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November 28, 2012
Pebble mine would stress salmon

Advocates of launching the Pebble mining project near Bristol Bay in southwest Alaska may not find much to like in EPA’s draft Assessment of Potential Mining Impacts on Salmon Ecosystems of Bristol Bay, Alaska.  In the draft, the Agency goes to great lengths to describe the unique ecological and wildlife characteristics of the area and how resident Alaskan native populations are heavily dependent on the health of the salmon population.  The draft points out that normal operation as well as any number of failures at the massive mining project desired by industry, with probabilities ranging from remote to certain, would inflict varying degrees of harm on the salmon-based culture and economy as well as on diverse wildlife that are also interconnected with the salmon.

When made final, the assessment will be used by the EPA to implement its obligations under the Clean Water Act.

Salmon culture

Bristol Bay supports all five species of Pacific salmon found in North America and 46 percent of the world’s sockeye salmon population, making it the largest sockeye salmon fishery in the world.  According to the EPA, between 1990 and 2010, the annual average inshore run of sockeye salmon in Bristol Bay was approximately 37.5 million fish.  Annual commercial harvest of sockeye over this same period averaged 27.5 million.  According to the Agency, the exceptional quality of the Bristol Bay watershed’s fish populations can be attributed to several factors, the most important of which is perhaps the watershed’s high-quality diverse aquatic habitats, which are untouched by human-engineered structures, and flow management controls. 

Largest mine

The Pebble deposit targeted for development by a group called the Pebble Partnership is north of Iliamna Lake, the largest undeveloped lake in the United States, and located in the watersheds of two biologically productive rivers and their tributaries.  If fully mined, the Pebble deposit could produce more than 11 billion metric tons of ore, mainly copper, which would make it the largest mine of its type in North America.  While there are no final plans for the size of the mine, the EPA developed several mining impact scenarios from a minimum size operation of about 15 square miles (mi2) to a maximum operation of 32 mi2.  Both size projects would require an 86-mile road with four pipelines for product concentrate, return water, diesel, and natural gas as well as facilities for ore processing and support services.

Normal operation

Even with all operations operating free of failure, the assessment anticipates the project would result in 55 to 87 miles of eliminated or blocked streams, reduced streamflow affecting another 1.2 to 6.2 miles, removal of 2,500 to 4,300 acres of wetlands, diminished habitat below road crossings, and such indirect effects as reduced food resources, shifts in the balance of surface water and groundwater inputs, and increases in summer water temperatures and decreases in winter water temperatures caused by water treatment. 

The failure scenarios in the assessment include failures of towering tailings dams that would destroy more than 20 miles of streams and degrade more streams and rivers for decades.  The assessment sees such dam failures as unlikely, with probabilities as low as once in 1 million years.  However, other types of failures associated with water collection and treatment during operation, immediately after closure, and far into the future are considered high to certain. 

The EPA emphasizes that the assessment is based on operation of one mine only and that the potential exists for multiple mines and associated infrastructure, which would pose similar risks.  The Agency adds that the assessment is not based on the plans of any mining company and that there are multiple uncertainties in areas such as the long-term fate of spilled tailings, the consequences of loss and degradation of fish habitat, and the actual response of Alaska native cultures. 

Click here to read EPA’s draft assessment.

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