EPA National Conference on Management and Treatment 01 Contaminated Sediments

/n-situ capping, the placement of a subaqueous covering or cap of clean isolating material over an in-situ deposit of contaminated sediment, is a potentially economical and effective approach for remediation of contaminated sediment. A number of sites have been remediated by in-situ capping operations worldwide. EPA has developed detailed guidelines for planning, design, construction, and monitoring of in-situ capping projects. This paper briefly describes the major aspects of in-situ capping as an option and provides a summary of recent case studies. /n-Situ Capping Defined /n-situ capping (ISC) refers to placement of a subaqueous covering or cap over an in-situ deposit of contaminated sediment. The cap may be constructed of clean sediments, sand, gravel, or may involve a more complex design with geotextiles, liners and multiple layers. In-situ capping can serve three primary functions: a. physical isolation of the contaminated sediment from the benthic environment, b. stabilization of contaminated sediments, preventing resuspension and transport toother sites, and C. reduction of the flux of dissolved contaminants into the water column. To achieve these results, an in-situ capping project must be treated as an engineered project with carefully considered design, construction, and monitoring. The basic criterion for a successful capping project is simply that the cap required to perform some or all of these functions be successfully designed, placed, and maintained. Design Guidance for In-Situ Capping Detailed guidelines for designing, constructing and managing in-situ capping as a sediment remediation alternative have been developed by the U.S. Environmental Protection Agency (USEPA) under the Assessment and Remediation of Contaminated Sediments Program, administered by USEPA’s Great Lakes National Program Office, in Chicago, IL. (1) The major activities associated with evaluating an ISC option include: 1. Set a cleanup objective, i.e., a contaminant concentration or other benchmark, The cleanup objective will be developed as a prerequisite to the evaluation of all remediation alternatives. 2. Characterize the contaminated sediment site under consideration for remediation. This includes gathering data on waterway features (water depths, bathymetry, currents, wave energies, etc.); waterway uses (navigation, recreation, water supply, wastewater discharge, etc.); and information on geotechnical conditions (stratification of underlying sediment layers, depth to bedrock, physical properties of foundation layers, potential for groundwater flow, etc.). Determine if advective processes are present and the ability of the cap to control advective contaminant losses. Determine any institutional constraints associated with placement of a cap at the site. 3. Characterize the contaminated sediments under consideration. This includes the physical, chemical, and biological characteristics of the sediments. These characteristics should be determined both horizontally and vertically. The results of the characterization, in concert with the cleanup objective, will determine the areal extent or boundaries of the area to be capped. 4. Make a preliminary determination on the feasibility of ISC based on information obtained about the site and sediments. If site conditions or institutional constraints indicate that ISC is not feasible, other remediation options must be considered. 5. Identify potential sources of capping materials, including clean sediments that might be dredged