Ferrographic separation, an innovative bacterial separation technique that achieves high-resolution visual enumeration of bacteria, will be investigated as a complementary method to other planned methods to monitor bacterial cell concentrations during bioaugmentation studies at the South Oyster field site. Initial studies will determine optimal operating conditions for ferrographic separation of Comamonas DA001 (or other candidate bacterium chosen by South Oyster researchers) spiked into South Oyster groundwater. Subsequent studies will determine concentrations of Comamonas in effluent samples from intact core studies performed by Drs. Mary DeFlaun and Mark Fuller (Envirogen, Inc.), to determine the effect of shipping (e.g. holding time, container, and temperature) on recovery efficiency of the ferrographic technique. In parallel with these studies, slides of ferrographically separated Comamonas will be shipped to Dr. David White at the University of Tennessee to determine whether pre-concentration of Comamonas prior to extraction for 13C analyses will enhance the resolution of 13C analyses. Bacterial transport experiments using intact cores at the University of Utah will be performed and modeled to support the project goal of relating bacterial transport kinetics to particular site facies and particular strains. The research proposed conforms to section II of the Acceleration Science Plan: Tracking Bacteria in Porous Media; Subsection 2.1, Detection Strategies: Methods Development.

Experiments being conducted under NABIR at a field site near Oyster, Virginia are identifying and quantifying microbial transport processes in sandy aquifers under varying biogeochemical conditions. At the field scale, multiple hydrologic and biogeochemical processes interact in a heterogeneous subsurface environment to complicate the interpretation of experimental results. In this complex environment, a well-designed suite of quantitative models can effectively serve as a focal point for the design and interpretation of microbial transport experiments, quantitative testing of research hypotheses, management and integration of data, and transfer of information between different scales.

This project is developing and applying a series of advanced hydrogeological models of tracer and bacterial transport, drawing on and integrating data provided by collaborators (e.g., geophysical data from Majer/LBNL, hydrologic data from Griffin/Golder, and geological data from Swift/ODU). Several levels of model complexity and various length scales are addressed through multiple linked models ranging from one-dimensional core-scale models of laboratory experiments to high-resolution heterogeneous models of field-scale transport. These models have been used for experimental design (e.g., location of multi-level samplers) and interpretation (e.g., testing of hypotheses regarding scaling of laboratory experiments for field-scale prediction). Most recently, we have developed a novel approach to the simulation of microbial exclusion phenomena, based on a modified particle-tracking method. The application of these models in the areas of data management and integration, parameter and process scaling, collaborative interaction, and experimental design is the focus of several specific research elements. The scaling element will develop three-dimensional core-scale flow and transport models to quantify microbe/solid surface interactions and obtain field-scale process representations. Tracer test inversion techniques will be evaluated in terms of their ability to enhance model predictions relative to other types of characterization data. The experimental design element will employ a collaborative tool for identifying, guiding, and documenting design decisions, and will integrate quantitative pre-modeling results with qualitative investigator input and practical considerations. The data management element will populate a web-based data and information repository with linkages to the numerical model framework, experimental design tools, and collaborative databases.

This research will lead to specific results of relevance to the subsurface microbiological sciences, will increase the overall value of data and information collected at the Oyster site, and will develop a systematic approach and knowledge base applicable to future research at other sites (and ultimately to bioremediation applications).