Four factors worked like 'perfect storm' to cause coal ash spill
June 27th, 2009 by Jennifer Walker-Journey
Four conditions created extra stress and movement in the massive coal ash pond at the Tennessee Valley Authority (TVA) Kingston, Tennessee plant and caused the impoundment to breach last December, sending a wave of toxic material on to 300 acres of nearby property, according to a study conducted by Los Angeles-based AECOM USA Inc. and released Thursday. Those factors include high water content of the ash, the height of the pile, the construction of sloping dikes over wet ash around the landfill, and a hidden layer of fly ash “slime” hidden 40 to 85 feet below the section of pond that breached.
This hidden layer of ash, called “slime” by AECOM engineer Bill Walton, was made up of fly ash, water and sediment and, though less than six inches thick, created instability in the pond. As it eluded detection by TVA engineer over the years, its “creep failure” of slimes and liquefaction triggered the massive spill.
These four factors worked together to create what Walton said acted almost like “a perfect storm.” Residents would likely call it a perfect disaster. The massive wave of coal ash that tumbled from the breached pond dumped more than a billion gallons of toxic coal ash on to a neighboring community, knocking homes off their foundation and pouring into the Emory River. Coal ash contains dangers toxins that have been linked to serious health concerns. Already, some residents in the area, including a young child, have tested positive for heavy metals in their blood.
The findings from AECOM will be reviewed by an advisory group made up of personnel from the Tennessee Department of Environment and Conservation, the University of Tennessee, the U.S. Environmental Protection Agency, the U.S. Army Corps of Engineers and geotechnical consultants from Science Applications International Corporation.
Stephen Smith, executive director of the Southern Alliance for Clean Energy, offers this perspective: “One would think that TVA, with its vast engineering experience, would have known to look for this material.”