JUNEAU, Alaska (AP) -- Build-out of a large-scale mine near the headwaters of a world-class salmon fishery in Alaska could wipe out as many as 90 miles of streams and alter stream flows, the U.S. Environmental Protection Agency said in a revised assessment released Friday.
The report said mining activity would claim at least 24 miles of streams in the Bristol Bay region, based on the scenarios evaluated, with the loss of wetlands ranging from 1,200 to 4,800 acres.
The EPA focused on the Pebble deposit and took into account information related to the proposed Pebble Mine but also noted the potential for multiple mines in the region, given the resource base, which it said would lead to further elimination or blocking of streams and wetland losses.
EPA initiated the review process in response to concerns raised by tribes and others about the impact large-scale mining could have on Bristol Bay fisheries. Critics of the EPA review — including the Pebble Limited Partnership, the group behind the proposed Pebble Mine — fear it could lead to the agency vetoing mining activity in the region.
Pebble Partnership CEO John Shively said the review was unnecessary, flawed and "consistent with the demands of those who want to deny the Pebble Partnership the right to submit a permit application."
The Alaska Department of Law also issued a statement.
"We believe the assessment is premature, as well as any action EPA might take based upon it," the state agency said. "Any consideration of impacts should be made within the context of an actual proposal and a Clean Water Act Section 404 permit application."
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.
EPA regional administrator Dennis McLerran said the revised report generally affirms conclusions reached in the initial report last year while including more details on transportation corridors, possible culvert failures and other factors.
It noted, for example, that culvert blockages or other failures would inhibit fish passage. It also said production of fish could be lost or diminished if blockages occurred during adult salmon immigration or juvenile salmon emigration and were not cleared for several days.
Extended blockages aren't likely during mine operations, but there could be a greater impact once mine operations end, the report states.
The report also noted that salmon could be affected by in-stream copper levels because leaching could occur during routine mine operations.
Tailing storage facilities and dams to hold mine waste are likely to be in place for hundreds to thousands of years because there is no plan for removal when mining operations end, according to the report. A tailings dam failure could wipe out or degrade rivers and streams for decades, though the risk of that is considered fairly low, the report states.
Conservationists said it was clear the mine would harm salmon and destroy streams, even if nothing ever goes wrong.
"Pebble is far bigger and more threatening to renewable resource jobs than any other mine proposal in Alaska and it's planned for the worst location possible," Tim Bristol, director of Trout Unlimited's Alaska program, said in a news release.
The new report updates an assessment EPA released last year and is meant to address concerns that were raised about things like missing data and incomplete information.
For example, rather than using a hypothetical mine scenario, EPA said it drew from plans developed for Northern Dynasty Minerals, which has a stake in the proposed Pebble Mine; data collected by Pebble Limited Partnership; and its own experts to come up with three different mine scenarios.
EPA said the scenarios realistically represent the type of development expected to happen in the Bristol Bay region. McLerran said it also accounts for modern mining practices. He said the focus has been on getting the science right so informed decisions can be made in the future.
U.S. Sen. Mark Begich, D-Alaska, said he opposes a pre-emptive veto of the Pebble Mine or other projects and added "an open, public process that answers Alaskans' questions and puts better science on the table is a good thing."
The revised assessment will undergo a new round of peer review and public comment before EPA releases a final report that could affect permitting decisions for the proposed mine. That final report is expected later this year.
Follow Becky Bohrer on Twitter at https://twitter.com/beckybohrerap .
EPA's Bristol Bay assessment: http://www2.epa.gov/bristolbay