Canadian firm Northern Dynasty Minerals, owner of the proposed copper, gold and molybdenum Pebble Mine in southwestern Alaska, has 90 days to outline how it would mitigate the “unavoidable adverse impacts” caused by mine discharges to the state's aquatic resources, the U.S. Army Corps of Engineers told the company in a letter made public on Aug. 24. 

The area of potential impact includes 2,825 acres of wetlands, 132 acres of open waters and 129 miles of streams.

Hours after the letter's release, the US Army issued a statement saying that while the Trump Administration "supports the mining industry,"  Pebble mine in its current appproach lacks mitigation steps for the environmental impacts.

“Therefore the Corps finds that the project as currently proposed cannot be permitted under Section 404 of the Clean Water Act,” the ARmy said, opening  speculation about the long controversial project's future.

The new requirements come one month after the Corps issued a final environmental impact statement (EIS) for the Pebble mine that paved the way for its development. According to media sources and speculation, the new hurdle comes amid rising opposition to the project from Trump administration insiders and associates.

Joel Reynolds, senior attorney at the Natural Resources Defense Council, said he expects it would be impossible for mine developers to mitigate the damage that the project would inflict on Bristol Bay and tribal lands in the area.

Discharges at the mine planned for bay headwaters would cause significant degradation to resources, with “in-kind compensatory mitigation” required for all direct and indirect adverse effects those discharges would cause, David Hobbie, Corps regional regulatory division chief said in the Aug. 20 letter to the company.

Tom Collier, CEO of Pebble Partnership, the U.S. based subsidiary managing the project, says the company began focusing on a preliminary mitigation plan six weeks ago in anticipation of the new requirement. “We believe our final comprehensive management plan submission will be submitted within weeks and will satisfy all of the requirements of the letter,” he says.

Mitigation also is required for effects of a planned transportation corridor as part of the development crossing 460 acres of wetlands, 232 acres of open waters and 55 miles of streams. The transportation corridor includes mine and port access roads, and a port on the western shore of Cook Inlet.

In its July 24 EIS, the Corps said the mine would not have a measurable effect on fisheries, which contradicted a 2014 review by the U.S. Environmental Protection Agency that said Pebble Mine would have significant effects on streams, wetlands and fisheries in the bay watershed.

Pebble proposed to develop the surface mine about 200 miles southwest of Anchorage and 60 miles west of Cook Inlet. The project would include an open pit mine, with associated infrastructure to include a 270-MW power generating plant and a natural gas pipeline from the Kenai Peninsula across Cook Inlet to the mine.

The company could use various mechanisms for mitigation, the Corps said in its letter, including mitigation banks and in-lieu fee programs.

“Pebble Mine would destroy five and a half square miles of wetlands and open waters and harm nearly 200 miles of pristine streams," said NRDC's Reynolds. "Now that the Corps has finally set the bar that the Clean Water Act and science require, Northern Dynasty can’t meet it.”  He called on EPA to veto the project.

Collier said, however, that anyone suggesting that Pebble will not be able to comply with the letter's mandates or that compliance will significantly delay the record of decision, which had been set for the end of summer, "must be ignorant of the extensive preparation we have undertaken ... to meet the requirements.”

Northern Dynasty said Aug. 24 that it has launched an advertising campaign targeting the administration, saying that it has made “tremendous progress” restoring objectivity, certainty, timeliness and science-based decision-making to statutory permitting.

“Now is not the time to return to Obama-era politicization of regulatory reviews for major project developments,” the company said in a statement.

A small number of unelected but “high-profile” conservatives have suggested that President Donald Trump should weigh in on the final steps of permitting, the company said. It denied published reports that the administration is planning such an action.

Northern Dynasty shares fell 38% to 90-cents per share on Aug. 24, from a close Aug. 21 of $1.45.