CHARACTERIZATION OF DISSOLVED ORGANIC CARBON IN A BIOSTIMULATED AQUIFER

The Integrated Field Challenge Site at Rifle, Colorado (RIFC) is home to a legacy of subsurface uranium contamination resulting from mill operations. Research at RIFC has shown that acetate amendment (as an electron donor and carbon source), and the consequential growth of iron-reducing microbial communities results in the bioreduction of uranium. As microbial communities metabolize, dissolved and particulate organic carbon concentration and composition changes. Subsurface DOC affects the biogeochemistry of an aquifer through equilibrium metal complexation and microbially mediated electron transfer and metabolic reactions. Accordingly, a qualitative understanding of DOC composition and evolution over the course of bioremediation may prove to be a useful tool in modeling the fate and transport of uranium. A simple organic matter fractionation scheme involving XAD-8 and XAD-4 resins was used to isolate and measure hydrophobic, transphilic, and hydrophilic organic carbon. Data will be presented outlining the changes in DOC composition from temporally and spatially varying RIFC groundwater samples. Spectrofluorometric data will also be presented. The broader context of what changes to bulk DOC composition can tell us about microbial activity over the course of bioremediation will be addressed.