Minnesota's plan to reduce air pollution over northern parks and wilderness land won unanimous approval Tuesday from the Pollution Control Agency Citizens' Board amid fresh criticism from federal officials that it's too soft on the mining industry.

Federal land managers and conservation groups opposed the plan, arguing that at least some coal-fired power plants and 10 taconite furnaces in Minnesota should be ordered to install advanced control technologies to reduce visible haze.

Instead, state regulators say the iron mining industry must use "good combustion practices," a less-costly option than installing advanced, low-emission furnaces. One taconite plant has installed that technology, and it eventually may be required across the industry -- but not now.

In a detailed criticism of the state's taconite regulations, Trent Wickman, an engineer for the U.S. Forest Service in Duluth, said Minnesota is mandating "essentially well-tuned furnaces" when it should be developing standards for advanced technology.

Under the state's plan, emission "limits" on taconite plants will be "above current actual emissions," he said.

Coal-fired power plants that cause haze also avoided a costly requirement advocated by federal land managers and others to install advanced pollution controls called selective catalytic reduction (SCR). The technology can cost hundreds of millions of dollars per plant.

Haze, or reduced visibility, affects Voyageurs National Park and the Boundary Waters Canoe Area Wilderness (BWCA) in northern Minnesota and Isle Royale National Park on Lake Superior. Reducing haze over pristine areas has long been explicitly required under the U.S. Clean Air Act.

But the law, which aims to clear the skies by 2064, has long been unenforced, and after repeated court and regulatory delays, the government now faces a deadline to take the first steps to confront the problem.

Conservation groups said they will ask the U.S. Environmental Protection Agency, which has final say over the regulations, to reject Minnesota's approach and impose a stricter one.

"We disagree that there aren't available controls that could eliminate some of the pollution that taconite facilities are emitting," said Kevin Reuther, an attorney for parks and conservation groups. He also said the groups will urge the EPA to impose stringent, plant-specific controls on two older units at the state's largest coal-fired power plant near Becker, Minn.

Catherine Neuschler, a pollution-control planner at the MPCA, defended the state plan, saying it is "a strong step toward meeting our visibility goals." Stringent plant-specific requirements would not guarantee better results and might not withstand a court challenge by regulated industries, she and other officials said.

The National Park Service also opposed the state's regulatory plan, arguing that stricter emission controls are needed to reduce haze. But state officials are counting on other clean air regulations to do the job.

Taconite plants also face other regulations relating to emissions near taconite plants. State officials say those rules eventually may force the mining industry to install lower-emission furnaces.

Two units at U.S. Steel's Minntac plant in Mountain Iron are using the technology, and Neuschler said she expects other plants will need to shift to it in five years.

The board's vote was delayed from March so regulators could work out a deal with Cliffs Natural Resources, operator of three taconite plants on the Iron Range. It had warned that some of its furnaces might not meet the standards and might be forced to shut down. In the revised requirements, Cliffs must install better monitoring equipment if its emissions get too high.

For power plants, state regulators say a separate cap-and-trade emissions program designed to clear the air over Eastern cities should help reduce northern Minnesota haze. But that program is being challenged in federal court, leaving its fate in doubt.

Xcel Energy, which owns the Sherco power plant near Becker, is required to add controls on the plant's two oldest units, but not expensive SCR technology. Xcel has said it is going ahead with $50 million in pollution upgrades at the plant, which it argues is not the main source of haze over northern park and wilderness lands.

David Shaffer • 612-673-7090