UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
OFFICE OF
SOLID WASTE AND EMERGENCY RESPONSE
APR 2 2 1991
OSWER DIRECTIVE 9355.0-30
MEMORANDUM
SUBJECT:
FROM:
TO:
Role of the Baseline Risk Assessment in Superfund
Remedy Selection Decisions
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Don R. Clay
Assistant
Directors, Waste Management Division
Regions I, IV, V, VII, VIII
Director, Emergency and Remedial Response Division
Region II
Directors, Hazardous Waste Management Division
Regions III, VI, IX
Director, Hazardous Waste Division,
Region X
Purpose
The purpose of this memorandum is to clarify the role of the
baseline risk assessment in developing Superfund remedial
alternatives and supporting risk management decisions.
Specifically, the following points are made in the memorandum:
° Where the cumulative carcinogenic site risk to an individual
based on reasonable maximum exposure for both current and
future land use is less than 10(-4) and the non-carcinogenic
hazard quotient is less than 1, action generally is not
warranted unless there are adverse environmental impacts.
However, if MCLs or non-zero MCLGs are exceeded, action
generally is warranted.
° Other chemical-specific ARARs may also be used to determine
whether a site warrants remediation.
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° A risk manager may also decide that a baseline risk level
less than 10(-4)is unacceptable due to site specific reasons
and that remedial action is warranted.
° Compliance with a chemical-specific ARAR generally will be
considered protective even if it is outside the risk range
(unless) there are extenuating circumstances such as
exposure to multiple contaminants or pathways of exposure).
° The upper boundary of the risk range is not a discrete line
at 1 X 10(-4), although EPA generally uses 1 x 10 (-4) in
making risk management decisions. A specific risk estimate
around 10(-4) may be considered acceptable if justified
based on site-specific conditions.
° The ROD should clearly justify the use of any non-standard
exposure factors and the need for remedial action if
baseline risks are within the generally acceptable risk
range. The ROD should also include a table listing the
final remediation goals and the corresponding risk level for
each chemical of concern.
Background
The 1990 National Contingency Plan (NCP) (55 Fed. Reg.
8665-8865(Mar. 8, 1990)) calls for a site-specific baseline risk
assessment to be conducted, as appropriate, as part of the
remedial investigation(Section 300.430(d) (1)). Specifically, the
NCP states that the baseline risk assessment should "characterize
the current and potential threats to human health and the
environment that may be posed by contaminants migrating to ground
water or surface water, releasing to air, leaching through soil,
remaining in the soil, and bioaccumulating in the food chain"
(Section 300.430(d)(4)). The primary purpose of the baseline
risk assessment is to provide risk managers with an understanding
of the actual and potential risks to human health and the
environment posed by the site and any uncertainties associated
with the assessment. This information may be useful in
determining whether a current or potential threat to human health
or the environment exists that warrants remedial action.
The "Risk Assessment Guidance for Superfund: Volume I,
Human Health Evaluation Manual - Part A" (HHEM)(EPA/540/1-89/002)
provides guidance on how to conduct the human health portion of
the baseline risk assessment. Volume II of the "Risk Assessment
Guidance for Superfund" the "Environmental Evaluation Manual"
(EPA/540/1-89/001) and the companion manual, "Ecological
Assessment of Hazardous Waste Sites: A Field and Laboratory
Reference" (EPA/600/3-89/013) provide guidance on conducting the
environmental portion of the baseline risk assessment. Other
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pertinent guidance includes the "Guidance for Conducting Remedial
Investigations and Feasibility Studies Under CERCLA" (RI/FS
guidance, EPA/540/G-89/004), which describes how the baseline
risk assessment fits into the overall RI/FS process. "Guidance
on Preparing Superfund Decision Documents" (ROD guidance)
(EPA/624/1-87/001) provides information on how to document the
results of the baseline risk assessment in the ROD.
Objective
The objective of this memorandum is to provide further
guidance on how to use the baseline risk assessment to make risk
management decisions such as determining whether remedial action
under CERCLA Sections 104 or 106 is necessary. This memorandum
also clarifies the use of the baseline risk assessment in
selecting appropriate remedies under CERCLA Section 121, promotes
consistency in preparing site-specific risk assessments, and
helps ensure that appropriate documentation from the baseline
risk assessment is included in Superfund remedy selection
documents.
Implementation
RISKS WARRANTING REMEDIAL ACTION
Whenever there is a release or substantial threat of release
of a hazardous substance into the environment (or a release or
threat of release into the environment of a pollutant or
contaminant "which may present an imminent and substantial danger
to public health or welfare"), Section 104(a)(1) of CERCLA
provides EPA with the authority to take any response action
consistent with the National Contingency Plan it deems necessary
to protect public health or welfare or the environment. Section
106 of CERCLA grants EPA the authority to require potentially
responsible parties (or others) to perform removal or remedial
actions "when the President determines that there may be an
imminent and substantial endangerment to the public health or
welfare or the environment because of an actual or threatened
release of a hazardous substance form a facility."
As a general policy and in order to operate a unified
Superfund program, EPA generally uses the results of the baseline
risk assessment to establish the basis for taking a remedial
action using either Section 104 or 106 authority. EPA may use
the results of the baseline risk assessments to determine whether
a release or threatened release poses an unacceptable risk to
human health or the environment that warrants remedial action and
to determine if a site presents an imminent and substantial
endangerment. The risk assessment methodology for all sites
should be the same regardless of whether the RI/FS or remedial
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design and remedial action is performed by EPA or potentially
responsible parties.
Generally, where the baseline risk assessment indicates that
a cumulative site risk to an individual using reasonable maximum
exposure assumptions for either current or future land use
exceeds the 10 (-4) lifetime excess cancer risk end of the risk
range, action under CERCLA is generally warranted at the site.
For sites where the cumulative site risk to an individual based
on reasonable maximum exposure for both current and future land
use is less than 10 (-4), action generally is not warranted, but
may be warranted if a chemical specific standard that defines
acceptable risk is violated or unless there are noncarcinogenic
effects or an adverse environmental impact that warrants action.
A risk manager may also decide that a lower level of risk to
human health is unacceptable and that remedial action is
warranted where, for example, there are uncertainties in the risk
assessment results. Records of Decision for remedial actions
taken at sites posing risks within the 10 (-4) to 10 (-6) risk
range must explain why remedial why remedial action is warranted.
The cumulative site baseline risk should include all media
that the reasonable maximum exposure scenario indicates are
appropriate to combine and should not assume that institutional
controls or fences will account for risk reduction. For
noncarcinogenic effects of toxicants, unacceptable risk occurs
when exposures exceed levels which represent concentrations to
which the human population, including sensitive subgroups, may be
exposed without adverse effect during a lifetime or part of a
lifetime, as appropriate to address teratogenic and developmental
effects.
Chemical specific standards that define acceptable risk
levels (e.g., non-zero MCLGs, MCLs) also may be used to determine
whether an exposure is associated with an unacceptable risk to
human health or the environment and whether remedial action under
Section 104 or 106 is warranted. For ground water actions, MCLs
and non-zero MCLGs will generally be used to gauge whether
remedial action is warranted.
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. Once a decision has been made to
make an action, the Agency has expressed a reference for cleanups
achieving the more protective end of the range (i.e., 10 (-6)),
although waste management strategies achieving reductions in site
risks anywhere within the risk range may be deemed acceptable by
the EPA risk manager. Furthermore, the upper boundary of the
risk range is not a discrete line at 1 x 10 (-4), although EPA
generally uses 1 x 10 (-4) in making risk management decisions. A
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specific risk estimate around 10 (-4) may be considered acceptable
if justified based on site-specific conditions, including any
remaining uncertainties on the nature and extent of contamination
and associated risks. Therefore, in certain cases EPA may
consider risk estimates slightly greater than 1 x 10 (-4) to be
protective.
When an ARAR for a specific chemical (or in some cases a
group of chemicals) defines an acceptable level of exposure,
compliance with the ARAR will generally be considered protective
even if it is outside the risk range (unless there are
extenuating circumstances such as exposure to multiple
contaminants or pathways of exposure). Conversely, in certain
situations EPA may determine that risks less than 1 x 10 (-4) are
not sufficiently protective and warrant remedial action.
Where current conditions have not resulted in a release
posing risks that warrant action but there is a significant
possibility that a release will occur that is likely to result in
an unacceptable risk, remedial action may also be taken. The
significance of the potential future release may be evaluated in
part based on the quantities of material at the site and the
environmental setting.
RISKS CONSIDERED IN RISK MANAGEMENT DECISION
As noted above, both current and reasonably likely future
risks need to be considered in order to demonstrate that a site
does not present an unacceptable risk to human health and the
environment. An adequate consideration of future risk may
necessitate the assessment of risks assuming a land use different
from that which currently exists at the site. The potential land
use associated with the highest level of exposure and risk that
can reasonably be expected to occur should be addressed in the
baseline risk assessment. Further, this land use and these
exposure assumptions should be used in developing remediation
goals.
The preamble to the NCP states that EPA will consider future
land use as residential in many cases. In general, residential
areas should be assumed to remain residential; and undeveloped
areas can be assumed to be residential in the future unless sites
are in areas where residential land use is unreasonable. Often
the exposure scenarios based on potential future residential land
use provide the greatest risk estimates (e.g., reasonable maximum
exposure scenario) and are important considerations in deciding
whether to take action (55 Fed. Reg. at 8710).
However, the NCP also states that "the assumption of future
residential land use may not be justifiable if the probability
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that the site will support residential use in the future is
small. "Sites that are surrounded by operating industrial
facilities can be assumed to remain as industrial area unless
there is an indication that this is not appropriate. Other land
uses, such as recreational or agricultural, may be used, if
appropriate. When exposures based on reasonable future land
use are used to estimate risk, the NCP preamble states that the
ROD "should include a qualitative assessment of the likelihood
that the assumed future land use will occur" (55 Fed. Reg. at
8710).
Unacceptable environmental risks also may prompt remedial
action and may occur where there is no significant risk to human
health. Threats or potential threats to sensitive habitats, such
as wetlands, and critical habitats of species protected under the
Endangered Species Acts are especially important to consider when
determining whether to take an action under CERCLA Section 104 or
106. Ambient Water Quality Criteria for aquatic organisms are
chemical-specific standards that will generally be considered
when determining whether to take an action based on the
environmental risk of releases to surface waters.
NO-ACTION DECISIONS
If the baseline risk assessment and the comparison of
exposure concentrations to chemical-specific standards indicates
that there is no unacceptable risk to human health or the
environment and that no remedial action is warranted, then the
CERCLA Section 121 cleanup standards for selection of a Superfund
remedy, including the requirement to meet applicable or relevant
and appropriate requirements (ARARs), are not triggered. CERCLA
section 121 (a) requires only that those remedial actions that
are "determined to be necessary ... Under section 104 or ... 106
... be selected in accordance with section 121." If EPA
determines that an action is necessary, the remedial action must
attain ARARs, unless a waiver is invoked. Of course, sites that
do not warrant action under CERCLA sections 104 or 106 may
warrant action under another State or Federal statute, such as
RCRA subtitle D requirements for the appropriate closure of a
solid waste landfill.
The decision not to take action at an NPL site under section
104 and 106 should also be documented in a ROD. The decision
documentation process should include the preparation of a
proposed plan for public comment, ROD and eventually a closeout
report and Federal Register deletion notice.
POINT OF DEPARTURE WHEN ACTION WARRANTED
Once remedial action has been determined to be warranted,
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the results of the baseline risk assessment may be used to modify
preliminary remediation goals. These preliminary goals are
developed at scoping based on ARARs and the 10 (-6) cancer risk
point of departure pursuant to NCP section 300.430 (e) (2) (I) .
USE OF BASELINE RISK ASSESSMENT TO MODIFY PRELIMINARY REMEDIATION
GOALS
Remediation goals developed under CERCLA section 121 are
generally medium-specific chemical concentrations that will pose
no unacceptable threat to human health and the environment.
preliminary remediation goals are developed early in the RI/FS
process based on ARARs and other readily available information,
such as concentrations associated with 10 (-6) cancer risk or a
hazard quotient equal to one for noncarcinogens calculated from
EPA toxicity information. These preliminary goals may be
modified based on results of the baseline risk assessment, which
clarifies exposure pathways and may identify situations where
cumulative risk of multiple contaminants or multiple exposure
pathways at the site indicate the need for more or less stringent
cleanup levels than those initially developed as preliminary
remediation goals. In addition to being modified based on the
baseline risk assessment, preliminary remediation goals and the
corresponding cleanup levels may also be modified based on the
given waste management strategy selected at the time of remedy
selection that is based on the balancing of the nine criteria
used for remedy selection (55 Fed. Reg. at 8717 and 8718) .
EARLY AND INTERIM ACTIONS
Early operable unit actions (e.g., hot spot removal and
treatment) and interim actions (e.g., temporary storage or ground
water plume containment) may be taken to respond to an immediate
site threat or to take advantage of an opportunity to
significantly reduce risk quickly (55 Fed. Reg. at 8705) . For
example, an interim containment action may be particularly useful
early in the process for complicated ground water remedial
actions, where concentrations greater than MCLS provide a good
indication that remediation of a potential drinking water source
is necessary; such quick remedial action is important to prevent
further spread of the contaminant plume while a final ground
water remedy is being developed.
Early and interim action RODs do not require a completed
baseline risk assessment, although enough information must be
available to demonstrate the potential for risk and the need to
take action. Data sufficient to support the interim action
decision can be extracted from the ongoing RI/FS for the site and
set out in a focused feasibility study or other appropriate
document that includes a short analysis of a limited number of
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alternatives (55 Fed. Reg. at 8704) . These data should include a
summary of contaminants of concern, concentrations and relevant
exposure information. A discussion should accompany these data
explaining the need for immediate remedial action based on the
presence of contamination that, if left unaddressed in the
short-term, either contributes immediate risk or is likely to
contribute to increased site risk or degradation of the
environment/ natural resources. The early and interim action
RODs should note that some exposure pathways at the site may not
be addressed by the action.
An interim action ROD eventually must be followed by a
subsequent ROD for that operable unit based on the complete
RI/FS, that includes the baseline risk assessment, in order to
document long-term protection of human health and the environment
at that portion of the site. The interim action ROD, however,
should demonstrate qualitatively (and quantitatively if possible)
that there is a risk or potential for risk and explain how the
temporary measures selected will address a portion of this risk.
DOCUMENTATION OF BASELINE RISK ASSESSMENT RESULTS IN THE ROD
The Summary of Site Risks section of the ROD should include
a discussion of the risks associated with current and future land
use and a table presenting these risk levels for each exposure
medium (e.g., direct contact with soil by potential future
residents exposed via incidental soil ingestion and dermal
contact). In some situations, risks from exposure via more than
one medium (e.g, soil and drinking water) will affect the same
potentially exposed individual at the same time. It is
appropriate in these situations to combine the risk that an
individual may be exposed to from a site.
In addition to summarizing the baseline risk assessment
information, the ROD (except no-action RODs) should include how
remedial alternatives will reduce risks by achieving cleanup
levels through treatment or by eliminating exposures through
engineering controls for each contaminant of concern in each
appropriate medium.
The Comparative Analysis should include a discussion of each
of the nine criteria; consideration of risk is part of the
discussion of several of the criteria. The discussion of overall
protection of human health and the environment should include a
discussion of how the remedy will eliminate, reduce, or control
risks identified in the baseline risk assessment posed through
each pathway and whether exposure levels will be reduced to
acceptable levels. For example, if direct human contact with
contaminated soil is identified as a significant risk at a site,
the ROD (except no-action RODs) should indicate how the selected
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remedy will eliminate or control exposures to ensure protection
of human health. The discussion of long-term effectiveness and
permanence should include, where appropriate, an assessment of
the residual risk from untreated residual waste remaining at the
site. The short-term effectiveness discussion should address
risks during remedial action to those on-site and nearby.
Finally, that part of the Decision Summary in the ROD that
focuses on the selected remedy should show:
° the chemical-specific remediation level and
corresponding chemical-specific risk level(s) to be
attained at the conclusion of the response action and
the points (or area) of compliance for the media being
addressed; and
° The lead agency's basis for the remediation levels
(e.g., risk calculation, ARARs).
The attached table, "Remediation levels and Corresponding Risks,"
provides a direct means of displaying this information for health
risks and, where appropriate, environment protection (Table 1).
The table should be completed for all media for which the ROD
selects final cleanup levels. The table should serve as a
summary of text in the selected remedy section of the ROD
Decision Summary. For interim action RODs, only qualitative
statements may be possible.
Additional guidance on the baseline risk assessment and its
role in remedy selection is available from several sources. For
guidance on the baseline risk assessment contact:
David Bennett, Chief
Toxics Integration Branch (OS-230)
Hazardous Site Evaluation Division
Office of Emergency and Remedial Response
phone: (FTS) or (202) 475-9486.
For additional guidance on the interaction of the baseline risk
assessment and Superfund remedy selection, contact:
David Cooper
Remedial Operations and Guidance Branch (OS-220W)
Hazardous Site Control Division
Office of Emergency and Remedial Response
phone: (FTS) 398-8361
commercial phone: (703) 308-8361.
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For guidance on enforcement-lead sites contact:
Stephen Ells
Guidance and Evaluation Branch (OS-510)
CERCLA Enforcement Division
Office of Waste Programs Enforcement
phone: (FTS) or (202) 475-9803.
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 enforceable 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. Remedy selection decisions are made and justified
on a case-specific basis. The Agency also reserves the right to
change this guidance at any time without public notice.
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TABLE 1
Remediation Goals and Corresponding RisksŁ
Medium
SOIL
GROUND
WATER
SEDIMENT
Final
Remediation
Remediation
Chemical Level6
A
B
C
B
C
F
G
Q
2.0 ppm
17.0 ppm
5.0 ppm
0.1 ppm
4.0 ppm
7.0 ppm
15.0 ppm
100.0 ppm
Levels
Point of
Compliancef
All facility
grounds
Waste
Management
Unit
Boundary
Downstream
from point A
Basis
of Goal
HI
Risk
GWRisk
Risk
MCL
MCLG
MCL
Ecological
Effects
Corresponding
Chemical-Specific
Cancer
N/A
1.0 x 10"5
N/A
1.0 x 10"5
1.0 x 10"5
N/A
6.0 x 10"6
N/A
Risk Levels0
RME Riskd
Non-Cancer
0.5
N/A
N/A
N/A
N/A
0.2
0.09
N/A
a. Prepare summary sheets for selected remedy.
b. Final Remediation Levels are based on preliminary remediation goals
developed in the Feasibility Study (FS) (RI/FS Guidance 4.2.1) as modified
through the nine criteria evaluation and engineering design. In the process
of achieving remediation levels for each chemical, some chemicals will be
reduced to concentrations below their remediation levels.
c. Chemical-specific risks correspond to associated remediation levels.
Risks do not consider effects of exposures to other chemicals or media.
If appropriate, risks may be summed to calculate media-specific risks.
Short-term effectiveness is not considered.
d. Cancer risks are measured as individual incremental lifetime; non-cancer
as Hazard Quotients.
e. Bases for values should be explained in the earlier Record Of Decision
(ROD) table.
f. Bases for location and method for determining attainment (e.g., maximum
value detected over area XYZ) should be explained in the description of the
selected remedy.
N/A - Not applicable
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