No Granite Is Found in Collapsed Piece of Dam

Inspectors were stunned to discover that the collapsed portion of a mountaintop reservoir dam was made of rocky fill instead of the granite that was assumed for decades to be the main material, the state’s chief reservoir inspector said Thursday.

James Alexander, director of the Missouri Department of Natural Resources’ Dam and Reservoir Safety Program, said the broken portion of retaining wall -- 70 to 80 feet high and about two football fields wide -- appeared to consist entirely of soil and smaller rock.

“We were shocked,” he said, to see the “rubble material.”

Alexander inspected the dam after the accident Wednesday that released a billion gallons of water down the side of Proffit Mountain.

The 50-acre upper reservoir of the Taum Sauk Lake Hydroelectric Plant near Lesterville, Mo., breached shortly after 5 a.m. The torrent of water ripped through a state park, then down along the Black River, knocking cars and trucks off a rural highway.

The water tore from its foundation the home of Jerry Toops, park superintendent. Toops, his wife, Lisa, and their three young children survived, but the children were being treated at a St. Louis hospital for hypothermia.

The breach apparently occurred after an automated system malfunctioned and pumped too much water into the reservoir. A backup system also failed, said Gary Rainwater, chairman and chief executive of the utility AmerenUE, based in St. Louis.

Inspectors from AmerenUE and the state were assisting the Federal Energy Regulatory Commission, which oversees the plant, with the investigation.

FERC officials did not return phone calls seeking comment. Asked to respond to Alexander’s comments, AmerenUE issued a statement that read: “We will address this as part of our investigation.”