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A new report released today documents the record of chronic pipeline spills, uncontrolled seepage, and other failures at operating U.S. copper mines, and finds that the proposed Pebble Mine would have an extremely high likelihood of releasing toxic substances into the Bristol Bay watershed — which supports the world’s largest wild sockeye salmon fishery. The Earthworks report supports the findings of the Bristol Bay watershed assessment recently released by the U.S. Environmental Protection Agency.

The report findings undermine Pebble proponents’ claims that the mine would not harm sensitive fish habitat. According to current ore estimates, the Pebble Mine would be the largest copper porphyry mine in the U.S.

“Our research demonstrates that pipeline spills and uncontrolled mine seepage are a frequent problem at copper mines operating in the U.S. today,” said Bonnie Gestring of Earthworks. “Pebble says they can prevent these problems through technology, but the record says otherwise.”

The EPA recently released a study of the risks of developing the Pebble deposit, which finds that the mine footprint alone would result in the direct loss of up to 87 miles of streams that provide important habitat for salmon. It also predicts the likelihood of additional serious impacts from pipeline breaks, and the failure to capture and treat mine seepage.

The Earthworks report examines 14 of the 16 U.S. copper porphyry mines representing 89% of U.S. copper production in 2010 – the most recent data on copper production available from the U.S. Geological Survey. It found that:

  • 100% of mines had pipeline spills or other accidental releases.
  • 13 of the 14 mines (92%), failed to control contaminated mine seepage, resulting in significant water quality impacts.
  • 4 out of 14 mines (28%) experienced a partial failure of the tailings impoundment. These included: a 1997 partial failure of the tailings impoundment at the Pinto Valley Mine, where the creek bed and surrounding upland were buried under material as deep as 42 feet; a 1993 partial failure at the Ray Mine, when heavy precipitation caused the Gila River to flood and breach the tailings impoundment, carrying pollutants 11 miles downriver; and a 1980 failure at the Tyrone Mine, when 2.6 million cubic yards of tailings were released, and flowed 8 kilometers downstream.
  • Examples of recent pipeline spills include a 2012 spill at the Ray Mine, which washed tailings into the Gila River, a 2008 pipeline spill at the Morenci Mine of 186,000 gallons of sulfuric acid along two miles of Chase Creek – a tributary of the San Francisco River, and a 2009 spill of 2 million gallons of process water at the Bagdad Mine.

“Copper porphyry deposits are notorious for acid mine drainage and other water quality impacts,” Gestring said. “The EPA’s watershed assessment provides a sound scientific basis for the agency to protect the Bristol Bay fishery by initiating Section 404c of the Clean Water Act.”

Many of the operating copper porphyry mines are located in the arid southwest, where precipitation is limited, and communication between surface and groundwater resources is limited. More significant impacts could be expected at mines in wetter climates, with abundant surface water and shallow groundwater, such as is the case in the Bristol Bay region.

Copper porphyry is a form of copper deposit that is often characterized as low-grade, and often contains other minerals such as gold and molybdenum. Copper porphyry deposits are almost all mined in industrial-scale open pit operations. ###

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