EPA
United States
Environmental
Protection
Agency
Office of
Solid Waste and
Emergency Response
Publication 9345.0-051
December 1991
ECO Update
Office of Emergency and Remedial Response
Hazardous Site Evaluation Division (OS-230)
Intermittent Bulletin
Volume 1, Number 2
Ecological Assessment of Superfund Sites: An Overview
This document is the second issue of the ECO Update series
of intermittent bulletins, published by the Toxics Integration
Branch, Hazardous Site Evaluation Division, Office of
Emergency and Remedial Response. Practical experience
with the process of ecological assessment at Superfund sites
has pointed to the need for information and guidance
concerning both the scientific and management aspects of
ecological assessment. The ECO Update series is intended to
fill this need.
Ecological Assessment of Superfund Sites: An Overview is an
updated framework for ecological assessment in the Superfund
program. As such, it offers a description of ecological
assessment components and a discussion of how they fit into
the Remedial Investigation and Feasibility Study (RI/FS)
process. Ecological assessment in the removal process will be
addressed in a future ECO Update.
The ECO Update Series
ECO Updates are a series of Intermittent Bulletins
intended to facilitate ecological assessment of Superfund sites.
Each Bulletin focuses on one aspect of ecological studies or
ecological assessment in the remedial process. Individual
Bulletins may discuss either technical methods or the
management of ecological assessments.
Limiting each Bulletin to a specific topic allows flexibility
for the user to select only those Bulletins that are applicable to
the site in question or the user's needs. For example, some
sites do not require toxicity tests, so investigators would not
need to consult Bulletins specific to testing. A user who needs
only general information on Natural Resource Trustees can
refer to a specific Bulletin on that topic and not have to look
through a larger document containing other, less relevant
information.
The Bulletin series is written for both general and technical
audiences, which includes EPA site managers and staff,
contractors, State personnel, and anyone else involved in the
performance, supervision, or evaluation of ecological
assessments in Superfund.
Ecological assessment involves considerable professional
judgement. The ECO Updates assume that readers will confer
with qualified scientists for site-specific advice. These
Bulletins are not step-by-step guides on how to accomplish an
assessment. The series supplements the advisory process
involving Regional Biological Technical Assistance Groups
(BTAGs). EPA staff should consult their BTAG coordinator
for more detailed information on ecological assessment in
their Region.
Background
The Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA), as amended,
requires EPA to remediate uncontrolled hazardous waste sites
in ways that will protect both human health and the
environment. To fulfill this mandate, the National Oil and
Hazardous Materials Contingency Plan (NCP) requires that
IN THIS BULLETIN
Backgrou nd 1
What is an Ecological Assessment? 2
Ecological Assessment in the RI/FS Process 5
ECO Update is a Bulletin series on ecological assessment of Superfund sites. These Bulletins serve as supplements to Risk Assessment Guidance for Superfund, Volume
II: Environmental Evaluation Manual (EPA/540-1-89/001). The information presented is intended as guidance to EPA and other government employees. It does not
constitute rulemaking by the Agency, and may not be relied on to create a substantive or procedural right enforceable by any other person. The Government may take
action that is at variance with these Bulletins
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the baseline risk assessment, which is conducted during the
Remedial Investigation and Feasibility Study (RI/FS),
"characterize the current and potential threats to human health
and the environment."1 The NCP also specifies that
"[environmental evaluations shall be performed to assess
threats to the environment, especially sensitive habitats and
critical habitats of species protected under the Endangered
Species Act."2
In December 1988, the Office of Emergency and Remedial
Response (OERR) and the Office of Waste Programs
Enforcement issued a joint memorandum to Regional Division
responsible for Superfund, directing that "thorough and
consistent" ecological assessments be performed at all
Superfund sites in both the removal and remedial programs.
In particular, the directive called on the Regions to incorporate
ecological assessments into the RI/FS stage during
development of the work plan, and to discuss the ecological
assessment in the Proposed Plan for site remediation.
To assist the Regions in implementing this policy, OERR
issued the Superfund Environmental Evaluation Manual 3 in
March 1989 to provide site managers with a general
framework for understanding the ecological assessment
process. The manual is predicated on the understanding that
ecological assessment combines careful observation, data
collection, testing, and professional judgement. Hence, the
manual's principal goal is to introduce the subject to site
managers and encourage them to seek the advice and
assistance of the Regional BTAG.4
What is an Ecological Assessment?
The Environmental Evaluation Manual defines ecological
assessment as:
... a qualitative and/or quantitative appraisal of the actual
or potential effects of a hazardous waste site on plants and
animals other than people or domesticated species.
In practical terms, ecological assessment comprises four
interrelated activities:
• Problem Formulation—qualitative evaluation of
contaminant release, migration, and fate; identification
of contaminants of concern, receptors, exposure
pathways, and known ecological effects of the
1 40 CFR Part 300.430 (d)(4).
2 40 CFR Part 300.430(e)(2)(i)(G).
3 U.S. Environmental Protection Agency, Risk Assessment Guidance for
Superfund, Volume II: Environmental Evaluation Manual (EPA/540-1-
89/001), 1989.
4 These groups are sometimes known by different names, depending on
the Region, and not all Regions have established BTAGs. Readers should
check with the appropriate Superfund manager for the name of the BTAG
coordinator or other sources of technical assistance in their Region.
contaminants; and selection of endpoints for further
study.
• Exposure Assessment—quantification of
contaminant release, migration, and fate;
characterization of exposure pathways and receptors;
and measurement or estimation of exposure point
concentrations.
• Ecological Effects Assessment—literature reviews,
field studies, and toxicity tests, linking contaminant
concentrations to effects on ecological receptors.
• Risk Characterization—measurement or estimation
of both current and future adverse effects.
These components of ecological assessment are illustrated
in Figure 1. As the diagram indicates, each element in the
process can affect others. In reality, investigators frequently
find that the components do not always follow one another in
a stepwise manner, and may actually find themselves working
on aspects of all four components at the same time.
Problem Formulation
Problem Formulation defines the objectives and scope of
the ecological assessment. This component of an ecological
assessment primarily involves a review of existing data
(including previous studies of the site, such as the Preliminary
Assessment, Site Inspection, RI Field Investigation, and other
sources). Its end product is a conceptual model that identifies
the environmental values to be protected, the data needed, and
the analyses to be used.
The problem formulation component may be difficult to
distinguish from exposure assessment or ecological effects
assessment. This situation arises from elements (e.g., effects
and receptors) shared among these three components. Problem
formulation differs from the other two components in the level
of detail and quantification. The difference lies in the
distinction between identification (i.e., naming and listing) of
these common elements and characterization (i.e.,
description and quantification). In problem formulation,
investigators:
• Focus on collecting preliminary information necessary
to design the exposure and ecological effects
assessment, and
• Identify data needed to complete those assessments.
Qualitative Evaluation of Contaminant Release,
Migration, and Fate
This portion of problem formulation describes what is
known about contaminated media, contaminant movement,
and the geographical extent of current and future
contamination. Ecological considerations for contaminant
release, migration, and fate include:
5 An endpoint is an expected or anticipated effect of a contaminant on an
ecological receptor. Endpoints are discussed at greater length in the section
on Problem Identification.
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• Ground water discharge to surface water and
wetlands,
• Transport of contaminated sediment,
• Runoff from and erosion of contaminated soils, and
• Bioaccumulation and bioconcentration.
Identification of Contaminants of Concern
Not all contaminants warrant equal attention with regard to
risk. Further, not all contaminants that pose human health
risks are important with respect to ecological risk—and vice
versa. Factors to consider in identifying a contaminant of
ecological concern include its:
• Environmental concentration in media (soils,
surface water, ground water, sediments, air, and biota)
representing ecological exposure pathways;
• Frequency of occurrence, defining the prevalence of
the contaminant in site media;
• Background levels, indicating the concentrations that
cannot be attributed to the site;
• Unavailability, or presence in a form that can affect
organisms;
• Physical-chemical properties, such as volatility and
solubility;
• Potential for bioaccumulation or bioconcentration,
based on its physical-chemical properties and its
tendency to occur in biota at higher concentrations
than the surrounding environment;
• Potency, or the amount of toxicant capable of
producing adverse effects; and
• Effects, such as acute lethality or sublethal responses
(e.g., reproductive impairment).
Identification of Exposure Pathways
Based on the analysis of contaminant release, migration,
and fate, investigators identify potential exposure pathways
for ecological receptors. An exposure pathway is the link
between a contaminant source and a receptor. In evaluating
exposure pathways, the analyst should consider all media
(groundwater, surface water, sediments, soils, air, and biota)
that are or could be contaminated. For example, exposure
may be the result of direct contact with contaminated media
(e.g., dermal, uptake through gills, ingestion) or exposure
through the food chain. Investigators should consider all
potential receptors when identifying exposure pathways.
Identification of Receptors
Receptors are individual organisms, populations, or
communities that can be exposed to a contaminant.
Identification of receptors arises from a review of the fate,
migration, and potential release of contaminants. Ecologists
begin by identifying potentially exposed habitats on or near
the site using a wide variety of methods, including field
reconnaissance, aerial photography, satellite imagery, and a
review of previous studies to accomplish this task. As they
identify potentially exposed habitats, ecologists develop lists
of species known or likely to occur in each habitat.
Identification of receptors should include:
• Species considered essential to, or indicative of, the
healthy functioning of the habitat (e.g., stream
invertebrates);
• Rare endangered or threatened species on or near the
site; and
• Species protected under Federal or State law (e.g.,
Migratory Bird Treaty Act, Marine Mammal
Protection Act).
Identification of Known Effects
Many sources, including databases and publications,
contain information on ecological effects of contaminants.
For example, EPA's Ambient Water Quality Criteria (AWQC)
Documents and AQUatic Toxicity Information REtrieval
(AQUIRE) database contain peer-reviewed data describing
effects of contaminants on aquatic (freshwater and marine)
organisms. Data on terrestrial effects and aquatic information
not included in the AWQC documents or AQUIRE are
available in the published literature. Where appropriate, data
on chemicals similar but not identical to site contaminants can
help characterize likely effects. Modeling techniques, such as
Quantitative Structure Activity Relationships (QSAR),
sometimes help in identifying surrogate chemicals for data
collection. These methods require specialized expertise to
ensure proper selection of surrogates and interpretation of
results.
Site managers should obtain information from other
investigations conducted on or near the site, to help target the
ecological assessment toward the most relevant questions.
Examples of such information include:
• Field or laboratory studies from previous
investigations of the site;
• Corroborated reports of unusual events such as fish
kills, other animal mortality, highly stressed
vegetation, or absence of species that experts would
expect in the habitat; and
• Fish or wildlife consumption advisories issued by
State or local government agencies.
Selection ofEndpoints
Investigators next identify effects requiring further study.
These are known as endpoints. Risk assessors distinguish
between two types of endpoints. An assessment endpoint
describes the effects that drive decision making, such as
reduction of key populations or disruption of community
structure. Measurement endpoints approximate, represent,
or lead to the assessment endpoint, using field or laboratory
methods.6 An assessment endpoint often has more than one
6 Glenn W. Suter II, "Ecological Endpoints," Chapter 2 in USEPA,
Ecological Assessment of Hazardous Waste Sites: A Field and Laboratory
Reference (EPA/600/3-89/013).
December 1991 • Vol. 1, No.
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Ecological Assessment of Superfund Sites: Overview
Figure 1
PROBLEM FORMULATION
Qualitatively evaluate contaminant release, migration, and fate
Identify:
• Contaminants of ecological concern
• Receptors
• Exposure pathways
• Known effects
Select endpoints of concern
Specify objectives and scope
EXPOSURE ASSESSMENT
Quantify release, migration, and fate
Characterize receptors
Measure or estimate exposure point
concentrations
ECOLOGICAL EFFECTS
ASSESSMENT
Literature
Toxicity testing
Field Studies
RISK CHARACTERIZATION
• Current adverse effects
• Future adverse effects
• Uncertainty analysis
• Ecological significance
REMEDIAL OBJECTIVES
ANALYSIS OF
REMEDIAL ALTERNATIVES
• REMEDY SELECTION
• RECORD OF DECISION
• REMEDIAL DESIGN
• REMEDIAL ACTION
December 1991 • Vol. 1, No.
ECO Update
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measurement endpoint associated with it. Most studies have
more than one set of assessment and measurement endpoints.
The critical step in selecting endpoints is deciding what
effects are important to remedial decision making. The
assessment endpoint should reflect a potentially significant
ecological impact. Primary criteria for selecting measurement
endpoints are based on their usefulness in linking field or
laboratory data to the assessment endpoint.
For example, the assessment endpoint for a particular site
might be the probability of a significant reduction of a fish
population. The measurement endpoint used to arrive at such
a probability might be the chemical concentration shown to
cause a reduction in survival, growth, or reproduction in a
standard laboratory toxicity test.
Ecologists often select more definitive site-specific
measurement and assessment endpoints during the exposure
assessment component. Information on contaminant
migration, fate and other factors, discussed below under
"Exposure Assessment," influences the choice of appropriate
endpoints.
Specifying Objectives and Scope
The purpose of the activities described above is to identify
the preliminary objectives and scope of the ecological
assessment and additional data needed to complete the
assessment. This is critical to the assessment process. It
ensures that data collection, field studies, laboratory tests, and
the overall assessment can answer the questions relevant to
making remedial decisions.
Ecological assessment is an iterative process. As such,
investigators often must revise the objectives and scope of the
ecological assessment as they collect and analyze site data.
Using such information, they can identify a need for more
study, different studies, or fewer studies.
Exposure Assessment
Exposure assessment quantifies the magnitude and type of
actual and/or potential exposures of ecological receptors to
site contaminants. The key elements in exposure assessment
are:
• Quantification of contaminant release, migration, and
fate;
• Characterization of receptors; and
• Measurement or estimation of exposure point
concentrations.
Exposure assessment often involves considerable effort
and technical expertise to complete. Site managers should
consult with their Regional BTAG to identify specific
approaches for evaluating ecological exposure.
Quantification of Release, Migration, and Fate
In the Exposure Assessment phase, investigators develop
estimates of current and future contaminant levels in affected
media, including all relevant spatial and temporal
characteristics of the contamination. These estimates can then
be used to determine exposure point concentrations (discussed
below).
Direct sampling of media yields information on the current
location and concentration of contaminants. Fate-and-
transport models predict the movement of contaminants from
the source and between media. Site managers should consult
their BTAGs and other Regional specialists about sampling
design, sample placement and timing, and the availability and
selection of models applicable to their sites.
Characterization of Receptors
Most sites requiring ecological assessments contain a large
number of species, populations, and communities — from
microbes to mammals, from algae to trees. Evaluating risks
for each and every species present is impossible. To develop a
reasonable and practicable evaluation, the investigator focuses
on a limited number of receptors for the assessment.
Ecologists select these receptors based on the endpoints of
concern and specific characteristics of the site under study.
In characterizing receptors, investigators collect
information (primary from published literature) on the species'
feeding habits, life histories, habitat preferences, and other
attributes that could affect their exposure or sensitivity to
contaminants.
Exposure Point Concentrations
After identifying receptors, and selecting a subset of those
receptors, investigators estimate the concentration of
contaminant(s) in the media to which the receptors are
exposed. This is known as the exposure point concentration,
which investigators measure in the environmental medium or
estimate using assumptions and/or fate-and-transport
modeling.
The amount of contaminant a receptor takes in depends on
such factors as:
• The properties of the contaminant,
• The way the organism assimilates it (e.g., direct
absorption, ingestion),
The nature of the receptors (e.g., behavior, life
history), and
• The physical/chemical properties of the media (e.g.,
pH, hardness, organic carbon content).
If a contaminant is known or expected to bioconcentrate or
bioaccumulate, investigators collect and analyze samples
from biota at two or more trophic levels (e.g., plant,
herbivore, carnivore) along with surrounding media. Risk
assessors use this information in two ways:
• Directly, as exposure point concentrations for dietary
exposure pathways for ecological receptors; or
• Indirectly, for calculating site-specific
bioconcentration factors (BCFs) or bioaccumulation
factors (BAFs) to predict the food-chain transfer of
contaminants to organisms at higher trophic levels.
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Ecological Effects Assessment
This component concerns quantitatively linking
concentrations of contaminants to adverse effects in receptors.
Literature reviews, field studies, and/or toxicity testing
provide this "dose-response" information: that is, how much
toxicant is associated with how much of an adverse effect.
Literature Reviews
Organisms differ widely in their ability to tolerate
toxicants, depending on several factors, including
environmental conditions, the nature of the chemical, the age
and reproductive status of the organism, and inherent
differences among species. Literature reviews can provide
specific dose-response information for the species under
study.
Dose-response information is useful in risk
characterization (discussed below) or as the basis for further
ecological effects studies. By comparing measured
concentrations of contaminants in site media with literature
values for adverse effects, investigation can decide whether
they need to proceed with site-specific investigations such as
field studies or toxicity tests.
Field Studies
Ecological field studies offer direct or corroborative
evidence of a link between contamination and ecological
effects. Such evidence could include:
• Reduction in population sizes of species,
• Absence of species normally occurring in the habitat,
• Presence of species associated primarily with stressed
habitats,
• Changes in community diversity or trophic structure,
and
• Incidence of lesions, tumors, or other pathologies.
Ecologists usually compare data on observed adverse
effects to information obtained from a reference area not
affected by contamination from the site. For instance, for a
stream contaminated by a waste site, the reference site might
be an area upstream from the source of contamination, or a
nearby-uncontaminated stream with similar physical
characteristics.
Investigators must collect chemical and biological data
simultaneously. This allows them to determine if a correlation
exists between contaminant concentrations and ecological
effects.
Toxicity Testing
Toxicity tests evaluate the effects of contaminated media
on the survival, growth, reproduction, and metabolism of test
organisms. When ecologists review test results along with
data on chemical concentrations and biological observations
from field studies, they often find convincing evidence that
observed or predicted effects are attributable to the presence of
hazardous substances. Investigators also use toxicity tests to
demonstrate the spatial extent of contamination and identify
areas of high contaminant concentrations.
Risk Characterization
The science of risk assessment in ecology has not evolved
to the point where scientists can make standard risk
calculations for common risk scenarios, as they often do in
human health evaluations at Superfund sites. Risk
characterization in ecological assessment is a process of
applying professional judgement to determine whether adverse
effects are occurring or will occur as a result of contamination
associated with a site.
Risk characterization is primarily a process of comparing
the results of the exposure assessment with the results of the
ecological effects assessment. Available methods (either
quantitative or qualitative) seek to answer the following
questions:
• Are ecological receptors currently exposed to site
contaminants at levels capable of causing harm, or is
future exposure likely?
• If adverse ecological effects are observed or predicted,
what are the types, extent, and severity of the effects?
• What are the uncertainties associated with the risk
characterization?
The risk characterization concludes with a risk description,
which (1) includes a summary of the risks and uncertainties,
and (2) interprets the ecological significance of the observed
or predicted effects. The risk description is a key step in
communicating ecological risks to site managers and decision
makers. When ecologists interpret and communicate
ecological significance for the risk description, they should
consider such factors as the nature and magnitude of the
effects, the spatial and temporal distribution of the effects, and
the potential for recovery.
Ecological Assessment in the RI/FS
Process
Because the RI/FS supports risk-management decision
making, assessment of ecological risk plays an essential role.
Figure 2 shows where ecological information is necessary in
the RI/FS and post-RI/FS activities.
Scoping of the RI/FS
Scoping of the ecological assessment should begin with,
and be included as part of, the overall RI/FS scoping process
to :
• Help identify the kinds of remedial decisions that site
managers need to make,
• Determine the types of ecological data investigators
need to support decision making, and
December 1991 • Vol. 1, No.
ECO Update
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• Design field and/or laboratory studies for collecting
those data.
Ecologists should participate in developing a conceptual
model of the site. The ecological portion of this model is
developed during the Problem Formulation phase of the
ecological assessment.
Ecological assessment can be complex undertaking. For
this reason, site mangers need to consult with their BTAGs
while preparing work scopes. For most sites, Remedial
Project Managers should develop a phased approach to the
ecological assessment with expert review at each phase. In
this way, investigators can use data or observations from one
phase to determine the most appropriate studies for the next
phase.
RI/FS Site Characterization
The Site Characterization phase of the RI/FS requires a
baseline risk assessment, which includes an ecological
assessment. The purposes of this ecological assessment are to:
• Describe the observed or potential magnitude of
adverse ecological effects at the site and the primary
cause of the effects, and
• Characterize the ecological consequences of the
further action" remedial alternative.
no
Site managers should ensure that ecological studies for the
baseline risk assessment are completed during the field
investigation phase of site characterization.
Feasibility Study
Ecological information contributes to the Feasibility Study
(FS) process by assisting decision makers in the assessment
and selection of remedial alternatives. In developing
preliminary remediation goals (PRGs), investigators must
address the results of the ecological assessment and other
ecological issues specified in criteria, guidance, and applicable
or relevant and appropriate requirements (ARARs).
Most FSs examine numerous remedial alternatives. In
such cases, site managers must screen the alternatives to
narrow the list that will be evaluated in detail. The ecological
assessment helps this detailed analysis of alternatives by
identifying risks or benefits of each with respect to ecological
receptors. The analyses and conclusions of the ecological
assessment can provide information on:
• The effectiveness of the alternative in reducing
ecological risks associated with contamination, and
• The ecological effects that may result from the
remedial action (e.g., habitat destruction).
The ecological assessment can provide information for
ecological monitoring during remedial and post-remedial
activities. For detailed advice on applying ecological
information to the FS process, site managers should consult
their Regional BTAGs.
December 1991 • Vol. 1, No.
ECO Update
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Ecological Assessment in the RI/FS Process
Figure 2
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PROBLEM
FORMULATION
Review ecological
datacollected from site
inspection and other
sites
Review sampling/data
collection plans
Formulate preliminary
remediation goals
Determine level of effort
for baseline ecological
risk assessment
Refine remedial
goals based on risk
assessment and
ARARs
•Recp'Vd: of Deei4ion;
Conduct risk
evaluation of
remedial
alternatives
Ecological
Monitoring
CONDUCT BASELINE ECOLOGICAL
ASSESSMENT
Exposure Assessment
Ecological Effects Assessment
Risk Characterization
December 1991 • Vol. 1, No.
ECO Update
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