Contaminated Marine Sediments Assessment and Remediation (1989) / Chapter Skim
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Management Strategies for Disposal of Contaminated Sediments
Management Strategies for Disposal of Contaminated Sediments
Pages 200-220
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has since devoted major research efforts toward development of testing protocols and contaminant control measures for both open-water and confined disposal alternatives. In 1984, efforts were initiated to develop an overall management strategy based on these efforts.
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A more detailed presentation of the management strategy is available from the COE Waterways Experiment Station (Francingues et al., 1985~. MANAGEMENT STRATEGY The selection of an appropriate strategy is partially dependent on the nature of the dredged material, nature and level of contamination, the physicochemical nature of the disposal site environment, available dredging alternatives, project size, and site-specific physical and chemical conditions, all of which influence the potential for environmental impacts.
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For openwater disposal, contaminant problems may be either water column or benthic related. Confined disposal contaminant problems may be related to either water quality (effluent, surface runoff, or leachate)
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Where the Whys sical and chemical environment of a contaminated sediment is altered by disposal, chemical and biological processes important in determining environmental consequences of potentially toxic materials may be affected. The major disposal alternatives are open water (subaqueous environment)
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The acceptability of the proposed confined disposal operation can be evaluated by comparing the predicted contaminant concentrations with applicable water quality standards while considering an appropriate mixing zone. In some cases appropriate water column bioassays would be required if water quality criteria are exceeded.
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Laboratory testing protocols to predict leachate quality from dredged material disposal sites have been developed and applied, however additional evaluations of available leaching procedures are needed before a leaching test protocol for confined dredged material can be recommended. These evaluations are now an ongoing COE research effort.
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SELECTION OF A DISPOSAL ALTERNATIVE Disposal alternatives are divided into general classes: open water' confined, open water with restrictions, and confined disposal with restrictions. Disposal alternatives with restrictions are used whenever results of the testing protocols indicate they are needed.
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may be used to estimate the maximum concentration of the liquid and suspended particulate phases found at the disposal site after initial mixing. Confined Disposal Conventional confined disposal consists of placing or pumping the dredged material into a diked containment area where the material settles and consolidates.
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. It is possible that techniques and equipment can be developed that will provide a capped dredged material disposal area as secure from potential environmental harm as upland confined disposal areas.
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Confined Disposal with Restrictions Site Selection and Design Conventional confined disposal methods, described previously, can be modified to accommodate disposal of contaminated sediments in new, existing, and reusable disposal areas. The design or modification of these areas must consider the problems associated with contaminants and their effects on conventional design.
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Control measures include proper site selection as described earlier, dewatering to minimize leachate production, chemical admixing to prevent or retard leaching, lining the bottom to prevent leakage and seepage, capping the surface to minimize infiltration and thereby leachate production, vegetation to stabilize contaminants and to increase drying, and leachate collection, treatment, or recycling (Gambrel!
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These controls will be extremely site specific. Special considerations that are based on the physical nature and chemical composition of the dredged material will be required to effectively design a confined disposal facility.
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Applying the systematic detailed guidance will lead to a decision that restrictions are or are not required for aquatic disposal and/or upland disposal. IMPLEMENTATION COE Policy of contaminated sediments (Kelly The Management Strategy/Decision-Making Framework approach was adopted as official COE policy in 1985 for studies involving disposal ~ __,, 1985 ~ .
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Applications Strategy is now being applied routinely by the COE and the private sector. Recently, three studies of disposal alternatives incorporated the strategy in a comprehensive manner, utilizing testing approaches for both open-water and confined disposal: 2.
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1983. Contaminant uptake by Spartina alterniflora from an upland dredged material disposal site-application of a saltwater plant bioassay.
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1983. Prediction of surface runoff water quality from an upland dredged material disposal site.
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Vicksburg, Miss.: U.S. Army Engineer Waterways Experiment Station.
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