LITTLE ROCK — Environmentalist groups that have been fighting for years to halt construction of a coal-fired power plant in southwestern Arkansas said Thursday they have agreed to drop their legal challenges as part of a settlement with the company building the plant.

LITTLE ROCK — Environmentalist groups that have been fighting for years to halt construction of a coal-fired power plant in southwestern Arkansas said Thursday they have agreed to drop their legal challenges as part of a settlement with the company building the plant.

The Sierra Club, Audubon Arkansas and the National Audubon Society agreed to end legal actions in both federal and state court against the John W. Turk Jr. Power plant, which has been under construction in Hempstead County since 2008.

Under the settlement approved Thursday by U.S. District Judge Richard Kopf, Southwestern Electric Power Co., a subsidiary of American Electric Power, agreed to retire a 528-megawatt coal plant near Pittsburg, Texas, by the end of 2014 if possible and by the end of 2016 at the latest, among other concessions.

Once the Turk plant is in operation, the Texas plant will operate at no more than 60 percent of its annual capacity until it is retired.

Glen Hooks, senior representative of the Sierra Club’s Beyond Coal Campaign, said the Sierra Club would have liked to stop the Turk plant from being built, but at this stage “we realized that, strategically, probably the best thing for Arkansas was to get a good settlement.”

The Texas plant is roughly the same size as the Turk plant but lacks the Turk plant’s modern pollution-control technology, and its emissions blow into Arkansas, Hooks said. He called the settlement “a net win for Arkansas.”

“One of the main things that I wanted to do when settlement talks started is get enough concessions to offset the pollution that will be admitted by Turk. We’ve done that,” he said.

Ellen Fennell, executive director of Arkansas Audubon, said the $2 billion, 600-megawatt plant is 80 percent complete, and the opponents wanted to gain some concessions before the lawsuits “ran into a wall.”

She said SWEPCO already planned to close the Texas plant in 2014, but including a timeline for closure in a court-approved settlement agreement means the company will have to carry out the plan.

“We’re not jumping up and down that (the Turk plant) is coming online because, you know, it’s a coal-fired power plant, but we have reduced emissions” between the two plants, she said.

SWEPCO President and CEO Venita McCellon-Allen said Thursday in a news release, “We are proud to be building the Turk plant not only for the service it will provide our customers and the boost it is already giving to the Arkansas economy, but also because it demonstrates our commitment and ability to meet stringent environmental standards set by federal and state regulatory agencies.”

In addition to retiring the Texas plant, SWEPCO agreed not to build more than one generating unit at the Turk plant; not to build any new coal-fueled generating units in Arkansas within 30 miles of the site; to construct or secure 400 megawatts of renewable energy resources; to burn only coal from the Powder River Basin in Wyoming or coal with similar characteristics at the plant; and not to build new transmission lines for the plant in certain environmentally sensitive areas.

SWEPCO also agreed to monitor total annual emissions, wastewater discharge and groundwater quality in the area; to donate $8 million to The Nature Conservancy for land conservation in Arkansas; to donate $2 million to the Arkansas Community Foundation to fund grants for projects promoting clean energy and energy efficiency; and to reimburse the Sierra Club and Audubon for up to $2 million in attorney’s fees and costs.

The Hempstead County Hunting Club and other area landowners previously opposed the plant but dropped their opposition after reaching a settlement with SWEPCO in July.

Shreveport, La.-based SWEPCO serves 520,400 customers in Arkansas, Louisiana and Texas. Columbus, Ohio-based AEP provides electricity to more than 5 million customers in 11 states.