When sediments are rich in organic, anaerobic and aerobic processes, they generate biogenic gases, mainly methane (CH4) and carbon dioxide (CO2). A higher CH4 content in the gas is indicative of methanogenic conditions and a reductive environment. This condition facilitates the transfer of contaminants of concern (COCs) from the sediment through the surrounding water to the atmosphere. Prior research at Eagle Harbor (Bainbridge Island, Washington) demonstrated that when polycyclic aromatic hydrocarbon (PAH) contaminated sediment was capped, biogenic gas began to percolate through the cap matrix. Prior research on polychlorinated biphenyl (PCB)-contaminated sediment at Lake Hartwell (Clemson, South Carolina) demonstrated that as the organic concentration in Lake Hartwell increased, the generation of gas increased. The volume of gas generated was dependent on many factors including the amount of sediment, seasonal conditions, depth of the lake, and water temperature. The release of gas bubbles from sediments into overlying water (ebullition) is a major mechanism for the discharge of biogenic and geogenic gases into the water body. Microbial breakdown of sedimentary organic matter produces gas bubbles which are inherently hydrophobic and tend to accumulate both hydrophobic organic contaminants and colloids from porewater. Through this mechanism the ebullition of CH4 and CO2 in contaminated sediments may contribute to the release of CoCs from the sediment-water interface and into the water column. This report describes the performance of microcosm and a bench-scale column studies to attempt to understand and quantify the release of COCs from uncapped and capped sediments. The gas ebullition through the sediment bed was simulated by sparging mixed anaerobic gas at two flow rates (6.5 and 18.5 mL/min).

EPA "February 2010." "Terrence Lyons, Task order manager". Includes bibliographical references (p. 62). "EPA/600/R-10/062."

This report describes the performance of microcosm and a bench-scale column studies to attempt to understand and quantify the release of COCs from uncapped and capped sediments. The gas ebullition through the sediment bed was simulated by sparging mixed anaerobic gas at two flow rates (6.5 and 18.5 mL/min).