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The state of Utah and the utility company PacifiCorp are fighting a federal mandate that aims to reduce pollution at national parks.

The two entities filed separate petitions for review — the first step in an appeal — with the 10th Circuit Court of Appeals on Thursday and Friday.

In July, the Environmental Protection Agency adopted a regional haze plan to improve visibility by reducing emissions of nitrogen oxide. The federal plan would require the installation of more pollution controls at two Utah coal-fired power plants in Hunter and Huntington, believed to be contributing to haze in Mesa Verde, Grand Canyon, Black Canyon, Arches, Zion, Bryce Canyon and Capitol Reef national parks.

In adopting the plan, the EPA partially rejected an alternative haze reduction proposal drafted by the state that would have credited emission reductions from the April 2015 closure of PacifiCorp's central Utah Carbon plant.

The state, filing on behalf of the Utah Department of Environmental Quality, and PacifiCorp, parent company of plant owner Rocky Mountain Power, argues their plan complies with EPA regulations for restoring "natural" air conditions in 156 national parks and wilderness areas by 2064. The two entities say the EPA's plan would add more costs with incremental improvements to visibility.

PacifiCorp asks the court to reconsider the EPA's disapproval of the state's alternative to pollution controls. The state and PacifiCorp are not challenging the EPA's set emission limits for particulate matter.

National environmental advocacy groups expressed discontent with the court filings Friday. Amy Hojnowski with the Sierra Club's Beyond Coal campaign said in a statement that PacifiCorp's challenge to the EPA's plan is "out of touch with the needs and values of their customers, who want clean, healthy air in their national parks."

Michael Shea with HEAL Utah said: "We're dismayed that Rocky Mountain Power, instead of stepping up to protect Utah's families and scenic vistas, is choosing to throw ratepayer money at a legal case it can't win. It's time for the utility to invest in reducing dangerous pollution, not to further delay doing the right thing by dragging this into the courts."

A group of clean-air demonstrators delivered about 44,000 petitions to Rocky Mountain Power's Salt Lake City Office in August in an attempt to dissuade the company from fighting the pollution controls.

Twitter: @CourtneyLTanner