Efficiency of Capping Contaminated Sediments in Situ. 2. Mathematics of Diffusion-Adsorption in the Capping Layer

Simple analytical models for hydrophobic organic pollutant release from a contaminated sediment capped (covered) with a clean material are presented. Three situations are considered: a base case of uncapped contaminated sediment, a case associated with high sediment contamination levels with essentially constant contaminated layer pore-water concentration, and a more general case in which the leaching of the pollutant from the contaminated sediment layer is considered. The model results are compared to experimental data from laboratory bench-scale simulators. Both models show generally good agreement with the experimentally observed fluxes, indicating that the fundamental transport mechanisms are well understood. Sensitivity analysis suggests that the key factors controlling the effectiveness of a cap for isolating the benthic and pelagic communities from exposure to hydrophobic organic chemical pollutants are the cap thickness and its organic carbon content. A cap effectiveness factor is defined and plotted as a function of time and the above parameters.