The efficiency of capping to control air emissions from exposed contaminated sediments and dredged material

Experiments were conducted to ascertain the effects of the use of two different types of capping materials on the air emissions of semivolatile organic compounds from exposed, contaminated dredged material such as those occurring in a CDF. A 4-cm sand cap and a 2-cm fine-grained sediment cap were used to reduce emissions from sediment inoculated with dibenzofuran, phenanthrene, and pyrene. The experiments were performed in a flux chamber. The sediment was sectioned after the experiment to obtain the spatial concentration profiles in the contaminated layer and the cap layer. The fluxes of dibenzofuran, phenanthrene, and pyrene showed reductions of 90, 94, and 95%, respectively, after 3 months in the presence of a sediment cap compared to uncapped sediment. The model prediction of the flux and the concentration profiles was satisfactory. The porosity of the cap and the partitioning of the organic compound between the pore air and the cap material had the largest effect on flux through the cap. The model can be used to evaluate cap selection.