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Ameren UE shows off its re-tooled Taum Sauk reservoir

This article first appeared in the St. Louis Beacon, June 30, 2009 - About two-and-a-half hours south of St. Louis, Ameren is turning one of its most public disasters into an engineering showcase. The upper reservoir at the Taum Sauk hydroelectricity plant is being rebuilt -- and is setting new standards for reservoir safety, according to the utility.

A kidney bean-shaped, 55-acre pool replaces an earthen reservoir that experienced a 700-foot breach in December 2005. More than a billion gallons of water gushed down the northwestern side of Proffit Mountain, destroying a house, closing a county highway and flooding and damaging 281 acres of Johnson's Shut-Ins State Park.

Major improvements have been made to the design and construction of the new upper reservoir. The new reservoir is made of a combination of roller-compacted concrete and conventional concrete. The compacted concrete is less prone to cracking. When completed, more than 2.8 million cubic yards of concrete will have been used -- or about 3,000 miles of sidewalk.

The old reservoir was made of uncompacted rock and topped with a 10-foot concrete wall. For the foundation of the new reservoir, contractors dug almost 60 feet in search of stronger rock.

Besides these efforts to make the reservoir safer, the utility has also incorporated an overflow release structure in case of another breech. Should the reservoir overflow, six-foot high steps will slow water and channel it into an uninhabited portion of Ameren's land. Also, more redundant systems, including water-level sensors and video monitoring, watch for possible leaks or cracks.

"Some of the things that we're doing to comply with the FERC (Federal Energy Regulatory Commission) regulations and really make this state-of-the-art in terms of safety and instrumentation is our industry-setting water-level detection systems," said Mark Birk, vice president of Ameren's power operations. The systems have not been installed yet, but the designs are completed.

The reservoir is expected to be completed in May 2010, with an expected price tag of $480 million. More than 650 workers cover two shifts a day, six days a week to complete the project. Shiftwork is scheduled around the weather; hot, dry days can affect how the concrete cures. An evening shift often pours concrete, while an afternoon shift works on other projects.

The Taum Sauk plant holds a special place in Ameren's electricity production system. The plant can start in about 10 minutes -- a much shorter time than the 6-8 hours needed to fire up Ameren's coal plants, said Birk. It is also the most efficient way to store bulk electricity. Electricity made from the turbines is then placed in the grid. Taum Sauk can generate 440 megawatts -- about a third of the energy generated by the Callaway nuclear plant.

Demolition of the old reservoir and construction of the new plant began in December 2007.

Taum Sauk hydroelectricity plant originally opened in 1963. Electricity is generated pumping water through turbines between the two reservoirs. During hours of peak electricity usage, water will flow down to the lower reservoir.

Sarah Scully, an intern at the Beacon, is a student at the University of Missouri, Columbia.