1998 RESEARCH PROJECTS Program Element 6 Bacterial Transport PROJECT: The Influence of Heterogeneity and Growth on Microbial Transport in Saturated Porous Media PRINCIPAL INVESTIGATOR: Ellyn M. Murphy PROGRAM ELEMENT 6 Acceleration OBJECTIVE: The co-disposal of organic chelating agents with radionuclides at Department of Energy (DOE) sites has resulted in enhanced mobility of these hazardous wastes. The success of biogeochemical alterations of these complexes is ultimately controlled by the transport and distribution of bacteria in physically and chemically heterogeneous porous media. Bacterial transport work to date has emphasized inert biocolloids or bacteria in a non-growth state. Growth, however, has been shown to enhance the aqueous-phase concentration of bacteria in groundwater which enhances the likelihood of bacterial transport. Therefore, to accurately represent bacterial transport during intrinsic bioremediation, growth processes must be incorporated and coupled to a transient microbial population. APPROACH: Specific processes that control transport in heterogeneous porous media will be isolated by performing controlled intermediate-scale experiments using physical and chemical heterogeneity patterns found at DOE's Oyster Site in Virginia. These intermediate-scale experiments enable us to test the manifestation of pore-scale processes at larger scales, more representative of the complexities found in the field. The experimental data will be used to test theoretical scaling approaches that accurately represent nonlinear growth reactions. This interdisciplinary research project will provide fundamental information on i) the role of growth in initiating bacterial transport, ii) dominant processes controlling bacterial transport in heterogeneous porous media, and iii) valid scaling approaches for predicting these coupled, nonlinear processes at the field scale. PROJECT: Enhancement of Bacterial Transport in Aerobic and Anaerobic Environments: Assessing the Effects of Metal-Oxide Chemical Hetereogeneity PRINCIPAL INVESTIGATOR: Tullis C. Onstott PROGRAM ELEMENT 6 Acceleration OBJECTIVE: The research seeks to resolve technical problems and obstacles to successful accelerated bioremediation, and specifically the delivery of microorganisms to contaminated subsurface zones, or bioaugmentation, at the field scale. The application builds on multi-institutional research at a field site at Oyster, Virginia, and extrapolates field experience from aerobic portions of the site (the aerobic subsite) to a low dissolved oxygen/anaerobic subsite. The investigators responded to DOE's request to include supporting core and field characterization, site analysis capabilities and services (excluding drilling which will be funded independently by DOE/OBER through Golder Associates) in this application; these important scientific elements would otherwise be scattered across many institutions nationally. DOE's request is based partly on the concerns of some reviewers who stated that a lead investigator must have scientific (budgetary) control over supporting scientists to complete complex, cross-disciplinary research successfully. The investigators propose a challenging field research project to determine the influence of ferric iron hydroxide mineral coatings, manganese oxides, and bacterial adhesive properties on the field-scale migration of bacteria injected into anaerobic groundwater systems. At many mixed metal-organic contaminated sites, anaerobic conditions predominate. The research will address: (1) the potential for preferential adhesion of bacteria to Fe oxide phases, (2) the role of bacterial adhesion in determining the bacterial migration distance in zones that vary in permeability, and (3) the potential influence of microbial Fe reduction in enhancing bacterial transport by reducing the adhesion of dissimilatory iron reducing (DIRB) and other bacteria. This will be accomplished at the field scale by integrating disparate capabilities from eight universities and national laboratories, and specifically: Princeton University will assume overall responsibility for distribution of research funds, ensure collaboration among investigators, oversee the research efforts of the individual institutions, and organize several yearly research meetings. Princeton will share this responsibility with Envirogen Inc. Princeton University will also be responsible for the mineralogical/geochemical characterization of sediment and groundwater samples from Oyster (in cooperation with Old Dominion University) and for development of alternative isotope labeling approaches. Envirogen Inc. will conduct laboratory experiments on intact core, characterize membrane properties of microorganisms to be utilized for the field experiments, and organize field experiments. Montana State University will conduct bacterial tracer studies and isotopic analyses of suspended organic matter. Lawrence Berkeley National Laboratory will apply high resolution geophysical techniques to characterize the lower flow field site at Oyster, and assist in linking that flow field to a nearby pit by geophysical analysis. Old Dominion University will analyze the cores collected from the lower flow field at Oyster and will also characterize the porosity, grain size, and permeability of these samples. University of California-Davis will perform one-dimensional modeling of the intact core experimental data to determine adsorption/desorption parameters. Pacific Northwest National Laboratory will be responsible for applying three-dimensional, high resolution computer models of bacterial transport in porous media to the field data collected at Oyster. They will also provide assistance in the characterization of any facultative DIRB discovered at Oyster. (Companion support will be provided directly by DOE to Dr. J. Fredrickson to assist in investigations iron biogeochemistry as it controls bacterial attachment and mobility.) Florida State University will provide analytical services related to the characterization of microbial communities in subsurface sediment and water samples from laboratory column experiments carried out at Envirogen, Inc. The investigators' research plan includes laboratory experiments to define the role of Fe and Mn oxides on bacterial adhesion using radiolabeled bacteria in the field and intact cores from the Oyster field research site. Macroscopic distribution of bacteria throughout the core will be measured by liquid scintillation counting and autoradiography. The distribution of bacteria will be compared to the distribution of Fe and Mn oxides determined by XRD analysis of subsamples and by mapping microscopic distribution using scanning electron microscopy. Experiments will be repeated on intact cores in which Fe and Mn oxides have been selectively removed by chemical reduction and complexation. Field experiments at the Oyster field research site to quantify active transport of isotopically-labeled (stable C, N isotopes) indigenous strains in aerobic and anaerobic flow fields. To determine the importance of adhesion and chemical heterogeneity in bacterial transport, the relative migration distances of a wild-type and adhesion deficient variant of the same indigenous bacterial strain will be compared in a single injection experiment at the anaerobic subsite using two isotopic labels (C and N). Knowing the factors that affect transport will enable manipulation of the environment or the injected strains to effectively disperse bacteria throughout the zone of contamination with time. APPROACH: The investigators' approach includes integration of field scale observations with supporting core-scale (laboratory) studies with a focus on a series of exploratory, multi-institutional experiments on bacterial migration in the presence of in situ natural heterogeneities (dominated by iron oxides) at the aerobic subsite; this research at the Oyster site was interrupted with the termination of the Subsurface Science Program, with delays, loss of momentum, and dispersal of working teams. As a result, some investigators participating in this proposed research are as yet refining tools to study bacterial transport under aerobic conditions, and other methods including, validation of a 3D flow model, intact core studies of bacterial kinetics, and stable isotope labeling are in the final stages of testing. PROJECT: Vibration-accelerated Transport of Microbes in Subsurface Media PRINCIPAL INVESTIGATOR: Tom J. Phelps PROGRAM ELEMENT 6 Acceleration OBJECTIVE: The low rates of transport of microorganisms, particulates or colloids through porous subsurface media poses severe limitations on the impact and applicability of biological processes for the in situ remediation of subsurface contaminants. Nowhere are those limitations more acute than in remediation of radionuclides and metal contaminants in deep subsurface formations. Because classical approaches of bacterial strain selection have not overcome the limitations of filtration and retardation on particulate transport, the proposed research investigates the potential of vibration-based energies directed at subsurface environments to increase particulate transport up to 30-fold. The goal is to develop a conceptual framework for vibration-facilitated particulate transport through porous subsurface media based on laboratory experiments. It is hypothesized that vibrational energies will result in dramatically increased (up to thirty-fold greater) particulate and microbial transport. The objective is to examine the effects of vibrational energies on microbial and particulate transport in porous media using intact-core columns to develop a conceptual understanding of accelerated particulate transport based on empirical laboratory and field-scale experimental results. APPROACH: Our approach is to evaluate and assess the applicability of vibration-induced particulate transport though detailed hypothesis testing in laboratory experiments complimented by comparisons between vibration-induced transport and that obtained by traditional injection approaches. The rationale lies with the well-documented retardation and filtration of most mm-sized particulates within meters of injection and the need to overcome this retardation to effectively and efficiently deliver microbes, particulates or nutrients throughout a contaminant plume. Preliminary results indicate that vibration may increase dispersion (observed by the broadening of effluent conservative tracer peaks) and transport. Detailed experiments will further examine increased dispersion, transport and flow through laboratory columns. PROJECT: Heterogeneity of Sedimentary Aquifers: Expansion of "System" Stratigraphic Concepts, Calibrated Against 'Geophysical Imaging' by Ground Penetrating Radar. PRINCIPAL INVESTIGATOR: Donald J. P. Swift PROGRAM ELEMENT 6 Acceleration OBJECTIVE: The investigators' plan to determine the dominant physical (lithological, structural, and hydrological) characteristics that can be imaged by geophysical methods in situ and correlated with important physical and chemical properties that in turn can be related to microbial properties. The proposed research incorporates recent advances in sedimentation physics and geophysical imaging to determine: (1) the scale and methods that should be used to measure physical, chemical, and microbial properties in order to understand subsurface fluid and chemical transport properties, (2) the degree and scales of physical properties that control chemical and biological properties, and (3) how different types of heterogeneity can effectively be integrated into three dimensional models. The investigators will compare aerobic microbiological properties and processes in cross-stratified sediment units with uniform, horizontally stratified units, and to infer how physical and mineral properties influence microbial dynamics. These results will be extrapolated in time to appropriate DOE sites similar geology, such as Savannah River, and to a NABIR field site. APPROACH: The approach involves (1) geophysical imaging at the Oyster field site, with characterization using multiple geophysical tools, e.g., multi-borehole high frequency tomography in the saturated zone and high resolution pulse radar in the unsaturated zone; (2) core scale analysis using seismic and other measurements for geological analysis (grain size, texture, porosity, mineralogy), and microbial properties; and (3) integration of geological and hydrologic data into a field scale geophysical model (a 3-D physical model for the Oyster site) including physical constraints on fluid flow and microbial properties, and correlation of fluid flow predictions and moisture content measurements with bacterial heterogeneity and transport. [Back to Award Recipients Page]