Repairs to the Tennessee Valley Authority's Boone Dam have ballooned by at least 50% since work began in 2015, according to statements made by TVA president Bill Johnson during a recent quarterly earnings call.
The project, intended to address seepage at the structure, began in December 2015, at which point the federally-owned corporation estimated it would cost between $200 million and $300 million, and require between five and seven years to complete.
Now, however, TVA projects a final price tag closer to $450 million and at least five more years of work for completion.
"As we got farther into the work there, we learned more about what is actually happening and that provided us the data to make a more robust estimate," Johnson said on the call.
Located on the South Fork Holston River on the border between Tennessee's Sullivan and Washington counties, Boone Dam is a 160 feet high, 1,532 feet long structure that was completed in 1952.
TVA discovered seepage under the embankment in October 2014 in the form of a sinkhole at the base of the structure, eventually revealing a complex series of underground geological pathways allowing water from both upstream and downstream sources to cause internal erosion.
HydroWorld.com reported TVA had completed the first phase of repairs at Boone Dam in February 2016.This stage included drainage improvements, repairs to the initial sinkhole, a new control building parking area and exploratory drilling and grouting.
The complex is also home to the 89-MW Boone hydropower plant.
Johnson also said during the call that TVA expects to spend an additional $200 million on dam safety inspections and repairs through the next five years as part of the agency's usual operational program.
"These assets require regular maintenance and repairs to stay at peak performance, and TVA is committed to maintaining the dams that have been entrusted to us," Johnson said.
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