Susan Montoya Bryan, File, Associated Press
FILE - This April 6, 2006 file photo shows the Four Corners Power Plant, one of two coal-fired plants in northwest New Mexico, near Farmington, N.M. Owners of the 48-year-old plant, one of the nation's largest of its kind, are being sued by a coalition of environmental groups over allegations the plant has failed to install the best available equipment to control pollution.

ALBUQUERQUE, N.M. — A coalition of environmental groups on Tuesday sued the owners of one of the nation's largest coal-fired power plants over allegations that the plant has failed to install the best available equipment to control pollution.

The Sierra Club, the National Parks Conservation Association and a pair of Navajo groups contend in a lawsuit filed in federal court that the 48-year-old Four Corners Power Plant has repeatedly violated the Clean Air Act by not updating pollution controls when making other modifications.

The lawsuit asks the court to force the plant to install state-of-the-art equipment to reduce emissions.

"The goal of the lawsuit is to clean up the facility," said Suma Peesapati, an attorney with Earthjustice, which filed the lawsuit on behalf of the groups.

Located on the Navajo reservation in northwest New Mexico, the 2,040-megawatt plant is operated by Arizona Public Service Co. and provides power to customers in New Mexico, Arizona, California and Texas.

The lawsuit names Arizona Public Service, PNM Resources and other Southwestern utilities that own portions of the plant.

APS spokesman Damon Gross said Tuesday he would not be able to comment on the lawsuit since the utility has yet to review the complaint.

Peesapati said one of the biggest concerns is how emissions are affecting surrounding Navajo communities and other residents in the Four Corners region.

"I think if you talk to local residents about the pollution issues coming from the plant, you'll definitely hear some troubling stories," she said. "There aren't studies showing direct causation between the pollution from this plant and health effects, but we have seen elevated rates of respiratory illness and other illnesses in the surrounding communities."

According to the lawsuit, the owners have made two sets of modifications to the plant without obtaining construction permits and without installing pollution control technology required under the Clean Air Act.

The groups pointed to data from the U.S. Environmental Protection Agency that shows the Four Corners plant is one of the largest sources of air pollution in the country.

Last year, the plant last year emitted more than 38,000 tons of nitrogen oxide, more than 11,000 tons of sulfur dioxide and more than 14 million tons of carbon dioxide.

"The sheer scale of the plant's emissions, which reflect the severity of its ongoing air quality violations, raise major public health and environmental concerns," the lawsuit states.

Gross argued that the plant meets or exceeds all current state and federal environmental requirements.

The EPA released a proposal earlier this year that would trim nitrogen oxides at the plant by 87 percent. The plan would also reduce the effects the plant has on visibility at national parks and wilderness areas in the region by an average of 72 percent.

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Navajo officials also signed a lease extension for the plant in March that requires Four Corners to have the best available technology to reduce sulfur oxide and carbon dioxide emissions. That requirement was added over tribal lawmakers' concerns about pollution.

In addition to providing electricity for some 300,000 households in four states, the plant is a source of jobs and tax revenue for the Navajos.

The lawsuit argues that the plant's emissions disproportionately affect Navajos because of its location on tribal land.

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