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RGs should be represented as a range of values within acceptable risk levels so that the project manager may consider the other NCP criteria when selecting the final cleanup levels. For human health, general guidance is available regarding the exposure equations necessary to develop RG concentrations in various media for both cancer risks and non-cancer health hazards (see Section 2.3.) The development of the human health-based RGs should provide a range of risk levels (e.g., 10-6, 10-5, and 10-4 and a noncancer Hazard Index of 1 or less depending on the health end points of the specific contaminants of concern.) The development of the ecologically based RGs should also provide a range of risk levels based on the receptors of concern identified in the ecological risk assessment (see Section 2.3). Human health and ecological RGs should be developed through iterative discussions between the project manager, risk assessor, and modeler or other appropriate members of the team.
2.4.2 Cleanup Levels
At most CERCLA sites, RGs for human health and ecological receptors are developed into final, chemical-specific, sediment cleanup levels by weighing a number of factors, including site-specific uncertainty factors and the criteria for remedy selection found in the NCP at Title 40 Code of Federal Regulations (40 CFR) §300.430. These criteria include long-term effectiveness and permanence;
2-16 Chapter 2: Remedial Investigation Considerations reduction of toxicity, mobility and volume through treatment; short-term effectiveness; implementability;
cost; and state and community acceptance. Chapter 3, Section 3.2, NCP Remedy Selection Criteria discusses these criterion in detail. Regions should note, however, that some states do have chemical and/or biological standards for contaminated sediment (e.g., in development by the State of Washington and others) that may be ARARs at sediment sites.
Uncertainty factors that may be relevant to consider include (among others) the reliability of inputs and outputs of any model used to estimate risks and establish cleanup levels, reliability of the potential approaches to achieve those results, and the likelihood of occurrence for the exposure scenarios being considered. Other technical factors include (among others) limitations of remedial alternatives and detection and quantification limits of contaminants in environmental media. It is especially important to consider both background levels of contamination and what has been achieved at similar sites elsewhere, so that achievable cleanup levels are developed. All of these factors should be considered when establishing final cleanup levels that are within the risk range.
The derivation of ecologically based cleanup levels is a complex and interactive process incorporating contaminant fate and transport processes, toxicological considerations and potential habitat impacts of the remediation alternatives. Before selecting a cleanup level, the project manager, in consultation with the ecological risk assessor, should consider at least the following factors (U.S.
• The magnitude of the observed or expected effects of site releases and the level of biological organization affected (e.g., individual, local population, or community);
• The likelihood that these effects will occur or continue;
• The ecological relationship of the affected area to the surrounding habitat;
• Whether the affected area is a highly sensitive or ecologically unique environment; and • The recovery potential of the affected ecological receptors and expected persistence of the chemicals of concern under present site conditions.
Generally, for CERCLA actions, the ROD should include chemical-specific cleanup levels as provided in the NCP at 40 CFR §300.430(c)(2)(I)(A). The ROD should also indicate the approach that will be used to measure attainment of the cleanup levels and how cleanup levels relate to risk reduction.
At many sediment sites, especially but not exclusively those with bioaccumulative contaminants, the attainment of sediment cleanup levels may not coincide with the attainment of RAOs. For example, this may be due to the length of time needed for fish or the benthic community to recover. Where cleanup levels have been achieved but progress towards meeting RAOs is not as expected, the five-year review process, or where appropriate, a similar process conducted before five years, should be used to assess whether additional actions are needed. Consistent with the NCP (40 CFR §300.430(f)(4)(ii)), where contaminants remain present above unlimited use and unrestricted exposure levels, Superfund sites should be reviewed no less than every five years after initiation of the selected remedial action. Chapter 8, Remedial Action and Long-Term Monitoring, provides additional guidance on the information that should be collected for this review to be effective. As explained further in Chapter 8, the need for longterm monitoring is not limited to sites where five-year reviews are required. Most sites where
contaminated sediment has been removed also should be monitored for some period to ensure that cleanup levels and RAOs are met and will continue to be met.
2.5 WATERSHED CONSIDERATIONSA unique aspect of contaminated sediment sites is their relationship within the overall watershed, or drainage area, in which they are located. Within the watershed there often is a spectrum of issues that the project manager may need to consider. Foremost among them at many sites is to work with the state to ensure that fish consumption advisories are in place and well publicized. In addition, project managers should understand the role of the contaminated water body in the watershed, including the habitat or flood control functions it may serve, the presence of non-site-related contaminant sources in the watershed, and current and reasonably anticipated or desired future uses of the water body and surrounding land.
2.5.1 Role of the Contaminated Water Body
Most water bodies provide important habitat for spawning, migration, or food production for fish, shellfish, birds, and other aquatic and land-based animals. One significant issue is the protection of migratory fish. These are fish such as salmon, shad, and herring that migrate as adults from marine waters up estuaries and rivers to streams and lakes where they spawn. The juveniles spend varying lengths of time in freshwater before migrating to estuarine/marine waters. It can be difficult to evaluate the impact of a particular contaminated sediment site on wide-ranging species that may encounter several sources of contamination along their migratory route. This can be an important consideration when evaluating alternatives and establishing remediation goals for a site, as these fish populations may not show improvement if any link in their migratory route is missing, blocked, or toxic. For migratory species, it may be more appropriate to measure risk and remedy effectiveness in terms of risk to juveniles, or whatever part of the life cycle is spent at the site.
The size, topography, climate, and land use of a watershed, among other factors, may affect characteristics of a water body, such as water quality, sedimentation rate, sediment characteristics, seasonal water flows and current velocities, and the potential for ice formation. For example, watersheds with large wetland areas tend to store flood waters and enable ground water recharge, thereby protecting downstream areas from increased flooding, whereas an agricultural or urbanized watershed may have increased erosion and greater flow during storm events. Watershed changes can result from natural events, such as wildfires, or from human activities such as road and dam construction/removal, impoundment releases, and urban/suburban development. When considering watershed characteristics, it is generally important to consider both current and future watershed conditions.
Some sediment sites are located in watersheds with a large number of historical and ongoing point and non-point sources, from many potentially responsible parties. Where this is the case, it can be especially important to attain expert assistance to plan site characterization strategies that are well suited to the complexity of the issues and designed to answer specific questions. In urban watersheds and others with a large number of ongoing sources, it may be beneficial for a broader group of stakeholders to participate in setting priorities for site characterization and remediation efforts. In these areas, it can be especially important to consider background concentrations when developing remedial objectives and to evaluate the incremental improvement to the environment if an action is taken at a specific site in the watershed. Approaching management of a site within the watershed context may provide an opportunity 2-18 Chapter 2: Remedial Investigation Considerations to better determine the needs and coordinate the sequence and schedule of cleanup activities in the watershed.
2.5.2 Water Body and Land Uses Water body uses at sediment sites may include commercial navigation; commercial fisheries, shellfisheries, or aquaculture; boating, swimming, and other forms of recreation; other commercial or industrial uses; recreational or subsistence fishing or shellfishing; and other, less easily categorized uses.
Most water bodies used for commercial navigation, such as for shipping channels, turning basins, and port areas, are periodically dredged to conform to the minimum depth for the area prescribed by Congress; such dredging is typically performed or permitted by the U.S. Army Corps of Engineers (USACE). Other commercial or industrial uses of a site may include the presence of gravel pits, drinking water use, and industrial uses of water including cooling, washing, or waste water disposal.
The NCP preamble (55 FR 8710) states that both current and future land uses should be evaluated in assessing risks posed by contaminants at a Superfund site and discusses how Superfund remedies should be protective in light of reasonably anticipated future uses. EPA has provided further guidance on how to evaluate future land use in the OSWER Directive 9355.7-04, Land Use in the CERCLA Remedy Selection Process (U.S. EPA 1995a, also referred to as the “Land Use Guidance”). This guidance encourages early discussions with state and local land use planning authorities and the public, regarding reasonably anticipated future uses of properties associated with a National Priorities List (NPL) site. This coordination should begin during the scoping phase of the RI/FS, and ongoing coordination is recommended to ensure that any changes in expectations are incorporated into the remedial process.
There are additional factors the project manager should include in considering anticipated future uses for aquatic sites not specifically addressed in the Land Use Guidance. For example, future use of the site by ecological receptors may be a more important consideration for an aquatic sediment Superfund or RCRA site as compared to an upland terrestrial site. A remediated sediment site may attract more recreational, subsistence, and cultural uses, including fishing, swimming, and boating. Where applicable, the project manager should consider tribal treaty rights to collect fish or other aquatic resources. The project manager should also consider [generally as TBCs (or to be considered), see Chapter 3, Section 3.3 on ARARs] designated uses in the state’s water quality standards, priorities established as a result of total maximum daily loads (TMDLs), or pollution reduction efforts under various Clean Water Act (CWA) programs in projecting future waterway uses. In ports and harbors, the project manager should consult master plans developed by port and harbor authorities for projections of future use. The USACE should also be contacted regarding future navigational dredging of federally maintained channels.
There may be more parties to consult about anticipated future use at large sediment sites as opposed to typical upland sites. These parties include the community, environmental groups, natural resource trustees, Indian tribes, the local department of health, as well as local government, port and harbor authorities, and land use planning authorities. As with upland sites, consultation should start at the RI/FS scoping phase and continue throughout the life of the project. Different stakeholders often have divergent and conflicting ideas about future use at the site. Local residents and environmental groups may anticipate future habitat restoration and increased recreational and ecological use while local industrial landowners may project increased shipping and industrial use. The NCP preamble (55 FR
8710) states that, in the baseline risk assessment, more than one future use assumption should be considered when decision makers wish to understand the implications of different exposure scenarios.
Especially where there is some uncertainty regarding the anticipated future uses, the project manager should compare the potential risks associated with several use scenarios.
The identification of appropriate future use assumptions during the baseline risk assessment and the feasibility study should allow the project manager to focus on developing protective, practicable, and cost-effective remedial alternatives. In addition, coordination with stakeholders on land and water body uses leads to opportunities to coordinate Superfund or RCRA remediation in conjunction with local development or habitat restoration projects. For example, at some sites the EPA has worked with port authorities to combine Superfund or RCRA remedial dredging with dredging needed for navigation.
Others have combined capping needed for Superfund or RCRA remediation with habitat restoration, allowing PRPs to settle natural resource damage claims in conjunction with the cleanup. However, as noted in Chapter 1, Section 1.5, State, Tribal, and Trustee Involvement, whether remediation and restoration are addressed concurrently is a site-specific decision that involves input from a number of different parties.
2.6 SOURCE CONTROL
Identifying and controlling contaminant sources typically is critical to the effectiveness of any Superfund sediment cleanup. Source control generally is defined for the purposes of this guidance as those efforts are taken to eliminate or reduce, to the extent practicable, the release of contaminants from direct and indirect continuing sources to the water body under investigation. At some sediment sites, the original sources of the contamination have already been controlled, but subsequent sources such as contaminated floodplain soils, storm water discharges, and seeps of ground water or non-aqueous phase liquids (NAPLs) may continue to introduce contamination to a site. At sites with significant sediment mobility, areas of higher contaminant concentration may act as continuing sources for less-contaminated areas.
Some sources, especially those outside the boundaries of the Superfund or RCRA site, may best be handled under another authority, such as the CWA or a state program. These types of sites can present an opportunity for partnering with private industry and other governmental entities to identify and control sources on a watershed basis. Water bodies with sources outside the Superfund site can also present a need to balance the desire for watershed-wide solutions with practical considerations affecting a subset of responsible parties. It can be difficult to determine the proper party to investigate sources outside the Superfund site, but the site RI/FS must be sufficient to determine the extent of contamination coming onto the site and its likely effect on any actions at the site. A critical question often is whether an action in one part of the watershed is likely to result in significant and lasting risk reduction, given the probable timetable for other actions in the watershed.
Source control activities are often broad-ranging in scope. Source control may include application of regulatory mechanisms and remedial technologies to be implemented according to ARARs, including the application of technology-based and water quality-based National Pollutant Discharge Elimination System (NPDES) permitting to achieve and maintain sediment cleanup levels. Source
control actions may include, among others, the following: