ROGERSVILLE, Tenn. (WJHL) — The Tennessee Valley Authority (TVA) is seeking public input on proposed safety repairs to the John Sevier Dam on the Holston River near Rogersville.
The TVA wants to construct a roller-compacted concrete gravity dam to address issues with the 68-year-old dam’s northern earthen embankment.
A 2019 risk assessment found that water can overtop the embankment when the river level is high, which could lead to the embankment failing. It also identified a risk of failure from internal erosion under normal operating conditions due to leakage.
“While the John Sevier Dam has a history of overtopping during relatively routine flood events and has performed well to date during normal operating conditions, TVA considers the probabilities of an overtopping induced or internal erosion induced failure to be high enough that upgrades to the right embankment are warranted,” TVA said in a recent draft environmental assessment.
Measures have been taken to shore up the embankment until repairs can be made, the TVA said.
A dam failure could result in the release of mercury-contaminated sediment that has accumulated immediately upstream of the dam, TVA said. The mercury didn’t come from TVA, but from a chlorine plant that once operated in Saltville, Virginia, more than 100 miles upstream.
A fish consumption advisory already exists for black bass and catfish species in Cherokee Lake due to mercury. If the dam fails and contaminated sediment is released, the advisory could be extended further downstream and to include all fish species, TVA said. Mercury could also contaminate groundwater near the dam and downstream, resulting in long-term adverse effects.
According to the TVA, the Environmental Protection Agency believes the subsurface sediment upstream of the dam may pose “an unacceptable risk to human health and/or the environment” if the dam is deconstructed or if the sediment is otherwise disturbed.
TVA officials believe the installation of a roller-compacted concrete dam is the only option that addresses all of the dam safety concerns, however, the agency is weighing two other options: placing additional riprap rock to protect against erosion or taking no action.
Construction of a roller-compacted gravity dam would take 7–8 months and require up to 75 truckloads per day for the delivery of construction materials, according to TVA.
The new dam would be built downstream of the existing north embankment and connect to the northern end of the existing concrete spillway. The project would result in minimal changes to the current dam, TVA said.
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More information can be found on TVA’s website.
The dam was constructed in 1955 to provide cooling water for the adjacent John Sevier coal-fired power plant, which TVA retired in 2014 and later deconstructed. The reservoir continues to provide water to the John Sevier Combined Cycle Power Plant, a natural gas power plant that was brought online in 2012. The dam and reservoir are also popular fishing spots.