Key Points:

• A judge ruled the Arizona Corporation Commission lacked authority to reverse a decision from the Power Plant and Transmission Line Siting Committee

• The decision revolved around a plan from UniSource Energy to expand natural gas plant Black Mountain Generating Station 

• Judge Dewain Fox ruled in favor of Attorney General Kris Mayes and advocacy groups

The Arizona Corporation Commission lacked authority when it reversed a decision of the Power Plant and Transmission Line Siting Committee last year, a Maricopa County Superior Court judge ruled. 

In June 2024, the ACC voted to reverse an order from the Line Siting Committee that deemed that a UniSource Energy power plant expansion project was a new plant in need of a certificate of environmental compatibility. The ACC argued that UNSE’s project was exempt from obtaining the necessary certificate because it was an expansion of an existing plant, not a new plant meeting the megawatt threshold for review.

Attorney General Kris Mayes, the Sierra Club and Western Resources Advocates filed suit in September 2024, arguing that the ACC misinterpreted a statute outlining which power plant projects require environmental review. On Oct. 21, Maricopa County Superior Court Judge Dewain Fox ruled in favor of Mayes and the advocacy groups — but not because the ACC misinterpreted statutes.

In his decision, Fox wrote: “What did Arizona’s Legislature mean in 1971 when it defined the word “plant” in (statute)? That is the ultimate issue before the court in these consolidated appeals. But before the Court can answer that question, the Court must decide whether the Commission even had the authority to review the Committee’s decision.”

Fox said the ACC did not have authority to review the Line Siting Committee decision because the commission’s own rules only allow it to review written decisions where the committee issues or denies a certificate of environmental compatibility. The committee is charged with evaluating applications to build power plants and transmission projects throughout the state.

While Fox sided with the plaintiffs in the case, he chose not to weigh in on the original question regarding the definition of “plant” as used in state statute. 

Mayes’ office celebrated the ruling in a statement provided by her spokesman, Richie Taylor.

“Judge Fox’s decision affirms what Attorney General Mayes has said all along: that the Corporation Commission is not above the law, and it cannot make up the rules as it goes,” Taylor said. “Now, Unisource Energy will need to get a siting certificate to build its new power plant — just as the Legislature required.”

The case stems from UNSE’s planned expansion of its Black Mountain Generating Station near Kingman. The project will add four natural gas generating units, each with a rating of 50 megawatts, to the existing generating station.

State law requires power plants with a megawatt rating of 100 or more to obtain a certificate of environmental compatibility from the Line Siting Committee. UNSE asked the Line Siting Committee to approve a disclaimer of jurisdiction in April 2024, arguing that the 50 megawatt rating of the new generating units did not qualify as a plant under the statute’s definition.

The Line Siting Committee denied the disclaimer of jurisdiction, but did not issue or deny UNSE the appropriate certificate. Before the committee could decide on a certificate of environmental compatibility, UNSE asked the ACC to review the committee’s decision. Commissioners ultimately sided with UNSE.

Fox’s ruling determined that the ACC does not have the authority to review decisions from the Line Siting Committee on disclaimers of jurisdiction. Under the ACC’s own rules, it can only review a Line Siting Committee decision related to the issuance or denial of a certificate of environmental compatibility, Fox wrote.

“Neither UNSE nor the Commission cites any other authority empowering the Commission to review the Committee Order,” Fox wrote. “And the Court’s independent research did not reveal any such authority. Because the regulations promulgated by the Commission do not provide for the Commission to review an order by the Committee denying a request to disclaim jurisdiction.”

Fox deliberately left the question over the definition of “plant” open, saying the commission’s review of the Line Siting Committee decision was premature. He ordered the committee to consider UNSE’s request for an issuance of a certificate of environmental compatibility and said the issues surrounding the definition of “plant” in statute could be addressed after that decision is made. 

Emily Doerfler, an attorney for Western Resource Advocates, applauded Fox’s ruling and encouraged the ACC to defer to the Line Siting Committee in the future.

“The Line Siting Committee has decades of expertise in carefully reviewing applications like the Black Mountain expansion,” said Doerfler. “Moving forward, the Commission should rely on that expertise for similar applications.”

A spokesperson for the ACC did not immediately respond to a request for comment.