DULUTH -- The Minnesota Court of Appeals is reversing a decision that granted U.S. Steel a permit for continued operation of its Minntac taconite tailings basin in Mountain Iron.

The appeals court found that the Minnesota Pollution Control Agency, which issued the permit to U.S. Steel, failed in its interpretation of state water-quality rules and that the MPCA's decision on tailings discharge was unsupported.

Now, the permit decision heads back to the MPCA for further proceedings and review.

In a statement, the MPCA shared that it assessing next steps.

"The Minnesota Pollution Control Agency is dedicated to protecting Minnesota’s most valuable resource — its water," the statement read. "The MPCA will continue engaging with stakeholders to ensure the state’s groundwater and surface water are protected.”

The decision was part of a consolidated set of appeals, including those filed individually by U.S. Steel, WaterLegacy and the Fond du Lac Band of Lake Superior Chippewa.

Paula Maccabee, advocacy director and counsel for WaterLegacy, said the decision was an "important first step to set limits on sulfate pollution and protect Minnesota surface waters."

Like the MPCA, WaterLegacy is still reviewing the decision and determining what its next steps are.

The appeals court also decided that the state can't enforce groundwater standards. The Minnesota Center for Environmental Advocacy said that decision "handed mining companies a win."

Aaron Klemz, director of public engagement for the Minnesota Center for Environmental Advocacy, wrote in a statement: "The mining industry takes advantage of unclear standards and loopholes to gut our ability to protect Minnesota’s water. With even more dangerous sulfide mines proposed for Minnesota, today’s decision shows the Minnesota Pollution Control Agency either cannot or will not effectively protect Minnesotans from mining pollution."

U.S. Steel did not return a request for comment by the time of publication.