The rebuilding of Taum Sauk Upper Reservoir is a project of many superlatives. The upper bowl of the 440-MW pumped-storage system sits on top of Missouri’s highest peak, 1,590-ft Proffit Mountain. It is believed to be North America’s largest roller-compacted concrete dam. When the original earth-and-rockfill dike was over- topped and failed in December 2005, Missouri Gov. Matt Blunt (R) called the damage done by the 4,365 acre-ft of water it released “the worst man-made disaster in the history of Missouri.” And the $10-million civil penalty imposed on St. Louis-based utility AmerenUE by the Federal Energy Regulatory Commission for the failure was the largest FERC penalty ever in a hydroelectric case.

Today, the reservoir is nearly complete, and preparations are under way to start commercial operation. Roller-compacted concrete (RCC) placement was completed in November, and the new dam was topped out. Engineer-of-record Paul C. Rizzo Associates Inc. will begin a refill-testing program required by FERC in the first week of February and expects to complete it by March 1. “We could start commercial operation April 1,” says Carl M. Rizzo, vice president of construction management services.