[en] Liquid wastes have been generated by 40 years of Hanford Site operations. Previously, some of these wastes, which contain radioactive, hazardous, and regulated chemicals (including nitrates and organics), have been discharged to the soil column. Current Department of Energy (DOE) policy prohibits the disposal of contaminated liquids directly to the environment. Biodenitrification using facultative anaerobic microorganisms is a promising technology for removing nitrates from contaminated aqueous streams. This paper summarizes the results of biodenitrification studies performed by the Pacific Northwest Laboratory (PNL) in FY 1988 and FY 1989 to determine the applicability of biological denitrification and organic contaminant destruction to groundwaters and process effluents. The results described here are the outcome of laboratory screening tests to select and culture microorganisms capable of degrading nitrates and carbon tetrachloride (CCl₄), bench-scale experiments to determine reaction rate kinetics and yields, and pilot-plant demonstration tests to provide larger scale operating data and information for engineering design. Pilot-plant tests using simulated groundwater containing nitrates and CCl₄ were completed in FY 1989; and tests with actual groundwater are planned for FY 1990. 4 refs., 9 figs., 1 tab