PI: S.C. Brook, P.M. Jardine, I. L. Larsen, ORNL Environmental Sciences Division ( ESD); J.P. Gwo, ORNL Computer Science and Mathematics Division (CSMD); G. V. Wilson, Desert Research Institute, and A. T. Stone, Johns Hopkins University.
ABSTRACT
The overall goal of this proposed research is to provide an improved understanding and predictive capability of the mechanisms that allow chelate-degrading bacteria to be effective in the bioremediation of subsurface environments contaminated with toxic metals and radionuclides. The study is motivated by the likelihood that vadose zone microbial activity can effectively consume chelating organic ligands thus facilitating the immobilization of released metals and radionuclides via sorption and precipitation reactions. Our objectives are to (1) develop and improved understanding and predictive capability of the mechanisms governing the biodegradation of cobalt (Co)-NTA and uranium (U)-NTA in unsaturated, structured media from the pore scale to the field macrocosm scale (meter-sized pedon), (2) quantify the microbial and hydrologic conditions that influence the biodegradation of metal-chelating ligands, for the purpose of contaminant containment and remediation in heterogeneous, structured media, and (3) provide integrated experimental and theoretical methodologies for the scale-up of biohydrogeochemical processes from the microscopic scale to the macrocosm (pedon) scale. The proposed work consists of four multidisciplinary hypothesis-driven tasks that build on collaborations established within DOE's Subsurface Science Program. Our approach involves the use of (1) a variably saturated dynamic flow technique to quantify the biodegradation of Co(II)-NTA and U(VI)-NTA as a function of pore size in structured media, (2) multiscale experiments that are designed to control the hydrologic conditions and enhance the microbially induced immobilization of Co-NTA and U-NTA, and (3) existing models that couple microbial and hydrogeochemical processes to conduct multiscale process and parameter upscaling studies. The experimental results will provide new insights concerning the relationship between the biodegradation of radionuclide-chelate complexes and the pore structure and hydrologic connectivity in heterogeneous subsurface environments. Further, these results will enhance our ability to upscale laboratory- and pedon-scale biodegradation processes to the field scale. Although the proposed research is basic science in nature, the results will have direct relevance to ongoing or planned remediation efforts at DOE sites (e.g., Savannah River's Old Burial Ground, Paducah Gaseous Diffusion Plant, Hanford, WA, INEL-TAN site, ORNL's Y12 plant) and at other federal facilities (Dover AFB). Further, this proposal combines DOE's commitment to environmental restoration with its commitment to major facilities and higher education.
Date Begun: FY98