Superfund Site Profile

We would like to hear from you

The latest review of the environmental cleanup at the Silver Mountain Mine Superfund Site is underway. If you have information helpful to the review team, questions, or anything you would like us to consider during the review, please contact Jeremy Jennings, EPA Remedial Project Manager, at 206-553-2724 or 800-824-4372 ext. 2724 or

About the cleanup

The cleanup was completed in 1992. Measures implemented included:

  • Heap leach pile and collection pond treated to neutralize the cyanide;
  • Mine tailings and heap leach piles consolidated, covered, and seeded;
  • Drums of hazardous materials left on-site removed;
  • Mine entrance blocked for safety and to divert runoff;
  • Wells for groundwater monitoring installed; and
  • Site fenced for safety and to restrict access.

The Site is currently used to graze cattle. The Washington Department of Ecology inspects the site annually and, every five years, the U.S. Environmental Protection Agency conducts a review to make sure that the cleanup measures continue to protect people and the environment. Previous reviews indicated the protective measures were in place and effective. The current review report will be available October 2017.


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.