In June 2000, Cotter Corporation installed a PRB at its uranium ore processing millsite in Cañon City, Colorado. The PRB contains zero-valent iron (ZVI) that treated molybdenum and uranium contamination in ground water. This was the first PRB installed to treat molybdenum as the main contaminant. The PRB functioned well for about 1 year, after which molybdenum concentrations increased in the effluent.
The U.S. Environmental Protection Agency (EPA) Region 8 funded a collaboration among EPA, LM, Colorado Department of Public Health and the Environment, and Cotter Corporation to investigate possible causes of the decreasing treatment efficiency. In October 2004, Cotter excavated the west end of the PRB and collected samples of the ZVI treatment media. Personnel from DOE’s Environmental Sciences Laboratory conducted the following activities: digested and analyzed ZVI samples for calcium, molybdenum, and uranium; interrogated samples with a scanning electron microscope and electron microprobe; determined the hydraulic conductivity; and assessed reactivity of the ZVI samples in column tests.
Results of these activities are available in Performance Assessment and Recommendations for Rejuvenation of a Permeable Reactive Barrier: Cotter Corporation’s Cañon City, Colorado, Uranium Mill.