Sat Feb 11 2012
As a technical adviser with the Kentucky Council for Dix Dam Safety, I have recently reviewed a series of leakage and repair reports on the dam that were prepared by ARCADIS Inc. for Kentucky Utilities from 1991 through 2009. I will highlight two major findings from separate reports to show the complexity of the geological and engineering issues involved when trying to ascertain the current condition and safety of this 85-year-old dam, its foundations and both abutments.
From the 1991 Dix Dam Repair Report, principal conclusion #2 states: “Based on the minimal leakage through the face slab despite very large cracks and complete failure of the face slab in isolated areas, the underlying derrick-laid stone acts as a secondary barrier to leakage.” I would ask the following questions: If the 18-inch-thick concrete face slab was exhibiting signs of failure 19 years ago, what shape is it in today? The derrick stone is difficult to inspect. What happens if it also fails? What is the condition of the face slab that is now buried under 100 feet of sediment and debris and can’t be inspected? Does the additional weight of this saturated sediment now pose a stability risk to the bottom one-third of the dam? Finally, does the potential exist for a rapidly developing and substantial increase in leakage through expanding failures in the face slab and derrick stone near the foundation? This area would be hard to repair.
From the 2005 Underwater Inspection, major finding #4 states: “Although the source of most of the leakage that has developed since 1994 remains unclear, likely locations include the right (east) abutment contact and the deteriorated portion of the face slab near the top of joint (#NO). Leakage in these and other areas on the face slab is diffuse, making detection difficult. Other sources such as increased foundation leakage are possible? I would ask: How much has the foundation leakage increased? How much of this foundation leakage is now entering sinkholes or cracks in the karst limestone area below the dam or in the abutments, while eroding the rock foundation that supports the dam?
In the 2005 report, the “experts” go on to state: “As long as there is no significant change in the leakage, ARCADIS recommends that the decision to make additional investigation and repairs be guided by economic and other factors not directly related to dam safety.” Most importantly: How much leakage constitutes a significant change that would affect dam safety? Does KU know how much and where the foundation leakage is, since much of this leakage may bypass their weir detection system and run underground into the limestone karst? When dams fail, leakage can increase significantly, in a matter of seconds or minutes, making any needed repair impossible. Finally, I am certain the citizens of Frankfort will not be comforted to know that dam safety is not the major factor guiding the leakage repair program!
These conclusions and questions all point to the critical need for a third-party review by a leading dam expert. Unfortunately, none of them work for the Kentucky Division of Water. It is difficult to believe that after 30 years of providing minimal professional review or questioning of any of the lengthy and complicated technical reports on Dix Dam, the DOW is suddenly “up to the task.” Up till now, the most they have ever done is inspect the downstream face of Dix Dam every two years or so.
I would like to point out that Kentucky has another dam built on a karst limestone foundation: the Wolf Creek Dam. After grouting failed to stop the foundation leakage at this dam, much more expensive measures were and are now being employed by the Corps of Engineers. Does anyone really believe a $300 million repair will ever be willingly undertaken by KU, or recommended either by ARCADIS or DOW, when economic considerations, and not dam safety, are the stated primary concern? If ever a dam required an expert, comprehensive third-party review by geological and engineering experts, it’s the Dix Dam.
Jeff Vansant is an environmental scientist with the Kentucky Division of Forestry who was living on Herrington Lake when he became involved in the campaign for Dix Dam safety.
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