TRANSPORT OF DISSOLVED HYDROCARBONS INFLUENCED BY OXYGEN-LIMITED BIODEGRADATION .2. FIELD APPLICATION

An existing solute transport model is modified to allow simulation of soluble hydrocarbon transport in groundwater influenced by oxygen-limited biodegradation. The transport model is then applied to an abandoned creosoting site where biodegradation is known to occur. Oxygen exchange with the unsaturated zone and resulting biodegradation is approximated as a first-order decay in hydrocarbon concentration. The loss of hydrocarbon due to horizontal mixing with oxygenated groundwater and resulting biodegradation is simulated by generating oxygen and hydrocarbon distributions independently and then combining by superposition. This procedure is only applicable where absorption of hydrocarbon is negligible. The major transport parameters are obtained by calibrating the model to a chloride plume also present at the site. Simulated oxygen and hydrocarbon concentrations closely matched the observed values. Two cases are presented to illustrate the potential assimilative capacity of shallow aquifers.