Atop a 1,590-ft-high peak, Taum Sauk reservoir replaces a dam that suffered a catastrophic failure in 2005.

Dec. 14, 2005, wasn’t one of Missouri’s best days. A catastrophic breach in the 4,365-acre-ft upper reservoir atop Proffit Mountain, the state’s highest peak, knocked the 440-MW Taum Sauk Pumped Storage project off-line, devastated a popular state park and earned St. Louis utility Ameren UE a $10-million federal fine, the largest ever for a hydroelectric facility.

The utility was determined to rebuild, however, and tapped to lead the charge its engineer-of-record and primary failure investigator, Paul C. Rizzo, president and CEO of Rizzo Associates Inc., Monroeville, Pa. Together with a joint venture of ASI Constructors Inc., Pueblo West, Colo., and St. Louis-based Fred Weber Inc., the team conceived, designed and reconstructed the failed structure with North America’s largest roller-compacted concrete (RCC) dam. The new facility is a 1.26-mile-long, 120-ft-tall marvel of 3.1 million cu yd of RCC and conventional concrete enclosing 40 acres on the leveled mountaintop.

Squeezing in the project’s many components and coping with its daunting logistics wasn’t easy. “Lots of weekends, lots of nights and some very cold field conditions at times for our construction nomads—truly a very engaging and challenging effort,” says Rizzo. He says work proceeded in all directions around the RCC batch plants, with delivery points constantly changing. A site fatality during a nighttime RCC placement in 2009 halted work but did not generate government intervention and pushed the team to re-examine safety procedures, says Rizzo. Craig J. Giesmann, Ameren managing supervisor, extolled the project team as exemplary, with work completed on time in April 2010 and within the $490-million budget. Ever in search of dams to build and structures to test, Rizzo says he is off to Australia and Panama.