HR: 11:30h
AN: B32A-05    [Abstracts]
TI: A Comparison of Naturally-Occurring and Artificially Stimulated Uranium(VI) Bioreduction in Sediment from a Field-scale Experiment in Rifle, CO
AU: * Campbell, K M
EM: kcampbell@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd MS 465, Menlo Park, CA 94025, United States
AU: Williams, K H
EM: khwilliams@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., MS 90-1116, Berkeley, CA 94720, United States
AU: Lesher, E
EM: elesher@mines.edu
AF: Division of Environmental Science and Engineering, Colorado School of Mines, 1500 Illinois St., Golden, CO 90401, United States
AU: Davis, J A
EM: jadavis@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd MS 465, Menlo Park, CA 94025, United States
AU: Long, P E
EM: philip.long@pnl.gov
AF: Pacific Northwest National Laboratory, Mail Stop K9-33, Richland, WA 98816, United States
AB: Long-term remediation of uranium (U)-contaminated groundwater poses one of the greatest challenges in the clean-up of impacted sites. One solution is to reduce dissolved U(VI) to insoluble U(IV) precipitates by stimulating indigenous metal reducing bacterial populations in situ. Contamination from a former U mine tailings repository (Rifle, CO) provides a research site to study the efficacy of biostimulated U(VI) reduction at the field scale. Several cores were drilled in June 2007 across a region of naturally-occurring U(VI) bioreduction. The cores represent a cross section of sediment that ranges from minimally reducing to highly reducing. Anaerobic sediment samples from the cores were analyzed for labile U(VI) content by carbonate extraction in anoxic conditions (pH 9.4, 14 mM NaHCO3, 2.8 mM Na2CO¬3). A subset of the same core sections were dried and oxidized by exposure to air for 2 weeks. The carbonate extraction was repeated, and the amount of U(IV) present in the anaerobic sample was calculated by difference between the anoxic and oxidized extractions. An acid extraction was also performed on the oxidized sediments to compare the carbonate extractable and the acid extractable U fractions. The highest U concentrations were found in the highly bioreduced sediment, with the majority of U present as U(IV) (66-92%). The regions of highest bioreduction also correspond to elevated concentrations of solid phase organic carbon, suggesting that natural bioreduction is stimulated by zones of increased organic carbon content. The same field site was then used for an artificially stimulated bioreduction experiment, where the indigenous bacterial community was stimulated by injecting acetate upgradient of the core collection location. Carbonate and acid extractions were performed on core samples taken after the completion of the acetate injection. This work evaluates the composition of the sediment before and after biostimulation as a way of directly comparing the extent of natural U(VI) bioreduction to acetate-stimulated bioreduction in order to facilitate the design of a more effective bioremediation strategy for this site.
DE: 0400 BIOGEOSCIENCES
DE: 0418 Bioremediation
DE: 0461 Metals
DE: 0471 Oxidation/reduction reactions (4851)
DE: 0489 Trace element cycling (4875)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting