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PERMEABLE TREATMENT WALL EFFECTIVENESS MONITORING PROJECT, NEVADA STEWART MINE
MCCLOSKEY, A. L. PERMEABLE TREATMENT WALL EFFECTIVENESS MONITORING PROJECT, NEVADA STEWART MINE. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-06/153, 2007.
This report summarizes the results of Mine Waste Technology Program (MWTP) Activity III, Project 39, Permeable Treatment Wall Effectiveness Monitoring Project, implemented and funded by the U.S. Environmental Protection Agency (EPA) and jointly administered by EPA and the U.S. Department of Energy (DOE). This project addressed EPA’s technical issue of Mobile Toxic Constituents — Water through a field demonstration of a water treatment process based on the use of Apatite II™ treatment medium at a remote, inactive underground mine.
This project was undertaken to demonstrate the effectiveness of Apatite II™ (cleaned fishbone) to treat metal-laden water flowing from an abandoned mine. The Nevada Stewart Mine (NSM), located in the Coeur d’Alene Basin near Pinehurst, Idaho was selected as the site for the field demonstration. The NSM is part of the Bunker Hill Mining and Metallurgical Complex, which was placed on the National Priorities List (NPL) for Superfund cleanup of heavy metals, mainly zinc, lead, and cadmium.
To determine the effectiveness of the apatite material, a permeable treatment wall system [also referred to as the Apatite™II Treatment System (ATS)] was constructed by MSE, using funds provided by the U.S. Department of Energy. Subsequently, approximately 17 gallons per minute of the NSM adit discharge was directed through the ATS. The gravity fed ATS was designed and constructed using a baffled, up-flow system that contained a 3:1 mixture by volume of apatite and gravel. The composition and quality of the influent and effluent water from the system was monitored by MSE Technology Applications, Inc., using funding provided by the MWTP, on a monthly basis for a two-year period.
After evaluating the results from the ATS, it was concluded that the system effectively attenuated zinc, iron, manganese, lead, and cadmium as substantiated by the decrease in aqueous phase concentrations between the influent and effluent waters, and increases in those constituents within the solid phase media contained in the system’s three treatment tanks. The results from the ATS showed that a combination of mechanisms removed attenuated the metals from the NSM adit discharge. The only removal mechanism verified in the ATS was sulfide mineral precipitation. Other likely or possible removal mechanisms include phosphate mineral precipitation, adsorption, and cation substitution. Results from the microscopy, geochemical modeling, and data evaluation revealed that sulfide mineral precipitation was the main removal mechanism for zinc, forming a zinc sulfide.