Groundwater at Oak Ridge National Laboratory's Field Research Center (FRC) is contaminated with U(VI) and Tc(VII), has pH values as low as 3.3, and nitrate concentrations as high as 120 mM. The objective of this research was to determine if in-situ bio-immobilization is a viable treatment alternative for this water. A laboratory column packed with crushed limestone and bicarbonate was used to model in-situ pH adjustment. Denitrification and metal reduction were modeled in columns packed with FRC sediment with ethanol as the electron donor. Two intermediate-scale physical models deployed in the field were packed with limestone and sediment and were stimulated with ethanol to support denitrification, U(VI) reduction, and Tc(VII) reduction of FRC groundwater. The limestone/bicarbonate column maintained a pH of above 5 for nearly one hundred pore volumes without significant loss in hydraulic conductivity. The high-nitrate (~120 mM) column study provided rates of denitrification (~15.25 mM/day), ethanol utilization (~13 mM/day), and technetium reduction (~120 pM/day) by sediment microorganisms, but no uranium reduction was detected. Results of the low nitrate (3 mM) column study indicate that once the pH of FRC water is adjusted to pH ~7 and nitrate is removed, uranium (~3 μM) and technetium (~500 pM) reduction occurred with ethanol as the electron donor at rates of 0.5 μM/day and 57 pM/day. Similar results were obtained in two intermediate-scale (~3 m long) physical models. Data from the high-nitrate, low-pH model indicate that the pH was increased and nitrate and technetium reduction were occurring. Decreased U(VI) concentrations were measured in the presence of high nitrate concentrations. Thus, U(VI) precipitates may form or sorption of U(VI) may occur near the inlet in the pH adjustment region. The maximum pseudo-first order rates of reduction measured during the seventh week of model operation were: nitrate at 0.76 day⁻¹, Tc(VII) at 0.28 day⁻¹, and U(VI) at 0.12 day⁻¹. Ethanol concentrations were reduced from ~180 mM to zero in ~10 days during the seventh week of model operation. No Fe(II) production was measured. Concentration data collected from the low nitrate, neutral pH model indicate that nitrate, uranium, and technetium reduction were occurring, though the model had been operational for only ~6 weeks. No Fe(II) production was detected but sulfate reduction was occurring. The results of the laboratory experiments and the performance of the intermediate-scale physical models suggest that bio-immobilization is a viable treatment alternative for the contaminated groundwater at the FRC. / Graduation date: 2004

No description available.

The goal of the project was to develop a functional prototype of an environmental risk assessment parameter database on the World-Wide Web. The ability to develop a consolidated environmental database has become possible due to the phenomenal growth of the Internet and the World-Wide Web over the past few years. A large number of environmental resources do currently exist; however, with the large volume of information available, access, management, reliability, and retrievability have become increasingly difficult. To illustrate the prototype database, a practical environmental concern and the tools necessary to evaluate and characterize that concern were needed. Uranium (�������U) daughters leaching from abandoned mill tailing piles at three abandoned uranium mines in southwestern Colorado were chosen to demonstrate the database concept. The RESRAD environmental pathway modeling code served as the evaluation and characterization tool. Due to the size and complexity of RESRAD, a single radionuclide release rate equation was isolated as a controllable component of the code. The equation was a small part of the water pathway factor and examined the rate at which radionuclides absorbed in soil were leached by infiltrating water. This serves as the source term for groundwater contamination and directly applies to the �������U progeny leaching from mill tailing piles scenario. Parameters selected from the equation dealt with the background data that directly influenced the mobility of contaminates in the environment. Environmental data for the three Colorado sites were gathered and interpreted. Probability Density Functions (PDFs) were developed for input parameters and the results were then incorporated into the web site. / Graduation date: 1998

Uranium has been released into the environment due to improper practices associated with mining and refinement for energy and weapons production. Soluble U(VI) species such as uranyl carbonate can be reduced to form the insoluble U(IV) mineral uraninite (UO2) via microbial respiratory processes. Formation of UO2 diminishes uranium mobility and prevents uranium-laden groundwater from being discharged into surface water; however, oxygen and other oxidants re-solubilize UO2. Many organisms have been shown to reduce uranium, but variations in microbial physiology change the dynamics of microbial uranium reduction in situ and affect uraninite stability. Anaeromyxobacter dehalogenans is a metal-reducing delta-Proteobacterium in the myxobacteria family that displays remarkable respiratory versatility and efficiently reduces U(VI). The approach of this research was to enhance characterization of A. dehalogenans by identifying unique genetic traits, describing variability within the species, and examining the environmental distribution of A. dehalogenans strains. Genome analysis revealed that A. dehalogenans shares many traits with the myxobacteria including type IV pilus-based motility and an aerobic-like electron transport chain. In addition, the genome revealed genes that share sequence similarity with strict anaerobes and other metal-reducing organisms. Physiological examination of microaerophilism in A. dehalogenans strain 2CP-C revealed growth at sub-atmospheric oxygen partial pressure. Physiological characterization of novel isolates demonstrated that strain-level variation in the 16S rRNA gene coincides with metabolic changes that can be linked to the loss of specific gene homologs. Anaeromyxobacter spp. were present at the Oak Ridge Integrated Field-scale Subsurface Research Challenge (IFC) site and multiplex qPCR tools designed using a minor-groove binding probe gave insights into strain and species differences in the community. Finally, 16S rRNA gene sequences were identified which suggest a novel Anaeromyxobacter species that is responsible for uranium reduction at the Oak Ridge IFC site. This research contributes new knowledge of the ecophysiology of a widely distributed, metal-reducing bacterial group capable of uranium immobilization. The characterization of Anaeromyxobacter spp. helps to elucidate the dynamics of biological cycling of metals at oxic-anoxic interfaces, like those at the Oak Ridge IFC, and contributes to the broader study of microbial ecology in groundwater and sediment environments.

We quantified U removal and investigated the efficacy of uranium as a quantitative tracer of groundwater discharge in a headwater salt marsh of the Okatee River, Bluffton, SC. Determining the magnitude of U removal is important for advancing U as a tracer of paleo-oceanic conditions. Since salt marsh groundwater is typically enriched in nutrients and other biologically and chemically reactive species, quantifying groundwater discharge from marshes is critical for understanding the ability of salt marshes to modify the chemistry of important species in surface waters. We hypothesized that water-column U(VI) was removed by tidally-induced advection of surface water into permeable, anoxic salt marsh sediments, a process resulting in bacterially-mediated precipitation of insoluble U(IV)O2 and/or sorption of uranium to iron-oxides at the oxic/anoxic sediment interface. Furthermore, we suggested that hydraulic pressure gradients established by marsh-surface tidal inundation and seasonally-variable rainfall promote the discharge of salt-marsh-processed, uranium-depleted groundwater to tidal creeks, producing the surface-water U-removal signal. Groundwater and surface water data revealed non-conservative uranium behavior. We documented extensive uranium removal from shallow marsh groundwater and seasonally variable uranium removal from surface waters. These observations allowed for the calculation of seasonally-dependent salt marsh uranium removal rates. On a yearly basis, our removal rate (58 to 104 mol m-2 year-1) reemphasized the importance of anoxic coastal environments for U removal. High uranium removal, high barium concentration water observed seeping from creek banks at low tide supported our hypothesis that groundwater discharge must contribute to uranium removal documented in tidal surface waters. Average site groundwater provided an analytically reasonable endmember for explaining uranium depletion in surface water. Therefore, we used three endmember mixing models for estimating the fraction of surface water with presumed a groundwater signature. Our discharge estimates of 8 to 37 L m-2 day-1 agreed closely with previously published salt marsh values. Seasonality in discharge rates can be rationalized with appeal to seasonal patterns in observed rainfall, tidal forcing, and marsh surface bioturbation. Although more work is needed, the results of this portion of the study suggest that U may be an effective quantitative tracer of groundwater discharge from salt marshes.