HR: 0800h
AN: B31A-0971    [Abstracts]
TI: In Situ Biostimulation at a Former Uranium Mill Tailings Site: Multicomponent Biogeochemical Reactive Transport Modeling
AU: * Yabusaki, S
EM: yabusaki@pnl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352
AU: Fang, Y
EM: yilin.fang@pnl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352
AU: Long, P
EM: philip.long@pnl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352
AB: In situ biostimulation at a Former Uranium Mill Tailings Site: Multicomponent Biogeochemical Reactive Transport Modeling Field experiments conducted at a former uranium mill tailings site in western Colorado are being used to investigate microbially mediated immobilization of uranium as a potential future remediation option for such sites. While the general principle of biostimulating microbial communities to reduce aqueous hexavalent uranium to immobile uraninite has been demonstrated in the laboratory and field, the ability to predictably engineer long lasting immobilization will require a more complete understanding of field-scale processes and properties. For this study, numerical simulation of the flow field, geochemical conditions, and micriobial communities is used to interpret field-scale biogeochemical reactive transport observed during experiments performed in 2002 to 2004. One key issue is identifying bioavailable Fe(III) oxide, which is the principal electron acceptor utilized by the acetate- oxidizing Geobacter sp. These organisms are responsible for uranium bioreduction that results in the removal of sufficient U(VI) to lower uranium groundwater concentrations to at or near applicable standards. The depletion of bioavailable Fe(III) leads to succession by sulfate reducers that are considerably less effective at uranium bioreduction. An important modeling consideration are the abiotic reactions (e.g., mineral precipitation and dissolution, aqueous and surface complexation) involving the Fe(II) and sulfide produced during biostimulation. These components, strongly associated with the solid phases, may play an important role in the evolving reactivity of the mineral surfaces that are likely to impact long-term uranium immobilization.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 0418 Bioremediation
DE: 0432 Contaminant and organic biogeochemistry (0792)
DE: 0466 Modeling
SC: Biogeosciences [B]
MN: Fall Meeting 2005