State warned Minnesota Power about spills before 5-million-gallon coal plant leak

State pollution regulators told Minnesota Power it should take action to prevent wastewater spills from its massive coal plant in Cohasset, Minn., roughly three months before 5.5 million gallons of coal ash wastewater poured from a cracked pipe.

Duluth-based Minnesota Power reported 11 spills — all much smaller — between October 2021 and August 2023, including three of ash wastewater.

Those incidents were from other functions at the plant and unrelated to the July discharge, said Kurt Anderson, director of environmental and land management for Minnesota Power. Until the larger leak, the utility “had not had an issue with that system,” Anderson said.

When asked if the spills were connected, the Minnesota Pollution Control Agency (MPCA) said it was still investigating to learn more about the cause of the July spill.

In an April 2 letter, the MPCA also said the utility failed to immediately notify the state after six of the releases, one reason the agency issued a warning letter for alleged violations of a key water permit.

The MPCA said Minnesota Power should “submit and execute a plan to prevent future unauthorized discharges of water,” and asked the company to provide evidence, including pictures, that it had done so. KSTP TV first reported the letter last week.

The smaller spills ranged from 50 gallons of wash water from a truck bay to 1,000 gallons of ash silo wastewater, the byproduct of spraying coal to prevent dust. The causes were mostly attributed to equipment failures but there was one spill caused by a power outage, and another by a worker’s error.

The MPCA found that overall, the coal plant “appeared to be well maintained and in good working order.”

Anderson said the warning letter is the lowest level of enforcement actions and came after a routine compliance inspection. He said the majority of the spills were either contained or into soil that could be removed.

Anderson said after a spill Minnesota Power’s “first order of business” is containment and the utility notifies the authorities as soon as it can. The longest gap between discovery of a leak and reporting to the MPCA was about four hours, but most were less than an hour. Anderson said the MPCA determined, on this inspection, that anything longer than 42 minutes was too slow.

Minnesota Power made a few “relatively minor” changes as a result of the inspection, such as inspecting certain parts of the plant more often, Anderson said.

The major coal ash wastewater leak was discovered at the Boswell Energy Center on July 16. Minnesota Power first estimated it spilled about 1 million gallons of tainted water, drawn from the top of a disposal site for coal ash.

The company later revised that estimate to 5.5 million gallons and said the water had escaped for as many as five days. At least some of the water reached Blackwater Creek, which empties into Blackwater Lake, an impoundment of the Mississippi River.

In early August, the utility said testing showed sulfates about 20 times the state limit where the spill reached the creek. Sulfates can damage wild rice, which is harvested from Blackwater Lake and the creek.

Anderson said Minnesota Power has pumped 5.5 million gallons from the waterway and will continue to pump more. He said sulfate levels were now lower in some areas.

Boswell is Minnesota Power’s largest power plant, though the utility gets more than half its electricity from renewable sources. The company plans to retire one of its two remaining coal-fired units there by 2030 and the second by 2035 and add a significant amount of renewable power to help replace the fossil fuels.