Protecting Oregon's Environment
Oregon State Seal
Oregon Department of Environmental Quality

Land Quality

Environmental Cleanup

Environmental Cleanup Site Information (ECSI) Database
Site Summary Report - Details for Site ID 1449, Formosa Mine   

This report shows data entered as of January 17, 2017 at 5:42:40 PM

This report contains site details, organized into the following sections: 1) Site Photos (appears only if the site has photos); 2) General Site Information; 3) Site Characteristics; 4) Substance Contamination Information; 5) Investigative, Remedial and Administrative Actions; and 6) Site Environmental Controls (i.e., institutional or engineering controls; appears only if DEQ has applied one or more such controls to the site).  A key to certain acronyms and terms used in the report appears at the bottom of the page.

Note: DEQ may have posted online documents related to this site. If so, they would be available for viewing or downloading on ECSI Summary Page

Go to DEQ's Facility Profiler to see a site map as well is information on what other DEQ programs may be active at this site.

Site Photos
Click to View Photo Picture Date Caption Size
View Photo 06/26/2008 Acid mine drainage from the former Formosa Mine has led to a dead zone in the south fork of Middle Creek. 1597 Kb
View Photo 10/02/2007 An example of acid mine drainage from the former Formosa Mine site 1113 Kb

General Site Information

Site ID: 1449 Site Name: Formosa Mine CERCLIS No: 001002616
Address: 31S/6W/S26b  
  County: Douglas Region: Western
Other location information: About 7 miles south of Riddle on the SW slope of Silver Butte.
Investigation Status: Listed on CRL or Inventory
Brownfield Site: No NPL Site: Yes Orphan Site: Yes Study Area: No
Property: Twnshp/Range/Sect: 31S , 6W , 26 Tax Lots:
  Latitude: 42.8517 deg. Longitude: -123.3847 deg.  Site Size: 76 acres
Other Site Names:
  Silver Butte Mine

Site Characteristics

General Site Description:
Site History: The mine operated periodically during the 1900s, with the majority of production occurring between 1989 and 1994 under the ownership of Canadian mining company Formosa Explorations Inc. Copper and zinc was reported to have been produced at a rate of 350 to 400 tons per day.
Contamination Information: (3/12/2003 GA/SRS) When the mine closed in 1994, Formosa backfilled the mine workings with mill tailings, crushed ore, and limestone. Acid mine drainage (AMD) from the two adits was directed to a scree slope. Approximately 20,000 cubic yards of low-grade ore were placed into a lined cell at the site (referred to as the "encapsulation mound"). After the reclamation was completed, Formosa filed for bankruptcy. In 1997, it was discovered that the AMD control system had failed, and acidic wastes were discharging to Middle Creek and South Fork Middle Creek.
Manner and Time of Release: Release of acidic groundwater and runoff from abandoned mine.
Hazardous Substances/Waste Types: Acid mine drainage (primarily cadmium, copper, lead, and zinc).
Environmental/Health Threats: Acidic wastes from the Formosa Mine have discharged to Middle Creek and South Fork Middle Creek. Middle Creek is a tributary of Cow Creek, which is a source of drinking water for the City of Riddle. The two Middle Creeks are considered habitat for threatened Oregon Coast coho salmon and steelhead. Monitoring has indicated that 18 miles of the two creeks have been severely impacted by acid mine drainage from the Formosa Mine.
Status of Investigative or Remedial Action: (3/12/2003 GEA) In 1999, DEQ began working with the federal Bureau of Land Management (BLM) to investigate and clean up the site. BLM agreed to conduct a Remedial Investigation (RI) at the site. The RI was completed in May 2000. After declaring the mine an orphan site by DEQ in 2000, DEQ completed an interim removal action to address the acid mine drainage (AMD). The encapsulation mound was capped with a temporary plastic liner. AMD from the two adits was routed away from the headwaters of Middle Creek to a scree slope. (2/7/2005 GEA) DEQ and BLM completed the FS in January 2005.
Data Sources:

Substance Contamination Information

Substance Media Contaminated Concentration Level Date Recorded
CHROMIUM Other Adit Water dissolved chromium - .392 mg/L  
CHROMIUM Surface Water Dissolved Chromium - .006 mg/L  
COPPER Other Dissolved Copper - Adit water - 40.4 mg/L  
COPPER Surface Water Dissolved Copper - Surface Water (Middle Cr.) - 3.7 mg/L  
LEAD Other Dissolved Lead - Adit water - .015 mg/L  
LEAD Surface Water Dissolved Lead - Surface Water (Middle Cr.) - .007 mg/L  
ZINC Other Dissolved Zinc - adit Water - 137 mg/L  
ZINC Surface Water Dissolved Zinc - Surface Water (Middle Cr.) - 10.3 mg/L  

Investigative, Remedial and Administrative Actions

Action Start Date Compl. Date Resp. Staff Lead Pgm
REMEDIAL INVESTIGATION  (Primary Action) 06/26/2008   Greg Aitken ORP
View Full Report Showing Action History

Key to Certain Acronyms and Terms in this Report:

  • CERCLIS No.: The U.S. EPA's Hazardous Waste Site identification number, shown only if EPA has been involved at the site.
  • Region: DEQ divides the state into three regions, Eastern, Northwest, and Western; the regional office shown is responsible for site investigation/cleanup.
  • NPL Site: Is this site on EPA's National Priority List (i.e., a federal Superfund site)? (Y/N).
  • Orphan Site: Has DEQ's Orphan Program been active at this site? (Y/N). The Orphan Program uses state funds to clean up high-priority sites where owners and operators responsible for the contamination are absent, or are unable or unwilling to use their own resources for cleanup.
  • Study Area: Is this site a Study Area? (Y/N). Study Areas are groupings of individual ECSI sites that may be contributing to a larger, area-wide problem. ECSI assigns unique Site ID numbers to both individual sites and to Study Areas.
  • Pathways: A description of human or environmental resources that site contamination could affect.
  • Lead Pgm: This column refers to the Cleanup Program affiliation of the DEQ employee responsible for the action shown. SAS or SAP = Site Assessment; VCS or VCP = Voluntary Cleanup; ICP = Independent Cleanup; SRS or SRP = Site Response (enforcement cleanup); ORP = Orphan Program.

You may be able to obtain more information about this site by contacting Greg Aitken at the Western regional office or via email at If this does not work, you may contact Gil Wistar at (503) 229-5512, or via email at or contact the Western regional office.

[print version]

For more information about ECSI call Gil Wistar at 503-229-5512 or email.

For more information about DEQ's Land Quality programs, visit the DEQ contact page.

Oregon Department of Environmental Quality
Headquarters: 700 NE Multnomah Street, Suite 600, Portland, OR 97232
Phone: 503-229-5696 or toll free in Oregon 1-800-452-4011
Oregon Telecommunications Relay Service: 1-800-735-2900  FAX: 503-229-6124

The Oregon Department of Environmental Quality is a regulatory agency authorized to protect Oregon's environment by
the State of Oregon and the Environmental Protection Agency.

DEQ Web site privacy notice