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In addition, Chapter 5 discusses the potential advantages and limitations of in-situ capping. One advantage of in-situ capping is that it can quickly reduce exposure to contaminants. Also, compared to sediment removal it normally requires both less infrastructure in terms of material handling, dewatering, and disposal and is typically less disruptive to people in local communities. Compared to MNR, the potential for erosion and transport of contaminants is typically much lower. However, contaminated sediment is still left in place in the aquatic environment where contaminants could be exposed or dispersed if the cap is significantly disturbed or if contaminants move through the cap in significant amounts. Another potential limitation to in-situ capping may be that in some situations a preferred habitat may not be provided by the surficial cap materials which may be needed for erosion control.
Chapter 6, Dredging and Excavation, describes dredging technologies (conducted under water) and excavation technologies (typically conducted after water is diverted or drained). The chapter describes some of the key components involved in a sediment dredging or excavation remedy and describes site conditions that may be important when evaluating the feasibility and effectiveness of these remedies. A dredging or excavation alternative should include an evaluation of all phases of the project, including removal, staging, dewatering, water treatment, sediment transport, and sediment treatment, reuse, or disposal. Transport and disposal options for contaminated sediment are sometimes complex and controversial and should be investigated and discussed with stakeholders early in the project. In some cases, specialized methods of operation or equipment may be needed to minimize resuspension of sediment and transport of contaminants. Project managers should make realistic, site-specific predictions of residual contamination (i.e., contamination that remains within or adjacent to the dredged area after dredging) based on pilot studies or data from comparable sites. Where residuals are a concern, thin layer placement/backfilling, MNR, or capping may also be needed.
In addition, Chapter 6 discusses potential advantages and limitations of contaminated sediment removal by dredging and excavation. One of the principal advantages of dredging and excavation is often that, if they achieve cleanup levels for the site, they may result in the least uncertainty regarding future environmental exposure to contaminants because the contaminants are removed from the aquatic ecosystem and disposed in a controlled environment. Another potential advantage of removing contaminated sediment rather than managing it in place is that it may leave more flexibility regarding future use of the water body. Although dredging remedies at sites with bioaccumulative contaminants usually include fish consumption advisories for a period of time after sediment removal, other types of institutional controls that might be needed to protect a cap or a layer of natural sedimentation are usually not necessary. The principal limitations of sediment removal are that it is usually more complex and costly than in-situ management, and that the level of uncertainty associated with estimating residual
ivContaminated Sediment Remediation Guidancefor Hazardous Waste Sites
contamination can be high at some sites. The need for transport, storage, treatment (where applicable), and disposal facilities may lead to increased impacts on communities. In some parts of the country, disposal capacity may be limited in existing municipal or hazardous waste landfills and it may be difficult to site new local disposal facilities. Another limitation may include the potential for contaminant losses during dredging through resuspension, and to a generally lesser extent, through other processes such as volatilization during excavation, transport, treatment, or disposal. Finally, similar to in-situ capping, dredging or excavation typically includes at least a temporary destruction of the aquatic community and habitat within the remediation area.
Chapter 7, Remedy Selection Considerations, discusses risk management decision making, the NCP’s remedy selection framework, including considering sediment remedies and comparing net risk reduction, considering alternatives that include institutional controls, and considering a “no-action” decision. Where a remedy is necessary, the best route to overall risk reduction depends on a large number of site-specific considerations, some of which may be subject to significant uncertainty. Any decision regarding the specific choice of a remedy for contaminated sediment should be based on a careful consideration of the advantages and limitations of each available approach and a balancing of trade-offs among alternatives. This chapter includes two summary tables to help with this comparison process: one describes site characteristics and conditions especially conducive to each of the three potential remedy approaches for sediment (MNR, capping, and dredging), and the other lists examples of key differences between the three potential remedy approaches with respect to the NCP’s nine remedy selection criteria.
Documenting and communicating how and why remedy decisions were made are especially important at complex sites. The concept of comparing “net” risk reduction may assist in the remedy selection process by providing a framework for considering elements of alternatives which may reduce risk and elements which may allow risk to continue or temporarily increase. When considering remedies that include institutional controls, project managers should consider what entities possess the legal authority, capability and willingness to implement the control.
EPA’s policy has been and continues to be that there is no presumptive remedy for any contaminated sediment site, regardless of the contaminant or level of risk. At many sites, but especially at large sites, a combination of sediment cleanup methods may be the most effective way to manage the risk.
The remedy selection process for sediment sites should include a clear analysis of the uncertainties involved, including uncertainties concerning the predicted effectiveness of various alternatives and the time frames for achieving cleanup levels and, if possible, remedial action objectives. The uncertainty of factors very important to the remedy decision should be quantified, so far as this is possible. Where it is not possible to quantify uncertainty, sensitivity analysis may be helpful to determine which apparent differences between alternatives are most likely to be significant.
Chapter 8, Remedial Action and Long-Term Monitoring, provides a recommended approach to developing an effective monitoring plan at contaminated sediment sites. The chapter presents sample measures of sediment remedy effectiveness, in terms of remedy performance and risk reduction. A fully successful sediment remedy typically is one where the selected sediment chemical or biological cleanup levels have been met and maintained over time, and where all relevant risks have been reduced to acceptable levels based on the anticipated future uses of the water body and the goals and objectives stated in decision documents. The chapter also presents the key steps in designing and conducting a monitoring program at a sediment site, introduces some of the monitoring techniques available for physical, chemical, and biological measurements, and summarizes some of the factors to consider when
vContaminated Sediment Remediation Guidancefor Hazardous Waste Sites
monitoring remedies including MNR, in-situ capping, or dredging/excavation. A monitoring plan typically can be important for all types of sediment remedies, before, during and after remedial action.
The development of monitoring plans should follow a systematic planning process that identifies monitoring objectives, decision criteria, endpoints, and data collection and interpretation methods.
Project managers should ensure that adequate baseline data are available for comparison to monitoring data after a remedial action and that adequate background data are available, including any continuing off-site contaminant contributions. Monitoring before, during, and after sediment remediation generally will help not only to answer site-specific questions but to contribute to a better understanding of remedy performance at the national level.
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4.0 MONITORED NATURAL RECOVERY
This document provides technical and policy guidance for project managers and management teams making risk management decisions for contaminated sediment sites. It is primarily intended for federal and state project managers considering remedial response actions or non-time-critical removal actions under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), more commonly known as “Superfund.” Technical aspects of the guidance are also intended to assist project managers addressing sediment contamination under the Resource Conservation and Recovery Act (RCRA). Many aspects of this guidance may also be useful to other governmental organizations and potentially responsible parties (PRPs) that are conducting a sediment cleanup under CERCLA, RCRA, or other environmental statutes, such as the Clean Water Act (CWA) or the Water Resource Development Act (WRDA). This guidance may also be useful to members of the community and their technical representatives.
This guidance also provides information to the public and to the regulated community on how EPA intends to exercise its discretion in implementing its regulations at contaminated sediment sites. It is important to understand, however, that this document does not substitute for statutes EPA administers nor their implementing regulations, nor is it a regulation itself. Thus, this document does not impose legally binding requirements on EPA, states, or the regulated community, and may not apply to a particular situation based upon the specific circumstances. Rather, the document suggests approaches that may be used at particular sites as appropriate, given site-specific circumstances. EPA made many changes to this document based on public comment and external peer review of draft documents. Even though the document is now final, however, EPA welcomes public comments on the document at any time and will consider those comments in any future revisions to the document which EPA may make without public notice.
Guidance presented in this document can be applied to contaminated sediment in a wide variety of aquatic environments, including rivers, streams, wetlands, ponds, lakes, reservoirs, harbors, estuaries, bays, intertidal zones, and coastal ocean areas. Sediment in wastewater lagoons, detention/sedimentation ponds, on-site storage/containment facilities, or roadside ditches is not addressed. This guidance addresses both in-situ and ex-situ remedies for sediment, including monitored natural recovery (MNR), in-situ capping, and dredging and excavation. However, because the science and practice of sediment remediation are rapidly evolving, project managers are encouraged to test innovative approaches (e.g., including in-situ treatment options) that are beyond those discussed here, which may also effectively reduce risk from contaminated sediment.
Consideration of materials deposited in floodplains, whether called soil or sediment, is an important factor in reducing risk in aquatic environments. Much of the general approach recommended in this guidance can be applied to contaminated floodplains, although the technical considerations are written with aquatic sediment in mind. Control of upland soils and other upland source materials is also critical to reducing risk in aquatic environments, but in general, existing guidance should be used for
these materials [e.g., the U.S. Environmental Protection Agency’s (EPA’s) Soil Screening Guidance:
Users Guide (U.S. EPA 1996a)]. However, where floodplain soils may be a source of contamination to surface water or sediment, the fate and transport of contaminants in the soil should be evaluated.
1-1 Chapter 1: Introduction The emphasis of this guidance is on evaluating alternatives (e.g., the feasibility study stage of the Superfund process) and remedy selection, although the guidance presents some of the key remedial investigation issues at sediment sites. Following this introductory chapter, the guidance provides sediment-specific issues to consider during remedial investigations (see Chapter 2) and feasibility studies (see Chapter 3), followed by chapters concerning the three potential remedy approaches for sediment management (see Chapter 4, Monitored Natural Recovery; Chapter 5, In-Situ Capping; and Chapter 6, Dredging and Excavation). This guidance then presents information on selecting sediment remedies (see Chapter 7); and on monitoring sediment sites (see Chapter 8).
1.2 CONTAMINATED SEDIMENT
For the purposes of this guidance, contaminated sediment is soil, sand, organic matter, or other minerals that accumulate on the bottom of a water body and contain toxic or hazardous materials at levels that may adversely affect human health or the environment (U.S. EPA 1998a). Contaminants adsorbed to soil or in other forms may wash from land, be deposited from air, erode from aquatic banks or beds, or form from the underwater breakdown or buildup of minerals (U.S. EPA 1998a). Contaminated sediment may be present in wetlands, streams, rivers, lakes, reservoirs, harbors, along ocean margins, or in other water bodies. In this guidance, “water body” generally includes all of these environments. Some contaminants have both anthropogenic (or man-made) sources and natural sources (e.g., many metals and some organic compounds). This guidance addresses management of contaminants present above naturally occurring levels that may cause an unacceptable risk to humans or to ecological receptors.
Examples of primary and secondary sources of contaminants in sediment are included in Highlight 1-1.
Highlight 1-1: Potential Sources of Contaminants in Sediment • Direct pipeline or outfall discharges into a water body from industrial facilities, waste water treatment plants, storm water discharges, or combined sewer overflows • Chemical spills into a water body • Surface runoff or erosion of soil from floodplains and other contaminated sources on land, such as waste dumps, chemical storage facilities, mines and mine waste piles, and agricultural or urban areas • Air emissions from power plants, incinerators, pesticide applications, or other sources that may be transferred to a water body through precipitation or direct deposition • Upwelling or seepage of contaminated ground water or non-aqueous phase liquids (NAPL) into a water body • Direct disposal from docked and dry-docked ships, or release of contaminants from in-water structures and over-water structures or ship maintenance facilities Organic contaminants in sediment typically adsorb to fine sediment particles and exist in the pore water between sediment particles. Metals also adsorb to sediment and may bind to sulfides in the sediment. The relative proportion of contaminants between sediment and pore water depends on the type of contaminant and the physical and chemical properties of the sediment and water. Pore water in sediment generally is interconnected with both surface water and ground water, although the degree of 1-2 Chapter 1: Introduction interconnection may change from place-to-place and with flow changes in ground water and surface water.
Many contaminants persist for years or decades because the contaminant does not degrade or degrades very slowly in the aquatic environment. Contaminants sorbed to sediment normally develop an equilibrium with the dissolved fraction in the pore water and in the overlying surface water to be taken up by fish and other aquatic organisms. Some bottom-dwelling organisms ingest contaminated sediment, and in shallow water environments, humans may also come into direct contact with contaminated sediment. Some contaminants, such as most metals, are hazardous primarily because of direct toxicity.