«June 27, 2011 Robert M. Deacy, Sr., LP 5D-C FINAL REPORT – INSPECTION 2009-12910-04 – PEER REVIEW OF THE STABILITY ANALYSIS OF THE GYPSUM STACK ...»
Memorandum from the Office of the Inspector General
June 27, 2011
Robert M. Deacy, Sr., LP 5D-C
FINAL REPORT – INSPECTION 2009-12910-04 – PEER REVIEW OF THE STABILITY
ANALYSIS OF THE GYPSUM STACK AT THE WIDOWS CREEK FOSSIL PLANT
Attached is the subject final report for your review and action. Your written comments,
which addressed your management decision and/or actions taken, have been included in
the report. No further action is needed.
The Office of the Inspector General (OIG) contracted with Marshall Miller & Associates, Inc., to conduct this review. All work pertaining to this review was conducted by Marshall Miller. The OIG relied on Marshall Miller’s processes and procedures for quality control in the attached report. Information contained in this report may be subject to public disclosure. Please advise us of any sensitive information in this report that you recommend be withheld.
If you have any questions, please contact Deana D. Scoggins, Senior Auditor, at (423) 785-4822 or Greg R. Stinson, Director, Inspections, at (865) 633-7367. We appreciate the courtesy and cooperation received from your staff during this review.
Robert E. Martin Assistant Inspector General (Audits and Inspections) ET 3C-K DDS:FAJ Attachment cc: See page 2 Robert M. Deacy, Sr.
Page 2 June 27, 2011
Robert J. Fisher, LP 3K-C Michael B. Fussell, WT 9B-K Kimberly S. Greene, WT 7B-K Peyton T. Hairston, Jr., WT 7B-K John C. Kammeyer, LP 5D-C Tom Kilgore, WT 7B-K William R. McCollum, Jr., LP 6A-C Annette L. Moore, LP 3K-C Richard W. Moore, ET 4C-K Emily J. Reynolds, OCP 1L-NST John M. Thomas III, MR 6D-C Robert B. Wells, WT 9B-K Wendy Williams, WT 9B-K OIG File No. 2009-12910-04 Mr. John Montgomery, Stantec Peer Review of Stantec Consulting Services, Inc.
Report of Phase 2 Geotechnical Exploration, Gypsum Stack Dated February 5, 2010 Tennessee Valley Authority Widows Creek Fossil Plant (WCF) Stevenson, Jackson County, Alabama
TVA Office of the Inspector General Knoxville, Tennessee
Project No.: TVA106-11
September 8, 2010
Date of Issuance:
June 21, 2011 Marshall Miller & Associates, Inc.
ENERGY/ENVIRONMENTAL/ENGINEERING/CARBON MANAGEMENT5900 Triangle Driv
Item 1: TITLE PAGE Title of Report Peer Review of Stantec Consulting Services, Inc.
Report of Phase 2 Geotechnical Exploration and Slope Stability, Gypsum Stack, Widows Creek Fossil Plant Dated February 5, 2010 Tennessee Valley Authority Widows Creek Fossil Plant Stevenson, Jackson County, Alabama Project Location The project site is located in Stevenson, Jackson County, Alabama, at the confluence of Widows Creek and the Tennessee River.
Effective Date of Report September 8, 2010 Qualified Persons
Item 2: EXECUTIVE SUMMARY The Tennessee Valley Authority Office of the Inspector General retained Marshall Miller & Associates, Inc. (Marshall Miller) to conduct a peer review of the report entitled: Report of Phase 2 Geotechnical Exploration and Slope Stability, Gypsum Stack, Widows Creek Fossil Plant (Gypsum Stack Report) prepared by Stantec Consulting Services, Inc. (Stantec), of Lexington, Kentucky. The Widows Creek Fossil (WCF) Plant is located on the Guntersville Reservoir at the confluence of the Tennessee River and Widows Creek in Stevenson, Alabama.
1. Marshall Miller believes that Stantec’s evaluations of the WCF gypsum stack 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.
2. However, Marshall Miller did find that additional analyses and corresponding documentation are needed in order to assess the overall factor of safety of the stack in the midterm and long term, especially as the stack’s crest elevation approaches the maximum design height. Marshall Miller observed that the model used by Stantec is 20 feet lower than the final height of the stack. Height is a fundamental factor for the stability of slopes and has a direct influence on the factor of safety. In other words, the stack that Stantec analyzed is 20 feet shorter than the proposed final height of the stack and, therefore, is more stable. It does not reflect the final conditions of the pile.
Specifically, Marshall Miller found Stantec did not:
• Perform sufficient investigation of the clay foundation soils.
Exploration and Testing of Foundation Soils Marshall Miller reviewed the scope, procedures, and results of the subsurface exploration and laboratory testing programs performed by Stantec at the WCF gypsum stack. Based on this review, it is Marshall Miller’s professional opinion that Stantec applied appropriate and complementary suites of tests to characterize the engineering properties of the sedimented and cast gypsum-fly ash materials. However, it is also Marshall Miller’s professional opinion that Stantec did not perform enough exploration and testing of the foundation soils to support its reliance on historical data and its shear strength characterization of these materials. The foundation soils have a controlling influence on the slope stability, but Stantec’s Gypsum Stack Report does not supply sufficient data to characterize the foundation soils. Accordingly, Marshall Miller recommends that Stantec perform supplemental exploration, sampling, and testing programs to better determine the extent and consistency of the clay foundation soils, more thoroughly characterize the foundation soils, augment the available data, and support future evaluations. The characterization of the foundation soils would allow a more accurate assessment of the overall stability of the stack, which could be directly influenced by the properties of those soils.
Seepage Analysis Exit Gradients and Factors of Safety
Marshall Miller also reviewed Stantec’s seepage analyses of the WCF gypsum stack, including the material properties and boundary conditions. In Marshall Miller’s professional opinion, Stantec performed seepage analyses of the gypsum stack using generally accepted practices, including calibrating the seepage model using measured/observed conditions.
However, it appears that Stantec omitted the calculation of exit gradients and factors of safety against piping for the 5-year build-out configurations. Accordingly, Marshall Miller recommends that Stantec calculate the exit gradients and factors of safety against piping for the 5-year build-out configurations and document the results and their assessment thereof in an amendment to the WCF Gypsum Stack Report in order to provide an accurate representation of the seepage conditions within the final configuration of the stack and the factors of safety against piping associated with those conditions.
Clay Foundation Soil Data
Marshall Miller reviewed the results of Stantec’s gypsum stack slope stability analyses, including development of material shear strength properties. It is Marshall Miller’s professional opinion that Stantec performed stability analyses for static, long-term load conditions using appropriate methodologies. However, Marshall Miller noted that data on the clay foundation soils is lacking and has recommended additional investigation of the clay foundation. Stantec should revisit the seepage and slope stability analyses if necessitated by the findings of this additional investigation. Also, Marshall Miller believes that Stantec can improve its methodology to more rigorously characterize material properties in some instances. In order to avoid possible overstatement of the in-situ shear strength of the gypsum-fly ash material, Marshall Miller recommends that Stantec interpret shear strengths based on a definition of failure correlating with pore-pressure parameter A-bar equal to zero in instances when negative pore pressure (dilation) develops.
Periodic Reviews of 5-Year Transition to Dry Stacking/Landfilling
Management’s Response to Draft Report To address this report, TVA management had Stantec review and respond to the findings of this report. TVA management and its contractor provided additional information on the findings and recommendations in this report. For complete responses, please see appendices A – TVA Transmittal Memo and B – Stantec’s Response.
Marshall Miller Assessment of Management’s Comments to Draft Report
ITEM 1: TITLE PAGE
ITEM 2: EXECUTIVE SUMMARY
ITEM 3: TABLE OF CONTENTS
ITEM 4: INTRODUCTION
ITEM 5: MARSHALL MILLER PROJECT TEAM
ITEM 6: SCOPE OF SERVICE
ITEM 7: BACKGROUND
ITEM 8: GEOTECHNICAL EXPLORATION AND LABORATORYTESTING REVIEW
ITEM 9: SEEPAGE ANALYSES REVIEW
ITEM 10: SLOPE STABILITY ANALYSES REVIEW
APPENDICES MEMORANDUM DATED APRIL 5, 2011, FROM ROBERT M. DEACY TO ROBERT E. MARTIN
MEMORANDUM DATED APRIL 4, 2011, FROM STEPHEN H. BICKEL TO JOHN KAMMEYER
Item 4: INTRODUCTION The Tennessee Valley Authority (TVA) Office of the Inspector General (OIG) retained Marshall Miller & Associates, Inc. (Marshall Miller), to conduct a peer review of the report entitled: Report of Phase 2 Geotechnical Exploration and Slope Stability, Gypsum Stack, Widows Creek Fossil Plant (Gypsum Stack Report) prepared by Stantec Consulting Services, Inc. (Stantec), of Lexington, Kentucky. TVA retained Stantec to address geotechnical issues identified during the Phase 1 facility assessment and corresponding Phase 1 report. During its engagement, Marshall Miller reviewed the Gypsum Stack Report dated February 5, 2010, and has documented its results herein.
This report presents the following:
Item 5: MARSHALL MILLER PROJECT TEAM Marshall Miller, an employee-owned and Engineering News-Record Magazine top 500 company, began offering geologic services to the mining industry in 1975. Marshall Miller provides a range of services to the mining, utility, financial, governmental, and legal industries.
Marshall Miller employs nearly 200 engineers, geologists, scientists, and other professionals who work from regional offices in ten states.
Marshall Miller retained D’Appolonia, Engineering Division of Ground Technology, Inc., of Monroeville, Pennsylvania, for its expertise with tailings impoundments and dams, problem ground conditions, and forensic investigations.
The Marshall Miller Project Team comprises the following professionals:
• Mr. Peter Lawson – Executive Vice President & Principal-in-Charge.
• Mr. Richard G. Almes, P.E. – Principal Geotechnical Engineer.
• Mr. Christopher J. Lewis, P. E. – Principal Geotechnical Engineer. 4
Item 6: SCOPE OF SERVICE The OIG engaged Marshall Miller to provide a technical peer review of the geotechnical exploration, laboratory testing, and engineering analyses performed by Stantec for the gypsum stack at the Widows Creek Fossil Plant. Marshall Miller did not perform a parallel study (field exploration, laboratory testing, and engineering analyses) to the Stantec study of the existing gypsum stack conditions. Marshall Miller relied on the geotechnical exploration and test data provided in the Gypsum Stack Report to formulate the findings and recommendations in this report.
Marshall Miller peer reviewed Stantec’s Gypsum Stack Report dated February 5, 2010, and Appendices A through L received in electronic format (pdf files) on March 3, 2010.
Marshall Miller is unaware of newer versions of these documents. Marshall Miller based its professional opinions on the above-referenced documents.
Item 7: BACKGROUND The Widows Creek Fossil (WCF) Plant is located on the Guntersville Reservoir at the confluence of the Tennessee River and Widows Creek in Stevenson, Alabama. The WCF plant has eight coal-fired, turbine-generator units. Generators seven and eight are equipped with flue gas desulfurization units. The flue gas desulfurization units use limestone spray and forced oxidation to convert sulfur dioxide particles in the exhaust to gypsum (calcium sulfate).
Additionally, generator units seven and eight generate fly ash as a waste product from burning coal. The gypsum and fly ash are mixed, then wet sluiced in pipes to the gypsum-fly ash disposal facility (gypsum stack).
The gypsum stack is situated along the eastern side of Widows Creek, northeast of the WCF Plant. The facility initially operated by sluicing the gypsum-fly ash material to disposal ponds and decanting water to a clarification pond. In 1994, the gypsum stack was expanded and started using the wet stacking method. In its current configuration, the facility is comprised of four disposal ponds and one stilling pond. The wet stacking operation includes expanding disposal volume vertically by building perimeter dikes on top of hydraulically placed gypsum-fly ash material. The sluiced gypsum-fly ash arrives at the facility near the southwest corner of the gypsum stack and is then directed into the southern or northern rim ditch. The rim ditches flow to the rim-ditch outfall located at the northern corner of the gypsum stack.