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Plant-covered lakebed being cut for safety

W. Kenneth Medley II • Feb 6, 2019 at 12:00 AM

Work continues on the $457 million Boone Dam Project with the contractor, Treviicos-Nicholson Joint Venture, moving into onsite temporary offices, construction beginning on a concrete plant and vegetation causing safety concerns being cut away.

The project is on time and on budget, according to Mary Miller, Tennessee Valley Authority community relations manager for the project.

There are 120 workers coming and going daily, creating a need for a parking lot, which is being built.

Crews are also working to clear vegetation from areas around the lake. The plant life is a result of the low water levels, and is causing safety concerns.

“We are out actively providing supplemental vegetation management on Boone Lake,” said Miller, “We had heard from so many neighbors that they were concerned and wanted TVA to play a role in assisting with supplemental vegetation management.”

Dan Widener is the contact for residents who want to report additional areas to be cleared.

The TVA has a map on the Boone Dam Project website outlining areas crews will be clearing plants. Miller encourages community members to reach out to Widener and identify areas needing cut, but also said there are no guarantees. Safety concerns will be mitigating factors in determining whether an area is cut or not.

“Widener is actually going out talking to neighbors,” said Miller, “putting door hangers on their doors, they have a couple skid-steers out there and they are working, cutting the vegetation and mulching it.”

Drilling and grouting that began in the fall is complete, clearing the way for construction to begin on the diaphragm wall, a cutoff wall being built to stop water seepage under the dam. It will be built from materials that do not erode, according to the TVA project website.

A foundation is being built for a concrete batch plant to provide materials for the cutoff wall, which is being built atop the grouted bedrock layer.

Crews are also receiving additional training to ensure safety, according to Miller.

“The whole reason we had to lower the reservoir was in order to maintain the safety of the downstream public,” Miler said. “I like to emphasize, that this project is about safety, both the safety of our workers and the downstream public”

A sinkhole that formed in the bedrock under the dam’s foundation is the source of seepage that caused safety concerns dating back to October 2014. The sinkhole is a result of the epikarst layer of soil and rock being eroded by water. Karst and epikarst are typical of the soil and bedrock of the region, according to Chris Gregg, an East Tennessee State University geologyprofessor.

“One layer of rock leads to another layer at a greater depth,” said Gregg, “but it just so happens that for the areas underlaid by limestone, you get these karst features to develop. Karst is a term that we use to describe areas where the (underlying) rock has been dissolved.”

This type of erosion that forms karst rock features is what led to water seeping under the Boone Dam. Another area east of the dam is showing signs of seepage, an indicator of another potential hazard. However, Miller said steps have been taken to grout this area and ensure it is safe.

“There is karst throughout our region,” Miller said. “This cutoff wall is being designed to stop that internal erosion that was the initial problem. The geology has very much been taken into consideration, as to the solution, which is this underground cutoff wall.”

Efforts to ensure the modifications to the dam will last have been taken by designers, with the dam widened and made more solid. Arpita Nandi, ETSU Geosciences chair, who also teaches classes in engineering geology, said great efforts have been taken to solidify the surrounding terrain.

“The way I understand their design,” Nandi said, “they are making it as foolproof as possible on the dam side, plus surrounding a good amount of buffer area. Which has been solidified physically as much as possible, so that the water will not drain through those areas.”

Nandi added this will not stop water from creating new outlets, away from the buffer zone, a reminder that mother nature wins in the end.

A three-foot drawdown of Boone Lake will begin by the end of the week.

Widener can be reached by email [email protected] by telephone at 423-360-3813. For more information, visit the TVA Boone Dam Project website at www.tva.com/Newsroom/Boone-Dam-Project.

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