Inspector "shocked" to find fill in reservoir wall

ST. LOUIS (AP) -- Missouri inspectors were "shocked" to discover that the portion of a collapsed reservoir was made from rocky "fill" instead of the granite that was assumed for decades to be the main material, the state's chief dam and reservoir inspector said Thursday.

"I just thought it was a hollowed out bowl, and you had granite around the thing -- but that's not the case with the side that failed," said James Alexander, director of the Missouri Department of Natural Resources' Dam and Reservoir Safety Program.

In fact, Alexander said the entire northwest section of the reservoir that collapsed -- 70 to 80 feet high and about two football fields wide -- appeared to consist strictly of soil and smaller rock. He inspected the site after the accident on Wednesday.

"We were shocked," Alexander said. "You look at it and it looks like a rocky, soil-type rubble material that composed that one side."

The upper reservoir of AmerenUE's Taum Sauk hydroelectric plant breached shortly after 5 a.m. Wednesday, sending a torrent of 1 billion gallons of water rushing down the side of Proffit Mountain.

The water ripped through nearby Johnson's Shut-Ins State Park, then down along the Black River, knocking cars and trucks off a rural highway.

The rush of water caused significant damage to the popular state park, tearing from its foundation the home of park superintendent Jerry Toops, his wife, Lisa, and their three young children.

All five survived, but the children were being treated at Cardinal Glennon Children's Hospital in St. Louis. Hospital spokesman Bob Davidson said 5-year-old Tanner was in critical condition. His 3-year-old sister Tara and 7-month-old brother Tucker were upgraded to serious condition.

The breach apparently occurred after an automated malfunction pumped too much water into the reservoir. A backup system that should have caught the problem also apparently failed, AmerenUE chairman and chief executive Gary Rainwater said.

Inspectors from the St. Louis-based utility 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."

If a big portion of the retaining wall was mostly soil and smaller rock, it was likely doomed once too much water was pumped into the reservoir, said Charles Morris, an environmental engineering professor at the University of Missouri-Rolla. Like earthen levees that crumbled during the Great Flood of 1993, soil-based retention walls will erode when overtopped, he said.

Over the years, leaking has occurred at the reservoir, which was completed in 1963. AmerenUE installed a plastic liner about a year ago to limit the leaking.

While inspectors might not have been able to predict the collapse, inspectors would not have been as dismissive of the leaking if they knew a portion of the wall was made of fill, not granite, Alexander said.

"If I would have known that, yeah, that would be more of a concern," he said.

Information provided by AmerenUE said six million tons of granite was removed to level the top of the 1,590-foot-tall Proffit Mountain, and workers used the removed stone to build a sloping retaining wall 90 feet tall and covering an area the equivalent of 30 football fields.

The company said that in addition to granite, the reservoir was lined with concrete and asphalt.

Gov. Matt Blunt said AmerenUE would be held responsible for flood damage if an investigation finds the company liable. The company said it would respond to the needs of the flooded portion of Reynolds County, a county of just 6,700 residents in the Ozark Mountain foothills.

AmerenUE said the plant is inspected twice a year -- once by company inspectors, once by the FERC. Every five years, a private company is also brought in for an inspection.

FERC officials said Wednesday that the reservoir was inspected most recently in August and found to be properly operated and maintained.