Engineering Expert Witness On Massive Coal Ash Spill

A $3 million study blaming a massive coal ash spill in Tennessee on a complex combination of structural and geologic factors is wrong, says an engineering expert witness who evaluated the disaster for his own mining and utility clients. Though no one was injured, the disaster was one of the worst of its kind in the US and has brought new attention to the risks and lack of regulation of coal ash storage sites around the country. TVA, the nation’s largest public utility, estimates it could take years and up to $1 billion to clean up the mess. Residents fear lingering environmental harm.

Barry Thacker, who has been designing hydraulic-fill structures similar to the Kingston Fossil Plant landfill for 30 years. In a report shared with regulators, the expert witness concludes the Dec. 22 breach that sent 5.4 million cubic yards of toxic-laden muck into the Emory River and a lakeside neighborhood about 40 miles west of Knoxville occurred because of an undiagnosed and preventable buildup of water pressure against a perimeter clay dike.

Thacker doesn’t agree with the more exotic conclusion of Tennessee Valley Authority consultant AECOM USA Inc. last month that the spill was due to several factors in and under a mountainous dredge cell upstream of the dike, including liquifying soils and a deep, unknown, unstable layer of silt and ash dubbed “slimes.”

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