ST. LOUIS -- Ameren Corp. and state officials will continue settlement talks over the Taum Sauk reservoir collapse, even as utility regulators launch a new investigation into the disaster.

Three state agencies are close to offering Ameren a unified settlement deal that will outline how the utility can pay for damages associated with the collapse, said Missouri Department of Natural Resources deputy director Kurt Schaefer.

Schaefer said the settlement offer is being developed by the DNR, Attorney General Jay Nixon's office and the Missouri Department of Conservation. Schaefer said he is scheduled to meet with Ameren officials to discuss the settlement in the near future.

Ameren spokesman Tim Fox said the company will continue to participate in settlement talks amid the new probe from the Missouri Public Service Commission. He also said the investigation would not hinder cleanup efforts at Johnson's Shut-Ins State Park, which was devastated by a flood of 1.3 billion gallons of water from the reservoir breach.

PSC chairman Jeff Davis said he plans to use the agency's subpoena power to discover who at Ameren moved critical safety gauges -- called Warrick Probes -- to an unsafe level before the reservoir collapsed.

The probes were set along the top of the reservoir's wall and were designed to shut down automatic pumps that filled the basin if water ever hit the probes. But Ameren moved the probes so high that water never touched them Dec. 14, 2005, when the reservoir overflowed and collapsed, according to a Missouri State Highway Patrol report.

There was pressure to keep the basin as full as possible to generate profitable electricity, according to several e-mails and interviews cited in the report. Adjusting the probes upward meant they wouldn't be tripped off as often by high water levels. Ameren employees told patrol investigators during multiple interviews that someone adjusted the probes before the collapse, but they did not know exactly who did it.

"The question is, who moved the Warrick Probes, and were they directed to do so, or did they do it all on their own -- and that's before the collapse," Davis said. He also wants to know why two Ameren employees removed the probes immediately after the collapse and put them in a bucket.

"We know who put the Warrick Probes in the bucket. The question is why did they do it," Davis said.

Because the probes were removed, investigators might never know how high the probes were set or even if they were operational at the time of the reservoir collapse, said James Alexander, dam safety chief for the DNR.

Davis said the PSC investigation is in the early stages and he has not yet scheduled hearings. He said he intends to call Alexander as a witness.

Ameren Vice President Mark Birk identified Thomas Pierie and Robert Scott as the employees who removed the probes in a letter sent to the patrol that is dated May 23, 2006.

Pierie and Scott were both interviewed by patrol agents as the agency conducted an 18-month investigation into the collapse. Pierie was interviewed twice and Scott was interviewed once.

Pierie told the investigators that he tested the probes the day of the breach, but did not mention taking them down or explain why they were tested before state or federal regulators arrived, according to the report. Scott also did not mention taking them down.

Birk, the Ameren vice president, told a DNR engineer the probes were removed "on the day of the event, in the engineers (sic) excitement," according to the report.