FRC Area 3 Site Bioremediation (August 24, 2003 – August 7, 2005) Tests were performed in two phases: (1) a clean water flush to remove bulk nitrate, Al, and Ca (days 9-137). (2) biostimulation by repeated ethanol injection (days 138-present). Uranium is immobilized in the sediments at mg/kg Uranium concentration in the groundwater has dropped below US EPA drinking water maximum limit (0.03 mg/l) in the monitoring wells. An active remediation zone has been established with high microbial activity for denitrification, Fe(III) reduction, sulfate reduction and U(VI) reduction.

Well System for Field-scale Test for in situ Bioremediation of Uranium Contaminated site, FRC Area 3

Injection of Electron Donor (ethanol) for Bioremediation (day ) Started ethanol injection on day 137

Nitrate Concentration Changes during Remediation Clean water flush (day 9-137) Bioremediation (day ) To avoid production of nitrogen gas bubbles in subsurface and inhibition, nitrate should be reduced below 1 mM

U(VI) Concentrations in inner loop wells and MLS wells The maximum concentration of uranium in drinking water is 0.03 mg/l (US EPA). Injection and extraction wells Monitoring wells

Before bioremediation the uranium content in core samples from FW104 ranged from 0.03 to 0.8 g/kg Day 247 Day 409 Day 535Day 622Day 670 Variability in the content of U in the injection well sediment is likely due to variability in the removal of U during the surging operation. injection well monitoring well extraction well Uranium Content in Sediments from Injection, Monitoring and Extraction Wells during Bioremediation

Uranium Redox State – Day 535

The sediment changes color as microbial reduction progresses injection wellmonitoring well Day 333 Day 670 extraction well monitoring well injection well extraction well sample from day 670 incubated 3 days with no added ethanol extraction well sample from day 670 incubated 3 days after adding 100 mg/L ethanol Now black brown