Philip Jardine is a distinguished Research Staff Scientist at Oak Ridge National Laboratory. His research focus is on the influence of coupled processes on the fate and transport of inorganic contaminants in heterogeneous subsurface environments. He specializes in multiscale experimental quantification of nonequilibrium mass transfer processes in fractured and laminated soils and rock.

Presentation Description
In Situ Bioremediation Evaluated for Long-Term Immobilization of Uranium
In a multidisciplinary research study headed by Stanford University and Oak Ridge National Laboratory, field investigations were conducted to determine the impact of coupled processes on bio-enhanced sequestration of uranium in heterogeneous subsurface environments. Using a combination of multi-scale geophysical, chemical, microbial, and hydrological analytical tools, the researchers showed that the bioreduction of mobile uranium(VI) to sparingly soluble, less mobile uranium(IV) may impede the migration of contaminant uranium. The formation of sparingly soluble U(IV) was confirmed using x-ray absorption spectroscopy and bacteria known to reduce U(VI) were isolated from groundwater and sediments. The impact of intruding oxidants, such as dissolved oxygen and nitrate on stability of bioreduced U(IV) in the subsurface was also examined. The findings lend creditability to the notion that U bioreduction can be an important remedial process in heterogeneous subsurface sys tems containing a multitude of competing hydrological, geochemical, and microbial reactions. Long-term monitoring results indicated that very low aqueous-phase concentrations of uranium can be achieved despite high solid-phase U concentrations due to the low solubility of uranium(IV) and low rates of desorption/dissolution relative to the rate of reduction. The technical insights of these research findings are being considered in future DOE decision making and remediation efforts at the Oak Ridge site. Additional details regarding this research are available at http://www.esd.ornl.gov/orifrc/.