Field monitoring at the United Creosoting Company (UCC) site in Conroe, TX has shown that the shallow aquifer has become contaminated by leakage from two unlined ponds. A plume of hydrocarbon contaminated ground water is present and is contained within a large plume of elevated chloride concentrations. This difference in size could be due to two processes: adsorption and biodegradation. A series of field tests and computer simulations were performed to identify which processes were limiting the transport of the hydrocarbon. A seven day injection-production test was performed in the shallow semi-confined aquifer at the site and clearly demonstrated that adsorption was not significant in retarding the movement of naphthalene. Loss of naphthalene and paradichlorobenzene during the test suggested that biotransformation of the hydrocarbon could be significant. Previous laboratory studies (Lee and Ward, 1984) had shown the potential for rapid biotransformation of the hydrocarbon when oxygen was added but very minimal transformation in the absence of oxygen. In the shallow aquifer at the UCC site, oxygen is present at low concentrations and could potentially result in limited biotransformation of the hydrocarbon plume. In order to study this phenomenon, a series of numerical models were developed to simulate the transport of oxygen and hydrocarbon in ground water and resulting biodegradation. Numerical simulations generated with these models suggested that in most ground water environments, microbial kinetics will be rapid relative to mass transport and biodegradation will be limited by the rate of mixing between oxygen and hydrocarbon. The numerical models were then tested by comparing numerical simulations to field data collected at the UCC site and the results of a series of single well push-pull tests designed to measure in situ biotransformation. Finally, the calibrated model was used to compare various alternatives for restoration of the UCC site.