Sam Vinson, the principal project manager, said that is within the seven-year timeframe the agency expected at the onset of the project.
Workers have completed about 154 of the 307 individual pillars that will make up a concrete cutoff wall embedded in the dam’s earthen embankment. The cutoff wall, which the TVA expects will be finished by May 2021, is being installed to prevent internal erosion and halt underground seepage. An additional 53 pilings are in various stage of progress.
Vinson said those pilings are like a series of overlapping pickets in a fence, which will eventually make an underground barrier.
Once crews finish the cutoff wall, the TVA will begin site restoration, which will involve putting the beach back, returning public restrooms and restoring the 10-feet of elevation cut from the top of the dam. Dam safety officials will begin fluctuating the water level next spring to test the repair work, raising the level by no more than two feet per week. The agency plans to release the exact details of that plan to the public in October.
Over the course of the project, water levels have been kept between at 1,350-1,355 feet elevation, which is short of the summer pool of 1,382 and winter pool of 1,364 maintained during normal operations. Vinson said heavy flooding has caused the lake levels to exceed 1,355 at times, but crews have tried to keep it below 1,360.
The TVA has not had a case of COVID-19 at Boone Dam over the course of the repair project. Vinson said workers on site are practicing social distancing, and TVA has been providing personal protective equipment to anyone who is standing within six feet of another person.
When workers arrive on site, the agency screens them with questions about symptoms and conducts temperature checks. The agency also keeps track of employee travel. Some operations that can be performed remotely have been moved off site.
Crews have worked about 1.5 million hours as of last Friday.
In October 2014, the Tennessee Valley Authority discovered a sinkhole near the base of the Boone Dam embankment, which connects to the concrete portion of the structure.
Crews found water and sediment seeping from the riverbank, and in an effort to stop internal erosion along the embankment, the TVA began a repair process that required the agency to lower the water level.
Of the repair project’s $457 million budget, which includes contingencies, Vinson said about $215 million has been spent. He said the repair effort is well within budget.
The TVA will also continue mulching vegetation around the roughly 1,400 acres of exposed lakebed this year, which is one of several “good neighbor” efforts that the agency has undergone during the repair process. The TVA has also installed low-level boat ramps and put in a temporary beach.
Noting that plant life can help prevent erosion and maintain the fish population, Vinson said officials do not intend on cutting all the supplemental vegetation around Boone Lake. The agency cut about 650 acres last year and hopes to mulch about 900 acres this year, which will include places where plant life has already regrown.
The TVA will also use Environmental Protection Agency approved herbicides in areas that are difficult to reach with mulching equipment and places where plant life has returned, with plans to eventually cover 600 acres. Homeowners have the option to opt out of the program if they don’t want the agency to spray or mulch on their property.