A decision by the state’s highest court not to take a case on appeal means Georgia Power’s rate payers will continue to foot the bill for some of the cost of storing the company’s coal ash around the state, under the terms of a plan approved by state utility regulators.

A case brought by the Sierra Club had argued that Georgia Power has mishandled its coal ash and that costs it incurred to permanently store the material were imprudent and therefore should not be recoverable. The environmental organization had asked the state’s highest court to review an appeals court ruling affirming the Public Service Commission’s (PSC) approval of a 2019 plan that allowed Georgia Power to bake costs associated with closing its coal ash ponds into the rates customers pay.

But after a Fulton County Superior Court judge and the Georgia Court of Appeals had previously rejected the Sierra Club’s legal challenge, the state Supreme Court said it would not hear the case. The decision means rates approved by the Public Service Commission will remain in place.

Georgia Power spokesman Jacob Hawkins said the company agrees with the Georgia Supreme Court’s decision.

“As we have consistently stated, the issue of cost recovery was thoroughly discussed and evaluated through Georgia’s open and transparent regulatory process with the Georgia Public Service Commission, with the PSC’s decision affirmed by the Superior Court of Fulton County and by the Georgia Court of Appeals,” Hawkins said in an emailed statement.

Charline Whyte, a senior campaign representative for the Sierra Club’s Beyond Coal Campaign, called the court’s refusal to take up the case disappointing.

“It’s incredibly unfair to ask customers to pay for a mess that Georgia Power could have prevented in the first place,” Whyte said.

Coal ash is a fine, dust-like residue left behind from burning coal to generate electricity. It contains dangerous heavy metals like arsenic, cadmium, and mercury, which can foul the air and pollute water supplies if not handled properly.

Georgia Power is still seeking permits from state regulators to permanently store coal ash at many of its 29 ponds across the state. At some sites, the company is already excavating ash, transporting it to lined landfills, and partnering with companies to reuse the material in concrete.

But for its plants near Smyrna, Rome, Newnan, Carrollton and Juliette, Georgia Power has asked state regulators to approve plans to leave most of the residue in unlined pits. In some cases, the material would be left sitting in groundwater. Environmental groups have been fighting those plans for years, which they say pose a risk to human health and the environment.

“Despite getting a blank check from the PSC, Georgia Power still wants to cut corners by unsafely storing coal ash in unlined pits that are directly in contact with the groundwater below,” Whyte said.

Hawkins said the company’s ash ponds “are, and have always been, in compliance with federal and state rules and regulations.”

Georgia Power’s estimate of how much it will cost to close all of its ash ponds has grown from $7.6 billion in 2019 to nearly $9 billion, according to plans filed with the PSC earlier this year.

The PSC is expected to make a final decision next week about which parts of the company’s proposed plans to generate and deliver electricity to Georgians for the next 20 years to approve.

From there, the PSC will be tasked with deciding how much Georgia Power should be allowed to charge customers for their electricity and associated costs, like coal ash clean-up, over the next three years — as well as how much the company can profit. In a plan filed last month, Georgia Power signaled it will ask state regulators to approve a rate hike of nearly 12% over the next three years for its 2.7 million customers.

Those new rates will be the subject of hearings starting in September, culminating with the commission’s decision to approve or adjust them in late December.