Minnesota Power, however, questions data points cited by the environmental group.
In the latest battle over coal-burning power plants, the Sierra Club on Monday alleged that three Minnesota Power generating stations have repeatedly violated the U.S. Clean Air Act since 2009.
Attorneys for the environmental group, in a letter to Minnesota Power executives, said the company’s Boswell, Taconite Harbor and Laskin plants in northern Minnesota violated eight smokestack standards 12,774 times since 2009. The group threatened litigation, which can lead to enforcement action under a citizen lawsuit feature of the Clean Air Act.
But the Duluth-based utility said it’s not polluting the air and intends to challenge the group’s conclusions. And a Minnesota Pollution Control Agency (MPCA) official said the agency doesn’t plan enforcement action based on the Sierra Club’s analysis of the utility’s emission reports.
Two similar citizen lawsuits by the Sierra Club in Wisconsin resulted in settlements with other utilities to stop burning coal at seven coal-fired generators. The Sierra Club has a nationwide campaign called Beyond Coal to end coal burning, a major source of greenhouse gases.
The letter said Minnesota Power’s most common smokestack problem is the opacity of emissions, a measure of the smoke’s transparency. The Sierra Club reported 10,356 instances at three plants where the opacity level was briefly exceeded. The group contends this indicates high levels of soot, which can contribute to health problems.
Minnesota Power didn’t dispute the group’s numbers but said they are drawn from 3.5 million emission data points over five years. Overall, the company says, the plants are operating within permitted limits 99.7 percent of the time.
“Opacity doesn’t measure anything about pollutants at all,” Pat Mullen, vice president of marketing and corporate communications for the Duluth-based utility, said in an interview. “It can be as simple as whether the units have been shut down and you are restarting them. It can be based on the weather — you put hot steam in cold air and it is going to have a higher opacity.”
Katie Koelfgen, manager of the MPCA land and air compliance section, agreed with that view. “This type of monitoring is quite complex and just because deviations are reported does not necessarily indicate that there are violations,” she said in an interview.
The environmental group also alleged violations relating to the processes to remove mercury and other pollutants. “Across all three plants, most of the units seem to have significant operational problems with their pollution controls,” said James Saul, an attorney for the Sierra Club based in Madison, Wis.
The utility, which serves 144,000 customers including Iron Range mining companies, last year announced plans to retire three coal units but keep others. State regulators last September approved the utility’s $430 million environmental retrofit of its largest generator, Boswell Unit 4 in Cohasset, Minn.
Under the citizen lawsuit provisions of the federal law, the U.S. Environmental Protection Agency could join the case, as happened in two Sierra Club legal actions in Wisconsin. The EPA did not respond to requests for comment.
The two Sierra Club lawsuits in Wisconsin were filed by the same Madison law firm making the Minnesota Power allegations. In the 2012 and 2013 settlements, Dairyland Power Cooperative, Wisconsin Public Service Corp. and other utilities agreed to $1.1 billion in environmental upgrades and $3.4 million in fines.
David Shaffer • 612-673-7090 • @ShafferStrib