Peer Review of the Stability Analysis of Ash Disposal Areas 2 and 3 at the Johnsonville Fossil Plant

TVA OIG retained Marshall Miller & Associates, Inc. (Marshall Miller) to conduct a peer review of the Stantec Consulting Services, Inc. (Stantec) report on geotechnical exploration and slope stability for the Ash Disposal Areas 2 and 3 at the Johnsonville Fossil Plant. Marshall Miller believes that Stantec's evaluations provide a reasonable assessment of the margin of safety associated with the evaluated conditions, which indicates that the facility is not in danger of imminent failure.In Marshall Miller's opinion, Stantec followed generally accepted practices and arrived at reasonable predictions of exit gradients. With regard to Stantec's development of material shear strengths, Marshall Miller found Stantec arrived at reasonable shear strength properties for the generalized material layers and zones. However, Marshall Miller believes the calculated factors of safety against piping in the heterogeneous fill are overstated because Stantec used high values of critical gradient for the fill relative to its measured in-situ densities. Based on review of Stantec's slope stability analyses, it is Marshall Miller's opinion that Stantec performed stability analyses for static, long-term load conditions using appropriate methodologies and reasonable material properties.