The Federal Energy Regulatory Commission has named an independent panel of consultants to assist FERC dam safety engineers in a forensic engineering examination of the factors that contributed to the failure of the Taum Sauk Reservoir near Lesterville, Mo. The upper reservoir of the 450-MW pumped-storage hydroelectric project, owned by St. Louis-based AmerenUE, collapsed before dawn Dec. 14, spilling more than 1 billion gals of water down the side of Proffit Mountain, knocking one house off its foundation and injuring three children among its five occupants.

The members of the panel are Alfred J. Hendron Jr., Savoy, Ill., a self-employed consulting geotechnical engineer; Joseph L. Ehasz, Washington Group International, a geotechnical engineer, and Kermit Pul Jr., a mechanical/electrical engineer. When the reservoir wall collapsed, FERC dispatched five of its own engineers to investigate. Four remain a week later, and the three independent engineers will investigate next week, say FERC officials.

�Clearly there had been overtopping of the 10-ft parapet wall� around the reservoir, but engineers have determined that the 380-acre lower reservoir is �safe and secure,� says J. Mark Robinson, director of FERC�s office of energy projects. The mountaintop reservoir is only a receptacle for water pumped from the lower reservoir, with no spillway and not designed for water flow. Its wall is a rockfill structure with a concrete face, he says. Early press reports quoted speculation by James Alexander, director of the Missouri Dept. of Natural Resources, that photographs of the scene appear to show that the wall is composed of rocky fill instead of the granite blocks quarried to form the reservoir when it was built in 1963. But Robinson refuses to speculate, preferring to base his comments on facts, he says.

FERC inspects Taum Sauk once a year because it�s rated a high-hazard-potential dam, says Robinson. The high-hazard rating refers to the potential for downstream damage in the event of a failure, not to the risk of failure. The reservoir�s last inspection was in August. �The inspection goes to the areas we think likely of failure,� he says. The annual inspections have not turned up any major flaws. �All dams leak some,� Robinson says, adding, �This dam had been leaking for some time.� AmerenUE installed a geomembrane in 2004, which succeeded in stemming the leaks, he says. �The inspection indicated the dam was being maintained properly and being operated in accordance with the permit,� he says.