Options for In Situ Capping of Palos Verdes Shelf Contaminated Sediments
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS ENVIRONMENTAL LAB
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The U.S. Army Engineer Waterways Experiment Station WES has performed an evaluation of in situ capping options for sediment restoration of DDT and PCB contaminated sediments on the Palos Verdes PV shelf off the coast of Los Angeles, California, for Region 9 of the U.S. Environmental Protection Agency. In situ capping refers to placement of a covering or cap of clean material over an in situ deposit of contaminated sediment. This study included prioritizing areas of the PV shelf to be capped, determining an appropriate cap design or designs, developing an equipment selection and operations plan for placement of the cap, developing a monitoring plan to ensure successful cap placement and long-term cap effectiveness, and developing preliminary cost estimates. The primary functions of an in situ cap for the PV shelf would be physical stabilization of the contaminated sediment to retard suspension, reduction of bioaccumulation and movement of contaminants into the food chain, and reduction of the flux of dissolved contaminants into the water column. Two capping approaches were considered for selected areas of the shelf 1 placement of a thin cap which would isolate the contaminated material from shallow burrowing benthic organisms, providing a reduction in both the surficial sediment concentration and contaminant flux, and 2 placement of an isolation cap which would be of sufficient thickness to effectively isolate benthic organisms from the contaminated sediments, prevent bioaccumulation of contaminants, and effectively prevent contaminant flux for the long term.
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