SALT LAKE CITY — A federal court ruled that the U.S. Environmental Protection Agency engaged in "reasoned decision-making" in its ozone pollution classifications for multiple areas across the country, including its 2012 designation of Utah's Uintah Basin as unclassifiable.

The challenge to the Utah designation by the Utah Division of Air Quality and the EPA was brought by Utah Physicians for a Healthy Environment, Southern Utah Wilderness Alliance and WildEarth Guardians.

Those environmental groups argued that unusually high levels of ozone recorded by both private and government monitors justified a classification of the oil and gas producing region as "nonattainment," or in violation of the federal health standard for ground-level ozone.

Utah air quality regulators argued that two years' worth of government data was insufficient, and data collected by private companies could not be verified.

In its Tuesday decision, the D.C. Circuit Court of Appeals said the EPA had reasonably interpreted the Clean Air Act's most critical elements and in some circumstances had surpassed its obligation to engage in reasoned decision-making in its classification determinations.

With the Uintah Basin in particular, the court said the EPA appropriately rendered its "unclassifiable" determination based on the available information — backing Utah's assertion that it needed three full years of data to classify the region, not just two years.

Utah regulators praised the decision.

"The ruling is a significant win for Utah,” said Alan Matheson, the environmental adviser to Gov. Gary Herbert who is slated to take over as head of the Utah Department of Environmental Quality.

“We have been working for the past few years with key stakeholders to improve air quality in the Uintah Basin, and this ruling allows that process to move forward," Matheson said. "We feel we are making the right progress toward the right goal. This proactive and collaborative approach is how Utah best solves its air quality challenges.”

Environmental groups slammed the decision.

“(Tuesday's) ruling is unfortunate news for the people living and working in the Uintah Basin who must continue to breathe unhealthy air,” said Robin Cooley, the attorney for Earthjustice who argued the case. “The Environmental Protection Agency knows the air is unhealthy, and we will continue to hold their feet to the fire until they take the steps necessary to protect public health. Given the rampant oil and gas development in the Uinta Basin, there is no time to waste.”

The groups' 2013 lawsuit over the EPA's "unclassifiable" designation in eastern Utah came on the heels of the state's launch of its most extensive air pollution study to date — probing the cause of the anomalous formation of wintertime ozone in the region.

The $5.5 million cooperative effort involves the Bureau of Land Management, National Oceanic and Atmospheric Administration, the oil and gas industry, and universities, with scientists and researchers gathering yearly data on ozone levels and corresponding atmospheric conditions.

Study results, according to the division, have helped state oil and gas regulators upgrade the permitting and compliance process and form new rules to cut pollutants that help create ozone.

The court's ruling on ozone pollution classifications involved a collection of cases that were consolidated as one matter involving multiple petitions for review. In all of the cases, regardless of the EPA's classifications, the challengers argued that the federal agency acted in an arbitrary and capricious manner.

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