ST. LOUIS -- Missouri utility regulators will reopen their investigation into the Taum Sauk reservoir collapse after learning that Ameren Corp. readjusted crucial safety gauges at the facility and removed the gauges after the basin collapsed.

Missouri Public Service Commission chairman Jeff Davis said Tuesday he made the decision after learning that Ameren employees had removed the gauges immediately after the reservoir collapsed Dec. 14, 2005. The torrent of water devastated Johnson's Shut-Ins State Park.

"That certainly looks like they were doing something wrong and they were attempting to conceal it," Davis said. "When you know that the dam has collapsed, and there is going to be an investigation, why at that point would you touch anything?"

The Associated Press reported Monday on a Missouri State Highway Patrol report that found that Ameren moved the gauges to keep the profitable Taum Sauk facility running at full capacity, and that Ameren employees removed the gauges before state inspectors arrived at the scene after the collapse.

The PSC, which regulates utilities in Missouri, had conducted an earlier review of the disaster but had not found evidence to warrant penalties, Davis said. But he said commission staff had requested a copy of the patrol's recently released investigation, which details how the gauges were adjusted and removed.

Davis said PSC staff members will review the 2,000-page report. If it is found that Ameren operated the Taum Sauk plant in an unsafe manner, the company could face civil penalties, he said.

'We fully cooperated'

Ameren spokeswoman Susan Gallagher said the company has paid more than $40 million to repair damage from the reservoir collapse.

"We fully cooperated with the state and federal investigations and provided them with all the information we had," she said.

Over the last several days Gallagher has declined to say who moved the alarm probes before the collapse and who removed them the day of the collapse.

Ameren managers acknowledged to patrol investigators that someone moved the probes, and that only a handful of people knew how to adjust them. But no one admitted to knowing who moved the probes, the report said.

Ameren vice president Mark Birk said an Ameren engineer removed the probes the day of the collapse, although Ameren did not know who did it, according to the report.

The probes were set along the top of the mountaintop reservoir, and were designed to shut the plant down and prevent an overflow if water ever reached them.

The PSC investigated the collapse from December 2005 until January 2007, Davis said. The state agency closely followed investigators from the Federal Energy Regulatory Commission as they looked into the breach. FERC oversees the hydroelectric plant and levied $15 million in fines against Ameren -- the largest fine in the agency's history.

A report written by FERC's panel of independent consultants acknowledged that the probes were raised, and said the probes were likely so high the water did not touch them when the reservoir overflowed.

In the report, released in May 2006, FERC said it was unclear why the gauges were raised.

"We received no documents or interview responses indicating why or when the conductivity probes were raised to these elevations," the FERC report said.

The patrol report was far more detailed on the question of the probes and included several interviews indicating they had been readjusted and ultimately removed.

Davis said the FERC investigation didn't turn up any evidence of intentional wrongdoing on Ameren's part. At the time the PSC closed its investigation, Attorney General Jay Nixon also was suing Ameren over the reservoir breach.

"At that time, I didn't think there was that much left to do," Davis said.

Nixon said in late May he would not file criminal charges over the collapse because the highway patrol report did not identify any suspects in the case.

Patrol investigators concluded the 18-month investigation after finding no evidence of criminal wrongdoing, said spokesman Capt. Tim Hull.