The Minnesota Supreme Court will review a lower court's December decision that reversed a permit for U.S. Steel’s Minntac taconite plant in Mountain Iron and set long-range goals for the company to reduce pollutants leaking out of the plant's tailings basin.

In a Wednesday order signed by Chief Justice Lorie Gildea, the court sided with WaterLegacy, the Fond du Lac Band of Lake Superior Chippewa and the Minnesota Pollution Control Agency, which had each submitted petitions for review last month urging the Supreme Court to review the Minnesota Court of Appeals' December decision. Oral arguments have not been scheduled.

Last month, the MPCA, WaterLegacy and the Fond du Lac Band asked the Supreme Court to review the case, arguing the Court of Appeals erred by concluding drinking water standards do not apply to groundwater and, therefore, MPCA can not issue permits with conditions setting groundwater as that class of drinking water.

The MPCA said at the time the court "significantly departed from accepted and usual rules of regulatory interpretation" and now 81 active permits are called into question.

While the MPCA agreed with WaterLegacy and the Band on the groundwater and drinking water standards, it responded, arguing the Supreme Court should not review whether the Clean Water Act applies to discharges of pollution that move from groundwater to navigable waters.

"The U.S. Supreme Court will soon issue a decision resolving that question, and, in any event, the court of appeals correctly applied the law," Minnesota Attorney General Keith Ellison wrote in a response to petitions by WaterLegacy and the Fond du Lac Band.

In its response, U.S. Steel urged the court to deny the petitions for review for both the groundwater and drinking water question and Clean Water Act question.

The appeals came after the Court of Appeals found the MPCA failed in its interpretation of state water-quality rules and that the MPCA's decision on Minntac's tailings discharge was unsupported.

The decision reversed a water pollution discharge permit issued by the MPCA in late 2018, the first for Minntac since 1987. That 1987 permit had been up for reissuance since 1992, but was “administratively extended since then,” MPCA officials said.

The five-year permit issued in 2018 had 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 — where a wet slurry of mine waste left over after taconite pellets are processed resides — into nearby surface and groundwater.

Minntac is the largest taconite iron ore mining and processing operation in the U.S., with production of up to 16 million tons per year and 1,700 employees. It went online in 1967.