Characterization of Contaminant Migration Potential Through In-Place Sediment Caps

Abstract

By isolating contaminated sediments from overlying bodies of water, capping can effectively reduce ecosystem exposure to contaminants and minimize the possibility of contaminant transport into the food chain Magar, 2001 Palermo et al., 1998 USACE, 1998. However, because contaminated sediments are left in place, caps generally require long-term monitoring, and the risks of contaminant transport or sediment resuspension persist. Many contaminated marine sediment sites reside in shallow, coastal areas that are often impacted by advective processes i.e., groundwater flow, tidal pumping, and wave pumping, sorption controlled diffusive processes, and bioturbation. These forces contribute to the flux of contaminants through sediments and, ultimately, through a sediment cap. A theoretical foundation for contaminant transport through surface sediments exists Medine and McCutcheon, 1989, but remains untested for sediment caps exposed to advective forces. The scientific and engineering principles of capping need to be improved by testing and validating this theoretical foundation, and by establishing design criteria that account for processes governing vertical contaminant migration through sediment caps. The overall objective of this project is to enhance the scientific understanding of contaminant migration through sediment caps in areas with significant groundwater potential or tidal fluctuations. Specific objectives include the following 1 Examine contaminant mobility over time through an existing sediment cap 2 Measure the influence of porewater flux via groundwater advection and tidal pumping 3 Quantify aqueous contaminant mobility in the laboratory 4 Evaluate the fundamental mechanisms contributing to polycyclic aromatic hydrocarbon PAH sorption and retention in the laboratory.