Superfund Site Profile
The 5-acre Silver Mountain Mine site is located in Horse Springs Coulee, six miles northwest of Tonasket, Washington. It includes the area where a mine operated sporadically from 1928 to the 1960s to extract silver, copper and gold from soil and ore. From 1980 to 1981, site owners constructed a cyanide heap leach pile to extract silver and gold from the previously mined tailings by applying a sodium cyanide solution to the top of the heap. The cyanide-laden solution was then collected in a leachate pond at the base of the heap. The heap leach operation was abandoned in 1981 without cleanup of cyanide-contaminated materials. Mining operations generated mine-tailing wastes that contaminated groundwater. Cleanup has been completed. Site operation and maintenance activities and monitoring are ongoing. EPA took the site off the Superfund program’s National Priorities List (NPL) in 1997.