Xcel Energy earlier this month asked to join a lawsuit filed against the U.S. Environmental Protection Agency as another defendant in the unusual pairing.

In December, several environmental groups who blame poor EPA enforcement and the company’s Sherco coal-burning plant about 200 miles away from here for regional haze in Voyageurs National Park and other protected parks and wildernesses.

The six environmental groups, including Voyageurs National Park Association, filed the suit in U.S. District Court in an effort, they claim, to force the EPA to do its job and force Xcel to clean up “Minnesota’s dirtiest coal plant.”

Xcel owns the plant in question, the Sherburne County Generating Station (Sherco for short), in Becker, Minn. But the company noted that the ‘70s-era power plant is located very far from the national parks identified in the complaint, and is in full compliance with all provisions of the Clean Air Act, according to a statement issued Feb. 12.

Xcel also named EPA Administrator Lisa P. Jackson in conjunction with its 23-page memorandum to intervene in the case that has the potential of costing Xcel and its customers hundreds of millions of dollars to update the plant, a process the company says is already sufficiently underway.

“Our plant is the sole object of this lawsuit and the potential outcomes can have a significant impact on our customers,” said Laura McCarten, Xcel Energy regional vice president in a recent statement. “To protect our customers’ interests in clean, reliable and reasonably priced power, we are now asking the court to let us participate in the litigation.”

She added that Xcel also is evaluating Sherco’s long-term role with the state’s biggest energy company.

The environmental groups said they were forced to file the lawsuit because the EPA for years has ignored Sherco’s emissions problems and has evidence of a direct link – laid out in a 2009 U.S. Department of Interior report – that the plant contributes to regional haze in Minnesota and Michigan national parks as well as the Boundary Waters Canoe Area Wilderness.

In the memorandum, Xcel points out that contrary to the Department of Interior’s findings, an EPA consultant found no connection between Sherco and regional haze in the parks. The document also points out that there are other companies releasing emissions much closer to the parks than Sherco.

The EPA recently went against Minnesota Pollution Control Agency findings in a new lawsuit that says its federally required State Implementation Plan against emissions failed to appropriately demand reductions of pollutants it claims are released by a half-dozen taconite plants, almost all of which are on the Iron Range.

The Minnesota SIP, and other claims about its lack of oversight, research and findings, appear to be at the heart of the Sherco case, too.

The EPA says it does not discuss ongoing litigation.

The groups have essentially demanded that the EPA use the U.S. Clean Air Act to force Xcel to install modern technologies that make it possible to reduce regional haze by 90 percent.

The plaintiffs argue it is possible now to recreate natural conditions in the parks by 2064, if emissions-producing plants comply with RAVI and BART, which stand for Reasonably Attributable Visibility Impairment (RAVI) and Best Available Retrofit Technology (BART) standards.

The civil lawsuit could pit Xcel and the EPA against the VNPA, National Parks Conservation Program, Friends of Boundary Waters Canoe Area Wilderness, Fresh Energy, Sierra Club and Minnesota Center for Environmental Advocacy.

But McCarten said Xcel already is evaluating Sherco’s future operations and how best to comply “with all current and expected regulations.”

“We will submit our study to the Minnesota Public Utilities Commission by July 2013,” she said. “We believe this is a better venue to discuss these issues than in the courtroom.”

McCarten said that the EPA’s interest is in upholding the Clean Air Act, while Xcel will bring a detailed understanding of the environmental, economic and community interests of Sherco.

“We think our perspective in this lawsuit is important and that our customers would expect our involvement,” she said. “We are currently investing $50 million in improvements at Sherco (power generating) Units 1 & 2 that will cut sulfur dioxide and nitrogen oxide emissions by about half.”

In Xcel’s legal response, though, it estimates it would cost at least $280 million to comply with the environmental groups’ demands.

The company also has previously stated that it has a proven track record as stewards and recently spent $1.2 billion in the metro area in order to protect Minnesota’s great outdoors.