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| FORMOSA MINE | Douglas County, Oregon | |
Site Location:
The Formosa Mine site is a former copper, zinc and thorium mine in
Douglas County, in southwest Oregon, approximately 25 miles south of
Roseburg.
Site History:
Mining occurred from 1910-1937, after which there was a documented
thriving fishery as late as the 1980s. Formosa Exploration Inc. (FEI)
re-opened the mine from 1990 until 1993, producing 350 to 400 tons of
ore per day. Reclamation began in 1994 and proved ineffective in
addressing continuing releases to adjacent streams. This site is no
longer an active mine, but is an ongoing source of contamination to
Middle Creek and beyond.
Site Contamination/Contaminants:
Storm water-driven contaminant releases from the mine have lead to an
annual discharge of approximately five million gallons of acid rock
drainage, containing 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.
Potential Impacts on Surrounding Community/Environment:
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. The
resultant discharge has contaminated the entire 13 mile reach of Middle
Creek and the South Fork drainage, and Cow Creek.
Response Activities (to date):
As part of the reclamation of the mine, FEI removed a substantial
portion of nearly 20 tons of sphalerite along with some finely ground
pyritic waste rock it had released into Middle Creek before the mine's
closure in 1994. Other site reclamation efforts included: (1)
construction of an encapsulation mound and drain fields to try to
prevent seepage of acid mine drainage; and (2) backfilling of crushed
ore, tailings, and zinc concentrate into underground mine workings,
creating additional sources of contamination that are now draining into
ground water and surface water.
In November 2000, the Oregon Department of Environmental Quality
installed a water diversion system to try to divert drainage from Bureau
of Land Management land back to the much larger private portion of the
site. The diversion system has not been successful.
[The description of the site (release) is based on information available at the time the site was evaluated with the HRS. The description may change as additional information is gathered on the sources and extent of contamination. See 56 FR 5600, February 11, 1991, or subsequent FR notices.]
For more information about the hazardous substances identified in this narrative summary, including general information regarding the effects of exposure to these substances on human health, please see the Agency for Toxic Substances and Disease Registry (ATSDR) ToxFAQs. ATSDR ToxFAQs can be found on the Internet at http://www.atsdr.cdc.gov/toxfaq.html or by telephone at 1-888-42-ATSDR or 1-888-422-8737.