Field-Scale Evaluation of Biological Uranium Reduction and Reoxidation in the Near-Source Zone at the NABIR Field Research Center in Oak Ridge, TN

We have now added ethanol intermittently for over 700 days. Ethanol has been added weekly with each injection lasting for a few days. We are now observing: (1) Uranium immobilization at 700-2000 mg/kg. Baseline levels before remediation were 30-500 mg/kg. (2) Uranium concentrations in groundwater at the monitoring wells have fallen below the U.S. drinking water standard (30 ppb). This is an important milestone. (3) XANES analyses for day 535 indicate 51% U(IV) at the inner loop injection well, 35% U(IV) at MLS well 101-2, and 28% U(IV) at the extraction well. These numbers indicate that U(IV) reduction is not localized to the injection well, and is spreading through the aquifer. (4) We have had success removing trace levels of oxygen from recirculated water by addition of sulfite and related compounds. These compounds also provide the added benefit that in removing oxygen that themselves are oxidized to sulfate, an important electron acceptor needed for maintenance of our system