Movement under Lake Murray Dam walkway caused June closure

The Lake Murray Dam is undergoing repairs after inspections revealed structural issues, but a federal monitoring agency says the problems don’t present an immediate safety concern.

On June 23, the Federal Energy Regulatory Commission (FERC) sent a letter to Dominion Energy, who owns and manages hydroelectric operations at the Dreher Shoals Dam that forms Lake Murray, relaying their findings following a special inspection.

As initially reported by The State newspaper and confirmed by the Chronicle after receiving a copy of the letter, the FERC noted concerns about a sheet pile wall and the original embankment beneath the walkway that runs alongside S.C. Highway 6/N Lake Drive southbound on the lake side of the dam.

According to the letter, Raymond Ammarell, who is listed on the letter as chief dam safety engineer at Dominion, “initially reported the sheet pile wall incident via phone call and email to our office on June 22, 2023,” with a follow-up inspection being conducted the next day.

“The incident resulted in a rotation of the sheet pile wall towards the lake,” the letter states. “Additional damage included subsidence of concrete gutter and pedestrian walkway … which resulted in closure to the pedestrian walkway.”

That closure was announced to the public by the state Department of Transportation June 23, with the department noting that it was working with Dominion to repair a damaged portion of the walkway. Neither the department nor Dominion shared the extent of the damage or what caused it at that time.

SCDOT told the Chronicle repairs are set to be completed this month, deferring all questions about the dam itself to Dominion.

The letter notes that representatives from Dominion and SCDOT joined FERC representatives at the June 23 inspection, which “found no problems that would present an immediate concern for dam safety or continued operation at this time due to the reported incident. However, there are concerns for potential impacts to the southbound lane of SCDOT Highway 6 as discussed during the inspection and a Microsoft Teams meeting following the inspection.”

A second letter sent to Dominion by the FERC detailed a follow-up special inspection conducted June 30, which observed ongoing repairs. 

The letter notes that SCDOT and its contractors have removed the damaged walkway and gutter and begun to rebuild those portions. It further states that Dominion staff have been replacing removed riprap (the loose stone at the water’s edge) on the lake side of the wall and adding additional riprap as part of ongoing upstream slope maintenance that has been approved by the FERC.

The June 30 letter reaffirms that there is no immediate concern for dam safety or continued operation.

According to a statement from Dominion, heavy rainfall on June 21 and 22 caused a drainage gutter and wall along the walkway to settle, affecting the pavement. Following the completion of an initial assessment, Dominion Energy and an independent consultant identified no issues affecting the dam’s integrity.

“Working with the South Carolina Department of Transportation, we have temporarily closed that section of the walkway to repair the pavement,” the company said in the statement. “While visitors can still access the walkway from the Lexington side, they will not be able to travel the entire length of the dam while repairs are being made. Visitors should not walk past the barricades. We appreciate the community's patience while this work is completed.”

The Lexignton side of the dam is home to the public beach to which Dominion offers access during the warmer months, as well as a parking area for those who come to use the dam walkway. The Irmo side of the dam also features a Dominion park, but one that offers a boat ramp and no swimming.

According to the letter, Dominion was required to submit a written Dam Safety Incident Report addressing the issue within 14 days. The company didn’t immediately respond to the Chronicle’s request to view the report.

A letter listed in the FERC’s online database confirms the agency received Dominion’s report, but the report itself isn’t currently available to download.

Within the report, Dominion was required to include a plan and schedule to investigate the causes of the movement under the walkway, check the rest of the wall for similar issues and present a plan for enhanced monitoring of the embankment during and after repairs.