: When dredged materials proposed for open-water placement are found to require isolation form the benthic environment due to the presence of contaminants, capping may he appropriate for consideration as a management action. This report is intended to provide technical guidance for evaluation of capping projects. From a technical perspective, this guidance is applicable to dredged material capping projects in ocean waters as well as inland and near-coastal waters. Subaqueous dredged material capping is the controlled, accurate placement of contaminated dredged material at an appropriately selected open-water placement site, followed by a covering or cap of suitable isolating material. A number of capping operations under a variety of placement conditions have been accomplished. Conventional placement equipment and techniques are frequently used for a capping project, but these practices must be controlled more precisely than for conventional placement. Level bottom capping (LBC) is defined as the placement of a contaminated material in a mounded configuration and the subsequent covering of the mound with clean sediment. Contained aquatic disposal is similar to LBC but with the additional provision of some form of lateral confinement (e.g., placement in natural bottom depressions, constructed subaqueous pits, or behind subaqueous berms) to minimize spread of the materials on the bottom.

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Guidance for Subaqueous Dredged Material Capping.

The presence of persistent hydrophobic organic chemicals, e.g., polychlorinated biphenyls (PCBs), polynuclear aromatic hydrocarbons (PAHs), and polychlorinated dibenzodioxins (PCDDs) in aquatic systems continues to be a matter of intense concern [International Joint Commission (IJC) 1993]. Although the levels of many of these contaminants have decreased as much as 10–100 times (Gilbertson 1993; Borgmann and Whittle 1992), adverse symptoms associated with exposure to these chemicals in wild animals have persisted (Tillitt et al. 1992). In addition, accumulation of these contaminants in aquatic food chains and the potential for biological magnification in top carnivores, including man, are perceived to be ongoing health threats to consumers (Crossland et al. 1987; Van der Oost et al. 1994; Oliver and Niimi 1988; Rasmussen et al. 1990).

Mechanisms of Bioaccumulation in Aquatic Systems

Geochemical analysis and visual inspection of cores collected from capped dredged material mounds revealed that in many cores, cap material was clearly distinguishable, both visually and chemically...

Chemical Stability of Capped Dredged Material Disposal Mounds in Long Island Sound, Usa

: The US Army Engineer District, Seattle (CENWS), is participating in the Puget Sound Confined Disposal Site Study This study is aimed at determining the feasibility of establishing a system of multiuser disposal sites (MUDS) for disposal of contaminated sediments dredged from Puget Sound Most of the contaminated sediments within Puget Sound are located within the central portion of the sound and are associated with environmental cleanup projects directed through Federal or state enforcement actions, projects with restoration of aquatic habitat as their primary purpose, and dredging of Federal and non-Federal navigation channels The feasibility evaluation will be conducted in phases The initial programmatic phase resulted in a programmatic Environmental Impact Statement (PEIS) Site-specific evaluations along with a site-specific PElS will be conducted in subsequent phases Disposal alternatives that will be evaluated include: (a) level bottom capping and contained aquatic disposal (CAD), (b) nearshore (or island) confined disposal facilities (CDFs), (c) upland (CDF) disposal, (d) disposal in solid waste landfills, and (e) multiuser access to larger fill projects CENWS requested support from the US Army Corps of Engineers Engineer Research and Development Center (ERDC), Environmental Laboratory, Vicksburg, MS, in conducting the feasibility evaluations This report describes various subaqueous capping and confined (diked) disposal alternatives and provides conceptual designs and design and performance standards for these alternatives

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Multiuser disposal sites (MUDS) for contaminated sediments from Puget Sound : subaqueous capping and confined disposal alternatives

The historical release of contaminants into the environment has generated a legacy of contaminated sites throughout the world. For years, the sediments in water bodies adjoining these pollution sources served as sinks for contaminants, particularly hydrophobic organic compounds (HOCs) and heavy metals. Many of these original sources have been eliminated, but the sediments that formerly served as a pollutant sink now serve as sources of contamination and residual environmental risk. Assessment and remediation of these contaminated sediment sites have been the subject of much scientific analysis, public debate and technological innovation (NRC, 2001).There are few economically viable options for management of contaminated sediments. Capping sediments with a layer of clean material is one of few alternatives with a proven record of success for sediment remediation. This chapter is intended to describe the tools and techniques that are applicable for 55 assessment, design, implementation and monitoring of capping as a remedy for contaminated sediment sites.

Capping for Remediation of Contaminated Sediments

: The objective of the project was to assess the potential for placing a cap at the experimental Mud Dump site and to determine reductions in environmental impacts related to capping. Contaminated sediment from dredging projects in the Hudson Estuary, Newark Bay, and contiguous waters were capped first with fine sediments from the Bronx River and Westchester Creek, then with sand from the Ambrose Channel. The capping resulted in a layer of sand about 1m thick lying atop the contaminated sediment. Physical, chemical and biological studies were carried out to determine if the capping effort yielded an intact cap showing resistance to erosion, and if the effort reduced loss of organic and inorganic toxicants from the contaminated material to the water column. It was determined that a cap was successfully placed at the experimental dump site. The cap was still intact and in place after 16 months. Cap erosion was minor; predictions of cap life were in excess of 20 years under normal meteorological conditions. Major storm events, however, are capable of eroding the cap and exposing the contaminated material. During the 16 months of study, the contaminated material decreased in volume by about 4%. Part of the decrease was due to compaction and part was due to loss of solids during dumping and deposition.

S G O'Connor

Papers

Dredging Operations Technical Support Program. Evaluation of the 1980 Capping Operations at the Experimental Mud Dump Site, New York Bight Apex.