Peer Review of Dike C Buttressing

TVA OIG retained Marshall Miller & Associates, Inc. (Marshall Miller) to conduct a peer review of the Stantec Consulting Services, Inc. (Stantec) stability calculations and construction documents for the Dike C Buttress at the Kingston Fossil Plant (Kingston). Dike C refers to the remaining section of the Kingston coal ash containment that did not fail in the December 22, 2008, spill. It is Marshall Miller's opinion that the planned Dike C Buttress produces stability enhancements that are sufficient based on Stantec's drained slope stability analyses. Marshall Miller also believes that the construction improvements will satisfactorily address issues of "piping"/internal erosion, surface erosion, and scour over those Dike C areas that will be covered with an aggregate filter and be buttressed. However, Marshall Miller found that the specific design bases/criteria, relative improvement in stability, and reasoning for certain variations in the buttress configuration were not well documented within the materials that were supplied for review. The significance of the Marshall Miller observations and recommendations are dependent on the approach and conservatism that are applied in the design of the final closure plan. To address this report, TVA management had Stantec review and respond to the findings of Marshal Miller's report. TVA management and Stantec provided additional information on the findings and recommendations in Marshal Miller's report. Marshall Miller concluded that the additional information provided adequately addressed the concerns and recommendations identified in its report.