Kentucky regulators have affirmed a utility’s plan to build massive landfills near two power plants, saying that option will have the smallest effect on ratepayers.

In 2009, Louisville Gas and Electric and Kentucky Utilities got approval from the Kentucky Public Service Commission to build coal ash landfills at the company’s Ghent and Trimble County power plants. But the costs for both landfills skyrocketed, and a local quarry owner made a case that using his underground limestone mines to store the coal ash would be more cost-efficient for ratepayers.

In the order released Tuesday, the Public Service Commission ruled that even with the increased costs for the landfills, they’re still the least-expensive option. The quarry owner — Sterling Ventures — was proposing a plan that would involve sending the coal ash by barge and truck to its mine near Warsaw, Ky. The ash will have to be disposed of in compliance with new federal regulations, and Sterling argued placing the waste in a mine would have been considered “beneficial reuse” under the rule.

The Public Service commissioners weren’t convinced the plan would have been approved as “beneficial reuse” under the law, and said the plan wouldn’t have saved money. They also said transporting the waste via barge and truck would have been riskier than storing the waste in a landfill near the plant.

“We’re very pleased to get the ruling, and this will allow us to continue and move forward with these projects,” said LG&E/KU spokeswoman Chris Whelan.

The first phase of the Ghent project was supposed to cost $204 million; the final cost was $341 million. The first phase of Trimble’s landfill was estimated at $94 million, and the new estimate is $322 million — a nearly 350 percent increase.

Whelan said delays in the Trimble County project, as as well regulations and changing the landfill’s footprint, have contributed to the cost increase.

“Now that we have completed Ghent, we were able to implement some lessons learned. So we know where the cost variances are,” Whelan said. “All of those things have led to a better estimate than when we actually filed for [the Trimble landfill], but it did indicate we’re going to have some cost increases.”

LG&E/KU was seeking a PSC ruling that the commission’s earlier approval of the landfills applied to both projects as a whole, including planned expansions. But citing the enormous differences between the initial estimates and final costs of the first phase of both projects, the PSC told the company it would have to obtain approval for all the proposed expansions (two more at Ghent and three more at Trimble) individually.

Whelan said the company still needs three permits before beginning construction on the Trimble County landfill — from the Kentucky Division of Water, the Kentucky Division of Waste Management and the U.S. Army Corps of Engineers.

A call to Sterling Ventures for comment wasn’t returned Tuesday afternoon.