Silver Mountain Mine
County Rd 4371, Loomis, WA 98827


Ecology is proposing to remove the Silver Mountain Mine Site, located near Loomis in Okanogan County, from its Hazardous Sites List. The Hazardous Sites List is a statewide list of contaminated properties. The Site was included on the Hazardous Sites List due to is status as a Superfund site on EPA's National Priorities List.

Ecology has determined the site no longer poses a threat to human health or the environment. Therefore, Ecology has issued a determination of No Further Action and has recommended removing the site from the Hazardous Sites List.

Ecology is asking for your comments on the proposed removal of the Site from the Hazardous Sites List.

You are invited to:

•  Review the Silver Mountain Mine No Further Action letter dated October 20, 2021

•  Send your comments to Ecology for consideration. Comments will be accepted November 4, 2021 through December 6, 2021

After the comment period ends, Ecology will review comments received during the comment period and respond. Ecology will hold a public meeting if 10 or more people request one. If no significant changes are necessary, the site will be removed from the Hazardous Sites List.


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.

The Site is currently on 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.  In October 2021, Ecology 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.


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.  



Map showing site location as Okanogan County, WA SITE INFORMATION


View Electronic Documents

Cleanup Site Details Report

Facility Site ID: # 101

Cleanup Site ID: 3033

Loomis, Okanogan County

Status: Cleanup Complete-Active O&M/Monitoring   Get definitions of Status terminology

Jeff Newschwander
Periodic Review Coordinator
(509) 454-7842

Document Repositories:

Central Regional Office
1250 W Alder St
Union Gap, 98903-0009