A newly approved cleanup plan for the Navajo Generating Station offers a classic environmental trade-off — more pollution apparently will be cleaned up than originally planned, but much of the cleanup will be delayed for many years.

The coal-fired power plant, whose electricity pumps Central Arizona Project water to Tucson, will have to cut its nitrogen oxide emissions by 80 percent over the plant’s remaining life and close by 2044 under a plan approved Monday by the U.S. Environmental Protection Agency.

A coalition of interest groups including water users, the Navajo Tribe and conservationists is happy with the EPA’s decision because it ensures that the Navajo plant will stay open longer. The plan also means they won’t have to spend as much on cleanup as soon as they would have under an earlier plan.

But two leading environmental groups say it’s not strong enough due to what they see as lengthy delays in cleanup. They may sue to block its implementation.

Under the EPA’s plan, the Navajo station, located near Page at the Utah border, must close one of its three, 750-megawatt generating units or reduce total power generation by an equivalent amount by 2020. It must install better pollution controls on the other two units by 2030. The controls would use technology similar to that used in catalytic converters in cars.

An earlier EPA plan would have required all three units to install pollution controls by 2023. A still-earlier EPA plan would have required installation of controls by 2018.

The proposal is aimed at improving visibility at Grand Canyon National Park and 10 other national parks and wilderness areas.

The new plan will cause the plant to emit about 12.4 percent less total nitrogen oxide than it would have produced under the earlier EPA plans, an agency spreadsheet says. Over time, the cleanup should reduce the plant’s impact on visibility at the parks by 72 percent, said Jared Blumenfeld, administrator for the EPA’s Pacific Southwest Region, which includes Arizona.

At the same time, however, the new plan delays the deadline at which all the pollution reductions must kick in by seven years from the EPA’s most recent plan.

The EPA plan approved Monday matches many if not most of a suite of proposals that came from a coalition of interest groups. The coalition included CAP, the Navajo Tribe, the Gila River Indian Community, the Environmental Defense Fund, the Salt River Project, the U.S. Interior Department and Western Resource Advocates, another conservation group. They were seeking to balance pollution controls with the desire to keep the Navajo plant with its jobs as long as possible.

“This alternative not only saves crucial jobs and keeps vital revenue on the Navajo Nation, but opens the door to new, low-emitting energy development pursuant to the agreement,” said Stephen B. Etsitty, executive director of the Navajo Nation EPA.

Vickie Patton, the Defense Fund’s general counsel, said the EPA’s decision provides “the path forward for a more comprehensive solution to achieve cleaner air, climate security and a stronger clean-energy economy.”

But the Sierra Club and the National Parks Conservation Association said they were disappointed at the delays in the cleanup.

“It doesn’t do enough to protect public health and the Grand Canyon and other national parks and wilderness areas,” said Sandy Bahr, director of the Sierra Club’s Grand Canyon Chapter. “They are not requiring that they reduce emissions, like other power plants have to, within a five-year period, treating Arizona and Arizonans to more dirty air.

“It’s not treating the Grand Canyon like the world-renowned national treasure that it is,” Bahr said.

Under the Clean Air Act, power plants such as Navajo typically have five years to install the Best Available Retrofit Technology to reduce pollution for visibility purposes. Navajo got a “special exception” that isn’t fair, said Kevin Dahl, the Parks Conservation Association’s Southwest representative.

However, the EPA’s final rule on the plant, published Monday, said the agency recognizes that the circumstances for the Navajo plant create unusual and significant challenges for a five-year compliance schedule. For a number of reasons, the utilities and the Navajo Tribe running this plant said they might not be able to afford to keep the plant open under such a schedule. The EPA’s rules allow alternatives to the best technology practice if it can be shown that they’ll reduce emissions more.

To the CAP, the EPA’s decision is a welcome climax to five years of negotiations.

“The support that CAP received from our customers and stakeholders played a critical role in this very positive outcome,” said David Modeer, CAP’s general manager. “It’s a good day for all of us who live in Arizona.”

CAP water rates to Tucson and Phoenix users as well as farmers will go up by an unknown amount as a result of this decision, and in fact will rise more than if the earlier EPA plans had been approved and implemented, said Ted Cook, CAP’s assistant general manager for finance.

But if the earlier EPA plans also could have resulted in Navajo shutting down, that could have driven up electricity rates more if the water project had to hunt for power on the open market, CAP spokesman Mitch Basefsky said.

The Associated Press contributed to this story. Contact reporter Tony Davis at tdavis@tucson.com or 806-7746. Follow Davis on Twitter@tonydavis987.