According to the Associated Press, Harrison County chancery judge Jim Parsons made the ruling late Monday.

Sierra Club state director Louie Miller said it would appeal the decision.

The Mississippi Supreme Court overturned the plant's previous certificate, siding with the Sierra Club saying the Mississippi Public Service Commission had not provided sufficient explanation for upping the plant’s costs from $2.4 billion to $2.88 billion.

The PSC went on to grant a certificate to planned project owner Mississippi Power but the environmentalists challenged that as well.

“Mississippi Power customers are the ones who will benefit from this important decision," Mississippi Power president and chief executive officer Ed Day told the AP.

Miller argued the PSC made the wrong decision for a second time.

“The Kemper plant was a bad deal when it was first proposed but in the last few months we've seen huge cost overruns and delays, which will make this project even more unaffordable for coastal Mississippi Power customers," he said.

Parsons said that under state regulations he was required to uphold the PSC decision unless it was “not supported by the substantial evidence, is contrary to the manifest weight of the evidence, in excess of the statutory authority or jurisdiction of the commission, or violates constitutional rights”

Late last month, the Sierra Club lodged claims against Mississippi Power that costs for Kemper, which is being designed to use integrated gasification combined-cycle technology, were “spiraling out of control” and that the project was behind schedule and over budget.

Sierra Club officials pointed to an Institute for Energy Economics and Financial Analysis report showing Mississippi Power’s Kemper County coal plant was in “far worse shape” than the company was letting on in its public updates.

“The analysis reveals the plant, with its untested gasification technology, is behind schedule in both engineering and construction and at less than 50% complete, is likely to see further delays and cost overruns,” the group said at the time.

Mississippi Power spokesman Jeff Shepherd told regional newspaper the Sun Herald in November that the comments were “part of an ongoing campaign by this special interest group and its out-of-state energy industry opponents” to block the plant’s construction.

He said the Sierra Club’s lawsuit against the planned facility was at the center of increased costs for the plant to the tune of more than $300 million.

“The ratepayers of Mississippi will have the Sierra Club to thank for unnecessary increases that affect customers' bills,” Shepherd said.

Shepherd said the environmentalists were misleading the public by estimating the plant’s costs at $2.62 billion.

He told the newspaper that Mississippi Power would complete and operate the plant while maintaining affordable costs for customers.

“The project is more than 70% complete and on schedule," he said.