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In for the long haul. . . Boone Dam repair now looking at 5-7 years

Five to seven years is a long time and $300 million is a lot of money, but Tennessee Valley Authority officials are aiming for a permanent solution to the water seepage at Boone Dam.
“We can do it faster, but the next time we run into a sink hole you’ll be in the same situation,” Vice President John McCormick said during a public meeting held July 30 at the Millennium Center in Johnson City. “It’s not a long-term fix.”
According to McCormick, TVA vice president of safety, river management and environment, discovering the sink hole in October 2014 near the base of the embankment at Boone Dam is the result of a robust dam safety program. “Fifteen days later, we found the seepage,” he said.
Deterioration of the earthen embankment’s original foundation has been identified as the cause of the seepage and accompanying internal erosion.
After considering multiple options, TVA determined the best choice to stop the seepage and the water coming under the dam is constructing a concrete cut-off wall multiple feet in width and 250 feet deep. “This is a permanent repair for this reservoir,” McCormick said. “This is doing it right.”
Construction of Boone Dam, which is 160 feet tall and stretches 1,697 feet across the South Fork Holston River, began in 1950 and was completed in 1952.
More than one attendee asked whether it would be better to build a new dam.
John Kammeyer, vice president of civil projects, said the driving factor in declining that option is there is nothing wrong with the concrete porion of the dam. “To build a new dam beside the same embankment will take longer and cost more.”
The wall will be built by a private contractor selected through a bid process. “There are only three companies in the world who can do it,” he said.
A required environmental review will take until the first of 2016 to complete, and the goal is to finish the project within five years. “We’re doing everything we can as fast as we can as long as we can do it safely,” McCormick said.
Until then, the water level will remain at 1350-1355 feet, which is approximately 10 feet below the winter pool levels. The lower level will slow the deterioration and significantly decrease the amount of water that would flow downstream in the unlikely event of a breach.
Prior to construction of the seepage barrier, the earthen embankment will be strengthened through the injection of grout in portions of the foundation soils, the voids created by the deterioration and the underlying bedrock.
One individual asked if additional resources would enable the project to be completed in a shorter time frame, but Kammeyer said the limitation is related to space.
“The holes we have to drill are very close together and there is not a lot of lay down space,” he said. “We may not be able to use the larger pieces of equipment.”
Protecting the structure is another requirement. “We can’t go in and pump grout in multiple spaces without building water pressure that affects the safety of the dam,” he said.
In response to a question regarding the source of funds for the estimated $200-300 million project, McCormick said contingency dollars in the normal operating budget will be used. “There will be no rate increase because of this,” he added.
When homeowners complained about their loss of property values, Rebecca Tolene, vice president of natural resources, reminded them real estate is a long market. “We are working on this project to keep confidence in the market,” she said. “The lake is coming back.”
For more information on the project, visit www.tva.gov/boonedrawdown.