The Minnesota Court of Appeals reversed a decision that granted U.S. Steel a permit allowing the continued operation of its Minntac taconite iron ore mine 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 MPCA's decision regarding Minntac’s tailings discharge was unsupported.

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

The MPCA issued a water pollution discharge permit last year for the massive Minntac taconite iron ore processing center. The permit has been up for re-issuance since 1992.

The five-year permit set long-range goals for U.S. Steel to meet for reducing pollutants, like sulfates, that are leaking out of the site’s 8,000-acre tailings basin into nearby surface and groundwater.

In a statement, the MPCA shared that it’s 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 group 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."

Minntac is the largest taconite iron ore mining and processing operation in the U.S., with production up to 16 million tons per year and 1,500 employees. It went online in 1967.

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