EPA also sent inspectors out to examine the wet storage facilities at all of the nation's coal plants. It determined none had the critical problems of Kingston but ordered some minor remediation.

Additionally, EPA has begun the process to regulate coal ash. It has issued two draft rules, one of which would require phasing out all wet handling of coal waste and declare coal ash a hazardous material. The other option—favored by industry—would leave coal ash as a non-hazardous waste and regulation of the ponds to the states. More than 450,000 comments on the proposed rules poured into the EPA, which has postponed issuing final rules until it can sift through the high volume of comments.

Hoping to create certainty for coal utilities and circumvent EPA regulation of coal-ash ponds, legislation leaving overall management of coal-ash impoundments in the hands of states was introduced in the House of Representatives earlier this year, Roewer says. The bill, awaiting a vote by the full House, would also prevent EPA from classifying the waste as hazardous.

Disaster Breeds Innovation

On the worksite at Kingston, not only is cleanup ongoing, but San Diego-based Geocon has been hired to build the first segment of a Stantec-designed slurry wall around the base of the 90-acre failed coal-ash pond, which still retained 12 million cu yd of ash after the 2008 spill. That pond is being used to store the coal ash recovered in the non-time-critical work. Eventually, the entire pond will be capped and closed.

The slurry wall is a key pond fortification to keep the ash stored on-site, says Don Fuller, the Stantec principal engineer responsible for the wall's design. Without an armored perimeter, if an earthquake were to occur at either one of the two nearby seismic fault lines, the coal ash could liquefy, breach the exterior wall and again flood the Emory and nearby lands.

The slurry wall, to be built in seven segments, will total 12,000 linear ft and be about 80 ft deep, including three feet into bedrock. The outer wall will have fortifying perpendicular walls; it is designed to withstand 200,000 lb per linear ft of lateral load, Fuller says. To build the wall, a large backhoe will dig a trench that will be filled with bentonite, slag and cement.

The TVA has not released a cost estimate for the slurry wall. The wall was designed after running thousands of Fast Lagrangian Analysis of Continua computer models to determine the most effective design to prevent liquefaction, Fuller says. “You just can't evaluate dynamic loading with hand calculations,” he says. Similar slurry-wall designs have been used to mitigate large-scale dams, but they have not been used for a coal-ash pond or even landfills, Fuller says.

But Fuller says Stantec expects that other coal-ash ponds built on rivers in earthquake zones will need similar fixes to prevent liquefaction. “I don't know of another solution,” he said.

Another innovation arising out of the Kingston pond failure is TVA's switch to dry-ash storage. By the end of the decade, TVA expects to close all its wet ponds and install systems on its coal units that will capture the dry ash, Kammeyer said. The new dry-ash system is already in place at Kingston.