Rosemont Copper’s development plans in Arizona hit a roadblock last week after a Maricopa superior court judge overturned a state-issued permit for air quality, according to the Tucson Sentinel. Judge Crane McClennen sided with environmental activists, Save the Scenic Santa Ritas, ruling that the Arizona Department of Environmental Quality (ADEQ) issuing an air permit for the $1.5 billion open-pit copper mine was arbitrary and capricious.

In the lawsuit, the environmental activists argued that Rosemont had manipulated data to convince ADEQ that pollution from the mine would not affect local air quality. ADEQ disagreed. “We were surprised and very disappointed by the ruling,” ADEQ said in a prepared statement. “We continue to stand behind our firm belief that the air quality permit we issued is protective of public health and the environment.”

“The administrative law judge who made the recommendation that ADEQ Director Henry Darwin accepted was thorough in his review and analysis of the facts and the law. We do not believe that the Superior Court ruling was based on all of the evidence presented and we expect to file a notice of appeal as soon as possible,” ADEQ said. The agency said it would appeal the decision, however, the mine also faces several other challenges, according to the Tucson Sentinel. Earlier in March, the Pima County Supervisors voted to appeal the state’s conclusion that the mine would not affect the local watershed.

In July 2014, Hudbay Minerals acquired Augusta Resource Corp. and the Rosemont project, which hosts a large copper/molybdenum reserve that could account for about 10% of U.S. copper output if it were brought into full production.