Sixty-eight new post-tension anchors — each 19-inch stranded, low-corrosive steel — will be drilled through the face of the dam into about 100 feet of bedrock. The anchors will be mechanically tightened and sealed. Witt said new technology will allow the anchors to be unsealed and tightened in future years.

The sound of the hydro blaster is roaring as it crawls up the face of Bagnell Dam, signaling the early stages of a $52 million construction project that will ensure a stronger and safer dam for decades to come.

Removing several inches of decades-old concrete is just part of the massive project, which began in earnest last month. A series of 19-inch diameter post-tension anchors will be installed to help hold the gravity dam in place, and 66 million pounds of concrete will be added between the piers just under the Bagnell Dam road.

"These improvements will help hold back the incredible force and pressure of nearly 100 feet of water," Warren Witt, director of hydro operations at Bagnell Dam, explained.

The last major structural update at Bagnell Dam was completed in the late 1980s when 277 post-tension anchors were installed to hold the dam into the bedrock. The anchors were the best technology at the time and have performed very well since they were installed and the dam remains structurally sound, Witt said.

"It's important to note that the dam hasn't moved, it's not falling apart," Witt explained during a recent on-site meeting. "As part of our Federal Energy Regulatory Commission license we're required to conduct regular safety inspections."

In addition to daily, weekly and quarterly inspections by Ameren experts, Bagnell Dam is inspected annually by an independent safety engineer.

When the dam was built in 1929-30, it was believed that a maximum flood level would never top the dam. But after further hydrological study, it was determined the lake could reach as high as 670 feet above sea level — well above full pool of 660. The additional pressure behind the dam could result in catastrophic issues. The analysis in the 1980s indicated it could overflow the dam, but current analysis no longer shows that, according to Witt.

The aging dam and the potential for a major flood led Ameren Missouri officials to move forward with the construction project.

Re-emphasizing the structural integrity of the dam, Witt said officials understood anchors imbedded in the 1980s would not hold forever. Eventually, the anchors will corrode.

"They haven't yet, but they won't hold another 100 years," Witt said.

Sixty-eight new post-tension anchors — each 19-inch stranded, low-corrosive steel — will be drilled through the face of the dam into about 100 feet of bedrock. The anchors will be mechanically tightened and sealed. Witt said new technology will allow the anchors to be unsealed and tightened in future years.

The hydro-blasting equipment is removing up to nine inches of surface concrete that will be replaced with new material. The series of piers along the top of the face of the dam under the roadway will be filled with concrete to give the dam additional strength and weight.

Most of the work on the face of the dam will be done with man-lifts specially rigged for the project. A removable bridge will be built in the spillway area over the river for easy removal in case of high-water conditions.

The hydro-blasting and drilling through the dam into bedrock will remove tons of material. Special troughs and settling ponds are being built to capture the material. A filtering system is also in place to remove material before the final product is sent to the Lake Ozark Sewage Treatment Plant.

The Department of Natural Resources will monitor the project.

"This project is about keeping this vital asset providing clean energy in the long term using the best possible engineering available today," Witt said. "Osage Energy Center just marked its 85th year in service. Work we started in March will ensure it operates reliably and safely, affording the quality of life for hundreds of thousands who enjoy all that the Lake of the Ozarks has to offer each year."

Construction is scheduled for weekdays in consideration of Ameren's customers and Lake residents, Witt said. In addition, there will be no long-term road closures scheduled for the area. The work will not have any effect on the energy generating capacity of the Osage Energy Center.