Abstract

This report summarizes the results of the Mine Waste Technology Program Activity III, Project 39, Permeable Treatment Wall Effectiveness Monitoring Project, implemented and funded by EPA and jointly administered by EPA and the U.S. Department of Energy. 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 demonstrated 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 mine is part of the Bunker Hill Mining and Metallurgical Complex, which was placed on the National Priorities List 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 Technology Applications, Inc. (MSE). Approximately 17 gallons per minute of the mine 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 monthly by MSE for two years.

An evaluation of the results from the ATS showed that the system effectively attenuated zinc, iron, manganese, lead, and cadmium. This was 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 also showed that a combination of mechanisms removed 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.

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Norma Lewis

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