Oxygen Transport across the Capillary Fringe in LNAPL Pool-Source Zones

Abstract

Transfer of oxygen across the capillary fringe and water table is a critical oxygen source for aerobic biodegradation of hydrocarbon light nonaqueous phase liquids (LNAPLs) at or near the water table. However, significant resistance to oxygen mass transfer may be associated with the capillary fringe. This work evaluates the hypothesis that a decrease in the water-saturated thickness of the capillary fringe due to the presence of a hydrocarbon LNAPL, and the reduced resistance to oxygen mass transfer in the hydrocarbon phase, will enhance oxygen transfer relative to natural reaeration. Oxygen flux in the absence and presence of an LNAPL pool is conceptually evaluated using the two-film model. Abiotic experiments in a bench-scale sand-tank reactor demonstrated that oxygen transport through the water table interface was enhanced when an LNAPL (dodecane) pool was present at the water table compared to natural reaeration. Biotic experiments demonstrated that the increased oxygen transport in the presence of the LNAPL pool also increased biodegradation of a solute (glucose) plume passing beneath the LNAPL pool. Biodegradation also apparently further bioenhanced the oxygen transfer.