The earthen dikes supporting a huge coal ash landfill at a Tennessee power plant were "on the verge of failure" long before they collapsed and sent tons of toxic muck into a river and lakeside community, an engineering consultant said Thursday.
Engineer Bill Walton of AECOM USA Inc. said his firm's $3 million study for the Tennessee Valley Authority found several factors combined to lead to the Dec. 22 dike breach at TVA's Kingston Fossil Plant. Among them was a thin layer of fly ash "slime" deep in the pile that moved and put pressure on the dikes.
Walton said the disaster could have happened at any moment — maybe a year before, maybe the next day.
The consultant said it was not his job to assess blame for the spill that has brought national attention to the risks and limited regulation of storing coal ash, which can contain toxic metals such as arsenic, mercury and selenium.
The report's conclusions, however, suggested better engineering and inspections would have helped.
Was there negligence?
Rep. Eddie Bernice Johnson, D-Texas, whose House Subcommittee on Water Resources and Environment has been holding hearings on the disaster, called the report "enlightening and disturbing." She said it would help explain why the spill happened and help prevent them.
Meanwhile, Earthjustice attorney Lisa Evans criticized the report's authors for not examining "what role agency negligence played in the disaster."
TVA Chief Operating Officer Bill McCollum said the nation's largest public utility is focused on the $1 billion ash cleanup and restoration of the Roane County community, and intends to use the report to improve operations at Kingston and TVA's 10 other coal-fired power plants.
"I don't have any way to look back at this point, to revisit all the decisions that were made in the past, from 1950 to today," McCollum said.
McCollum's predecessors notably decided after a 2006 leak at Kingston to install trench drains rather than do a $25 million conversion to dry storage or install a $5 million landfill liner. TVA is now planning to convert Kingston to dry-ash storage.
Slime, water led to failure
Walton's 10-volume, 6,000-page report said four conditions combined to produce the stresses and movement in the pile that led to the release of more than 5 million cubic yards of ash into the Emory River and several homes, covering 300 acres.
Those factors included the high water content of the ash, the increasing height of the ash pile and the construction of sloping dikes over wet ash surrounding the landfill.
The fourth factor, discovered by Walton's team after more than two months of forensic analysis, was a half-inch to 6-inch "slime" layer of loose fly ash and silt running 40 to 85 feet below the portion of the pile that collapsed.
Walton said the slime, which tended to "creep" and add hydraulic pressures to the dikes, was something like yogurt — seemingly stiff until it is stirred and becomes fluid.
"If you don't have the slime layer, you don't have the failure at this time," he said, though he would refused to say it was the sole trigger of the spill. He said he didn't know of similar "slime" existed at other ash landfills around the country.
Stephen Smith, director of the Southern Alliance for Clean Energy, praised the report for dismissing TVA's claims that the disaster may have happened because of natural causes, including heavy rainfall, minor earthquakes and freezing temperatures. However, Smith noted engineering failures and wondered how many times TVA managers missed opportunities to find the slime layer with sampling.
A Tennessee Department of Environment and Conservation panel that includes representatives from the Army Corps of Engineers and the U.S. Environmental Protection Agency will review the report.
Meanwhile, TVA's Inspector General's Office expects to release its own report on the cause next month.