A federal plan that would have required Rocky Mountain Power to install new pollution controls at two coal-fired power plants is now on hold indefinitely.

On Monday, the U.S. 10th Circuit Court of Appeals granted requests for a stay to prevent that order from taking effect prior to a decision in a related lawsuit against the Environmental Protection Agency. The court also put hearings in that case on hold indefinitely after top EPA officials said they want to reconsider the agency’s past decision to push forward with the plan.

But earlier this summer, current EPA administrator Scott Pruitt delivered a letter to Utah Gov. Gary Herbert indicating the EPA intended to reconsider that decision, saying new information had prompted a second look.

While advocates for clean air in Utah criticized Monday’s announcement, a state regulator said he welcomed the court’s decision.

The state had worked closely with the EPA to develop the original compliance plan that federal authorities ultimately rejected, said Dave McNeill, air quality planning manager for the state Department of Environmental Quality. By putting the current lawsuit on hold, he said, Utah regulators and the EPA will be able to work together to develop new models to compare the efficacy of the two plans.

The EPA’s original models suggested that installing the pollution-control systems, using technology known as selective catalytic reduction, would result in only slight visibility improvements at national landmarks such as Arches and Canyonlands national parks.

New computer models, McNeill said, may suggest even smaller improvements than what was originally predicted by the EPA.

But air-quality advocates, many of whom called for the EPA to rejects the state’s approach to regional haze, warned the court’s decision might let Utah off the hook in taking action.

“The ruling will give the EPA the ability to consider alternative options to its original ruling,” HEAL Utah said in a statement. “The most troubling is the state of Utah’s preferred plan, which called for no meaningful changes to the plants’ current operations.”

The National Parks Conservation Association also joined in criticizing the court orders.

“The now-stalled plan required Utah’s Hunter and Huntington coal plants to simply have the same level of pollution control as other coal-fired power plants across the country,” Cory MacNulty, the groups senior program manager, said in a statement. “By allowing two of Utah’s dirtiest power plants to continue polluting Utah’s skies, EPA Administrator Pruitt’s action diminishes the scenic views that draw people to our national parks and puts the health of residents and visitors at risk.”

HEAL Utah and other advocacy groups signaled that they are reviewing legal options in light of the court’s ruling.

The state’s plan did require Rocky Mountain Power to install pollution controls worth hundreds of millions of dollars, McNeill countered. When its plan was originally drafted a decade ago, he said, selective catalytic reduction wasn’t a viable technology, and so it wasn’t considered in Utah’s plan. Other states have since included the new technology as an option for pollution control.

“We did a lot, long before anyone else in the country did,” McNeill said. “When we wrote this thing, we did the most we could, and everyone just ignores that.”