The Minnesota Pollution Control Agency on Wednesday defended in court air permits it granted to PolyMet, the company hoping to open the state’s first copper-nickel mine, amid challenges by environmental groups that say the state agency failed to examine a report that showed the company was eyeing a mine almost four times larger than it had proposed in permit applications.

The groups argue a report released by PolyMet in March 2018 outlines the company's plans to recover 118,000 tons of ore per day, known as “throughput,” instead of 32,000 tons per day, the amount listed by the company in permit applications. The air permits, issued in December 2018, allow the company to release 250 tons of regulated pollutants per year.

PolyMet would surpass those emission limits if it were to exceed a 32,000-tons-per-day throughput, Evan Mulholland, an attorney for the Minnesota Center for Environmental Advocacy, argued at the Minnesota Court of Appeals on Wednesday. He argued the case on behalf of the Sierra Club, Fond du Lac Band of Lake Superior Chippewa, Center for Biological Diversity and Friends of the Boundary Waters Wilderness as well, groups that had also filed the appeal last year.

“These facts show that PolyMet presented one thing to the public and to the state, but something quite different to its investors and creditors,” Mulholland said.

Mulholland called it “a sham permit” because he believes the company intends to increase production — and emissions — beyond what is allowed in the permit.

But MPCA attorney Emily Schilling said the agency wouldn’t let that happen. The permits set “hundreds of conditions on throughput to ensure that at no point during the milling process, the grinding process, should there be an ability for PolyMet to increase throughput, and therefore emissions, that could to lead to a violation of the standard,” Schilling said.

PolyMet would have to reapply for permits if it formally planned such an expansion.

Chief Judge Edward Cleary asked Schilling if it would be harder for the MPCA to stop PolyMet or enforce the standards once people were hired and mining began.

“I think it’s not that it’s much harder to stop them, it would be not in the permittee’s best interest to start construction if they knew that — if they had to come back and reapply backed all over again,” Schilling said. She added later, “They don’t get a free pass simply because the machine is running.”

Jay Johnson, attorney for PolyMet, said if the company were, then it would do so by restarting the process with regulators.

“It's never going to happen that PolyMet is going to try to circumvent the law and like (MPCA) said, and I agree, the law is if you go back and change a project, then you have to pretend that it was never constructed in the first place,” Johnson said.

The court has 90 days, until April 7, to rule on the air permit.

The air permit case is one of several legal challenges faced by the planned open-pit copper-nickel mine, processing facility and tailings dam near Babbitt and Hoyt Lakes.

The Minnesota Court of Appeals is expected to issue a decision by Jan. 13 on the suspended dam safety permits and permit to mine. On Jan. 21 a hearing will begin on the MPCA’s request to the Environmental Protection Agency to refrain from commenting on a PolyMet draft water permit until the public comment period ended.

Opponents argue the project could send tainted runoff into the St. Louis River watershed and Lake Superior, while supporters say the project will provide more than 300 jobs on the Iron Range and move the area's economy away from iron ore dependence.