Simulation of benzene transport and biodegradation during transient hydraulic conditions

Abstract

MODFLOW and BIOMOC were used to simulate transport and biodegradation of benzene in the alluvial aquifer adjacent to the Chena River. MODFLOW was used to calculate ground water fluxes at the boundaries of the BIOMOC model, which was used to model transport and biodegradation of benzene. A benzene plume located 300 ft. southeast of the study site is superimposed onto the cross-sectional model of the study area. Only saturated zone processes were modeled. Anaerobic biodegradation was the only simulated biodegradation process. The simulation shows 0.003% of the theoretical benzene entering the saturated zone is biodegraded, 0.6% is adsorbed by solids, and 99.4% leaves the model boundaries. The simulation predicts theoretical concentrations of benzene are 2 to 8 ug/l when discharging into the river. Field data do not support this finding. Processes not simulated, such as aerobic degradation at the water table, may make significant contributions toward limiting benzene transport.