Sediment Capping and Natural Recovery, Contaminant Transport Fundamentals With Applications to Sediment Caps

Abstract

Abstract : Engineered sediment caps and natural recovery are in situ remedial alternatives for contaminated sediments, which consist of the artificial or natural placement of a layer of material over a sediment deposit, respectively. In addition to physical isolation and the prevention of sediment erosion, the objective of these approaches includes mitigating the loss of dissolved contaminants from the sediment deposit to the overlying surface water. Whether engineered or placed naturally through sedimentation, migration of contaminants through the cover layer needs to be evaluated to forecast performance and compare the effectiveness of capping or natural recovery to other remedial options such as dredging. This report reviews the techniques commonly used to predict the migration of contaminants through sediment cover layers and to assess performance. Predicted upon the planar nature of the sediment deposit and cover layer, these techniques commonly take the form of vertically oriented one-dimensional (1-D) methods and models. These 1-D approaches use input values describing the characteristics of the sediment cap and the hydrogeologic surroundings and generate output values that are used to project cover-layer performance. The assumptions implicit in the use of the 1-D methods and models are also discussed. Much of the information in this report was gathered from standard references in the hydrogeologic literature.