What Caused the Spill at TVA's Kingston Plant?

Failure was not instantaneous, but "a progressive sequence of ruptures over a period of approximately one hour" that released the 5.4 million cubic yards of fly ash and dike material on December 22, 2008.

Last week, TVA released a comprehensive report which detailed the probable cause of the failure. In a nutshell, there was an inherent weakness under the dike that probably contributed to the failure.

This weakness consisted of a six-inch thick "slimes" layer of flyash, eroded dike soils and re-deposited river sediments formed from how the plant was operated in the 1950s. The layer was named for its slippery, viscous feel. Creep failure of this slime layer occurred under the loose wet ash which may have started the failure sequence.

Meanwhile, EPA now is reviewing all 427 coal-ash impoundments in the U.S., including those recently identified as having “high hazard potential." North Carolina which has 12 of these ponds, more than any other state, is also considering a bill that would tighten regulations for coal-ash disposal and would prohibit construction of new ash ponds.

Images from Root Cause Analysis full report.

Related Post: How Do You Clean Up A Fly Ash Spill?