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Closure of an Ash Storage Facility at Kingston Thermal Plant

Tennessee Valley Authority¡¯s (TVA) Kingston Fossil Plant supplies power that is critical to the regional economy. For over 50 years, coal ash by-products were stored in ponds and wet stacks along the Emory River. A failure in 2008 released over 5 million cubic yards of ash, impacting 40 residences, destroying a public highway, and closing the river. In response, we quickly mobilized to assist TVA with emergency actions.

Designs to stabilize the site and support construction of critical infrastructure were prepared for the recovery. This included extensive instrumentation and a monitoring program to verify stable conditions during rapid stacking of recovered ash. Concurrently, engineering designs were developed for the site closure. Regulations required the recovered ash stack withstand a 2,500-year seismic event. Our team realized that widespread liquefaction would occur within the foundation ash and native silt/sand layers during such an event; thus, foundation improvements were required.

A sophisticated, dynamic numerical simulation of the facility was completed for the design earthquake event, in addition to conventional ground response, liquefaction, slope stability, and 3D structural analyses. Our solution of a stabilized perimeter consisting of buried, cement-bentonite slurry walls keyed into bedrock at depths up to 70 feet does not require dewatering. The largest wall of its kind in the U.S. at nearly 64,000 linear feet¡ªthe equivalent of 12 miles¡ªit is designed to withstand a magnitude 6.0 earthquake. More than 200,000 tons of cement and other materials were used. The new capped facility contains roughly 12 million cubic yards of coal ash produced by the power plant over the last six decades including ash recovered from the 2008 failure.

We are proud to have worked with TVA to close the site and restore the environment shared with their neighbors.