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Title: Guidance for subaqueous dredged material capping
Authors: United States. Army. Corps of Engineers. New England District.
Texas A & M University.
Geotechnical Laboratory (U.S.)
Coastal and Hydraulics Laboratory (U.S.)
Dredging Operations and Environmental Research Program (U.S.)
Palermo, Michael R.
Clausner, James E.
Rollings, Marian P.
Williams, Gregory L.
Myers, Tommy E.
Fredette, Thomas J., 1955-
Randall, Robert E., 1940-
Keywords: Capping
Dredged material
Open-water disposal
Contaminated sediments
Dredging spoil
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report ; DOER-1
Description: Technical Report
Abstract: 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 be 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. The main body of this report describes specific procedures for all aspects of capping project evaluation and design. A recommended sequence of design activities is presented, and specific design steps are organized into flowcharts as necessary. A number of appendixes are also included in this report that provide detailed information on specific testing procedures, predictive models, etc. A capping operation must be treated as an engineered project with carefully considered design, construction, and monitoring to ensure that the design is adequate. There is a strong interdependence between all components of the design for a capping project. By following an efficient sequence of activities for design, unnecessary data collection and evaluations can be avoided, and a fully integrated design is obtained. The major components of the project design and evaluation process include site selection, equipment and placement techniques, geotechnical considerations, mixing and dispersion during placement, required capping sediment thickness, material spread and mounding during placement, cap stability, and monitoring. Processes influencing the cap design include bioturbation, consolidation, erosion, and potential for advection or diffusion of contaminants. The basic criterion for a successful capping operation is simply that the cap thickness required to isolate the contaminated material from the environment be successfully placed and maintained. The cost of capping is generally lower than alternatives involving confined (diked) disposal facilities. The geochemical environment for subaqueous capping favors long-term stability of contaminants as compared with the upland environment where geochemical changes may favor increased mobility of contaminants. Capping is therefore an attractive alternative for disposal of contaminated sediments from both economic and environmental standpoints.
Appears in Collections:Technical Report

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