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Our understanding of subsurface microbiology is hindered by the inaccessibility of this environment, particularly when the hydrogeologic medium is contaminated with toxic substances. Research in our labs indicated that the composition of the growth medium (e.g., bicarbonate complexation of U(VI)) and the underlying mineral phase (e.g., hematite) significantly affects the rate and extent of U(VI) reduction and immobilization through a variety of effects. Our research was aimed at elucidating those effects to a much greater extent, while exploring the potential for U(IV) reoxidation and subsequent re-mobilization, which also appears to depend on the mineral phases present in the system. In situ coupons with a variety of mineral phases were placed in monitoring wells at the NABIR FRC. These coupons showed that the mineral phase composition significantly affected the resulting attached phase microbial community. Our comparative use of both batch and open flow reactors (more representative of field conditions) indicates that hydrodynamics and continual influx of substrate and contaminants can also yield significantly different results than those obtained with closed serum bottles. To this end, the following overall experimental hypothesis tested was the following: On a mineral surface under anaerobic conditions, accumulations of secondary inorganic precipitates are controlled by a) the bacteria associated with the mineral surface, b) the electron acceptors available for anaerobic bacterial respiration, and c) local hydrodynamics and pH buffers govern micro- and meso-scale interaction of U in the presence of electron donors and acceptors, and nutrients

osti oai (u.s. department of energy office of scientific and technical information)

FINAL REPORT - Biogeochemistry of Uranium Under Reducing and Re-oxidizing Conditions:An Integrated Laboratory and Field Study and Acceptable Endpoints for Metals and Radionuclides: Quantifying the Stability of Uranium and Lead Immobilized Under Sulfate Reducing Conditions