DETROIT (AP) — Over and over, Michigan environmental regulators sounded alarms as they reviewed a proposed large, open-pit ore mine in the Upper Peninsula near the Menominee River, prized for walleye fishing and a major tributary to Lake Michigan.

The mine would send acidic mining wastes into the river and surrounding waterways, which would then spill into the Great Lake, staff said. More acres of wetlands would be harmed than the mining company was projecting, evaluators found.

Then the U.S. Environmental Protection Agency and then-Michigan Department of Environmental Quality approved the mine anyway.

The Detroit Free Press reports that at stake in whether the Back Forty Mine proceeds is the potential endangerment of one of the most important rivers in Michigan, part of a system that drains more than 4,000 square miles of the U.P. and northern Wisconsin, and a river culturally iconic to the Menominee Indians of Wisconsin, whose creation story includes that they come from the river’s mouth. Sacred burial grounds of the tribe are potentially threatened by the mine. The tribe is now among those appealing wetlands and surface water permit approvals for the mine.

The level of DEQ staff concern, and at times frustration, with Canadian company Aquila Resources’ plan to mine for gold, zinc and copper within 150 feet of the river — in the western U.P. on the Michigan-Wisconsin border — has only now come to light, through agency documents presented as evidence in the appeal pending before an administrative law judge.

The open-pit sulfide mine would operate on 83 acres and its pit would be 2,000 feet by 2,500 feet, and 750 feet deep, according to the company. The life of the mine is planned at approximately seven years, and Aquila estimates it will produce:

∫ 512 million pounds of zinc

∫ 468,000 ounces of gold

∫ 51 million pounds of copper

∫ 24 million pounds of lead

∫ 4.5 million ounces of silver.

An on-site processing mill also will crush and refine minerals and ores through flotation, separation and the use of cyanide, according to the company’s plans.

The DEQ emails, letters and memos show concern that Aquila Resources and its engineering firm, Green Bay, Wisconsin-based Foth Infrastructure and Environment, LLC, was understating the project’s impact on the river and surrounding wetlands, according to regulators. The methods Aquila was using to measure wetlands impacts were improper, and the mining company wasn’t changing them, DEQ staff said. The U.S. Environmental Protection Agency shared similar concerns, documents show.

Eric Chatterson, a geology specialist in DEQ’s Water Resources Division, wrote there was a “high likelihood” that crushed minerals and ores from the mine “will be observed in the groundwater that discharges to the Menominee River and Shakey River,” in an April 5, 2018, email to a department colleague. He added that the problems would continue when the mine ultimately closed, stating, “Impacted groundwater from the backfilled pit is expected to migrate to local surface water sources.”

That’s a particular concern for many, as sulfide ores exposed to air and water undergo chemical reactions that create sulfuric acid that harms water quality and is toxic to fish and smaller aquatic organisms.

Aquila’s permit request, according to DEQ staff, was also failing to capture the mine’s full impact on surrounding wetlands, which are vital to natural habitat, erosion protection and water quality. An unsigned, undated DEQ memo said of the groundwater model Aquila Resources was using as part of its permit application: “It provides little to no use in assessing impacts to nearby wetlands.”

DEQ officials found that at some locations around the mine, operations would reduce the groundwater feeding wetlands “in excess of 6 inches to greater than 5 feet throughout the modeled life of the mine,” wrote Kristi Wilson of the DEQ’s Water Resources Division to Aquila Resources officials on Jan. 19, 2018.

The EPA was similarly concerned. Christopher Korleski, director of the Water Division at EPA’s Region 5 that includes Michigan, wrote the DEQ’s Coleen O’Keefe on March 8, 2018, stating the agency objected to the issuance of a permit for the mine for, among other reasons, that the company had not yet demonstrated that “the mine site plan is protective of water quality throughout the life of the mine and post-closure.”

But two months later, on May 3, 2018, following a meeting with Aquila officials and “supplemental information” being presented to the EPA, Korleski changed his stance.

“Based on the information EPA has received from Aquila, a number of objections identified in EPA’s March 8 letter have been resolved,” he stated. “In addition, we believe that there is a ready pathway for the resolution of EPA’s remaining objections through MDEQ’s inclusion of specific conditions in a final permit issued by June 6, 2018.”

But the information provided by Aquila provided little of new substance, said Janette Brimmer, an attorney with the environmental nonprofit Earthjustice who is representing the Menominee tribe in its permit appeal.

For example, regarding EPA’s concern about potential adverse impacts to water quality at the mine’s closure, the agency accepted Aquila’s statement that the closure plan would not be developed until after the mining pit was excavated, “allowing the use of the mineralogy data from the pit walls to factor into the plan,” and that any final closure plan would require review and approval by DEQ. Regarding secondary wetlands impacts, Aquila stated it was “working with MDEQ to address concerns regarding the assessment of secondary impacts using modeling and water budgets.”

“That’s the million-dollar question: What changed?” Brimmer said. “Nothing changed. Nothing changed on the ground. The data didn’t change. Nothing changed other than, presumably, the politics. I would have liked to have been a fly on the wall in those EPA Region 5 meetings (with Aquila officials).”