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Detailed guidance on performing ecological risk assessments is provided in Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessment (U.S. EPA 1997d, also referred to as “ERAGS” ). In addition, OSWER Directive 9285.7-28P, Ecological Risk Assessment and Risk Management Principles for Superfund Sites (U.S. EPA 1999b), provides risk managers with several principles to consider when making ecological risk management decisions. As stated in the Role of the Ecological Risk Assessment in the Baseline Risk Assessment (U.S. EPA 1994b), the purpose of the ecological risk assessment is 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.
Although not EPA guidance, project managers may find useful the Navy guidance Implementation Guide for Assessing and Managing Contaminated Sediment at Navy Facilities, which provides information on performing human health and ecological risk assessments at contaminated sediment sites [U.S. Naval Facilities Engineering Command (FEC) 2003].
2.3.1 Screening Risk Assessment
A screening risk assessment typically is performed to identify the contaminants of potential concern (COPCs) and the portions of a site that may present an unacceptable risk to human health or the environment.
Currently, there are no widely accepted sediment screening values for human health risk from either direct contact with sediment or from eating fish or shellfish, although research is ongoing. For floodplain and beach soils, human health soil screening levels may be used. Widely accepted screening values do exist for ecological risk from direct toxicity, although, similar to the situation for human health risk, screening values for risk to wildlife and fish from bioaccumulative contaminants have not yet been fully developed. Each of these issues is discussed further below. In cases where screening levels do exist, or may be developed in the future, it is very important for project managers to keep in mind that screening values are not designed to be used as default cleanup levels and generally should not be used for that purpose. In evaluating whether specific screening values are appropriate for a particular site, project managers should consider whether the source of the data used to develop the screening values are relevant to site conditions, and understand the methods by which the screening values were derived.
Project managers may also find ecological screening values or human health screening level exposure assumptions useful for evaluating whether detection levels for sediment analytical work are sufficiently low to be useful for risk assessment.
2-9 2-10 Highlight 2-3: Sample Pictorial-Style Conceptual Site Model Focusing on Human and Ecological Threats
When evaluating human health risks from direct contact with sediments and from bioaccumulative contaminants in fish and shellfish, RAGS (U.S. EPA 1989), and other risk guidance discussed above, should be followed to identify the COPCs that may present an unacceptable risk. In general, if bioaccumulative contaminants are found in biota at levels above site background, they should not be screened out and should be carried into the baseline risk assessment.
When evaluating human health risks from direct contact with floodplain or beach soils, OSWER and several regions have soil screening values that may be useful. Human health soil screening levels (SSLs) for residential and industrial properties are available through EPA’s Superfund Web site at http://www.epa.gov/superfund/resources/soil, which provide a generic approach and exposure assumptions for evaluation of risks from direct contact with soil.
When screening ecological risk to benthic biota from direct toxicity, project managers should consult EPA’s Eco-Updates EcoTox Thresholds (U.S. EPA 1996c) and The Role of Screening-Level Risk Assessment and Refining Contaminants of Concern in Baseline Ecological Risk Assessments (U.S. EPA 2001f), which describes the process of screening COPCs. The EPA’s equilibrium-partitioning sediment benchmarks are available at http://www.epa.gov/nheerl/publications/, and the Superfund program’s Ecotox Thresholds (ETs) are available at http://www.epa.gov/oswer/riskassessment/pdf/eco_updt.pdf can be used as screening values for risk to benthic biota from direct toxicity. Other published sediment guidelines [e.g., National Oceanic and Atmospheric Administration (NOAA) Screening Quick Reference Tables (SQuiRTs), http://response.restoration.noaa.gov/cpr/sediment/squirt/squirt.html] can also be used as screening values. Table 3-1 in the Navy guidance (U.S. Navy FEC 2003) also provides a list of citations for ecological screening values for sediment.
When screening ecological risks to terrestrial receptors from contaminated floodplain soils, the OSWER Directive 9285.7-55, Guidance for Developing Ecological Soil Screening Levels [(Eco-SSLs), U.S. EPA 2003c, http://www.epa.gov/oswer/riskassessment/ecorisk/ecossl.htm] should be used. EcoSSLs for some receptors have been developed for aluminum, antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, copper, dieldrin, iron, lead, manganese, nickel, pentachlorophenol, selenium, trinitrotoluene (TNT), and zinc. Screening values for dichloro diphenyl trichlorethane (DDT), polycyclic aromatic hydrocarbons (PAHs), silver, and vanadium are currently under development.
For ecological risk to wildlife or fish from food chain effects, widely accepted screening values have not yet been fully developed. As for the human health risk assessment, if bioaccumulative contaminants are found in biota at levels above site background, they generally should not be screened out and should be carried into the baseline risk assessment for ecological risk as well.
2.3.2 Baseline Risk Assessment
At contaminated sediment sites with bioaccumulative contaminants, the human health exposure pathway driving the risk is usually ingestion of biota, most commonly the ingestion of fish by recreational anglers and sometimes by subsistence anglers. However, depending on the contaminant and the use of the site there can also be significant risks from direct contact with the sediment, water, or floodplain soils, through incidental ingestion and dermal contact.
Generally, the ecological risk assessment should consider the risks to invertebrates, plants, fish and wildlife from direct exposure and from food chain expsoures. The selection of appropriate site
specific assessment endpoints is a critical component of the ecological risk assessment. Once assessment endpoints have been selected, testable hypotheses and measurement endpoints can be developed to evaluate the potential threat of the contaminants of potential concern to the assessment endpoints. PCBs, for example, bioaccumulate in food chains and can diminish reproductive success in upper trophic level species (e.g., mink, kingfishers) exposed to contaminants through their diet. Therefore, reduced reproductive success in fish-eating birds and mammals may be an appropriate assessment endpoint. An appropriate measurement endpoint in this case might be contaminant concentrations in fish or in the sediment where the concentrations in these media can be related to reproductive effects in the top predator that eats the fish. The sediment concentration range associated with an acceptable level of reproductive success usually would constitute the remediation goal.
2.3.3 Risks from Remedial Alternatives
Although significant attention has been paid to evaluating baseline risks, traditionally less emphasis has been placed on evaluating risks from remedial alternatives, in part because these risks may be difficult to quantify. In 1991, the EPA issued a supplement to the RAGS Guidance, Risk Assessment Guidance for Superfund: Volume 1 - Human Health Evaluation Manual, Part C, Risk Evaluation of Remedial Alternatives (U.S. EPA 1991a). Although the 1991 guidance addresses only human health risks, it does note that remedial actions, by their nature, can alter or destroy aquatic and terrestrial habitat, and advises that this potential for destruction or alteration of habitat and subsequent consequences be evaluated and considered during the selection and implementation of a remedial alternative.
The short-term and long-term risks to human health and the environment that may be introduced by implementing each of the remedial alternatives should be estimated and considered in the remedy selection process. Generally, the types, magnitude, and time frames of risk associated with each alternative is extremely site specific. Increases to current risks and the creation of new exposure pathways and risk should be considered.
Implementing a MNR remedy should cause no increase in baseline risks and no creation of new risks, although existing risks may change due to disturbance or significant watershed changes.
Implementing in-situ capping might result in increased risk of exposure to contaminants released to the surface water during capping; other community impacts (e.g., accidents, noise, residential or commercial disruption; worker exposure during transport of cap materials and cap placement; and disruption of the benthic community. Existing risks of exposure to contaminants may also occur if contaminants are released through the cap. Implementing dredging or excavation might result in increased risk of exposure to contaminants released during sediment removal, transport, or disposal; other community impacts (e.g., accidents, noise, residential or commercial disruption); worker exposure during sediment removal and handling; and disruption of the benthic community. Risks of exposure to contaminants in residual contamination may also occur. Each of these risks or potential exposure pathways may exist for different periods of time; some are relatively short-lived, while others may exist for a longer period of time. The analysis of risk from implementation of various alternatives is important for remedy selection, and is discussed in more detail in the remedy-specific chapters of this guidance and in Chapter 7, Section 7.4, Comparing Net Risk Reduction.
2-14 Chapter 2: Remedial Investigation Considerations
2.4 CLEANUP GOALS In selecting the most appropriate remedy for a site, usually it is important to develop clearly defined remedial action objectives (RAOs) and contaminant-specific remediation goals (RGs). RAOs are generally used in developing and comparing alternatives for a site and in providing the basis for developing more specific RGs, which in turn are used by project managers to select final sediment cleanup levels based on the other NCP remedy selection criteria. RAOs, RGs, and cleanup levels are normally dependent on each other and represent three steps along a continuum leading from RI/FS scoping to the selection of a remedial action that will be protective of human health and the environment, meet applicable or relevant and appropriate requirements (ARARs), and provide the best balance among the remaining NCP criteria. Under CERCLA, RAOs and cleanup levels generally are final when the record of decision (ROD) is signed. Where the site is not available for unlimited access and unrestricted use, their protectiveness is reviewed every five years.
2.4.1 Remedial Action Objectives and Remediation Goals
RAOs are intended to provide a general description of what the cleanup is expected to accomplish, and help focus the development of the remedial alternatives in the feasibility study. RAOs are typically derived from the conceptual site model (Section 2.2), and address the significant exposure pathways. RAOs may vary widely for different parts of the site based on the exposure pathways and receptors, regardless of whether these parts of the site are managed separately as operable units under CERCLA. For example, a sediment site may include a recreational area used by fishermen and children, as well as a wetland that provides critical habitat for fish and wildlife. Though both areas may contain similarly contaminated sediment, the different receptors and exposure pathways may lead a project manager to develop different RAOs and RGs for each area that are protective of the different receptors.
The development of RAOs should also include a discussion of how they address all the unacceptable human health and ecological risks identified in the risk assessment. Examples of RAOs specific for sediment sites are included in Highlight 2-6. Sediment sites also may need RAOs for other media (e.g., soils, ground water, or surface water). When developing RAOs, project managers should evaluate whether the RAO is achievable by remediation of the site or if it requires additional actions outside the control of the project manager. For example, complete biota recovery may depend on the cleanup of sources that are regulated under other authorities. The project manager may discuss these other actions in the ROD and explain how the site remediation is expected to contribute to meeting areawide goals outside the scope of the site, such as goals related to watershed concerns, but RAOs should reflect objectives that are achievable from the site cleanup.
Generally, preliminary remediation goals (PRGs) that are protective of human health and the environment are developed early in the remedial investigation process based on readily available screening levels for both human health and ecological risks (although project managers should be aware that currently available screening levels for sediment may be limited; see Section 2.3.1).
Highlight 2-6: Sample Remedial Action Objectives for Contaminated Sediment Sites
• Reduce to acceptable levels the risks to children and adults from the incidental ingestion of and dermal exposure to contaminated sediment while playing, wading, or swimming at the site
• Reduce to acceptable levels the toxicity to benthic aquatic organisms at the site As more information is generated during the investigation, these PRGs should be replaced with site-specific RGs by incorporating an improved understanding of site conditions (e.g., site-specific information on fish ingestion rates and bioaccumulation of contaminants in sediment into biota; resource use; other human activities), and other site-specific factors, such as the bioavailability of contaminants.
The human health and ecological risk assessors should identify appropriate RGs for each contaminant of concern in each medium of significance. RGs for sediment often address direct contact for humans and biota to the sediment as well as bioaccumulation through the food chain. The concentrations of bioaccumulative contaminants in fish typically are a function of both the sediment and water concentrations of the contaminant, and are, to some extent, species-dependent. The development of the sediment RGs may involve a variety of different approaches that range from the simple application of a bioaccumulation factor from sediment to fish or more sophisticated food chain modeling. The method used and the level of complexity in the back calculation from fish to sediment should be consistent with the approaches used in the human health and ecological risk assessments.