A geochemical modeling study of the effects of urea-degrading bacteria on groundwater contaminated with acid mine drainage

grantor: University of TorontoAqueous geochemical computer modeling was carried out for an aquifer contaminated with acid mine drainage at the South Bay mine site to test the feasibility of a proposed bioremediation treatment plan. The treatment consists of adding urea to the aquifer to stimulate growth of indigenous urea-degrading bacteria that produce carbonate and ammonium. These products have the potential for neutralizing the groundwater and precipitating iron oxides, which may remove heavy metals from solution through sorption processes. With aqueous geochemical data for piezometers situated along a hydraulic gradient from the tailings area to the aquifer's discharge zone, a model of the aquifer's geochemistry was constructed with the program MINEQL +. Once the model was calibrated to ensure that calculated pH values matched measured field pH values, titrations with the urea-degradation products were undertaken to simulate introduction of the urea-degradation products into the groundwater over time. The amount of carbonate and ammonium required to raise the pH in the piezometers to 8.0-8.1 ranged from 3.5 * 10 -5 M - 0.24 M and 7.0 * 10-5 M - 0.48 M, respectively. As is evident with observed pH increases and oxide supersaturation as a result of the titrations, the metabolic products of microbial urea degradation have been proven to have considerable potential for treating contaminated groundwater at South Bay.M.Sc