Minntac Taconite

Minntac Taconite facilityThe Minntac Taconite Facility, owned by the United States Steel Corporation, is located near the city of Mountain Iron in central St. Louis County. Minntac began production of taconite pellets in 1967 and is the largest taconite producer in North American with an annual production of up to 15 million long tons of pellets.

Low grade taconite iron ore of the Biwabik Iron Formation is extracted from a connected series of open pit mines stretching over an area of approximately eight miles long and up to a mile wide. The mined ore is then sent to the processing plant where it is crushed into a fine powder, concentrated by magnetic separation and flotation, formed into marble-sized balls, and then heated in large furnaces to form hardened pellets that are shipped to US Steel-owned blast furnaces in Indiana.

The waste material from the crushing and concentration process, called tailings, are transported in a slurried form for disposal in the 8700 acre Minntac tailings basin just north of the plant. There, the tailings particles settle out and the water is recycled back for reuse at the plant.


Permits held with MPCA

  • NPDES/SDS water quality permit for operation of the tailings basin
  • NPDES/SDS water quality permit for mine pit dewatering discharges from its mining area
  • Air quality permits for air emissions from the mining area, processing facility and tailings basin

SDS water quality permit

In 1987 MPCA issued US Steel an NPDES/SDS permit that authorized discharges from the basin. The permit expired in 1992 but because US Steel submitted a timely application for reissuance of the permit, it has been legally able to continue operating under the expired permit.

Since that time, MPCA efforts have focused on reducing the environmental impacts from the tailings basin, primarily through evaluation of treatment options, capturing and reusing surface discharges, and evaluating impacts to the surrounding groundwater. Much of this work was required through a series of enforcement actions with the ultimate goal of reissuing the permit with updated requirements that would bring the facility in compliance with all surface and groundwater standards.

The most recent permitting effort for the Minntac tailings basin focused on specific steps to reduce the pollutant levels of the water within the tailings basin, resulting in a reduced concentration of pollutants in the seepage leaving the tailings basin. A draft permit was made available for public comment in November 2016. Revisions were made to the draft permit based on received comments and a proposed permit was sent to EPA for final review in November 2018. The final permit became effective December 1, 2018.

2018 Minntac tailings basin permit

Legal status

  • April 2019 – Fond du Lac Band, WaterLegacy and US Steel appealed the reissuance of the tailings basin permit, on varying grounds, to the Minnesota Court of Appeals. 
  • December 2019 – Minnesota Court of Appeals reached a decision that resulted in the reissuance of the permit being reversed and was remanded to the MPCA for further proceedings. 
  • January 2020 – Fond du Lac, WaterLegacy, US Steel and the MPCA filed separate petitions for review to the Minnesota Supreme Court requesting reconsideration of different aspects of the Court of Appeals decision.  
  • As of early August 2020, the Minnesota Supreme Court has not rendered a final decision.

NPDES/SDS permits issued by the MPCA to other facilities where the permit includes a Class 1 limit for discharges to groundwater are located here. The groundwater discharge limits in these permits are similar in nature to the limit at issue in the MinnTac permit.