Missouri's Mountaintop Reservoir Masterpiece

The rebuild of the $490 million Taum Sauk Upper Reservoir Dam in Ironton, Mo., took more than four years to construct the largest roller-compacted dam in North America.

By Evan Lancaster

It is of utmost importance that all components of America's aquatic infrastructure operate flawlessly in order to assist with trade, agriculture, hydroelectricity and other essential needs. It is also equally crucial to be aware of what can happen when flaws occur.

Located in Ironton, Mo., the Taum Sauk Dam Upper Reservoir, a 440-megawatt-hours (MW) pumped-storage system, pumps water overnight from its lower reservoir component through a 6,000-foot penstock into a vertical shaft that meets the upper reservoir at 1,500 feet. The water then contacts a pair of 220-MW hydro-turbines and is discharged back into the lower reservoir. But in 2005, operational disaster struck.

On Dec. 14, 2005, a 700-foot section of the upper reservoir dike of the Taum Sauk Dam failed, sending more than 1 billion gallons of water down Mt. Proffit, the highest peak in the state at 1,590 feet. Although no injuries were reported, Gov. Matt Blunt called the catastrophe "the worst man-made disaster in the history of Missouri."

The $490 million rebuild was essentially covered by insurance proceeds due to dam failure, according to Craig Giesmann, project manager at Ameren Missouri, the owner of the Taum Sauk Dam and the state's largest provider of electric and gas. The Taum Sauk Upper Reservoir was originally designed in 1963, and after the 2005 breach, it was discovered that several aspects of the dam were not up to current construction standards.

Ameren Missouri, civil engineer Paul C. Rizzo Associates Inc. and Ozark Constructors LLC - a joint partnership of Fred Weber Inc. and ASI Constructors - needed to meet major federal regulation requirements before repairs could begin in 2006.

Rizzo and Associates completed an Environmental Impact Report in order to analyze the damage caused by the breach and discovered that flaws in the original plans could not be repaired. The report cited that sub-quality material, outdated construction practices and human error all contributed to the December 2005 overflow.

By tearing down the remaining walls of the previous dam, the construction team was able to utilize the previous site for many aspects of reconstruction, including leveling the foundation, keeping the original formation as a blueprint and using the underlying rock to rebuild the new walls. Additionally, the existing rockfill was used for crushing aggregates for the new dam.

The Taum Sauk Upper Reservoir Dam is the first pumped-storage project to use roller-compacted concrete (RCC) for a water retaining purpose and is the largest roller-compacted dam in North America, with more than 2 million cubic feet of RCC. The project received the United States Society of Dams (USSD) 2010 "Construction Project of the Year" award. "It was a large scale project, something the entire world was looking at," Giesmann said.

Engineer of record Paul Rizzo, of Paul C. Rizzo Associates, attributed the majority of challenging aspects of this build to the location alone. "There were many challenges with such a large and unique project, but one of the biggest was dealing with the foundation conditions of the site," he said. "Although we anticipated what we found during excavation, preparing the areas to receive RCC was a long, labor-intensive procedure, which required constant monitoring and inspection by our personnel."

Roger L. Gagliano of Ozark Constructors LLC agreed with location and engineering challenges. "What it [the project] involved was working multiple locations and multiple sequencing activities."

In order to accurately ensure the quality of materials used for this project, the engineering firm sought out Fall Line Testing & Inspection LLC, a specialist in on-site RCC testing. Fall Line built a 6,000-square-foot on-site testing laboratory, including a 2,000 square-foot concrete curing facility. The laboratory served as the on-site Mix Design Testing Facility, as well as Fall Line's headquarters for providing testing oversight quality assurance and quality control for the project.

In addition to using recycled materials from the previous site, the use of more than 160,000 tons of fly ash - waste material created by the combustion of coal - from a nearby coal-fired plant was used to further promote aspects of environmental sustainability and strengthen the grade of the RCC.

"Most dams are built in valleys, and the big environmental issues are things like wetlands, aquatic habitat and controlling stormwater to handle peak flood events," Andrew Aceves, environmental coordinator at Paul C. Rizzo Associates Inc., said. "Pumped storage facilities like Taum Sauk, perched on a mountain peak are rare, and therefore, this different environment required a different set of tools and techniques to protect it," he continued.

Recreating this behemoth on a mountaintop did not come without its challenges. In order to operate smoothly, workforce was increased, enabling the building team to take advantage of manpower, daylight and tolerable conditions. Giesmann noted that many of the challenges came from the actual geography of the build. Having to create roads for construction was a challenge that began before construction started. "The largest challenges were initially getting the infrastructure there and getting tools and large-scale construction equipment [in place]," he explained. "We had to rebuild and upgrade a lot of roads that went to the top of the mountain where the plant was located."

The project needed alternate power sources, along with water transports to the top of Mt. Proffit. "We had to build five electrical substations in only a few months so we could power all of the crushing and concrete plants," Giesmann added. Many factors, ranging from natural to mechanical, weighed heavily on the schedule and created less than perfect conditions for crews to operate successfully.

Gagliano added that it's impossible to foresee the unexpected when dealing with frigid winters and hot summers, and the engineering team agreed with weather challenges. "Trying to place RCC year-round was a continuous challenge. During the winter months we had to keep the placement lifts clean and at an acceptable temperature," Charlie Weatherford, assistant resident engineer at Paul C. Rizzo Associates Inc., said. "Likewise, during the summer months we struggled to place RCC during daylight hours due to high temperatures, even though we took steps to cool the RCC mix."

Being able to plan ahead was by far the most important aspect when completing a build of this magnitude. Gagliano offered advice to others working on similar projects by saying, "Planning is the most important element here; use your best efforts in terms of planning, and try to use different approaches when difficulties arise."

The entire project took more than four years, working in twice-a-day shifts from eight to 10 hours at a time. This project created hundreds of jobs locally, and according to a study by Southeast Missouri State University, it increased state income by $48 million. During the final months of completion in 2008, the construction team celebrated the first 1 million work hours without a lost time incident.

Today, the project covers 54.5 acres and stands more than 6,000 feet long, 120 feet tall and 150 feet wide. Completion of the Taum Sauk Upper Reservoir rebuild was marked in Feburary 2010 when the first water was pumped into the new dam via the lower reservoir on Feb. 27, 2010, which met the requirements of the FERC-approved Upper Reservoir Refill Program.

Evan Lancaster is an editorial assistant at American Infrastructure. He may be contacted at elancaster@penpubinc.com.