The battle over the proposed Pebble Mine has been waged far outside the state's borders, with environmental activists like actor Robert Redford opposing development. Multinational jewelers have said they won't use minerals mined from the Alaska prospect, and pension funds from California and New York City pressured London-based Rio Tinto, a major shareholder of mine owner Northern Dynasty Minerals Ltd., to divest last year.
The Bristol Bay watershed produces about 46 percent of the world's wild sockeye salmon, and salmon are key to the way of life for two groups of Alaska Natives living in the region, Yup'ik Eskimos and the Dena'ina. The report said the response of Native cultures to any mining impacts was unclear, though it said it could involve more than the need to compensate for lost food and include some degree of cultural disruption.
EPA initiated the review process in response to a request in 2010 from tribes and others in the region concerned about the impact of the proposed Pebble Mine on Bristol Bay fisheries. The report, however, is not meant to be about a single project.
Some see the mine as a way to provide jobs in the region, but others fear it would disrupt or devastate the local way of life. A citizens' initiative scheduled to appear on the August primary ballot would require legislative approval for any large-scale mine in the region.
Supporters of the EPA process hoped it would lead the agency to block or limit the project, while opponents saw it as an example of government overreach and feared it would lead to a pre-emptive veto.
EPA has said its goal with the watershed assessment is to get the science right. In the report, EPA said the assessment will inform possible future government actions.
EPA said the report is not an in-depth assessment of a specific mine but a study of the possible impacts of reasonably foreseeable mining activities in the region. The agency said it drew on a preliminary plan published by Northern Dynasty Minerals and consulted with mining experts on reasonable scenarios.
The president of Northern Dynasty Minerals, in November, said if it appeared EPA was moving to take pre-emptive steps to in any way restrict permitting, the company would probably launch the permitting process on its own without waiting for a new partner.
The Pebble Partnership has called the mine deposit one of the largest of its kind in the world, with the potential of producing 80.6 billion pounds of copper, 107.4 million ounces of gold and 5.6 billion pounds of molybdenum over decades.
While EPA focused on the effects of one mine, the agency, in its report, said it's possible that several mines could be developed in the watersheds studied, each of which would pose risks similar to those highlighted in the report.
The report also found that polluted water from the mine site could get into streams through runoff or uncollected leachate, even with the use of modern mining practices, raising in-stream copper levels that could affect salmon. It noted that culvert blockages or other failures could impede fish passage and that failure of a tailings dam where mining waste is stored could be catastrophic though the probability of such a failure is considered quite low.