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United States Environmental Protection Agency EPA-540-R-05-012
Office of Solid Waste and Emergency Response OSWER 9355.0-85
The Contaminated Sediment Remediation Guidance for Hazardous Waste Sites is available to
download from EPA’s Superfund program Web site at
http://www.epa.gov/superfund/resources/sediment/guidance.htm. Hard copies of the document can be obtained at no charge by contacting by contacting EPA’s National Service Center for Environmental Publications (NSCEP) at (800) 490-9198 or ordered via the Internet at http://www.epa.gov/nscep/ordering.htm.
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Contaminated Sediment Remediation Guidance for Hazardous Waste Sites
ACKNOWLEDGMENTSInitial drafts of this document were prepared by an Inter-Agency workgroup led by the U.S.
Environmental Protection Agency (EPA) Office of Emergency and Remedial Response [now Office of Superfund Remediation and Technology Innovation (OSRTI)]. In addition to EPA, the workgroup
included representatives from the following organizations:
National Oceanic and Atmospheric Administration (NOAA) U.S. Army Corps of Engineers (USACE) U.S. Fish and Wildlife Service (USFWS) Representatives of other organizations contributed to the document by commenting on early
drafts. These included the following:
Environment Canada U.S. Navy U.S. Geological Survey U.S. Department of Energy Oregon Department of Environmental Quality Massachusetts Department of Environmental Quality Wisconsin Department of Natural Resources The following individuals led subgroups to draft various sections of the document or otherwise
contributed substantially to the overall character of the guidance:
The following individuals drafted sections of the document or assisted in various substantial ways
in preparation of the guidance, and EPA also sincerely appreciates their assistance:
Technical support for this project was provided by Rebecca Tirrell, Molly Wenner, Aaron George, William Zobel, and others at CSC Systems & Solutions LLC. Workgroup facilitation services were provided by Kim Fletcher, SRA International, Inc., and by Jim Fary, EPA OSRTI. EPA very much appreciates their able support.
Ernie Watkins, Chair, Contaminated Sediment Remediation Guidance Workgroup, 1998-2001 Leah Evison, Project Manager, Office of Superfund Remediation and Technology Innovation, 2001-2005 Contaminated Sediment Remediation Guidance for Hazardous Waste Sites Executive Summary In 2004, the U.S. Environmental Protection Agency (EPA) released the Updated Report on the Incidence and Severity of Sediment Contamination in Surface Waters of the United States: National Sediment Quality Survey, which identifies areas in all regions of the country where sediment may be contaminated at potentially harmful levels (U.S. EPA 2004a). Contaminated sediment can significantly impair the navigational and recreational uses of rivers and harbors in the U.S. [National Research Council (NRC) 1997 and 2001] and can be a contributing factor in many of the 3,221 fish consumption advisories nationwide (U.S. EPA 2005a). As of 2004, EPA had decided to take action to clean up contaminated sediment at approximately 140 sites, including federal facilities, under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and additional sites under the Resource Conservation and Recovery Act [(RCRA), U.S. EPA 2004a]. The remedies for more than 60 sites are large enough that they are being tracked at the national level. Many other sites are being cleaned up under state authorities, other federal authorities, or as voluntary actions.
This document provides technical and policy guidance for project managers and management teams making remedy decisions for contaminated sediment sites. It is primarily intended for federal and state project managers considering actions under CERCLA, although technical aspects of the guidance are also intended to assist project managers addressing sediment contamination under RCRA. Many aspects of this guidance also will be useful to other governmental organizations and potentially responsible parties (PRPs) that may be conducting a sediment cleanup. Although aspects related to site characterization and risk assessment are addressed, the guidance focuses on considerations regarding feasibility studies and remedy selection for contaminated sediment. The guidance is lengthy, and users may wish to consult sections most applicable to their current need. To help in this process, a short summary of each of the eight chapters is provided below. Sediment cleanup is a complex issue, and as new techniques evolve, EPA will issue new or updated guidance on specific aspects of contaminated sediment assessment and remediation. Links to guidance and additional information about contaminated sediments at Superfund sites are available at http://www.epa.gov/superfund/resources/sediment.
Chapter 1, Introduction, describes the general backdrop for contaminated sediment remediation and reiterates EPA’s previously issued Office of Solid Waste and Emergency Response (OSWER) Directive 9285.6-08, Principles for Managing Contaminated Sediment Risks at Hazardous Waste Sites (U.S. EPA 2002a). Other issues addressed in Chapter 1 include the role of the natural resource trustees, states, Indian tribes, and communities at sediment sites. Where there are natural resource damages associated with sediment sites, coordination between the remedial and trusteeship roles at the federal, state, and tribal levels is especially important. In addition to their role as natural resource trustees, certain state cleanup agencies and certain Indian tribes or nations have an important role as co-regulators and/or affected parties and as sources of essential information. Communities of people who live and work adjacent to water bodies containing contaminated sediment should be given understandable information about the safety of their activities, and be provided significant opportunities for involvement in the EPA’s decision-making process for sediment cleanup.
Chapter 2, Remedy Investigation Considerations, introduces investigation issues unique to the sediment environment, including those related to characterizing the site, developing conceptual site models, understanding current and future watershed conditions, controlling sources, and developing cleanup goals. Especially important at sediment sites is the development of an accurate conceptual site
iContaminated Sediment Remediation Guidancefor Hazardous Waste Sites
model, which identifies contaminant sources, transport mechanisms, exposure pathways, and receptors at various levels of the food chain. Project managers should consider the role of a sediment site in the watershed context, including other potential contaminant sources, key issues within the watershed, and current and reasonably anticipated or desired future uses of the water body and adjacent land. Important parts of site characterization and remedy selection include the identification and, where feasible, control of significant continuing sources of contamination and an accurate understanding of their contribution to site risk and potential for recontamination. It is also generally important that remedial action objectives, remediation goals, and cleanup levels are based on site-specific data and are clearly defined. At most Superfund sites, chemical-specific remediation goals should be developed into final sediment cleanup levels by weighing the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) balancing and modifying criteria.
In addition, Chapter 2 introduces issues relating to sediment mobility and contaminant fate and transport, and modeling at sediment sites. In most aquatic environments, surface sediment and associated contaminants move over time. An important part of the remedial investigation at many sediment sites is a site-specific assessment of whether movement of contaminated sediment (surface and subsurface), or of contaminants alone, is occurring or may occur at scales and rates that will significantly change their contribution to risk. For example, is significant sedimentation of cleaner sediment burying contaminated sediment, and, if so, how quickly, and is erosion likely to re-expose those contaminants in the future?
An accurate assessment of sediment mobility and contaminant fate and transport can be one of the most important factors in identifying areas suitable for monitored natural recovery (MNR), in-situ caps, or near-water confined disposal facilities (CDFs). Evaluation of alternatives should include consideration of disruption from man-made (anthropogenic) causes such as propeller scour and natural causes such as floods and ice scour. Generally, this evaluation should include the 100-year flood and other events with a similar probability of occurrence. Project managers should make use of the variety of field and laboratory measurement methods available for evaluating site characteristics. For example, the shear stress necessary to erode sediment or the increase in exposure of biota that might be expected from any contaminants transported to surface water from ground water.
Where appropriate, project managers also should make use of numerical models for predicting future conditions at a site. There is a wide range of models, from simple to complex, which can be applied to contaminated sediment sites. Where numerical models are used, verification, calibration, and validation should be typically preformed to yield a scientifically defensible study. While quantitative uncertainty analyses can be performed for watershed loading and food web models, at the current time they cannot be generally performed for fate and transport models. However, frequently a sensitivity analysis can be used to identify the model parameters that have most impact on model results, so that the project team can ensure that these parameters are well constrained by site data.
Chapter 3, Feasibility Study Considerations, supplements existing EPA guidance by offering sediment-specific guidance about developing alternatives, applying the NCP remedy selection criteria, identifying applicable or relevant and appropriate requirements (ARARs), evaluating effectiveness and permanence, estimating cost, and using institutional controls. Major alternatives include dredging and excavation, in-situ capping, and MNR. Innovative lab and field testing of in-situ treatment in the form of reactive caps or sediment additives are underway and may be useful in the future. Due to the limited number of cleanup methods available for contaminated sediment, generally project managers should evaluate each of the three potential remedy approaches (sediment removal, capping, and MNR) at every
iiContaminated Sediment Remediation Guidancefor Hazardous Waste Sites
sediment site. At large or complex sites, project managers have found that alternatives that combine a variety of approaches are frequently cost effective. Pursuant to CERCLA section 121, all final remedial actions at CERCLA sites must be protective of human health and the environment, and must comply with ARARs unless a waiver is justified. Developing accurate cost estimates is an important part of evaluating sediment alternatives. Project managers should evaluate capital costs, operation and maintenance costs (including long-term monitoring), and net present value. When evaluating alternatives with respect to effectiveness and permanence, it is important to remember that each of the three potential remedy approaches may be capable of reaching acceptable levels of effectiveness and permanence, and that sitespecific characteristics should be reviewed during the alternatives evaluation to ensure that the alternative selected will be effective in that environment. Institutional controls are frequently evaluated as part of sediment alternatives to prevent or reduce human exposure to contaminants. Common types of institutional controls at sediment sites include fish consumption advisories, commercial fishing bans, and waterway use restrictions. In some cases, land use restrictions or structure maintenance agreements have also been important elements of an alternative.
Chapter 4, Monitored Natural Recovery, describes the natural processes that should be considered when evaluating MNR as a remedy, and briefly discusses enhanced natural recovery through thin-layer placement of sand or other material. MNR is a remedy that typically uses known, ongoing, naturally occurring processes to contain, destroy, or otherwise reduce the bioavailability or toxicity of contaminants in sediment. An MNR remedy generally includes site-specific cleanup levels and remedial action objectives, and monitoring to assess whether risk is being reduced as expected. Although a “no action” decision may also include monitoring, in this case the monitoring is intended to ensure that an already-acceptable level of risk is maintained (e.g., that deeply buried contaminants are not re-exposed by erosion). Although burial by clean sediment is often the dominant process relied upon for natural recovery, multiple physical, biological, and chemical mechanisms frequently act together to reduce risk.
Evaluation of MNR should be usually based on site-specific data, including multiple lines of evidence such as decreasing trends of contaminant levels in fish, in surface water, and in sediment. Project managers should evaluate the long-term stability of the sediment bed and the mobility of contaminants within it. Contingency measures should be included as part of a MNR remedy when there is significant uncertainty that the remedial action objectives will be achieved within the predicted time frame.
Generally, MNR should be used either in conjunction with source control or active sediment remediation.
In addition, Chapter 4 discusses the potential advantages and limitations of MNR. In most cases, the two key advantages of MNR are its relatively low implementation cost and its non-invasive nature.
While costs associated with site characterization and modeling can be extensive, the costs associated with implementing MNR are primarily associated with monitoring. Because no construction or infrastructure is needed, it is generally much less disruptive to human communities and the ecosystem than active remedies. Two key limitations of MNR may be that it generally leaves contaminants in place without engineered containment and that it can be slow in reducing risks in comparison to active remedies. As with any risk reduction approach that takes a period of time to reach remediation goals, remedies that include MNR frequently rely upon institutional controls, such as fish consumption advisories, to control human exposure during the recovery period. At most sites, some people will disregard advisories despite best efforts to communicate risk, and advisories have no ability to reduce ecological exposures.
Chapter 5, In-Situ Capping, summarizes the major capping technologies and describes the site conditions that are important to understand in evaluating the feasibility and effectiveness of in-situ
capping. In-situ capping refers to the placement of a subaqueous covering or cap of clean material over contaminated sediment that remains in place. Caps are generally constructed of clean sediment, sand, or gravel, but can also include geotextiles, liners, or the addition of material, such as organic carbon, to attenuate the flux of contaminants into the overlying water. Depending on the contaminants and sediment conditions present, a cap is generally designed to reduce risk through the following primary functions: 1) physical isolation of the contaminated sediment sufficient to reduce exposure due to direct contact and to reduce the ability of burrowing organisms to move contaminants to the cap surface; 2) stabilization of contaminated sediment and erosion protection of sediment and cap sufficient to reduce resuspension and transport of contaminants into the water column; and 3) chemical isolation of contaminated sediment sufficient to reduce exposure from dissolved contaminants that may be transported into the water column.