Processes, Properties, and Conditions Controlling In Situ Bioremediation of Uranium in Shallow, Alluvial Aquifers (NUREG/CR-7014, PNNL-19026)

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Publication Information

Manuscript Completed: March 2010
Date Published: July 2010

Prepared by:
S.B. Yabusaki, Y. Fang, S.R. Waichler, and P.E. Long

Pacific Northwest National Laboratory
902 Battelle Boulevard
Richland, WA 99352

M. Fuhrmann, NRC Project Manager

NRC Job Code N6648

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

Uranium can be removed from groundwater by adding an electron donor to the subsurface that stimulates growth of native bacteria, generating conditions that result in precipitation of uranium. The long-term efficacy of this technology is unproven. Numerical modeling results for uranium bioremediation in a shallow, alluvial aquifer are provided to establish a broad framework for understanding processes associated with bioremediation of uranium and to bound conditions under which bioremediation could succeed in the long-term and conditions under which it is likely to fail. The models are benchmarked against experiments conducted at the Rifle, Colorado site. Sensitivity analysis of model parameters were conducted, examining: alternatives to the acetate electron donor (lactate and ethanol), oxygen and nitrate terminal electron acceptors, multiphase flow, density and gas entrapment processes, and hypothetical flood events. Sensitivity of simulated aqueous U(VI) concentrations to process model parameters suggest that groundwater flow rate, uranium bioreduction rate, and sulfate bioreduction parameters exert the most impact on bioremediation effectiveness. The simulated scenarios are used to assess potential performance issues for site conditions and other bioremediation approaches.