PILOT TESTS OF ENHANCED DENITRIFICATION USING ETHANOL

Uranium mining and processing near Monument Valley, AZ has resulted in the formation of a large nitrate plume in a shallow alluvial aquifer. The results of prior field and bench-scale characterization studies indicate that the nitrate plume is undergoing a slow rate of attenuation via denitrification, and that denitrification rates can potentially be increased by an order of magnitude with the addition of ethanol as a carbon substrate. The objectives of the present study were to investigate the potential of using ethanol to enhance the natural denitrification occurring in the alluvial aquifer. Pilot tests were conducted using the single well, push-pull method. Sediment and groundwater samples were collected to characterize microbial population composition and gene expression before and after the addition of ethanol. Compound-specific stable isotope analysis (¹⁵N and ¹⁸O) was conducted to characterize nitrate transformation. Geochemical data (e.g., NO₃, NO₂, and N₂O) were collected to help characterize reaction rates and nitrogen mass balance. The results of the study will be used in the evaluation and design of a full-scale remedial action.