Over the coming months, Minnesota Power will evaluate what “modest controls” it may add on Boswell units 1 and 2, the plant’s smallest units with combined generating capacity of 140 MW, according to Al Rudeck, the utility’s vice president of strategy and planning. Minnesota Power already is installing scrubbers on Boswell units 3 and 4, its largest units.

The scrubbers are expected to enable Boswell’s biggest units to comply with EPA’s new Mercury and Air Toxics Standards Rule, which takes effect in 2016, he said.

Deb Amberg, Allete senior vice president, general counsel and secretary, said the company had been in discussions with the EPA since 2008 to settle the alleged violations. “We are pleased to have reached a settlement that recognizes the significant investments we’ve already made to reduce emissions,” she said. “It is consistent with our Energy/Forward resource strategy to reduce emissions, diversify our energy mix and advance renewable energy.”

Under the settlement, Minnesota Power also agreed to add 200 MW of wind energy and spend $4.2 million over the next five years in conservation and clean energy projects.

By the end of 2014, Minnesota Power will be positioned to meet Minnesota’s renewable standard of 25% by 2025 — more than a decade earlier than required by law.

In August 2008 and April 2011, Minnesota Power received notices of violation from the EPA alleging the utility made past modifications at its Boswell, Laskin, and Rapids Energy Centers generating stations between 1981 and 2005 without following appropriate pre-construction review and permitting requirements under the Clean Air Act.

Minnesota Power said that while it believes the projects specified in the NOVs were in full compliance with the federal law, it entered into the settlement agreement to avoid unnecessary costs and delays associated with litigation.

Before the settlement is final, it must be approved by the U.S. District Court for the District of Minnesota. A final ruling is expected before the end of August.