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Report finds shoddy work partly to blame for reservoir collapse
The Taum Sauk reservoir wasn't built out of bedrock stone as it was supposed to be.
ST. LOUIS -- Shoddy construction and instrumentation problems were partly to blame for the December collapse of Ameren Corp.'s Taum Sauk reservoir, according to a company-commissioned report released Friday.
The report was written by dam safety consultant Paul C. Rizzo, hired by the St. Louis-based utility to investigate the cause of the reservoir collapse. The reservoir, part of Ameren's mountaintop Taum Sauk hydroelectric plant, breached Dec. 14, unleashing 1 billion gallons of water that swept through Johnson's Shut-Ins State Park, injuring a family of five.
The Federal Energy Regulatory Commission and the Missouri attorney general's office continue to investigate.
Rizzo's report said the earthen reservoir that opened in 1963 was built out of soft soil and rock "fill" material instead of bedrock stone as it was supposed to be. It said the company used "substandard" construction methods for that era.
The report has been submitted to the FERC, which regulated the reservoir. The agency will release its own report on the accident early this summer, Ameren said.
Rizzo's report also cited instrumentation problems at Taum Sauk, in a rural area about 120 miles southwest of St. Louis. The earthen wall gave way quickly because it consisted of so much soil, which had already absorbed a lot of water from leakage. The soft earth collapsed within minutes of the overflowing, the report said.
Inspectors were shocked
Rocky fill material in the reservoir walls was discovered immediately after the collapse by Missouri Department of Natural Resources inspectors who visited the reservoir site, said James Alexander, director of the DNR's Dam and Reservoir Safety Program.
Alexander said the broken portion of retaining wall -- 70 feet to 80 feet high and about two football fields wide -- appeared to consist entirely of soil and smaller rock. He said inspectors were shocked by the fill material, having assumed for decades the wall was made of bedrock.
Although FERC personnel inspected the reservoir regularly, they couldn't tell the dike was shoddily constructed because the fill material was hidden from view, Rizzo's report said.
Gary Rainwater, Ameren's president and chief executive officer, said the company has already begun a review of safety procedures companywide in the wake of the Taum Sauk collapse.
"Guided further by the Rizzo report, that review will continue, and all necessary corrective measures will be taken," Rainwater said.
Ameren has created a dam safety program that includes development of an updated dam inspection plan and site-specific safety and instrumentation training.
The company said it will also:
* Establish a quality assurance team to review all procedures.
* Re-examine safety procedures at all facilities.
* Evaluate how the company trains employees in safety and operations to ensure they understand warning signs of plant failure.
"The Taum Sauk breach has caused a great deal of soul-searching at our company, particularly because our investigation shows that everyone involved in this incident was well-intentioned," said Thomas R. Voss, executive vice president and chief operating officer.
"At every step of the way our employees took actions they believed were sufficient to protect the facility's safety. In hindsight, those steps clearly proved inadequate. It is incumbent upon us to do everything in our power to guard against something like this ever happening again."