Formosa Mine: Douglas County, Oregon | Region 10 | US EPA

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Formosa Mine: Douglas County, Oregon

The Formosa Mine Superfund Site is located on Silver Butte, about 10 miles south of the town of Riddle, in Douglas County, Oregon. The site was added to the National Priorities List in 2007.

The acid rock drainage flowing from the mine and mine materials have severely degraded 13 miles of Middle Creek and the South Fork of Middle Creek, affecting macroinvertebrates, resident fish, coastal steelhead trout, and Oregon coastal Coho salmon.

The Record of Decision (cleanup plan) for Operable Unit 1 (OU1) was released in April 2016. Operable Unit 1 includes surface and subsurface mine materials.

In a separate evaluation, EPA will develop a Proposed Plan for Operable Unit 2 (OU2), which includes groundwater, surface water and mine materials within the underground mine workings.

A diversion system at the site is being maintained cooperatively between EPA, the Oregon Department of Ecology, and the Bureau of Land Management to keep contaminated water away from the creek.

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      Acid Mine Drainage from the Formosa Mine has killed all life in the south fork of Middle Creek.

      A water diversion system has been attempted to keep some of the contamination from the south fork of Middle Creek

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