CCR Surface Impoundment Location Restrictions Demonstration. MidAmerican Energy Company, Louisa Generating Station

Transcription

1 CCR Surface Impoundment Location Restrictions Demonstration MidAmerican Energy Company, Louisa Generating Station Final October 17, 2018

2 CCR Surface Impoundment Location Restrictions Demonstration Prepared for MidAmerican Energy Company, Louisa Generating Station Muscatine, Iowa Final October 17, 2018 Prepared by Burns & McDonnell Engineering Company, Inc. Kansas City, Missouri COPYRIGHT 2018 BURNS & McDONNELL ENGINEERING COMPANY, INC.

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4 (jd Kira Wylam, P.E. (liu/23129) Date: I 0 / f *7 j Kira Wylam License Number My license renewal date is December 31, 2018 Nathan Textor, P.E. (Ia #23013) Date: to /ll/[ % Nathan Textor License Number My license renewal date is December 31, 2018 Sections covered by this seal: 3.3, 3.4 and 3.5.

5 LGS CCR Surface Impoundment Table of Contents TABLE OF CONTENTS Page No. 1.0 SUMMARY OF OBJECTIVES REVIEW OF AVAILABLE INFORMATION Geologic Information Geotechnical Investigations Design Drawings Impoundment Inspections Groundwater Information Seismic LOCATION RESTRICTIONS DEMONSTRATION Placement Above the Uppermost Aquifer Wetlands Fault Areas Seismic Impact Zones Unstable Areas REPORT LIMITATIONS APPENDIX A EXCERPT FROM CCR RULE APPENDIX B SITE PLAN MidAmerican Energy Company TOC-1 Burns & McDonnell

6 LGS CCR Surface Impoundment List of Abbreviations LIST OF ABBREVIATIONS Abbreviation ASCE BMcD CCR CFR EPA Impoundment LGS MEC RCRA U.S.C. USGS Term/Phrase/Name American Society of Civil Engineers Burns & McDonnell Coal Combustion Residual Code of Federal Regulations Environmental Protection Agency CCR Surface Impoundment Louisa Generating Station MidAmerican Energy Company Resource Conservation and Recovery Act United States Code United States Geological Survey MidAmerican Energy Company i Burns & McDonnell

7 LGS CCR Surface Impoundment Summary of Objectives 1.0 SUMMARY OF OBJECTIVES On April 17, 2015, the Environmental Protection Agency (EPA) issued the final version of the federal Coal Combustion Residual Rule (CCR Rule) to regulate the disposal of coal combustion residual (CCR) materials generated at coal-fired units. The rule is administered as part of the Resource Conservation and Recovery Act (RCRA, 42 United States Code [U.S.C.] 6901 et seq.), using the Subtitle D approach. MidAmerican Energy Company (MEC) is subject to the CCR Rule. Per the requirements of 40 Code of Federal Regulations (CFR) through , a location restrictions demonstration for all Active CCR Impoundments is required. A qualified professional engineer must determine that the results of the assessments meets the requirements of through On behalf of MEC, Burns & McDonnell (BMcD) has completed the Location Restrictions Demonstration of the Louisa Generating Station CCR Surface Impoundment which is currently undergoing closure. An excerpt from the CCR Rule describing the requirements that are addressed in this report are included in Appendix A. This report contains a description of the information available to support the location restrictions demonstration and the assessment of each of the required location restriction demonstrations. Based on this assessment, the CCR Surface Impoundment does not meet the requirements of the location restrictions demonstration. MidAmerican Energy Company 1-1 Burns & McDonnell

8 LGS CCR Surface Impoundment Review of Available Information 2.0 REVIEW OF AVAILABLE INFORMATION Louisa Generating Station (LGS) is a coal-fired power plant located near Muscatine, Iowa that is owned and operated by MEC. The LGS CCR Surface Impoundment (Impoundment) is a surface impoundment previously utilized to impound water and sluiced CCR as part of the plant ash handling system. All CCR and non-ccr wastewater flows were discontinued to the Impoundment after November 13, 2017, and is currently undergoing closure. The following subsections provide information associated with the Impoundment including geologic/geotechnical information, design drawings, inspections, groundwater information and seismic information. This information was reviewed to provide an understanding of the characteristics if the Impoundment that are related to the location restrictions. Its application to the requirements of the CCR Rule are discussed further in Section 3.0. A general site plan of the area is included in Appendix B. 2.1 Geologic Information Based on a review of the Iowa Geological Survey s Map of the Surface Deposits of Louisa County, Iowa, (1900), the site is underlain by the alluvium from the Mississippi River. Borings indicate the alluvium is sand with varying amounts of silt. Bedrock was encountered between elevations of feet and feet. No karst activity has been noted in these counties per the Iowa Geological Survey s Geologic Hazards webpage ( No underground mines are mapped in this area per the Iowa Geological Survey s Iowa Coal Mines online map. 2.2 Geotechnical Investigations Multiple geotechnical investigations have been performed at the Impoundment site. In 2010, an investigation was performed by Terracon to support a slope stability evaluation of the Impoundment. This investigation included drilling a total of five (5) borings to characterize the embankment and subsurface conditions. The borings were drilled to a depth of 40 feet below grade. In 2016, an investigation was performed by Braun Intertec to support evaluations related to Structural Stability and Safety Factor Assessments required by the CCR Rule. This investigation included drilling a total of 33 borings to characterize the embankment, CCR and underlying materials of the Impoundment. The borings were drilled between depths of 20.0 and feet below grade. MidAmerican Energy Company 2-1 Burns & McDonnell

9 LGS CCR Surface Impoundment Review of Available Information In 2018, an investigation was performed by Terracon to determine conditions in the interior of the Impoundment including depth of CCR and clay liner. This investigation included drilling a total of 12 borings to characterize the Impoundment interior subsurface conditions. The borings were drilled between depths of 19 and 38 feet below grade. Embankments are comprised of cohesionless soils. Underlying the embankments are fine to coarse sands with varying amount of silts and some intermittent clay layers. Sands increase in density with depth. CCR was encountered at an elevation of feet and above during the 2018 Terracon investigation. A sandy clay liner was encountered below the CCR. 2.3 Design Drawings Design drawings for the Impoundment were prepared by Black and Veatch in The drawings indicate the base of the Impoundment was to be excavated to an approximate elevation of 542 feet. Specifications note that any unsuitable materials will be removed from the subgrade before scarifying and recompaction of the subgrade is to occur. No construction quality assurance information is available for the Impoundment. 2.4 Impoundment Inspections As part of the CCR Rule, inspections are required for the following: On a 7-day basis, a qualified individual inspects for any appearances of actual or potential structural weakness and other conditions that could disrupt the operation of the Impoundment. On an annual basis, a qualified and certified engineer in the state of Iowa ensures that design, construction, operation, and maintenance of the Impoundment is consistent with recognized and generally accepted good engineering practices. Weekly inspections performed by MEC during 2018 were reviewed by BMcD. No appearances of actual or potential structural weaknesses were observed by MEC during these inspections. The 2017 annual inspection was performed by HGM Associates, Inc. on October 4, 2017, and documented in a report dated January 12, Based upon BMcD s review, no appearances of actual or potential structural weaknesses were observed by HGM Associates, Inc. at the time of their inspection. MidAmerican Energy Company 2-2 Burns & McDonnell

10 LGS CCR Surface Impoundment Review of Available Information If future inspections find the appearance of actual or potential structural weakness caused by unstable conditions, generally accepted good engineering practices should be incorporated, at that time, to mitigate the unstable condition. 2.5 Groundwater Information Uppermost groundwater elevation data from the CCR Impoundment monitoring well network presented in the 2017 Annual Groundwater Monitoring and Corrective Action Report prepared by Terracon Consultants, Inc. and dated January 30, 2018, were reviewed. 2.6 Seismic Data on the United States Geological Survey (USGS) website were reviewed to understand seismic characteristics of the site including peak ground acceleration and proximity of nearby faults. Utilizing the USGS 2014 Unified Hazard Tool v4.1.1, the peak ground acceleration for an earthquake with a probability of occurrence of 2 percent in 50 years was determined to be g at this site. This acceleration is associated with a Site Class B/C which corresponds to a weak rock. Based on investigations performed at the site, the site is characterized as a Site Class D. Since Site Class D material is weaker than Site Class B/C, it will cause amplification of the seismic acceleration. Per approaches put forward in American Society of Civil Engineers (ASCE) 7-10, the amplification factor for a Site Class D is 1.6. Utilizing this factor, the peak ground acceleration for this site for the design earthquake is g. Utilizing the USGS U.S. Quaternary Faults and Folds Database mapping application, there are no Quaternary age faults in the vicinity of the Impoundment. It should be noted that the Quaternary period covers the last 2.6 million years and includes the Holocene epoch (the last 11,700 years). Therefore, the information from USGS mapping application covers the time range for active faults as required by the CCR Rule. The USGS Unified Hazard Tool can be found at and the USGS U.S. Quaternary Faults and Folds Database mapping application can be found at MidAmerican Energy Company 2-3 Burns & McDonnell

11 LGS CCR Surface Impoundment 3.0 LOCATION RESTRICTIONS DEMONSTRATION Pursuant to 40 CFR to , an existing CCR Surface Impoundment must meet requirements associated with the five location restrictions: Placement above the uppermost aquifer, Wetlands, Fault Areas, Seismic impact zones, and Unstable areas. Discussions on each of these requirements will be made below with determinations made based on review of the previously discussed information. 3.1 Placement Above the Uppermost Aquifer Per 40 CFR , existing CCR surface impoundments must be constructed with a base that is located no less than 1.52 meters (five feet) above the upper limit of the uppermost aquifer, or must demonstrate that there will not be an intermittent, recurring or sustained hydraulic connection between any portion of the base of the CCR unit and the uppermost aquifer due to normal fluctuations in ground elevations (including the seasonal high water table). The uppermost groundwater elevations measured during nine (9) monitoring events conducted from December 2015 through October 2017 were above feet above mean sea level and are within five (5) feet of the minimum elevation (538.5 feet) where CCR was encountered within the Impoundment during the 2018 Terracon geotechnical investigation. Therefore, the Impoundment does not meet the separation requirements of (a). 3.2 Wetlands For regulatory purposes, a wetland is defined as those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions (40 CFR 232.2). Per 40 CFR , existing surface impoundments must not be located in wetlands as defined in of this chapter. 40 CFR states that waste treatment systems, including treatment ponds or lagoons designed to meet the requirements of the Clean Water Act are not Waters of the United States. The Impoundment is MidAmerican Energy Company 3-1 Burns & McDonnell

12 LGS CCR Surface Impoundment a part of a wastewater treatment system with an NPDES permit. As such, and per 40 CRF 232.2, there are no jurisdiction wetlands within the Impoundment. Therefore, the Impoundment meets the wetlands requirements of (a). 3.3 Fault Areas Per 40 CFR , existing CCR surface impoundments must not be located within 60 meters (200 feet) of the outermost damage zone of a fault that has had displacement in the Holocene time. Based on available information provided by USGS, there are no faults within 60 meters (200 feet) of the Impoundment that have been active within the Holocene epoch. Therefore, the Impoundment meets the requirements of (a). 3.4 Seismic Impact Zones Per 40 CFR , existing CCR surface impoundments must not be located in seismic impact zones. A seismic impact zone is defined by the CCR Rule as an area having a 2% or greater probability that the maximum expected horizontal acceleration is 0.10 g in 50 years. Based on available information provided by USGS and ASCE methodology, the peak ground acceleration for a seismic event with a 2% probability of occurring in 50 years is g at this site. Therefore, the Impoundment meets the requirements of (a). 3.5 Unstable Areas Per 40 CFR , existing CCR surface impoundments must not be located in an unstable area unless the owner or operator demonstrates that recognized and generally accepted good engineering practices have been incorporated into design to ensure that the integrity of the structural components of the CCR unit will not be disrupted. The following factors must be considered as part of the unstable area determination: On-site or local soil conditions that may results in significant differential settling, On-site or local geologic or geomorphologic features, and On-site or local human-made features or events (both surface and subsurface). Based on a review of available subsurface information, the materials beneath the Impoundment are not susceptible to large scale differential settling, including settlement caused by placed CCR and fill or from liquefaction during a design seismic event. Inspections do not indicate any indications of detrimental settlement features such as cracking of the embankment. There are also no noted geologic features prone to settlement, such as karst, and no man-made features, such as mines, indicated near the site. Therefore, the Impoundment meets the requirements discussed in (a). MidAmerican Energy Company 3-2 Burns & McDonnell

13 LGS CCR Surface Impoundment Report Limitations 4.0 REPORT LIMITATIONS This report is based on the information reviewed and described herein. A review of available design documents, geotechnical investigations, groundwater data and inspection reports was performed as part of this demonstration to aid in the understanding of previous work performed. This review is not an assurance of the work performed by others as indicated in the documents reviewed including design, construction, testing, operation, and inspection of the Impoundment. MidAmerican Energy Company 4-1 Burns & McDonnell

14 APPENDIX A EXCERPT FROM CCR RULE

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18 APPENDIX B SITE PLAN

19 OUTFALL 002 BOTTOM ASH POND 2018 BURNS & M cdonnell ENGINEERING COM PANY, INC. COPYRIGHT date designed OCT. 9, 2018 K. WYLAM MIDAMERICAN ENERGY COMPANY LOUISA LOCATION RESTRICTIONS SITE PLAN 0 400' 800' SCALE IN FEET project contract SK - MISSISSIPPI RIVER N Z:\Clients\ENR\MidAmEnr\86505_MECLouisaCCRPr\Design\Civil\Dwgs\Sketches\CCR Compliance Report\86505SK003_LR.dgn

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