Silver Mountain Mine

In 1902, underground hard rock mining for silver and gold began at the site.  By 1956, developing the mine produced several tailings piles in a mine dump consisting of waste and mineralized rock. A cyanide heap leach pile, built in 1980, extracted silver and gold from the previously mined tailings. A mixture of sodium cyanide and water was sprayed on the top of the heap.  The cyanide-laden solution collected in a leachate pond at the base of the heap. In 1981, the site was abandoned without cleanup or treatment of chemicals on the site. Cyanide solution remained in the leachate collection pond and in the heap pile. Also left onsite were several empty cyanide drums and large containers of carbon.  

In 1995, the Site was added to Ecology’s Hazardous Sites List as a federally-supervised Superfund site.

Ecology provided immediate reduction of risks at the site by neutralizing the cyanide solution in 1981 and removing drums of hazardous material left onsite in 1985. Remedial actions occurred at the site in 1992 under the Environmental Protection Agency (EPA). These remedial actions included consolidation of mined material, closure of the mine entrance, capping of the heap leach pile, fence construction at the site boundary and hydro seeding throughout the site.

Long term monitoring is necessary to observe the integrity of the cap and repair as necessary. This will take place through the five-year review process. Institutional controls were also implemented to prevent use of the capped area for any purpose, as well as to restrict use of groundwater from the Site.

In September 1997, EPA deleted the site from the National Priorities List.  

Ecology has determined that no further remedial action is necessary to clean up contamination at the Site.  This determination is dependent on the continued performance and effectiveness of the post-cleanup controls and monitoring.  In December 2021, the site was removed from Ecology's Hazardous Sites List.  

Ecology conducts regular site inspections and, every five years, EPA conducts a review to make sure that the cleanup measures continue to protect people and the environment. Periodic reviews at the site indicate the protective measures were in place and effective.