A study was conducted with a rotating biological contactor (RBC) for treatment of leachate from the Stringfellow hazardous waste site in Riverside County, California. The leachate was transported from California to Cincinnati, where a pilot sized RBC was installed at the U.S. EPA's Testing and Evaluation (T&E) Facility. A series of kinetic runs were made with primary effluent from the City of Cincinnati's Mill Creek Sewage Treatment Plant to develop a biomass on the disks and to obtain a standard kinetic removal rate. These runs were then followed with Stringfellow leachate experiments that included operations at various ratios of leachate to primary effluent, operations at 100% leachate, and operations to increase the percentage removal of dissolved organics. The paper reports on the results from these experiments and the effectiveness of an RBC to adequately treat leachate from the Stringfellow hazardous waste site.