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.
- OU1 Record of Decision (PDF) (200 pp, 15MB) - April 2016
- OU1 Proposed Plan (PDF) (32 pp, 2.8MB) - January 2015
- OU2 Baseline Ecological Risk Assessment (PDF) (208 pp, 6.3MB) - July 2014
- OU1 Feasibility Study Report (PDF) (451 pp, 12MB) - January 2013
- Final Remedial Investigation for Operable Unit 1 (PDF) (265 pp, 10MB) - January 2012
- Formosa Mine Public Health Assessment (PDF) (60 pp, 1.5MB) - January 2010 (Agency for Toxic Substances and Disease Registry)
- Sampling and Analysis Plan for Surface Water, Groundwater, and Surface Soil and Waste Rock Sampling (PDF) (318 pp, 18.3MB) - September 2009
- Formosa Mine Data Summary Report (PDF) (413 pp, 15MB) - June 2009
- Community Involvement Plan (PDF) (6 pp, 72K) - Updated May 2009
- Federal Register Notice: Formosa Mine Added to National Priorities List (NPL) (PDF) (8 pp, 205K) - September 19, 2007
- Administrative Record Index (PDF) (11pp. 30KB)
- National Priorities List Site Narrative (describes the site based on information available when it was scored under the Hazard Ranking System)
- Hazard Ranking System Documentation Record (PDF) (71 pp, 5.6MB) - March 2007
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