An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »


Natural Resource Damages: ERAs and NRDAs

On this page:


This Web page provides Natural Resource Trustees and the general public with information about the Ecological Risk Assessment (ERA) process. CERCLA Section 104 requires that EPA remediate uncontrolled hazardous waste sites in ways that will protect human health and the environment. As the first step to fulfill this mandate, the NCP requires that a baseline risk assessment "characterize the current and potential threats to human health and the environment" [40 CFR §300.430 (d)(4)]. 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" [40 CFR §300.430 (e)(2)(i)(G)].

ERA has evolved from human health-based risk assessment to include evaluations of impacts to the environment. During the 1980s, risk assessment emerged as a prominent regulatory issue and consideration of ecological impacts began to influence regulatory and policy decisions. The use of ecological information for decision-making expanded slowly through the 1980s, as illustrated by the regulation of diazinon (a pesticide) due to potential impacts on bird populations.  

In March 1989, EPA released Risk Management Guidance for Superfund, Volume 2: Environmental Evaluation Manual. This guidance was among the first documents to address ecological risk (EPA540-/1-89/001). In 1992, the Agency published the Framework for Ecological Risk Assessment (EPA/63-R-92/001); it included the first statement of principles for ERAs. In April 1998, EPA published the Guidelines for Ecological Risk Assessment (EPA/630/R-95/002F), which superseded the 1992 guidance. These documents describe methods for conventional single-species chemical-based risk assessments, and techniques for assessing risk to ecosystems from multiple exposures (or stressors) and multiple effects (or endpoints) [ECO Update: Ecological Assessment of Superfund Sites: An Overview. EPA 9345.0-05I. Vol. 1, Number 2, December 1991].

EPA does most ERAs during the remedial investigation and feasibility study (RI/FS) phase of the Superfund response process. They evaluate the likelihood of adverse ecological effects as a result of exposure to physical stressors (e.g., cleanup activities) or chemical stressors (e.g., releases of hazardous substances), which are defined as any physical, chemical or biological entities that can induce adverse responses at a site. These assessments often contain detailed information regarding the contact or co-occurrence of stressors (or agents) with the biological community at a site. Exposure profiles identify ecological receptors (tissues, organisms, populations, communities and ecosystems), habitats and pathways of exposure. The profiles also identify the sources and distribution of stressors in the environment. Other information in ERAs may include evaluations of individual species, populations of species, general trophic levels, communities, habitat types, ecosystems and landscapes.

Top of Page

What Is an Ecological Risk Assessment?

An ERA evaluates the potential adverse effects of human activities on the organisms that make up ecosystems. The risk assessment process provides a way to develop, organize and present scientific information so that it is relevant to environmental decisions. When done for a particular place such as a watershed, the ERA process can help identify vulnerable and valued resources, prioritize data collection activity, and link human activities to their potential effects. ERA results provide a basis for comparing different management options, enabling decision-makers and the public to make better-informed decisions about the management of ecological resources.

The Framework for Ecological Risk Assessment (EPA/63-/R-92/001) describes the ERA framework. It is discussed further in the Guidelines for Ecological Risk Assessment (EPA/630/R-95/002F). The framework consists of three phases: problem formulation, analysis and risk characterization. The analysis phase has two parts – characterization of exposure and characterization of effects.

Problem formulation involves identifying goals and assessment endpoints, preparing a conceptual model, and developing an analysis plan. An assessment endpoint is an explicit expression of the environmental value (species, ecological resource or habitat type) to be protected. Assessment endpoints relate to statutory mandates (e.g., protection of the environment) and must be specific enough to guide the development of the risk assessment study at a particular site. Useful assessment endpoints define both the valued ecological resource and a characteristic of the resource to protect (e.g., reproductive success, production per unit area, areal extent).

The conceptual model describes a series of working hypotheses of how the exposures might affect the ecological components of an environment. The model also describes the ecosystem or ecosystem components potentially at risk and the relationships between assessment and measures of effects and exposure scenarios. Measures of effects are changes in attributes of assessment endpoints or their surrogates in response to the stressors to which they were exposed. Two additional types of measures are used since data other than those used to evaluated responses (i.e., measures of effects) is often required for an ERA. These are measures of exposures (which include the stressor and source measurements) and measures of ecosystems and receptor characteristics (which include water quality conditions, soil parameters and habitat measures). The analysis plan specifies the data required to evaluate impacts to the assessment endpoints as well as data analysis methods.

The analysis phase involves creation of profiles to evaluate the exposure of ecological receptors to stressors and the relationships between stressor levels and ecological effects. Risk characterization is the process of estimating risk through integration of exposure and stressor- response profiles [Guidelines for Ecological Risk Assessment].

The ERA framework is conceptually similar to the approach used for human health risk assessments. However, it has a distinctive emphasis in three areas. First, an ERA can consider effects beyond the individual or species level; it may examine a variety of assessment endpoints, such as an entire population, community or ecosystem. Second, the ecological values to be protected are selected from a wide range of possibilities based on scientific and policy considerations. Finally, ERAs consider nonchemical stressors to the environment, such as loss of wildlife habitat [Guidelines for Ecological Risk Assessment]. An ERA includes the three general phases: problem formulation, analysis and risk characterization.

Top of Page

The Superfund Ecological Risk Assessment Process

EPA’s guidance for ERAs in the Superfund Program – Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments (EPA 540-R-97-006, 1997) – combines scientific methods and stakeholder input. ERAs for the Superfund Program refer to a qualitative and/or quantitative appraisal of the actual or potential impacts of contaminants from a hazardous waste site on plants and animals other than humans and domesticated species. A risk does not exist unless an exposure could cause one or more adverse effects, and that exposure co-occurs with or contacts an ecological component long enough and at a sufficient intensity to elicit the identified adverse effect. (See related information on the Superfund Risk Assessment Home Page.)

The goal of the ERA process in the Superfund Program is to provide risk information that will help risk managers at Superfund sites make informed decisions about releases of hazardous substances. The specific objectives of the process are to identify and characterize current and potential threats to the environment from a hazardous substance release, and to identify cleanup levels that would protect those natural resources from risk. The ERA process for Superfund consists of eight steps.

Step 1: Screening Level – Problem Formulation and Ecological Effects Evaluation

This step provides the following information:

  • Description of the environmental setting, including habitat types, observed species and species likely to be present based on habitat types documented, and threatened, rare and endangered species.
  • Description of contaminants known or suspected to exist at a site and the maximum concentrations in each medium.
  • Potential contaminant fate and transport mechanisms.
  • Mechanisms of ecotoxicity associated with contaminants and categories of receptors that may be affected.
  • Complete exposure pathways that might exist.
  • Screening ecotoxicity values equivalent to chronic No Observable Adverse Effects Levels (NOAELs) based on conservative assumptions.

Step 2: Screening Level – Preliminary Exposure Estimate and Risk Calculations

In the second step, risk is estimated by comparing maximum documented exposure concentrations with the ecotoxicity screening values developed in Step 1. Based on the outcome, the risk manager will decide that the screening-level ERA is adequate to determine that ecological threats are negligible, or that the process should continue to the more detailed ERA outlined in steps 3 through 7 below.

Step 3: Problem Formulation

Step 3 refines the screening-level problem formulation and, with input from stakeholders and other involved parties, expands on the ecological issues of concern at the site. The results of the screening assessment and additional site-specific information are used to determine the scope and goals of the baseline ERA and form the basis of the conceptual model, which is completed in Step 4. A conceptual model describes a series of working hypotheses of how an exposure might affect the ecological components of an environment.

Step 4: Study Design and Data Quality Objective Process

Step 4 completes the conceptual model started in Step 3 by developing the measure of effect. The conceptual model is then used as the basis to develop the study design and data quality objectives (DQOs). The end products of Step 4 are the Work Plan (WP) and the Sampling and Analysis Plan (SAP). The WP documents the decisions and evaluations made during problem formulation and identifies additional research tasks needed to fully evaluate the risks to ecological resources. The SAP provides a detailed description of sampling and data-gathering procedures, as well as a description of the steps required to achieve study objectives.

Step 5: Verification of Field Sampling Design

In this step, the sampling plan, exposure pathways and measures of effects are evaluated. The goal is to verify that the SAP is appropriate for the site.

Step 6: Site Investigation and Data Analysis

Step 6 involves the collection of information to characterize exposures and ecological effects at the site. While much of the data for characterizing potential ecological effects will have been collected during Step 3, the site investigation provides evidence of existing ecological impacts and additional exposure-effects information response information. The site investigation and data analysis should follow the WP and SAP developed in Step 4.

Step 7: Risk Characterization

This step integrates the results of the exposure profile and exposure-effects information (or stressor-response analysis). It is the final phase of the risk assessment process. Risk characterization includes two major components: risk estimation and risk description. Risk estimation involves integrating exposure profiles with the exposure-effects information and summarizing the associated uncertainties. Risk descriptions provide information important for interpreting the risk results. In the Superfund Program, they also identify a threshold for adverse effects on the assessment endpoints.

Step 8: Risk Management

The risk assessment should have established whether a risk is present and defined the range or magnitude of that risk. With this information, a site risk manager must integrate the risk assessment results with other considerations to make and justify risk management decisions. Other considerations in making risk management decisions include existing background levels of contamination, available cleanup technologies, and costs of alternative actions and remedy selections.

Top of Page

Ecological Risk Management Decisions at Superfund Sites

In October 1999, EPA published Ecological Risk Assessment and Risk Management Principles for Superfund Sites (OSWER Directive 9285.7-28P). This final guidance helps Superfund risk managers make consistent ecological risk management decisions based on sound science and communicate site risks to the public. It provides risk managers with six principles to consider when making ecological risk management decisions. The guidance states that all ERAs should follow the eight-step process described in Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments (EPA 540-R-97-006, 1997). The process is summarized above.

The Risk Management Principles supplement the ERA guidance and help remedial project managers and on-scene coordinators in planning ERAs of appropriate scope and complexity, and in identifying response alternatives that are protective of the environment. By adhering to these principles, risk managers will be able to present a clear rationale for their ecological risk management actions as presented to the public in the proposed plan and the Record of Decision steps of the Superfund response process. In addition, the guidance provides a question and answer section to help guide risk managers and assessors through the eight-step ERA process. The guidance asks risk managers to adhere to six principles (summarized below) when scoping ERAs and making ecological risk management decisions.

Principle 1: Superfund's Goal Is to Reduce Ecological Risks to Levels that Will Result in the Recovery and Maintenance of Healthy Local Populations and Communities of Biota

Superfund risk managers and risk assessors should select assessment endpoints and measures that are ecologically relevant to the site, and include species exposed to and sensitive to site-related contaminants.

Principle 2: Coordinate with Federal, Tribal and State Natural Resource Trustees

EPA recognizes that its response actions may not lead to complete recovery of site ecosystems. Additional restoration by Natural Resource Trustees may be needed to bring natural resources back to baseline conditions in an acceptable timeframe. EPA and Trustees should coordinate EPA investigations of risk with Trustee investigations of resource injuries to ensure efficient use of federal and state resources.

Principle 3: Use Site-specific Ecological Risk Data to Support Cleanup Decisions

Site-specific data should be collected and used, wherever practical, to determine whether site releases present unacceptable risks and to develop quantitative cleanup levels that are protective. Site-specific data includes plant and animal tissue residue data, bioavailability factors, and population- or community-level effect studies.

Principle 4: Characterize Site Risks

When evaluating ecological risks and the potential for response alternatives to achieve acceptable levels of protection, Superfund risk managers should characterize risk in terms of magnitude, severity and distribution, as well as the potential for recovery of affected receptors.

Principle 5: Communicate Risks to the Public

The scientific basis and ecological relevance of assessment endpoints used in a site risk assessment should be clearly communicated to the public.

Principle 6: Remediate Unacceptable Ecological Risks

Superfund's goal is to eliminate unacceptable risks due to any release or threatened release. Contaminated media that may affect the ability of local populations of plants or animals to recover and maintain themselves in a healthy state at or near a site should be remediated to an acceptable level.

Top of Page

On this page:


This Web page provides EPA staff and the general public with more information on the Natural Resource Damage Assessment (NRDA) process. Natural Resource Trustees conduct NRDAs to calculate the monetary cost of restoring injuries to natural resources that result from releases of hazardous substances or discharges of oil. Damages to natural resources are evaluated by identifying the functions or “services” provided by the resources, determining the baseline level of the services provided by the injured resource(s), and quantifying the reduction in service levels as a result of the contamination. Regulations for assessing NRD are part of both CERCLA and OPA.

If natural resources are injured by a discharge or release of a mixture of oil and hazardous substances, U.S. Department of Interior (DOI) regulations are used. The Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) regulations are applicable only in assessing damages resulting from discharges of oil.

DOI Regulations

CERCLA section 301(c) requires regulations for the assessment of damages for injury to, destruction of or loss of natural resources resulting from a discharge of oil or release of a hazardous substance. Executive Order 12580 delegated responsibility for this rulemaking to DOI.

DOI's regulations provide a framework and standards for the NRDA process in coastal and marine environments (Type A) and other environments (Type B). The Type A process involves the use of a computer model to assess damages that result from chemical or oil discharges in coastal and marine environments. The Type B process is for situations that require an individual approach. Both Type A and Type B regulations call for four sequential phases in the assessment of damages [43 CFR 11]:

Phase 1: Pre-assessment Screen. Phase 1 determines if additional action is warranted. Trustees must determine whether an injury has occurred and a pathway of exposure exists. The pre-assessment screen is a prerequisite to conducting a formal NRDA.

Phase 2: Assessment Plan. Trustees must confirm the exposure of Trust Resources and develop an Assessment Plan to identify how the potential damages will be evaluated. Type A Assessment Plans document that conditions for use of Type A procedures are met, provide site-specific data inputs the Trustee will use to run the computer model, and provide the results of a preliminary application of the model. Type B Assessment Plans to identify site-specific studies the Trustees will conduct and quality control/assurance procedures. Draft Assessment Plans under both Type A and Type B procedures must be available for public review and comment.

Phase 3: Assessment Implementation. Phase 3 gathers the data necessary to quantify the injuries and determine damages. The work consists of three steps: injury determination, quantification and damage determination. Under Type A Assessment Plans, a computer model performs these steps. Under Type B Assessment Plans, laboratory and field studies perform the steps. Trustees quantify injuries by identifying the functions or "services" provided by the resource; determining the baseline level of such services; and quantifying the reduction in service levels that result from the impacts.

Phase 4: Post-Assessment. Trustees prepare a Report of Assessment detailing Phase 3 results. When Trustees use a Type A Assessment Plan, the report will include the output of the final computer model application. The report usually proposes a reasonable number of restoration alternatives, including natural attenuation. The report selects a preferred alternative based on several factors, including technical feasibility, relationship of costs to benefits, and consistency with response actions.

The regulations also require that Trustees coordinate assessment efforts, including the pre-assessment screen, with the lead response agency in any situation where response activity is planned or underway [40 CFR 11.23(f)]. The Trustee Information and Query Report provides information regarding activities underway at CERCLA sites.

Top of Page

NOAA Regulations

OPA section 1006(e)(1) requires that NOAA develop regulations for the assessment of NRD that may result from a discharge of oil (except for any part of oil defined as a "hazardous substance" by CERCLA).

NOAA's regulations provide a framework for conducting NRDAs that achieve restoration under OPA. NOAA's natural resource damage assessment regulations include three phases [15 CFR 990].

Phase 1: Pre-assessment. Trustees first determine whether they have jurisdiction under OPA. Then Trustees must determine whether to conduct restoration planning. Trustees determine if it is likely that the discharge has caused an injury, if response actions will adequately address the injuries, and if feasible restoration alternatives exist. If so, Trustees are to proceed with the NRDA.

Phase 2: Restoration Planning. This phase has two basic components: injury assessment and restoration selection. Injury assessment evaluates whether the discharge has resulted in an adverse change in natural resources and/or services. During the restoration selection stage, the Trustee determines the need for, and scale of, restoration actions. For injury assessments, Trustees quantify the degree and the spatial and temporal extent of the injuries in comparison to baseline conditions. Trustees must develop a Draft Restoration Plan that identifies a primary restoration action to return injured resources to baseline conditions and a compensatory restoration action to compensate for the interim loss of services pending return to baseline conditions. This involves evaluating the range of primary and compensatory restoration alternatives, selecting and justifying a preferred alternative, and preparing the plans. The regulation identifies six criteria that must be used to evaluate restoration alternatives. The public must be given the opportunity to comment on the Draft Restoration Plan.

Phase 3: Restoration Implementation. The Final Restoration Plan is presented to potentially responsible parties (PRPs) for implementation or to fund Trustees' implementation costs.

Trustees must coordinate their activities with other Trustees, response agencies and PRPs when operations take place at the same time [15 CFR 990.14]. Trustees may develop pre-incident Memoranda of Understanding (MOUs) to more efficiently coordinate their activities with response agencies [15 CFR 990.14(b)].

Top of Page