The effort has involved scores of workers, millions of dollars and hours upon hours of work.
And more than a million hours of work.
In October 2014, the Tennessee Valley Authority discovered a sinkhole near the base of the Boone Dam embankment, an earthen wall that 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 seven-year repair process that required the agency to lower the water level.
Although crews are currently working on the dam’s cutoff wall, which a TVA spokesperson has said is the centerpiece of the repair effort, the agency expects the entire project will be complete in July 2022.
Here’s a numerical breakdown of the project as it stands right now:
11: The total number of cylindrical pillars that have been installed as part of the underground cutoff wall. The wall is designed to stop internal erosion along the earthen embankment and prevent underground seepage. The wall will be composed of about 300 overlapping, tightly-packed cylindrical columns that will be embedded in the dam’s earthen embankment. Crews are in the process of constructing 28 more of those columns.
The TVA expects to complete the cutoff wall in May 2021. After that portion of the repair work is finished, crews will begin testing the repair work by raising and lowering the water level.
1.2 million: The number of worker hours invested in the Boone Dam repair project across its entire life span. Over the past several weeks, Kevin Holbrook, the senior manager of civil construction with the Tennessee Valley Authority, said crews have started working on a 24-hour basis five days a week. They’re also working 12 hours during the day on Saturdays.
If need be, that gives them the option to make up work on Saturday night and Sunday.
At night, he said the agency is averaging 40 workers, which could increase to 60 as production ramps up on the cutoff wall. Holbrook anticipates the day shift average of about 160 to 180 workers won’t increase.
$170 million: The amount of money the TVA has spent on the repair effort out of a total project budget of $450 million.
“We’re on track to meet our budget schedule obligations,” Holbrook said. “There’s definitely a lot of different components between now and completion that we’ve budgeted for, and we’re confident that will come in on track.”
649: The total acres of vegetation that TVA has cut as part of its supplemental vegetation management program.
When the TVA lowered the reservoir in 2014 from its summer pool levels of about 1,382 feet to an interim level of about 1,350 feet, principal project manager Sam Vinson said that exposed about 1,400 acres of lakebed.
In response to requests from property owners, Vinson said the agency rolled out a vegetation management plan last September, which has involved mulching excess plant life in some of those exposed areas.
The agency had originally tallied about 500 acres that it planned on clearing, but added extra locations based on input from members of the public.
Vinson said the agency has tried to balance the removal of the vegetation with the natural benefits associated with plant life, which can help prevent shoreline erosion and maintain a healthy fish population. Vinson said the TVA has also partnered with the Tennessee Wildlife Resources Agency to plant roughly 400 acres of vegetation as a means to reduce erosion risk, help fish habitats and protect exposed cultural sites.
$2.1 million: The initial budget set for the vegetation management project. Vinson said the agency is within that budget, which is separate from the money that has been set aside for the repair project.
“We’ve spent about 30% of that and we still have two growing seasons to make,” Vinson said, “so we’re right on track with the budget.”