A deficiency in the concrete wall construction of the basin at the Gatlinburg Wastewater Treatment Plant led to the basin wall collapsing, killing two employees in April, a report from the state issued Thursday says.
“Walls were cast in a manner that produced a cold joint between the cast wall which fell” and three interior intersecting walls, according to the report from the Tennessee Occupational Safety and Health Administration (TOSHA).
TOSHA announced in early October that it found no safety violations at the plant, and this week released a five-page report that was the basis for that finding. When TOSHA announced in early October there were no safety violations, it didn’t give a probable cause of the basin wall collapse.
The new report does. What its inspectors call a “cold smooth joint” led to leakage of acidic waste across the joint, and “as a result, corroded the rebar splice couplers over a number of years.”
The couplers were not believed to have failed at one time, but gradually over the life of the basin, the report said.
When the findings of no safety violations were announced earlier this month, Veolia spokeswoman Karole Colangelo said, “Although the findings from TOSHA reinforce our emphasis on employee safety, it does not dismiss the fact that two Veolia Water employees perished in this tragic accident, and company employees continue to mourn their deaths.”
“It was assumed the two operators were making adjustments to the effluent flow inside the equalization basin,” the report says. While the men were working, the wall collapsed and fell on the building in which they were working.
The collapse sent about 850,000 gallons of untreated wastewater into the Little Pigeon River and forced the city to pump more untreated water into the river until it could come up with a temporary solution a few days later.
According to the workers’ last journal entry at 5:30 a.m. that day, the basin contained 1.3 million gallons of water and was 85 percent full. The water level was recorded at 25.5 feet. The report says interviews with operators and plant officials show the average water level was 4-8 feet.
The plant is owned by the city but managed by Veolia Water North America Operating Services LLC. Veolia officials told the state inspectors that both Crowder Construction Co., that built the plant and Flynt Engineering Co., that designed it are out of business. The basin was finished in 1996.
TOSHA learned that after the basin was finished in 1996 the north wall had cracks and a lateral displacement/bowing of the wall and walkway. Veolia told the state that buttresses were installed that “corrected” the problems with the wall and walkway.
TOSHA noted that the flow control building where the workers were is still not accessible, but the state says “we have no probable reason to think that access to this area would reveal any additional information that would result in citation being issued to Veolia.”
The report says the contractor used “splicing couplers” instead of dowels, as required in the original drawings, noting that while that was a “deviation” from the design, it was probably not the cause of the collapse. The report did say that “formation of a cold joint resulted in accelerated corrosion of the couplers.”
TOSHA reviewed the original design of the basin and found the design of walls “adequate.”