The Fond du Lac Band of Lake Superior Chippewa and several environmental groups sued the U.S. Army Corps of Engineers on Tuesday over the federal agency's decision to permit the controversial PolyMet copper-nickel mine earlier this year.

In separate lawsuits filed Tuesday in U.S. District Court in Minneapolis, both claim the Army Corps violated the Clean Water Act and the National Environmental Policy Act in March when it issued PolyMet's wetlands permit, which allows the company to discharge dredged and fill material into more than 900 acres of wetlands as the company develops and builds its mine.

The lawsuit filed by the Friends of the Boundary Waters Wilderness, Center for Biological Diversity and Minnesota Center of Environmental Advocacy claims the Army Corps "failed to conduct an adequate environmental review" under the National Environmental Policy Act because the Army Corps "significantly changed the plan for mitigating wetland impacts" after issuing its Final Environmental Impact Statement in 2015.

The groups also claimed the Army Corps did not consider evidence that the mine could be larger than planned, the risk of a tailings dam failure or the impacts on secondary wetlands.

In its lawsuit, the Fond du Lac Band, which is 70 miles downstream from the mine site, claimed the Army Corps did not provide the Band with a hearing on its objections.

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If built, the mine would damage the land and water the Band hunts and fishes on, the Band argues.

Additionally, the Band named the Environmental Protection Agency as a defendant in its lawsuit.

The Band said that because concerns and comments made by EPA staffers reviewing a draft of PolyMet's water permit were read to the Minnesota Pollution Control Agency over the phone and kept out of the public record, the court should order the "EPA to reconsider its decision not to object to the permit until a proper review takes place.

The permit in question, a national pollutant discharge elimination system, or NPDES, permit, which regulates water discharged from industrial activities, was placed on hold by the Minnesota Court of Appeals last month as the court considers the "procedural irregularities" in the commenting process. Separately, the EPA's Office of Inspector General and Minnesota Office of the Legislative Auditor are also investigating the commenting and permitting process.

The MPCA, which awarded the permit last year, has staunchly defended the permit, but has acknowledged the need to improve transparency in the permitting process.

The lawsuits filed Tuesday are just the latest facing the agencies that permitted the proposed PolyMet copper nickel mine near Hoyt Lakes, the first mine of its kind to be permitted in Minnesota.

In a statement, PolyMet spokesperson Bruce Richardson said the company remained confident in the agencies responsible for its permitting.

"We are reviewing the complaints and we remain confident that the agency’s decisions were fully consistent with all applicable laws," Richardson said.

The Army Corps and EPA did not immediately respond to the News Tribune's request for comment.