The Arizona Corporation Commission is scheduled to vote on a request to exempt a 200-megawatt power plant expansion in Mohave County from environmental review, a move critics say would ignore decades of precedent and undermine the commission’s ability to regulate new power plants in the future.

The vote comes over a month after the commission’s Power Plant and Transmission Line Siting Committee voted to deny the request from UniSource Energy, the Mohave County plant’s owner. 

Arizona law requires utilities to apply for a certificate of environmental compatibility before constructing power plants larger than 100 megawatts to assess the effect it will have on the surrounding community. 

But UniSource Energy argued it should be able to skip that step, because its Mohave County expansion will be made up of four, individual 50-megawatt units.

UniSource attorney Meghan Grabel cited the specific language of the law,  which defines a power plant as a “separate thermal electric, nuclear or hydroelectric generating unit with a nameplate rating of 100 megawatts or more.”

“There is no dispute that the nameplate rating for each of the new generators to be added to the Black Mountain Generation Station will be under 100 megawatts,” she said.

Critics argued that interpretation ignored the intent of the law, first passed by the Arizona Legislature in 1971, because all four of the 50-megawatt units will be located on the same site.

“The Commission routinely treats generating facilities with multiple units as single power plants, not separate plants,” Patrick Woolsey, an attorney with the Sierra Club, told the Arizona Power Plant and Transmission Line Siting Committee in April. 

He said that since the law was passed, “utilities have repeatedly applied for [certificates of environmental compatibility] power plants or plant expansions with total capacities over 100 megawatts, even where the capacity of individual generating turbines was under 100 megawatts, and the Commission has issued [certificates of environmental compatibility] for such plants.” 

The committee agreed, rejecting UniSource’s request on a 9-2 vote. 

“The Applicant’s interpretation … would circumvent the manifest purpose of the line siting statutes and deprive the people of Arizona who are affected by the construction of these major facilities of their ability to participate in the process to mitigate the adverse impacts on the environment and their quality of life,” according to an order authored by Committee Chair Adam Stafford.

UniSource appealed the committee’s decision, prompting the Corporation Commission to schedule a hearing to consider the request on June 11. 

→ Get more Arizona politics news