A new study commissioned by a Bristol Bay seafood marketing group paints a doomsday scenario if the bulk tailings dam at the proposed Pebble mine ever suffered a catastrophic breach, an outcome the U.S Army Corps of Engineers has called very remote and one the mine developer has taken steps to avoid.
Billions of gallons of mud would smother valley bottoms, covering vast stretches of salmon habitat, according to an executive summary released Friday. Finely ground-up waste material from mining would travel downstream and spill into Bristol Bay more than 200 river miles from the mine site, threatening the valuable salmon fishery.
“Given the fine-grained nature of the material, it is extremely likely that these tailings would continue to Bristol Bay, where they would eventually settle out in the Nushagak River estuary,” the summary says.
The impact could last decades.
The Bristol Bay Regional Seafood Development Association, founded by fishermen and funded with a 1 percent tax on the harvest, paid $80,000 for the study, said Andy Wink, the group’s executive director.
The group said the full report, based on major tailings-dam failures worldwide, including Mount Polley in British Columbia in 2014, will be finalized for release in the coming days.
The Corps could not comment on the executive summary on Friday, said John Budnik, a spokesman with the agency.
Mine developer Pebble Limited Partnership said on Friday the proposed designs for its tailings facilities improves upon the “unconscionable” and “avoidable” dam failures at Mount Polley and Brumadinho mine in Brazil this year.
“The Pebble design is fundamentally different from Mount Polley and those who continue to state otherwise are being intentionally deceptive with Alaskans,” said Mike Heatwole, a spokesman with Pebble Limited.
If built, Pebble would be an open-pit mine about 200 miles southwest of Anchorage, straddling salmon-producing headwaters of the Bristol Bay fishery.
Pebble’s bulk tailings dam would rise about 550 feet and hold about 30 billion cubic feet of waste material, enough for every man, woman and child to get roughly 4 cubic feet if they wanted, said the report’s lead scientist, Cameron Wobus, with Lynker Technologies, a consulting firm in Boulder, Colorado.
Wobus provided a summary of the findings at a press event in Anchorage on Friday.
About 12 billion cubic feet would be released if the dam ruptured, an amount many, many times larger than the Corps showed in an analysis of tailings release scenarios in its new draft environmental impact statement, he said.
The Corps’ draft report opened for public comment for 90 days starting Friday, part of the regulatory process required before the mine can be permitted.
The Corps’ report says such a “catastrophic" release is “extremely unlikely."
The agency’s review does not analyze a full breach of the tailings dam, Wobus said. It instead looks at a much smaller partial breach.
Heatwole, with Pebble Limited, said the Corps thoroughly reviewed Pebble’s plan and possible failures at the tailings facilities.
“Their conclusions are pretty clear -- no population level impacts would be expected for fish from tailings release scenarios and a catastrophic failure of the tailings facility is highly unlikely," Heatwole said.
The Corps’ analysis is “woefully inadequate," said Mike Friccero, a Bristol Bay fisherman and marketing group board member. It looks at “very minor" tailings releases. It’s an effort by the Trump administration to “shove” the mine down fishermen’s throats, he said.
The small marketing group worked with The Nature Conservancy to hire the consulting firm that did the study, he said.
The federal government should be analyzing a full breach of the tailings dam, not fishermen, but the agency isn’t legally required to do so, Friccero said.
“Modern history has shown us that (catastrophic dam failures) are more likely than they want us to think,” he said.
Heatwole, with Pebble, said water was a factor in the failures at Mount Polley and Brazil.
"We have taken this fully into account in our designs,” he said.
Heatwole said the “lessons learned” from Mount Polley influenced Pebble’s design of the main tailings dam that will hold non-acid-generating waste rock, he said. It will be a “flow-through facility" so water does not accumulate. A buttress has been added to provide additional support, “making our approach conservative and above industry norms for factors of safety,” he said.
A smaller tailings facility that holds potentially acid-generating rock will be located near the mine pit, Heatwole said. “It will be lined, and will be returned to the pit upon closure, thereby ensuring no post-closure risk.”
Pebble’s plans call for extracting 1.4 billion tons of ore and 200 million tons of waste rock over 20 years.
Pebble hired Knight Piesold to design their tailings facilities. The same firm designed the Mount Polley facility that failed, Wobus said.
Heatwole said Knight Piesold is a “credentialed, reputable" business. They withdrew from the Mount Polley project four years before the dam failed, he said.
Pebble Limited’s chief executive, Tom Collier, said in 2015, after the Mount Polley disaster, that he’d submit the engineering design for Pebble’s tailings storage facility to an independent review before initiating permitting.
“It remains Collier’s commitment to do so prior to seeking our state dam certification – the key permit for tailings design, construction, operation and closure,” Heatwole said.
Heatwole said Pebble Limited has not said when the process for acquiring that and other state permits will begin.