I am writing this letter in response to your article concerning a Feb. 6 community meeting about the Ledbetter Dam. I am requesting you consider publishing this letter as a service to your readers, especially those who live near Ledbetter Dam.
I would like to share some insights concerning the state’s view of this dam, which Mr. Dean Brooks may not have clearly articulated at this meeting. My name is Steven M. McEvoy, PE. I am the State Dam Safety Engineer and staff member of the Land Quality Section (LQS), Division of Energy, Mineral, and Land Resources (DEMLR) in the N.C. Department of Environment and Natural Resources (NCDENR).
As background, on July 17, 2012 staff from the Fayetteville office of the LQS responded to a call from the Richmond County office of Emergency Management (RCEM) advising that several newly discovered leaks had emerged on the downstream face of the Ledbetter Dam. This dam was classified as “high hazard” by LQS as failure of the dam would threaten public safety downstream and possible endanger lives. Upon inspection, LQS staff confirmed that new leaks had developed in the dam and advised RCEM to have the dam owners immediately begin to drain the reservoir in case these leaks were progressive in nature. LQS further assisted RCEM by quickly identifying properties downstream that would obviously be threatened in the event of dam failure. LQS then further defined those downstream properties threatened by dam failure through engineering analysis. Based on Richmond County’s geographic information systems property data, 19 downstream properties along Happy Valley Road, Terry Bridge Road, Creek Run Lane, Lakeside Drive, Hudson Street and Roberdel Road were identified in this analysis.
In addition, Roberdel Lake Dam, which serves as the water supply for the city of Rockingham and is located downstream of Ledbetter Dam, could be damaged by high flows resulting from a failure of the Ledbetter Dam.
As the reservoir was being lowered, LQS asked the dam owners under authority of the North Carolina Dam Safety Law of 1967 (NCGS 143-215.23) to retain the services of a professional engineer to evaluate the structural integrity of the dam. On July 20, 2012, the LQS issued a Notice of Deficiency, detailing six specific deficiencies noted in the dam. The owners hired Mr. Cyr of Kleinschmidt Associates to address these deficiencies. Mr. Cyr submitted a preliminary report received by LQS on Dec. 7, 2012 which listed proposed solutions to the six deficiencies. On Dec. 14, 2012, after review of the preliminary report submittal, LQS forwarded a letter to Mr. Cyr requesting some additional information relative to his proposals. The deficiencies, Mr. Cyr’s proposed solutions, and LQS’s responses are summarized below:
1. DEFICIENCY: Two cracks in the box structure left of the principle spillway had water actively flowing from the cracks with changes observed in the amount of water flowing from the cracks.
2. DEFICIENCY: Two smaller cracks in the box structure left of the principle spillway with leakage were noted along the ridge below the top of the structure and halfway up the wall.
ENGINEER’S PROPOSAL: The preliminary report proposed doweling into the upstream side of fractured walls and pouring an 8-inch concrete veneer to stop the seepage from flowing through the intensely fractured wall areas.
LQS RESPONSE: LQS is concerned that the heavily fractured walls of the dam may be a symptom of weakening concrete as the dam structure is more than 100 years old. Newly formed leaks through the exterior walls seem to indicate an advancing condition. Standard engineering practice would call for some type of testing of concrete samples from the wall to verify the integrity of the concrete.
3. DEFICIENCY: The downstream slope of the earthen berm portion of the dam had an area that was saturated. Seepage was occurring at the bend approximately one third up the slope from the toe; seepage was also observed at the toe halfway between the turn and the principle spillway.
ENGINEER’S PROPOSAL: None offered.
LQS RESPONSE: LQS realizes the engineer cannot respond to this item until the hydraulic load is re-applied to the earthen embankment (water is impounded behind the dam) and the seepage re-appears. LQS is willing to work with the engineer to address this more thoroughly when the reservoir is re-filled after completion of concrete repairs.
4. DEFICIENCY: The overflow portion of the principle spillway was observed to be pitted, cracked and spilling over most of its surface.
ENGINEER’S PROPOSAL: The engineer simply states that “a comparison of various photos of the downstream side of the intake taken at various times indicated there has been little change in the extent of staining/leakage since the mid 1980s. The engineer then concluded that “there was nothing observed that indicated a need for investigation or immediate repair.”
LQS RESPONSE: These various photos were taken at a distance with older film cameras and do not offer very high resolution. LQS has the same concerns here as in Item 2 above.
5. DEFICIENCY: A hydraulic evaluation of the spillway system should be completed to ensure compliance with NCAC 15A 2K.0205.
ENGINEER’S PROPOSAL: The engineer did not provide a stability analysis at design storm elevation (high flow conditions) nor did he comment on the previous stability analysis, which was performed at normal pool elevation.
LQS RESPONSE: If the engineer will provide a stability analysis of the masonry/concrete portion of the dam under appropriate hydraulic head and show that it is stable against overturning and sliding, this matter should be resolved.
6. DEFICIENCY: The bottom drain should be operable without additional equipment being transported to the site.
ENGINEER’S PROPOSAL: The engineer states that it would be advantageous if all three reservoir control gates were fitted with hydraulic gate lift assemblies. No definitive recommendation is provided.
LQS RESPONSE: LQS is concerned that the current owners of the dam live nearly 60 miles from the dam site by road and must be called upon to gather equipment and travel to the dam site in order to operate the gates in the event of emergency. This could be problematic if the current owners cannot be reached for some reason during an emergency or if the current owners sell the dam to a new absentee owner or a new local owner who cannot operate the gates.
In summary, LQS is concerned with public safety downstream of this dam. This is the principal reason North Carolina has a safe dams program. This dam is old, shows signs of deterioration, drains a large surface area (84 square miles) and therefore warrants a high level of care. We will continue to work with the owners of this dam to ensure it is repaired in timely manner and is maintained in safe working condition.
— McEvoy, is a state dam safety engineer with the N.C. Division of Energy, Mineral and Land Resources.
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