Superfund Research Program
Sequestration Processes for Attenuation and Treatment of Arsenic and other Toxic Elements in Mine Waters
Final Progress Reports
During the past year Brusseau and his researchers continued the transition of their research focus, in preparation for the next funding cycle, to the development and testing of innovative methods for characterization and remediation of acid rock drainage and groundwater at hardrock mining sites. This effort applies the knowledge generated by the PI's current and prior projects to enhance the accuracy of risk assessments and improve the effectiveness of remediation strategies for mining sites contaminated by arsenic, selenium, and sulfate. In support of this transition, Brusseau and co-workers have conducted pilot-scale field tests at the Monument Valley uranium milling site in NE AZ to investigate the feasibility and sustainability of in situ bioremediation to treat groundwater contaminated by nitrate, sulfate, and uranium. The field tests were supplemented by bench-scale tests, stable-isotope analysis, and mathematical modeling. The results of site characterization activities conducted prior to the test indicated slow rates of denitrification and the absence of measurable bacterial sulfate reduction. The injection of an electron donor induced denitrification and bacterial sulfate reduction, as confirmed by exponential decreases of nitrate and sulfate concentrations in concert with changes in oxidation-reduction potential, redox species, alkalinity, production of hydrogen sulfide, and fractionation of delta15N-nitrate and delta34S-sulfate. The induction of reducing conditions caused a significant decrease in the concentration of uranium in groundwater, demonstrating feasibility of in-situ biosequestration at this site. Of great significance, the three-day, single injection of electron donor produced reducing conditions that were sustained for approximately three years.