Collapsed Wall at Tenn. Treatment Plant Was Defective, OSHA Says
The April wall collapse at a Gatlinburg, Tenn., wastewater treatment plant that killed two workers was caused by deficient construction that allowed gradual corrosion of the rebar inside it, a state safety report said.
The report, written by Mahammad Ayub, director of the federal Occupational Safety and Health Administration office of engineering, and Mary Misciagna, Tennessee Occupational Safety and Health safety supervisor, did not find workplace safety violations, so the state is not issuing citations against the city of Gatlinburg, the plant owner or its operator, Veolia Water North America.
John D. Eslinger, 53, a lead operator, and Donald A. Storey, 44, an operator, were killed on April 5 (ENR 4/13 p. 25) when a 115-ft-long wall section of the equalization basin separated and collapsed onto the flow control building where they were working.
“The cause of the failure was a deficiency in the concrete wall construction,” Ayub wrote in a summary report released on Oct. 27. “Walls were cast in a manner that produced a cold joint between the east wall, which fell, and the three orthogonal interior intersecting walls. The intersecting walls were critical to the structural integrity of the east wall.”
Over the years, that cold joint made possible acidic wastewater leakage that corroded the rebar splice couplers, according to Ayub.
Neither the contractor, Crowder Construction Co., Bristol, Tenn., nor the engineer, Flynt Engineering Co., Knoxville, is in business now, he said.
The equalization basin was built in 1994-96, and the blueprints for the design are dated 1992.
“The contractor used splicing couplers instead of dowels, as required by the original drawings,” but that did not cause the collapse, Ayub said.
Also, “The rebars were not threaded to the required length inside the coupler at all locations,” Ayub said.
The rebar and couplers were not galvanized nor did they have epoxy coating, “which could have prolonged the life of the basin,” Ayub said.
The wall design was “adequate,” based on a review of the original design, he said.
Ayub termed the use of horizontal dowels between the north wall and the east and west walls as “adequate” but said they “reduced the efficiency of the joints.”
The exterior walls are all 18 in. thick and the interior baffle walls 12 in. thick, according to the specifications in the design documents, he said.
The basin was built to hold 30 ft of liquid, or about 1.5 million gallons, and has an average operating depth of 4 ft to 8 ft, the report said. The collapse followed two days of heavy rain, and the basin held 25.5 ft, or about 1.3 million gal, according to plant data. More than two million gallongs of sewage poured into the Little Pigeon River after the incident.
Wastewater levels had been greater than 20 ft “on multiple occasions” and had reached 26 ft twice during the past year, the report said.
The flow control building where the men were working is still covered with parts of the wall and effluent piping.
Ayub and Misciagna, however, said, “There is no probable reason that access to this area would reveal any additional information that would result in citation being issued to Veolia.”
The only previous incident involving structural integrity entailed cracks and bowing in the north wall soon after construction, which was remedied by the installation of a reinforcing concrete buttress, they said.
Soon after the collapse, the city of Gatlinburg hired Construction Engineering Consultants, Knoxville, to investigate.
Albert J. Harb, a Knoxville attorney hired by the city, said that no report on the cause of the collapse will be issued until it can be "complete, accurate and based upon full knowledge of all available facts."
