Albuquerque • Environmental groups are accusing U.S. regulators of violating clean water rules by repeatedly delaying action on a discharge permit for a coal-fired power plant that provides electricity for customers in three Western states.

The Sierra Club and others contend in papers filed Wednesday in federal court that without a new permit, the communities surrounding the Four Corners Power Plant in northwestern New Mexico remain exposed to heavy metals and other pollutants that are released into drainages that eventually lead to the San Juan River.

They are seeking to force the U.S. Environmental Protection Agency to take action on a permit renewal application that was initially filed in 2006.

They called the delays unreasonable, saying that in the 12 years the agency has failed to take final action, there have been technological advances that could have further reduced degradation of the area’s water quality.

“The water pollution permit for the Four Corners coal plant is based on facts and technology from last century,” Gloria Smith, an attorney with the Sierra Club, said in a statement. “In 2018, it is unconscionable for the EPA not to protect public health and the environment from the coal pollution that now flows into the San Juan River.”

An agency spokeswoman did not immediately return a message seeking comment.

Arizona Public Service Co., the utility that runs the plant, said the permit has been extended administratively by the agency over the years and that it is meeting water quality regulations.

Federal regulators have done numerous inspections and no violations have been found, utility spokeswoman Suzanne Trevino said Thursday.

The Four Corners plant is on tribal land and produces electricity for customers in Arizona, New Mexico and Texas. It’s one of three coal-fired generating stations in the region that have scaled back operations as utilities shift toward natural gas and renewable sources because of regulations and economic forces.

Critics have long complained that the Four Corners plant and the nearby San Juan Generating Station emit more pollution than any other source in North America and that the pollution degrades air and water resources throughout the San Juan Basin.

The two remaining units at Four Corners burn about 19,000 tons of coal a day, according to the complaint.

Water discharge permits are supposed to be renewed every five years as part of a process that includes public comment and a chance for people to appeal once a final permit is issued.

The environmentalists say that hasn’t happened in the case of the Four Corners permit. They argue that the result has been unnecessary delays in the monitoring and management of pollution seeping from the plant’s coal ash disposal areas as well as a delay in the collection and dissemination of information about the effects of pollution on endangered fish in the San Juan River.