EPA ID# ORN001002616
EPA Region 10

4th Congressional District

Other Names:
Last Update: April, 2010

Hide details for Site DescriptionSite Description

The Formosa Mine Superfund Site is located on Silver Butte in Douglas County,Oregon, approximately 25 miles south of Roseburg. This abandoned mine discharges millions of gallons of acid rock drainage (ARD) and toxic metals into the upper reaches of Middle Creek and South Fork Middle Creek every year. Habitat for aquatic life in the Middle Creek Watershed, which once included endangered Coho salmon and other sensitive aquatic species, is absent or severely damaged for 18 miles downstream of the mine.

Copper and zinc were mined at the site from 1910-1937. Formosa Exploration Inc. re-opened the mine and operated from 1990 until 1993. Reclamation work done starting in 1994 and proved ineffective in keeping contamination from being released to adjacent streams. This site is no longer an active mine, but is an ongoing source of contamination to Middle Creek and beyond.

Site Responsibility: This site is being addressed through state and federal actions.

NPL Listing HistoryDates
Proposed Date:03/07/2007
Removed Date:
Withdrawal Date:
Final Date:09/19/2007
Deleted Date:

Hide details for Threats and ContaminantsThreats and Contaminants

Media Affected: Surface water, ground water, soil and sediments
Storm water-driven contaminant releases from the mine are estimated at five million gallons of acid rock drainage, which contains up to 30,000 pounds of dissolved copper and zinc, along with other metals. Heavy metals concentrations in Middle Creek and the South Fork, and into Cow Creek, exceed aquatic life standards by a factor of between 10 and 100. The heavy metals are severely degrading the aquatic habitat for macroinvertebrates, resident fish, coastal steelhead trout, and Oregon coastal coho salmon.

The primary sources of these metals is underground mine workings, surface tailing piles and the transport of metals to these creeks via ground water and surface storm water flow. Significant concentrations of arsenic, barium, copper, lead, mercury, nickel, and zinc have been detected in all source samples collected at the site. Low pH shallow ground water and adit drainage to surface water, both laden with high concentrations of metals, have been draining into the headwaters of Middle Creek and the South Fork of Middle Creek.

Hide details for Cleanup ProgressCleanup Progress

EPA completed the Operable Unit 1 Remedial Investigation report in February 2011. The RI documents the nature and extent of mine impacted materials. These materials pose a continuing source of metal contamination and acidic water to Middle Creek and South Fork Middle Creek. EPA is preparing a Feasibility Study to evaluate the cleanup altertnatives.

Hide details for Regional ContactsRegional Contacts

SITE MANAGER(S):Christopher Cora
PHONE NUMBER:206-553-1478
PHONE NUMBER:503-326-0247
Information pertaining to this site is housed at the following location(s):
On the internet at:

EPA Region 10 Superfund Records Center
1200 Sixth Avenue
Seattle, WA 98101

Riddle Branch, Douglas County Library
637 First Avenue
Riddle, Oregon 97469