution of background concentrations to risks associated with CERCLA releases may
be important for refining specific cleanup levels for COCs that warrant remedial action6.
Generally, under CERCLA, cleanup levels are not set at concentrations below natural
background levels. Similarly, for anthropogenic contaminant concentrations, the CERCLA
program normally does not set cleanup levels below anthropogenic background concentrations
(EPA, 1996; EPA, 1997b; EPA, 2000). The reasons for this approach include cost-effectiveness,
technical practicability, and the potential for recontamination of remediated areas by surrounding
areas with elevated background concentrations. In cases where area-wide contamination may
pose risks, but is beyond the authority provided under CERCLA, EPA may be able to help
identify other programs or regulatory authorities that are able to address the sources of area-wide
contamination, particularly anthropogenic (EPA, 1996; EPA, 1997b; EPA, 2000). In some
cases, as part of a response to address CERCLA releases of hazardous substances, pollutants,
and contaminants, EPA may also address some of the background contamination that is present
on a site due to area-wide contamination.
The determination of appropriate CERCLA response actions and chemical-specific
cleanup levels includes the consideration of nine criteria as provided in the National Oil and
Hazardous Substances Pollution Contingency Plan (NCP, 1990b). In cases where applicable or
relevant and appropriate requirements (ARARs) regarding cleanup to background levels apply to
a CERCLA action, the response action generally should be carried out in the manner prescribed
by the ARAR. In the case where a law or regulation is determined to be an ARAR and it
requires cleanup to background levels, the ARAR will normally apply and be incorporated into
the Record of Decision, unless the ARAR is waived.
Consideration of Background in Risk Communication
6For example, in cases where a risk-based cleanup goal for a COC is below background concentrations, the
cleanup level may be established based on background.
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EPA strives for transparency in decision-making (EPA, 1995c) and encourages programs
to better advise citizens about the environmental and public health risks they face (EPA, 1997c).
The presence of high background concentrations of COPCs may pose challenges for risk
communication. For example, the discussion of background may raise the expectation that EPA
will address those risks under CERCLA. The knowledge that background substances may pose
health or environmental risks could compound public concerns in some situations.
On the other hand, knowledge of background risks could help some community members
place CERCLA risks in perspective. Also, the information about site and background risks can
be helpful for both risk managers who make an appropriate CERCLA decision, and for members
of the public who should know about environmental risk factors that come to light during the
remedial investigation process.
As a general policy matter, EPA strives for early and frequent outreach to communities in
order to share information and encourage involvement (EPA, 200Ic). EPA has made a clear
commitment to fully, openly, and clearly characterize and communicate risks (EPA, 1995b;
EPA, 1995c). There is no one-size-fits-all technique that can help explain risks associated with
CERCLA releases or with background levels, or the basis of risk management decisions.
Approaches will depend on the site, the issues, and the level of community interest. Early on in
the process, Regions should clarify their understanding of stakeholder expectations and clearly
explain the relevant constraints and limitations of the CERCLA remedial process (EPA, 1999b;
EPA, 200Ic).
In some cases where area-wide contamination may pose a risk, but is beyond the
authority of the CERCLA program, communication of potential risks to the public may be most
effective when coordinated with public health agencies. Examples of situations where Regions
might coordinate risk communication with local, state or federal health officials are sites where
widespread lead contamination or high levels of naturally occurring radiation have been found,
but are not the subject of a CERCLA release into the environment. Public health agency
officials may combine education and outreach efforts to inform residents about ways to reduce
exposures and risks.
Hypothetical Case Examples
Three general hypothetical case examples are given to show how background may be
considered in risk assessment and risk management at CERCLA sites:
Case 1 presents an example of a chemical site with widespread background
contamination.
Case 2 presents an example of a radiation site with both natural- and release-related
sources.
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Case 3 presents an example of a site with hazardous substances, pollutants, and
contaminants from both natural- and release-related sources.
In these examples, it is presumed that adequate samples are collected from appropriate
background reference locations and evaluated using appropriate statistical methods. It is
presumed that background is not used to screen out substances from the risk assessment. For
simplicity, only one pathway7 is used for hypothetical human health risk assessments.8
Based on the presumptions above, the basic concepts these examples are designed to
highlight are:
• Background issues should be discussed in the risk characterization portion of the
baseline risk assessment in order to inform risk management decisions;
Information about unacceptable risks should be communicated to public; and,
• Other factors, such as the nine criteria provided in the NCP, should be considered
by the risk manager in making final decisions.
Hypothetical Case 1
The ABC Industrial Site risk assessment included all COPCs that exceed site-specific
risk-based concentrations for soil pathways. The results of the risk assessment identified the
following COPCs with risks above or at the high end of the 10"4 to 10"6 risk range: arsenic,
dieldrin, and 4,4-DDT. The hazard quotients were below 1.0.
Arsenic is a potential background substance - it is a common naturally occurring element
- but is also a hazardous substance that was released at this site. The available site
characterization data indicate that soil arsenic concentrations may be naturally occurring or
consistent with background concentrations. Dieldrin and DDT are present at high concentrations
that contribute to an unacceptable site risk. However, only dieldrin is known to be associated
7At most CERCLA sites, risks for the reasonably maximum exposed individual typically are combined across
several exposure pathways to estimate the total risks at a CERCLA site. This is done only for the pathways which
the same individual would be likely to face consistently (EPA, 1989). Depending on the particular CERCLA site,
risks could be calculated for the entire area of the site or for separate units (see Section 4.5 of RAGS (EPA, 1989)).
More technical guidance for characterizing background concentrations and comparing data sets is provided in EPA
(200 Ib) and other technical references cited previously in this document.
Guidance on the consideration of background concentrations during screening level ecological risk assessments
is provided in EPA (200 la).
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with the CERCLA site activities and releases. Since there are no known historical uses of DDT
at this CERCLA site, the RPM suspects that the DDT in soil originated from area-wide
agricultural pesticide applications in this part of the state. Based on this information, the RPM
requests additional sampling of background locations for arsenic and DDT analysis. A statistical
comparison of sampling data for arsenic and 4,4-DDT in on-site samples and background
samples indicates that site concentrations for DDT are consistent with background
concentrations. Local and regional data support the conclusion that DDT is an area-wide
contaminant. The additional data indicate that arsenic concentrations on the site are above
background concentrations. Therefore, the arsenic risks cannot be attributed solely to
background.
In this example, arsenic and dieldrin are the soil COCs for which cleanup goals should be
derived. The risk characterization should present information about DDT as an area-wide
background contaminant that is unrelated to releases at this site, and the Agency should explain
whether or not it will be addressed. The RPM should consider whether other regulatory
programs or authorities are able to address the area-wide DDT contamination in a coordinated
response effort. If available, the location(s) of additional information on pesticide use in this
part of the state should be provided for concerned citizens.
Hypothetical Case 2
At ABC Radium Production Site, site characterization data indicate that radium (Ra-226)
and inorganics are present in soil. Arsenic concentrations exceed screening levels but are
assumed to be within naturally occurring levels. To confirm this assumption, the RPM evaluates
site-specific background samples for comparison to site concentrations. The site-specific
background analysis confirms that arsenic concentrations collected on the site are consistent with
background concentrations in soils. There are no known regional anthropogenic sources of
arsenic (such as smelters or pesticide manufacturers). Arsenic, in this case, is considered to be a
naturally occurring substance and is excluded from further consideration in the quantification of
site risks. However, the finding of natural background arsenic at concentrations that may pose
health risks should be discussed in the text of the risk characterization.
The risk assessment indicates that Ra-226 exceeds the high end of the acceptable risk
range of 10"4 to 10"6. It is commonly known that Ra-226 occurs naturally in the environment.
Samples collected in an appropriate background location near this site indicate that Ra-226
levels from natural sources are lower than the site levels, but are associated with a risk at the
upper end of the risk range (10"4).
In this example, only Ra-226 should be a COC for which a cleanup goal should be
derived. The risk characterization, however, should include a discussion of natural background
levels of both arsenic and Ra-226.
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Hypothetical Case 3
XYZ Site contains buried chemical wastes, but some anecdotal accounts indicate that
radium may have been used. Preliminary site characterization data show that arsenic,
manganese, and Ra-226 concentrations exceed the site-specific, risk-based concentrations. A
comparison of arsenic and manganese concentrations in groundwater samples collected from
upgradient background locations indicates that only manganese site concentrations are consistent
with background levels and considered to be naturally occurring. Naturally occurring
manganese is not considered further in the quantification of risks, but is included in a qualitative
discussion of risks in the risk characterization.
The RPM decides to analyze for Ra-226 both at the site and in background locations
because it is commonly known that Ra-226 occurs naturally in the environment. Samples are
collected in an appropriate background location near this site. The samples indicate that Ra-226
levels at this site are not different from naturally occurring levels. Therefore, Ra-226 is not a
COPC for further consideration in the quantification of risks. Subsequent site investigation data
confirms the use of chemicals, but not radionuclides.
In this example, only arsenic risks are quantified in the risk assessment. The baseline
risk for groundwater indicates that arsenic poses an unacceptable risk. The risk characterization
should include a discussion of the natural Ra-226 and manganese concentrations because the
levels exceeded risk-based concentrations. Site characterization data indicate that site disposal
activities caused naturally occurring arsenic in soil to be mobilized and leach to groundwater.
Arsenic, therefore, is the subject of a CERCLA release into the environment and a cleanup goal
for it should be derived.
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References
EPA, 1989. Risk Assessment Guidance for Superfund (RAGS): Volume I: Human Health
Evaluation Manual (HHEM), (Part A), Interim Final, Office of Emergency and Remedial
Response, Washington, DC. EPA/540/1-89/002, OSWER 9285.70-02B.
EPA, 1991. Role of the Baseline Risk Assessment in Superfund Remedy Selection Decisions.,
Office of Emergency and Remedial Response, Washington, DC. OSWER 9355.0-30.
EPA, 1995a. Engineering Forum Issue Paper. Determination of Background Concentrations of
Inorganics in Soils and Sediments at Hazardous Waste Sites, R.P Breckenridge and A.B.
Crockett, Office of Research and Development, Office of Solid Waste and Emergency Response,
Washington, DC. EPA/540/S-96/500.
EPA, 1995b. Policy for Risk Characterization at the U. S. Environmental Protection Agency,
Science Policy Council, Washington, DC. http://www.epa.gov/OSP/spc/rcpolicy.htm.
EPA, 1995c. Risk Characterization Handbook, Science Policy Council, Washington, DC. EPA
100-B-00-002.
EPA, 1996. Soil Screening Guidance: User's Guide. Office of Emergency and Remedial
Response, Washington, DC. EPA/540-R-96/018, OSWER 9355.4-23.
EPA, 1997a. Ecological Risk Assessment Guidance for Superfund: Process for Designing and
Conducting Ecological Risk Assessments, Interim Final, EPA/540-R-97-006, OSWER 9285.7-
25.
EPA, 1997b. Rules of Thumb for Superfund Remedy Selection. Office of Emergency and
Remedial Response, Washington, DC. EPA 540-R-97-013, OSWER 9355.0-69.
EPA, 1997c. Cumulative Risk Assessment Guidance-Phase I Planning and Scoping, Science
Policy Council, Washington, DC. http://www.epa.gov/osp/spc/cumrisk2.htm.
EPA, 1999a. A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other
Remedy Selection Decision Documents, Office of Emergency and Remedial Response,
Washington, DC. OSWER 9200.1-23.P.
EPA, 1999b. Risk Assessment Guidance for Superfund: Volume 1 Human Health Evaluation
Manual Supplement to Part A: Community Involvement in Superfund Risk Assessments, Office of
Emergency and Remedial Response, Washington, DC. OSWER 9285.7-01E-P.
EPA, 2000. Soil Screening Guidance for Radionuclides: User's Guide, Office of Radiation and
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Indoor Air, OSWER 9355.4-16A.
EPA, 200 la. ECO Update, The Role of Screening-Level Risk Assessments and Refining
Contaminants of Concern in Baseline Ecological Risk Assessments, OSWER 9345.0-14.
EPA, 2001 b. Guidance for Characterizing Background Chemicals in Soil at Super fund Sites.,
External Review Draft, Office of Emergency and Remedial Response, OSWER. 9285.7-41.
EPA, 200 Ic. Early and Meaningful Community Involvement., Office of Emergency and
Remedial Response, OSWER 9230-0-9.
NCP, 1990a. Preamble to the National Oil and Hazardous Substances Pollution Contingency
Plan (NCP), 40 CFRPart 300, 53 Federal Register 51394 and 55 Federal Register 8666.
NCP, 1990b. National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40
CFR Part 300, 55 Federal Register 8666, March 8, 1990.
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