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USDA, Forest Service, Pacific Northwest Region, 74 pp, 2018

The Holden Mine produced about 200 million lbs of Cu, 40 million lbs of Zn, two million ounces of Ag, and 600,000 ounces of Au from ~10 million tons of ore. Excavation of 60 miles of underground tunnels produced 8.5 million tons of mill tailings placed on 90 acres of U.S. National Forest lands as well as 300,000 yd3 of waste rock piles. Direct release of hazardous materials from the mine, including acid mine drainage, heavy metals (Al, Cd, Cu, Fe, Pb, and Zn), and iron sulfide, affected about 125 acres of land. The remedy is being conducted in 2 phases. Phase 1, which began in 2013 with completion expected in 2018, includes regrading and capping the tailings and main waste rock piles, constructing a groundwater barrier wall and groundwater collection system around Tailings Pile 1 and the Lower West Area, constructing a new groundwater treatment facility, beginning in situ soil treatment (e.g., application of agricultural lime) in areas of interest, implementing institutional controls, and initiating performance verification monitoring. Phase 2 is expected to begin in 2023. In situ treatment is still under technical review and consideration for implementation due to environmental constraints, potential destruction of established forests and habitats, rough topography, and practicability of the remedy. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd597777.pdf

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