vvEPA
United States
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Resp onse
Publication 9345.0-14
EPA540/F-01/014
June 2001
ECO Update
Intermittent B ulletin
The Role of Screening-Level Risk Assessments and
Refining Contaminants of Concern in Baseline
Ecological Risk Assessments
Screening-Level Ecological Risk
Assessments (SLERAs)
Screening-Level Ecological Risk Assessments
are conservative assessments in that they provide a
high level of confidence in determining a low
probability of adverse risk, and they incorporate
uncertainty in a precautionary manner. It must be
stressed that SLERAs are not designed nor intended
to provide definitive estimates of actual risk,
generate cleanup goals and, in general, are not
based upon site-specific assumptions. Rather, the
purpo se of SLE RAs is to as sess the nee d, and if
required, the level of effort necessary, to conduct a
detailed or "baseline" ecological risk assessment for
a particular site or facility. Therefore, refinement of
contaminants of concern occurs in the baseline risk
assessment rather than in the SLERA.
It is also important to note that SLERAs, like
baseline ecological risk assessments, should take
place with input from Regional Ecological Risk
Assessors and/or the Biological Technical
Assistance Group as well as in coordination with
Natural Resource Trustees.
IN THIS BULLETIN
Introduction
The Purpose of Screening-Level ERAs 2
The Purpose of Baseline ERAs 2
Standard Components of ERAs 3
Refining Contaminants of Concern 3
Supplemental Component 1:
Background 3
Supplemental Component 2:
Frequency and Magnitude of Detection 4
Supplemental Component 3:
Dietary Considerations 4
Additional Considerations 4
The Role of Tiers and Sub-Tiers in ERA 5
Analogy: Reduction of COPCs and
Sieving Soil Particles 6
Summary 6
References and Other Resources 7
Introduction
This supplemental Ecological Risk Assessment
(ERA) guidance is intended to provide further
The ECO Update Bulletin series provides technical gukJance to EPA Regions and Stales on specific components ofthe ecologcal risk assessment
process at Superfund sites and RCRA Corrective Action facilities. These Bulletins seive as supplements to Ecological Risk Assessment Guidance for
Superfund: Process for Designing and Conducting Ecological Risk Assessments (EPA/540-R-97-006). This document does not substitute for
C ERG LA, RCRA or EPA's regulations, nor is ft a regubtion itself. Thus, itmay not be relied upon to create a substantive or procedural right
enforceabte by any other person and may not apply to a particubr situation based on the circumstances. The Government may take actbn that B at
variance with these Bulfetins.
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clarification and direction regarding Screening Level
Ecological Risk Assessments (SLERAs), as described
in Step 1- Preliminary Problem Formulation, and Step
2 - Preliminary Risk Calculation, of the Agency's
program guidance: Ecological Risk Assessment
Guidance for Superfund: Process for Designing and
Conducting Ecological Risk Assessm ents (U.S. EPA
1997).1 It also provides an approach for incorporating
additional components into the Problem Formulation
phase of more detailed (i.e., "baseline") ecological risk
assessments, particularly in Step 3.2, which discusses
refining contaminants of potential concern (COPCs).
The Superfund program guidance, which may be
applicable to RCRA Corrective Actions, describes a
process that incorporates flexibility in refining COPCs
in order to focus and streamline the overall ERA
process while still ensuring a consistent approach. This
guidance provides more detail on how to incorporate
that flexibility.
The Purpose of Screening-Level
Ecological Risk Assessments
Screening-Level Ecological Risk Assessments
provide a general indication of ihe potential for
ecological risk (or lack thereof) and may be conducted
for several purposes including: 1) to estimate the
likelihood that a particular ecological risk exists, 2) to
identify the need for site-specific data collection efforts,
or 3) to focus site-specific ecological risk assessments
where warranted.
It is important to note that this guidance adopts the
presumption that all data used in the SLERA are of
adequate quantity and quality, and if data deficiencies
are identified, either further data collection will be
undertaken or other means employed to more fully
characterize exposures (e.g., fate and transport
modeling). If, for example, the SLERA indicates that
adverse ecological effects are possible at environmental
concentrations below standard quantitation limits, a
"non-detect" based on those limits cannot be used as the
sole basis for a "no risk" decision. Further lines of
evidence (e.g., more refined/usable data, modeling
results, or other measures) are needed to fully
characterize the potential for adverse effects.
This guidance also reaffirms that a screening level
assessment, while abbreviated, is nonetheless a
complete risk assessment. Therefore, regardless of the
findings of the Scientific Management Decision Point
(SMDP) occurring after Step 2 (i.e., further assessment
or no further assessment required), each SLERA should
include documentation supporting the risk
characterization and uncertainty analysis.
The first three steps ofthe Superfund ecologicalrisk
assessment process are described in the text box on page 3.
If the SLERA risk characterization indicates the
need for further assessment, Step 3 is begun, and
decisions are made regarding additional elements of
problem formulation, analysis and decision point
criteria. This supplemental guidance addresses how
background, frequency and magnitude of detection, and
dietary considerations may be used to reduce the
COPCs. The use of site-specific information, as
provided for in this ECO Update, should be discussed
with the Regional Ecological Risk Assessors and/or
Biological Technical Assistance Group (BTAG) early
in the Problem Formulation phase of the baseline ERA.
It is the intent of this supplemental guidance to
promote consistency in the screening process, yet allow
for flexibility in application and timing of the elements
that can help streamline more detailed assessments.
Screening-Level Ecological Risk Assessments may be
completed in relatively short time frames, whereas
baseline ERAs may require much longer periods for
planning and implementation, particularly when
attempting to address seasonal or other cyclic events.
Regional Ecological Risk Assessors can use this
flexible approach when introducing components into
the Problem Formulation phase based on regional and
site-specific needs. This will effectively reduce the
COPCs carried through the baseline ERA and the time
required for its completion.
The Purpose of Baseline Ecological
Risk Assessments
Within the Office of Solid Waste and Emergency
Response (OSWER), the Superfiind and RCRA
Corrective Action cleanup programs generally use
baseline ecological risk assessments to: "1) identify and
characterize the current and potential threats to the
environment from a hazardous substance release, 2)
evaluate the ecological impacts of alternative
remediation strategies, and 3) establish cleanup levels
in the selected remedy that will protect those natural
resources at risk." (U.S. EPA 1994e, OSWER Directive
# 9285.7-17). The Superfund program guidance
outlines an eight-step process that meets the three
OSWER objectives for the baseline ERA while further
implementing the Agency's policy of writing risk
assessments that provide transparency in EPA's
decision making process and clarity in communication
with the public regarding environmental risk (U.S. EPA
1995, Risk Characterization Policy). In addition,
application of the information in this ECO Update
should further ensure that, for OSWER cleanups, core
assumptions and science policy are consistent and
comparable across programs, well grounded in science,
and fall within a "zone of reasonableness."
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Standard Components of ERAs
The following text box highlights the risk
assessment components common to both a SLERA and
the Problem Formulation phase of a baseline ERA. In
addition, the text helps to identify points in the ERA
process where additional components may be
considered in developing risk estimates.
Components of a SLERA
Although less detailed than a baseline ERA,
screening assessments still include all of the
following components:
• Screening level Problem Formulation and
Ecological Effects Characterization (Step 1)
* Identification of environmental setting and
preliminary contaminants of concern
»• Determination of contaminant fate and
transport p athways
»• Description of contaminant mechanisms of
ecotoxicity and categories of receptors
likely affected
* Identification of complete exposure
pathways and selection of generic
assessment endpoints
* Selection of screening ecotoxicity values
* Evaluation of uncertainties
• Screening level Expo sure Estimate and Risk
Calculation (Step 2)
»• Determination of screening-level exposure
estimate
* Calculation of risk estimate
»• Risk characterization and evaluation of
uncertainties
• Scientific Management Decision Point
indicating either negligible risk or
continuation to a baseline risk assessment
Components of a Baseline
Ecological Risk Assessment
Problem Formulation
Problem Formulation for a baseline ERA (Step
3) includes the following components:
• Refinement of the Contaminants of Potential
Concern (COPCs) by examining the
assumptions used in Steps 1 and 2
• Further characterization of ecological effects
of contaminants
Reviewing and refining information on
contaminant fate and transport, complete
exposure pathways, and ecosystems
potentially at risk
Selection of site-specific assessment endpoints
Development of a conceptual model and
associated risk questions
Scientific Management Decision Point
summarizing agreement on contaminants of
concern, assessment endpoints, exposure
pathways, and risk questions
Refining Contaminants of Concern
Screening is the comparison of site media
concentrations with conservative lexicologically based
numbers. Contaminants of concern may be refined to
help streamline the overall ERA process by considering
additional components early in the baseline ERA. After
consultation with your Regional Ecological Risk
Assessors and/or BTAG, one or more of the following
components may be included in Step 3.2 of Problem
Formulation. When added, it is important that the
resulting Risk Characterization and Uncertainty
Analysis fully address the issues listed for each
component and describe the rationale underlying the
selection of each comp onent.
These components need not be implemented in the
order presented in this document, nor do all the
components need to be implemented. If, however, any
contaminants are identified for exclusion from the
baseline ERA through application of any or all of the
three supplemental components described herein, it is
essential to evaluate bioaccumulation, biomagnification,
and bioconcentration of each such contaminant as well.
Supplemental Component 1: Background
Background concentrations of contaminants are
those concentrations found in areas surrounding a site,
but are unrelated to site releases. Contributions to these
contaminant concentrations come from two major
sources: first, natural sources (i.e., geologically derived
concentrations of chemicals in the environment not
influenced by human activity), and second, ambient or
anthropogenic sources (i.e., concentrations present due
to human activities, such as automobile use or pesticide
dispersion in farming areas).
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While contaminants of concern may be removed
from further assessment through comparison with
toxicological benchmarks, comparison with background
levels generally cannot be used to remove contaminants
of concern owing to the need to fully characterize site
risk. Such comparisons, however, can be used
effectively to focus the baseline risk assessment, if
needed. An example of the application of background
comparisons would be at a mining site with high levels
of naturally occurring background metals due to local or
nearby geological formations.
Consideration of background assumes that
background contaminant levels have been properly
determined. Until specific guidance on determining
background levels is available, consult with your
Regional Ecological Risk Assessors and/or BTAG to
select an acceptable approach including minimum data
requirements.
Issues to be discussed:
1. Potential toxicity of any contaminants identified as
below background (particularly when toxicity
benchmarks are lacking or when contaminants exceed
toxicity benchmarks);
2. Potential for adverse effects caused by interactions
between chemicals considered as background and those
COPCs to be further investigated; and
3. Enumeration of all criteria by which contaminants
are considered either background or site-related.
Supplemental Component 2: Frequency and
Magnitude of Detection
Use of this component presumes that the sampling
plan comports with Guidance for Data Useability in
Risk Assessment (U.S. EPA 1992e). In particular, the
sampling plan needs to characterize the full range of
variability and distribution in the data and also needs to
satisfactorily meet the criteria for completeness,
comparability, representativeness, precision, and
accuracy.
Similar to this supplemental guidance, current
EPA human health risk assessment guidance discusses
evaluation of COPCs based on frequency of detection
and provides conditions under which compounds may
be eliminated from further assessment. Owing to the
typically small datasets available for ERAs,
particularly screening-level assessments, compared to
most human health risk assessments, a number of the
conditions may not be applicable to ERAs.
Nonetheless, given adequate data quality, further
reduction o f COPC s through application of this
component may be determined acceptable following
consultation with the Regional Ecological Risk
Assessors and/or BTAG. Furthermore, the Project
Manager's approval should be obtained before
eliminating any chemicals from the risk assessment.
Issues to be discussed:
1. Influence of random and/or biased sampling on the
frequency and magnitude of detected values within the
distribution of data;
2. Spatial and temporal pattern of contaminants
identified as low frequency and/or low magnitude;
3. Comp arisen of risk-b ased dete ction limits with
toxicity benchmarks; and
4. Relationship of detected values to toxicity
benchmarks.
Supplemental Component 3: Dietary Considerations
A number of chemicals that may be site-related
function as nutrients in organisms serving as
physiological electrolytes, such as calcium, iron,
magnesium, sodium, and potassium. When present at
concentrations that allow them to function in this
manner, they typically pose little ecological risk.
Conversely, nutrients such as selenium, copper,
molybdenum, and boron, can transition from essential
to toxic at only slightly higher concentrations.
Issues to be discussed:
1. The suite of nutrients relevant to the range of
ecological receptors (wildlife vs. plants) considered at
the site;
2. The p otential for toxic effects resulting from site
concentrations relative to the toxicological benchmarks
for nutrients;
3. Whether contaminant interactions may result in a
nutrient deficiency for organisms of concern; and
4. Whether the nutrient deficiency level and the
toxicity benchmark are similar in magnitude.
Additional Considerations
For those COPCs identified by applying any of the
components listed above, it is essential to evaluate their
potential to bioaccumulate, bioconcentrate, and/or
biomagnify prior to eliminating them from further
consideration in the risk assessment. Compounds with
a high potential to accumulate and persist in the food
chain should be carried through the risk assessment.
Issues to be discussed:
1. The likelihood that contaminants identified for
removal from the list of COPCs could exert adverse
effects on higher trophic level organisms; and
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2. A determination that bioaccumulation and/or
biomagnification has been satisfactorily addressed
through modeling, site-related tissue measurements, or
other methods developed in consultation with the
Regional Ecological Risk Assessors and/or BTAG.
The Role of Tiers and Sub-Tiers
in ERA
The Superfund program guidance describes a
tiered approach for conducting ERAs and further
describes the potential need for additional sub-tiers or
iterations of specific activities at large or complex sites.
In addition to refining contaminants of concern,
effective use of sub-tiering will help focus the ERA
process and improve the quality of risk
characterizations.
The Two-Tier Process
A two-tier process for implementing an ERA is
outlined in Highlight 3-1 in the Superfund program
guidance. The first tier of this process (Steps 1 and 2)
is the screening-level ERA; the second tier (Steps 3
through 8) represents a baseline ERA. The two-tier
process is a means by which to quickly and efficiently
evaluate sites with minimal potential for ecological risk
and eliminate them from further evaluation in the
baseline ERA. The screening-level ERA also allows
contaminants that do not pose a substantial ecological
risk to be removed from the list of COP Cs prior to
conducting the baseline ERA.
Although a decision can be made to proceed with
cleanup after any tier of the ERA process, for some
sites of relatively small size or where the contamination
has a sharply defined boundary, it may be preferable to
cleanup the site to the screening values rather than to
spend time and resources determining a less
conservative cleanup number. For example, a pond
receiving a discharge may contain contaminated
sediments and removing these sediments (resulting in
remediation to conservatively derived levels) maybe
less costly than the studies necessary to determine the
site-specific risk based cleanup levels. Conversely, for
many sites, it is preferable to move directly to a
baseline ERA after the initial screening, and the
guidance routinely provides for this second tier.
Sub-Tiering
A sub-tier may consist of any incremental
iteration of the exposure, effects, or risk
characterizations being conducted within the ERA and
may occur at any point in Steps 3 through 7. It maybe
focused on a parameter, assumption, or assessment
endpoint and may be necessitated through discovery of
new information or new results from completed studies.
Sub-tiering has the goal of focusing the evaluation of
COPCs, so resources can be more effectively applied to
the ERA process. The use of sub-tiers is primarily a
function of the need to further reduce uncertainties in
the baseline ERA, but incremental costs may also limit
the amount or extent of additional activities.
To efficiently utilize sub-tiers, it is important to
establish agreement early on the planning, execution,
and documentation of the work to be performed. This
is due, in part, to the time and effort needed to produce
documents for the next sub-tier (e.g., conclusions of
SLERA and follow-on work plan). In practice, the
ecological risk assessor should provide support for
effective sub-tiering by anticipating the potential
sub-tiering options and facilitating agreement with the
risk manager regarding criteria for acceptance of the
resulting product. Anticipating results of successive
risk calculations and facilitating agreements may take
place at any appropriate time within the baseline ERA
based on the existing information.
Example: Relationship Between Sub-
Tiering and Reduction of COPCs
A screening-level ERA is to be conducted for
a site with numerous COPCs. The stakeholders
agree that the first evaluation will be to compare the
maximum media contaminant levels to the mo st
conservative ecotoxicity screening values, although
they expect that this will result in removal of only a
few COPCs from the list.
Moving from the screening phase into
Problem Formulation, experience predicts that there
will be COPCs with no toxicity benchmarks and
other COPCs that are analyzed for, but not detected
at risk-based detection limits. Therefore, the work
plan for the baseline ERA states that contaminants
included in the analysis of samples, but not
detected, will be removed from the list of COPCs.
Next, the plan states that a dietary exposure model
will be used for specified and retained COPCs
using conservative default assumptions, such as
100% absorption efficiency of all ingested material.
The work plan further states that, for specific
contaminants, an alternate lower absorption
efficiency factor may be applied, if these
contaminants are retained and if the lower factor is
"pre-approved". This process could then continue
as deemed appropriate and effective.
In this way, iterative evaluations (i.e., sub-
tiering) can be done in an objective and technically
sound manner, confidence may be increased in risk
estimates, and bias (or perceived bias) in the risk
characterization may be avoided by using input
from both the risk assessor and the risk manager.
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Documentation of Sub-Tiering
In terms of effectiveness of resource utilization,
sub-tiering has its greatest potential benefit at the point
in the ERA process before data intensive evaluations
are designed. The experience and ability of the risk
assessor to anticipate relevant risk questions and
associated risk calculations and the ability of the site
manager to organize the site documentation contribute
to the most effective use of sub-tiering. What is often
lacking and thereby a source of controversy, however,
is the approach used to document and support the
various decisions influencing work plans for each
particular tier or sub-tier of the ERA. The rationale for
each iteration, the questions to be answered, and
intended use of the resulting information should be
clearly defined and agreed upon with the Regional
Ecological Risk Assessors and/or BTAG.
Analogy: Reduction of COPCs and
Sieving Soil Particles
Reducing the list of COPCs within an ERA
has a direct analogy to the physical separation of
particles in soil particle size distribution analysis.
The physical screens allow a known size particle to
pass through the sieve (up to the diameter of the
screen mesh size). What is not known is the
absolute magnitude and size distribution of the
material retained by the screen. This is precisely
the rationale contained in the Superfund program
guidance for the use of screening in the ecological
risk assessment process. Upon the completion of a
conservative screen, if no materials (contaminants)
are retained by the screen, one can confidently state
that there is a minimal potential for ecological risk
to exist. Alternatively, if materials (contaminants)
are retained by the screen, one cannot conclude that
an ecological risk "actually" exists; the
characteristics of the material retained by the screen
are unknown, other than its size is above some
specified minimum value. This is the basis for the
statement in the Superfund program guidance that
screening level values do not constitute technically
defensible cleanup goals; those must be derived
through the baseline ERA process.
Continuing to draw up on the physic al analogy,
the next challenge is to devise a means of sorting
out desired material from extraneous material.
Within the baseline ERA, we wish to focus on the
contaminants that may actually pose an ecological
risk (commonly referred to as the risk drivers)
rather than on those CO PC's that
either do not actually pose an ecological risk, pose
only a minimal ecological risk, or pose an
ecological risk that is not related to the site and /or
cannot be effectively reduced.
To sort through the "material," larger mesh
sieves are used iteratively. This is done until: 1) all
of the material has passed through the screen and it
is concluded that the mesh size was not too large to
allow wanted material to pass through, 2) it can be
seen that additional iterations will not be
functionally effective and a "different" approach is
needed, or 3) the actual material desired is obtained.
Correlating these outcomes with the SMDPs at the
end of Step 2 of the Superfund program guidance
document, the outcomes may be restated as follows:
1) "There is adequate information to conclude that
ecological risks are negligible and therefore no need
for remediation on the basis of ecological risk," 2)
"The information is not adequate to make a decision
at this point, and the ecological risk assessment
process will continue to Step 3," or 3) "The
information indicates a potential for adverse
ecological effects, and a more thorough assessment
is warranted."
What corresponds to these incrementally
increasing mesh sizes within the ERA process?
First, it must be recognized that the same things are
always occurring in the thought process. Just as the
same thought process occurs in Steps 1 and 2 as
occurs in Steps 3 to 7, each iteration of the ERA,
whether called a tier, a sub-tier, or any other name,
includes similar considerations. In each successive
tier, however, more information is used and
assumptions and calculations are modified
appropriately. The key transition in the process is
from screening, which is conducted by comparison
with benchmarks, to the baseline ERA, where
comparisons generally require the use of negotiated
values agreed upon with Regional Ecological Risk
Assessors and/or BTAGs.
Summary
This supplemental guidance clarifies the two-tier
process for conducting ERAs at Superfund sites and
RCRA Corrective Action facilities discussed in U.S.
EPA 1 997. It describes the purpose of each tier (i.e.,
screening-level and baseline ERAs) and highlights
those components common to both. It further provides
an approach for refining contaminants of concern and
streamlining the ERA process. Readers are referred to
the references listed below for further information.
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References and Other Resources
(* cited in this bulletin)
U.S. EPA. 2000. Ecological Soil Screening Levels
(Eco-SSLs).
www.epa.gov/superfund/programs/risk/ecorisk/
ecossLhtm
U.S. EPA. 1999a. Ecological Risk Assessment and
Risk Management Principles for Superfund Sites,
Final. OSWER Directive # 9285.7-28 P.
www.epa.gov/superfund/programs/risk/ecorisk/
final99.pdf
U.S. EPA. 1999b. ECOTOX Version 2.0. Office of
Research and Development, National Health and
Environmental Effects Lab, Mid-Continent
Ecology Division.
www.epa.gov/ecotox
U.S. EPA. 1998. Guidelines for Ecological Risk
Assessment, Final. EPA/630/R-95/002F.
www.epa.gov/ncea/ecorsklitm
U. S. EPA. 1997.* Ecological Risk Assessment
Guidance for Superfund, Process for Designing
and Conducting Ecological Risk Assessments,
Interim Final. EPA 540-R-97-006, OSWER
Directive #9285.7-25.
www.epa.gov/superfund/programs/risk/ecorisk/
ecorisk.htm
U.S. EPA. 1996a. Ecological Significance and
Selection of Candidate Assessment Endpoin ts.
ECO Update, Interim Bulletin, Volume 3, Number
1. Washington, D.C. Office of Emergency and
Remedial Response, Hazardous Site Evaluation
Division. Publication 9345.0-1 IFsi. EPA/540/F-
95/037. NTIS PB95-963323.
U.S. EPA. 1996b. ECOTOX Thresholds. ECO
Update, Interim Bulletin, Volume 3, Number 2.
Washington, D.C. Office of Emergency and
Remedial Response, Hazardous Site Evaluation
Division. Publication 9345.0-12Fsi. EPA/540/F-
95/038. NTIS PB95-963324.
U. S. EPA. 1995 .* Policy for Risk Characterization at
the U.S. Environmental Protection Agency.
www.epa.gov/ordntrnt/ORD/spc/rcpolicy.htm
U.S. EPA. 1994a. Catalogue of Standard Toxicity
Tests for Ecological Risk Assessment. ECO
Update, Interim Bulletin, Volume 2, Number 2.
Washington, D.C. Office of Emergency and
Remedial Response, Hazardous Site Evaluation
Division. Publication 93450-051. EPA/540/F-
94/013. NTIS PB94-963304.
www.epa.g ov/oerrp age/superfund/programs/risk/
ecoup/v2no2.pdf
U.S. EPA. 1994b. Field Studies for Ecological Risk
Assessment. ECO Update, Interim Bulletin,
Volume 2, Number 3. Washington, D.C. Office
of Emergency and Remedial Response,
Hazardous Site Evaluation Division.
Publication 9345.051. EPA/540/F-94/014 . NTIS
PB94-963305.
www.epa.g ov/oerrp age/superfund/programs/risk/
ecoup/v2no3.pdf
U.S. EPA. 1994c. Selecting and Using Reference
Information in Superfund Risk Assessments. ECO
Update, Interim Bulletin, Volume 2, Number 4.
Washington, D.C. Office of Emergency and
Remedial Response, Hazardous Site Evaluation
Division. Publication 9345.10. EPA/540/F-
94/050. NTIS PB94-963319.
U.S. EPA. 1994d. Using Toxicity Tests in Ecological
Risk Assessment. ECO Update, Interim Bulletin,
Volume 2, Number 1. Washington, D.C. Office
of Emergency and Remedial Response,
Hazardous Site Evaluation Division.
Publication 9345.051. EPA/540/F-94/012 . NTIS
PB94-963303.
www.epa.gov/oerrpage/superfund/programs/risk/
ecoup/v2no 1 .pdf
U. S. EPA. \994s.* Role of the Eco logical Risk
Assessment In the Baseline Risk Assessment,
Final. OSWER Directive # 9285.7-17.
www.epa.gov/superfund/programs/risk/memo.pdf
U.S. EPA. 1992a. Briefing the BTAG: Initial
Description of Setting, History and Ecology of a
Site. ECO Update, Interim Bulletin, Volume 1,
Number 5. Washington, D.C. Office of
Emergency and Remedial Response, Hazardous
Site Evaluation Division. Publication 9345.0-051.
www.epa.g ov/oerrp age/superfund/programs/risk/
ecoup/v Ino5.pdf
U.S. EPA. 1992b. Developing a Work Scope for
Ecological Assessments. ECO Update, Interim
Bulletin, Volume 1, Number 4. Washington, D.C.
Office of Emergency and Remedial Response,
Hazardous Site Evaluation Division.
Publication 9345.0-051.
www.epa.g ov/oerrp age/superfund/programs/risk/
ecoup/v Ino4.pdf
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U.S. EPA. 1992c. Framework for Ecological Risk
Assessment. Washington, D.C. Risk Assessment
Forum. EPA/630/R-92/001.
U.S. EPA. 1992d. The Role of the Natural Resource
Trustees in the Superfund Process. ECO Update,
Interim Bulletin, Volume 1, Number 3.
Washington, D.C. Office of Emergency and
Remedial Response, Hazardous Site Evaluation
Division. Publication 9345.0-051.
www.epa.g ov/oerrp age/superfund/programs/risk/
ecoup/v Ino3.pdf
U.S. EPA. 1992e.* Guidance for Data Useability in
Risk Assessment (Part A), May 1992.
EPA 9285.7-09A/FS.
www.epa.g ov/oerrp age/superfund/programs/risk/
datause/parta.htm
U.S. EPA. 1991 a. Ecological Assessment ofSuperfund
Sites: An Overview. ECO Update, Interim
Bulletin, Volume 1, Number 2. Washington, D.C.
Office of Emergency and Remedial Response,
Hazardous Site Evaluation Division. Publication
9345-0-051.
www.epa.gov/oerrpage/superfund/programs/risk/
ecoup/v Ino2.pdf
U.S. EPA. 1991 b. The Role ofBTAGs in Ecological
Assessment. ECO Update, Interim Bulletin,
Volume 1, Number 1. Washington, D.C. Office
of Emergency and Remedial Response, Hazardous
Site Evaluation Division. Publication 9345-0-051.
www.epa.gov/oerrpage/superfund/programs/risk/
ecoup/v 1 no l.pdf
U.S. EPA. 1989. Risk Assessment Guidance for
Superfund, Volume II: Environmental Evaluation
Manual. EPA/540-1-89/001.
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