Safety Factor Assessment, Ponds B1, B2, and B3, Reid Gardner Generating Station (Slope Stability)

Transcription

1 TECHNICAL MEMORANDUM Safety Factor Assessment, Ponds B1, B2, and B3, Reid Gardner Generating Station (Slope Stability) PREPARED FOR: PREPARED BY: REVIEED BY: NV Energy Landon Kinney/Jacobs John Barker/Jacobs Dean Harris/Jacobs DATE: April 13, 2018 CH2M PROJECT NUMBER: APPROVED BY: Nathan Betts, PE /Jacobs Introduction This technical memorandum summarizes the methods and findings of the initial slope stability safety factor assessment for Ponds B1, B2, and B3, which are inactive coal combustion residuals (CCR) surface impoundments at the Reid Gardner Generating Station (Station). This assessment was performed to satisfy the requirements of 40 Code of Federal Regulations (40 CFR) Section ( ) (e) of the U.S. Environmental Protection Agency s CCR Rule. The CCR Rule requires that an assessment be certified by a qualified professional engineer and placed in the Station s operating record by April 17, 2018 ( (e)(2), (f)(1) and (e)(3)(v)). ithin 30 days of placement the State Director must be notified as required by (f)(11) and (d). Also within 30 days of placement, the assessment must be placed on a publicly accessible Internet site per (f)(11) and (d). Per (f)(3) this assessment must be performed every 5 years starting from the date that this initial assessment is placed in the operating record. Future assessments must meet the same requirements for certification, record keeping, notification, and posting on a publicly accessible Internet site. Background Ponds B1, B2, and B3 are currently being closed;ccr has been removed, the bottom liner systems have been removed, and the ponds have been rendered physically incapable of accepting process wastewater or other liquid CCR. The interior embankments which once separated Ponds B1, B2, and B3 were removed as part of the closure. Removal of the interior embankments hydraulically connected the three ponds, essentially creating one large B Pond. The exterior embankments were left in place and unaltered, with approximately 3H:1V slopes and the maximum embankment height of approximately 25 feet. The Nevada Division of ater Resources Dam Safety Office (the State Engineer) reclassified the ponds as low hazard dams on October 24, This is the lowest hazard rating possible for a dam under Nevada regulations. Jacobs (formerly CH2M) was the designer, construction manager, and field engineer for the removal work and coordination with the State Engineer. EN BOI 1

2 SAFETY FACTOR ASSESSMENT, PONDS B1, B2, AND B3, REID GARDNER GENERATING STATION (SLOPE STABILITY) Project Setting Ponds B1, B2, and B3 are three inactive coal combustion residuals (CCR) surface impoundments at NV Energy s Reid Gardner Generation Station (Station) near Moapa, Nevada. The Station is a retired coalfired electric power generation facility that produced approximately 600 megawatts (M) of power from four generating units. The Station is located approximately 45 miles northeast of Las Vegas, within the Moapa Valley. In addition to the units, the Station has ponds, a landfill, and other support facilities. The Station is bisected by an approximate 1.5-mile-long reach of the Muddy River, a perennial stream that flows from the northwest to the southeast. All three ponds are south of the Muddy River. The Station is also bisected by a Union Pacific Railroad line that runs east-west. Ponds B1, B2, and B3 are northwest of the railroad line. The area immediately around the ponds is sparsely vegetated and undeveloped. Regulatory Requirements Published on April 17, 2015, the CCR Rule regulates the disposal of CCRs as solid waste under Subtitle D of the Resource Conservation and Recovery Act. Ponds B1, B2, and B3 are classified as inactive CCR surface impoundments according to the definitions in of the CCR Rule because they stopped receiving CCR on October 14, 2015, but still contained water and CCR a. Notifications of intent to initiate closure were placed in the Station s operating record by December 17, 2015, and posted to the publicly accessible internet site by January 16, 2016 (CH2M, 2015a, 2015b, 2015c, and 2015d). These notifications were prepared to satisfy the early-closure provisions in of the CCR Rule. However, on June 14, 2016, the United States District Court of Appeals for the District of Columbia Circuit vacated, or removed, the early-closure provisions in On August 5, 2016, the USEPA proposed revisions to which required inactive CCR surface impoundments to comply with all requirements applicable to existing CCR surface impoundments, including the requirement to complete the initial slope stability safety factor assessment (e) contains the requirements for safety factor assessments for existing CCR surface impoundments. Inactive CCR surface impoundments must meet the same requirements per (a) and (e)(3)(v). In accordance with (e), the assessment must demonstrate that the calculated factors of safety for Ponds B1, B2, and B3 achieve the minimum factors of safety as follows: The calculated static factor of safety under the long-term, maximum storage pool loading condition must equal or exceed The calculated static factor of safety under the maximum surcharge pool loading condition must equal or exceed The calculated seismic factor of safety must equal or exceed For dikes constructed of soils that have susceptibility to liquefaction, the calculated liquefaction factor of safety must equal or exceed 1.20 o o Section (e) does not specify the seismic loading event that should be used in the assessment to calculate the seismic factor of safety. However, page of the Rule s preamble states that CCR surface impoundments must be assessed for the seismic loading event with a 2 percent probability of exceedance in 50 years, which equates to a return period of approximately 2,500 years, based on the U.S. Geological Survey (USGS) seismic hazard maps for the region where Ponds are located. This is in keeping with the seismic location restrictions in which require a demonstration that CCR impoundments are designed to resist the maximum horizontal acceleration in lithified earth material, which is defined as the 2 percent in 50-year event ( ). 2 EN BOI

3 SAFETY FACTOR ASSESSMENT, PONDS B1, B2, AND B3, REID GARDNER GENERATING STATION (SLOPE STABILITY) In accordance with (e), the owner or operator of the CCR unit must conduct and complete the assessments required every five years. Technical Data This section summarizes the data used to perform the safety factor assessment. Subsurface Conditions Data was taken from the 2011 Liquefaction Analysis performed by Stanley Consultants (Stanley, 2011). The summarized subsurface profile conditions for Ponds B1, B2, and B3 are clay fill material underlain by native lean clay that transitions to a silt and then a silty sand. The soil profile used for analysis is shown in Table 1. Table 1. Soil Profile a Material Name USCS Symbol Top of Layer Elevation (ft) Thickness (ft) Fill Material CH-CL Lean Clay CL Silty Clay CL-ML Silt ML Silty Sand SM Sand SP USCS = Unified Soil Classification System. a Soil profile is based on data shown in Boring B-5 from the 2011 Stanley Consultants Report Groundwater Groundwater was encountered during the geotechnical investigations performed by Stanley Consultants. At the analyzed section, Boring B-5, groundwater was encountered at 23 feet below ground surface (bgs). This boring was located on top of the embankment, therefore in consideration of the embankment thickness, the depth to groundwater is approximately 5 feet below native ground. For purposes of liquefaction evaluation, a groundwater depth of 20 feet below the top of embankment was considered. The depth to water used for analysis is generally consistent with more recently measured groundwater elevations. Material Properties Material properties used in the safety factor assessment are based on laboratory testing and analyses reported by Stanley Consultants (2011). Previous laboratory testing consisted of moisture content and dry density, Atterberg limits, unconfined compressive strength, grain size distribution, and organic content. To establish long-term static conditions, effective stress soil parameters were used for material above the groundwater table, and total stress soil parameters below the water table. The soil parameters used in analysis are shown in Table 2. Table 2. Material Properties Material Internal Friction Angle Cohesion Unit eight Reference Fill Material (CH-CL) 30 0 psf 116 pcf Engineering judgement Lean Clay (CL) psf 120 pcf Stanley, 2011 EN BOI 3

4 SAFETY FACTOR ASSESSMENT, PONDS B1, B2, AND B3, REID GARDNER GENERATING STATION (SLOPE STABILITY) Table 2. Material Properties Silty Clay (CL-ML) psf 115 pcf Stanley, 2011 Silt (ML) psf 123 pcf Stanley, 2011 Silty Sand (SM) 27 0 psf 120 pcf Stanley, 2011 Sand (SP) 32 0 psf 110 pcf Stanley, 2011 psf = pounds per square foot pcf = pounds per cubic foot As discussed later in the evaluation section, a liquefaction analysis was performed and the Silty Sand layer at 1564 to 1545 feet elevation was identified to be susceptible to liquefaction from the design seismic event. Residual strengths for liquefied soils have were estimated based on a method recommended by Kramer (2008), which uses a weighted average of four procedures. A residual strength value of 200 psf was estimated for the Silty Sand material. Evaluation Slope stability calculations were performed to quantitatively evaluate the conditions and document compliance with the technical requirements of the CCR Rule. The sections below summarize the technical considerations and approaches used to complete the safety factor assessment. Six cross-sections (A through F) were drawn through the existing pond berms and surrounding topography for initial review. From these seven sections, a single critical cross-section was selected for stability calculations to represent Ponds B1, B2, and B3. The critical cross-section was analyzed for the safety factor assessment because it represents the most severe case for the impoundment. The critical cross-section of Ponds B1, B2, and B3 was selected based on a review of the conditions and an estimation that this cross section appear to be most susceptible to failure among all cross-sections of the embankment. The cross-section locations are shown on the attached figure. Evaluation Criteria The stability evaluation is an analysis of potential sliding of the pond embankment material on a hypothetical or trial failure surface passing through the embankment, at the interface of the embankment and native subgrade soils, through native subgrade soils, or a combination of the three. Minimum required factors of safety for the conditions analyzed are listed in the CCR Rule and presented in Table 3. Table 3. Safety Factor Criteria Loading Condition Required Minimum Safety Factor Static, long-term maximum storage pool 1.50 Static, maximum surcharge pool 1.40 Seismic 1.00 Liquefaction 1.20 Long-term Stability Scenario As stated in the background section, CCR and bottom-liner systems have been removed from Ponds B1, B2 and B3, and the conveyance pipelines that originally delivered water to the ponds have been rendered physically incapable of transmitting process wastewater or other CCR. The inlet pipe to Ponds B1, B2, and B3 has been disabled in two locations. The upstream valves have been closed and the end of 4 EN BOI

5 SAFETY FACTOR ASSESSMENT, PONDS B1, B2, AND B3, REID GARDNER GENERATING STATION (SLOPE STABILITY) the inlet pipe is flanged, and farther upstream an airgap has been installed in the pipeline. Therefore, no water will be impounded in the ponds and no surcharge was modeled for slope stability analysis. This is shown graphically in the output of the global stability analysis (Attachment 1). Max Surcharge Scenario Because Ponds B1, B2, and B3 are inactive impoundment units with no access to process wastewater, this scenario is the same as the Long-term Stability Scenario. Therefore, the slope stability results for the Long-Term Stability scenario will apply for the Max Surcharge scenario. Seismicity The USGS online U.S. Seismic Design Maps (USGS, 2016) application was used to estimate peak ground acceleration (PGA) at the project site using location coordinates (latitude , longitude ). The U.S. Seismic Design Maps application provides parameter values from the 2009 National Earthquake Hazards Reduction Program s Recommended Seismic Provisions for New Buildings and Other Structures. This design code reference document provides seismic design parameter values that are used in major U.S. building codes (International Building Code, American Association of State Highway and Transportation Officials (AASHTO), and the American Society of Civil Engineers ASCE 7 Standard). The USGS application provided a PGA for the maximum considered earthquake event. The maximum considered earthquake event corresponds to an event with a 2 percent probability of exceedance in 50 years, which equates to a return period of approximately 2,500 years. The USGS application defines the PGA as 0.273g for Site Class B (the application references the USGS 2008 ground motion database). Based on engineering judgement, the site location should be classified as Site Class D. The site coefficient at zero-period, F pga, for Site Class D is 1.255, such that the PGA at the ground surface (A s) is 0.342g (A s = x 0.273g = 0.342g). For the evaluation of seismic stability of slopes and embankments, a pseudo-static stability analysis is commonly conducted. The pseudo-static stability analysis consists of conventional limit equilibrium static slope stability analysis completed with horizontal and vertical pseudo-static acceleration coefficients (k h and k v) that act upon the critical failure mass to simulate the inertia loading from earthquakes. A horizontal pseudo-static coefficient, k h, of 0.5 x A s and a vertical pseudo-static coefficient, k v, equal to zero should be used when seismic stability of slopes is evaluated, not considering liquefaction. A seismic acceleration of 0.17g (roughly half of 0.342g) was used in a pseudo-static analysis to evaluate the seismic loading scenario, and the effective loading through the duration of shaking. Note that the use of a reduced acceleration coefficient considers the ability of the slope to displace laterally, thereby reducing the effective acceleration acting on the slope failure mass. Liquefaction Scenario Liquefaction is defined as the loss of shear strength in a saturated soil due to excess hydrostatic pressure. In saturated cohesionless soils, such a strength loss can result from loads that are applied instantaneously or cyclically, particularly in loose fine to medium sands that are uniformly graded. All of the following general conditions are necessary for liquefaction to occur: A sustained ground acceleration that is large enough and acting over a long enough period to develop excess pore-water pressure, thereby reducing effective stress and soil strength. Predominantly cohesionless soil that has characteristic gradation and composition that makes it susceptible. Liquefaction has occurred in soils ranging from low plasticity silts to gravels. Clean or silty sands and non-plastic silts are most susceptible to liquefaction. EN BOI 5

6 SAFETY FACTOR ASSESSMENT, PONDS B1, B2, AND B3, REID GARDNER GENERATING STATION (SLOPE STABILITY) The state of the soil is characterized by a density that is low enough for the soil to exhibit contractive behavior when sheared undrained under the initial effective overburden stress. The presence of groundwater, resulting in a saturated or nearly saturated soil. Liquefaction potential was evaluated for saturated cohesionless soils using the equations and procedures that generally follow the recommendations provided in the Proceedings of the National Center for Earthquake Engineering Research orkshop on Evaluation of Liquefaction Resistance of Soil (NCEER, 2000) with updates from Youd et al. (2001). N-values for the liquefaction evaluation were obtained from the testing presented in the Liquefaction Analysis report (Stanley, 2011). Corrections were made for blow-count energy, overburden pressure, and fines content following methods recommended in Youd et al. (2001). A design earthquake magnitude of 6 was used in the liquefaction analysis. This magnitude was estimated based on research of historical earthquake events within 100 miles of the project site (Stanley, 2011). Hazards associated with liquefaction of the subsurface profile include loss of soil strength and volumetric strain of the soil following the seismic event. The loss of strength and volumetric strain lead to lateral spread, slope instability, and liquefaction-induced downdrag on deep foundations resulting from liquefaction-induced settlement of the subsurface. A liquefaction analysis was performed and the Silty Sand layer at 1545 to feet elevation was identified to be susceptible to liquefaction from the design seismic event. The material has field N- values of 1 and 5. A residual strength value of 200 psf was estimated for the Silty Sand material. Method of Analyses Jacobs used the limit equilibrium methods of slope stability analysis to perform the safety factor assessment using the program SLIDE Version (Rocscience, 2018). Jacobs used the Spencer Method (a limit equilibrium method) to perform the safety factor assessment. Limit equilibrium methods compare forces, moments, and stresses that cause instability of the mass of the embankment to those that resist the instability. The principle of the limit equilibrium method is to estimate the ratio of the available shear strength of the soil to the average shear stresses along assumed failure surface, without directly estimating the magnitude of displacement of the slope. Limit equilibrium methods include, but are not limited to, methods of slices. These methods are considered conventional stability analyses by the U.S. Army Corps of Engineers Slope Stability Engineer Manual (2003), which is generally considered by the geotechnical community as a summary of the state of the practice for these analyses. These methods are also considered to be conventional by the preamble to the CCR Rule (page 21383). SLIDE allows the user to control the generation of potential failure surfaces and their locations within the embankment or foundation materials. The analysis included an evaluation of circular and noncircular (block-shaped) surfaces to consider each configuration (through embankment, interface, through foundation, and combination embankment and foundation) stipulated by the CCR Rule. Critical Sections The attached figure provides a plan view of the cross-sections considered for the safety factor assessment. Section A-A is considered the critical cross-section for Pond B1, B2, and B3. Critical Direction The critical failure direction was considered for two directions: outward beyond the pond exterior, and inward into the pond interior. A model was created for each scenario in both directions to compare and select the critical failure direction. 6 EN BOI

7 Conclusions SAFETY FACTOR ASSESSMENT, PONDS B1, B2, AND B3, REID GARDNER GENERATING STATION (SLOPE STABILITY) The computed safety factors from the global stability analyses are listed in Table 4. For each scenario analyzed, the loading condition or scenario, failure surface type, analysis method, required factor of safety, and computed factor of safety are presented in the table. The loading conditions are described in the Evaluation Criteria section of this memorandum. The failure surface type describes direction of failure and circular type. The analysis method refers to the technical approach selected in Slide to compute factor of safety. Generally, Slide calculations resulted in lowest factors of safety that were associated with circular surfaces that extended through the embankment material and foundation material. Slide results show the inward failure direction is the most critical failure direction. Copies of the Slide output plots are included as Attachment 1 to this technical memorandum. Table 4. Safety Factor Assessment Results Section Scenario Failure Surface Type and Direction Analysis Method Required Safety Factor Computed Safety Factor Pond B1, B2, B3 Section A-A Static, long-term and Max Surcharge Circular Interior Spencer Pond B1, B2, B3 Section A-A Pond B1, B2, B3 Section A-A Seismic Circular Interior Spencer Post-Earthquake Liquefaction Circular Interior Spencer a Pond B1, B2, B3 Section A-A Static, long-term and Max Surcharge Non-circular Interior Spencer Pond B1, B2, B3 Section A-A Seismic Non-circular Interior Spencer Pond B1, B2, B3 Section A-A Post-Earthquake Liquefaction Non-circular interior Spencer a Pond B1, B2, B3 Section A-A Static, long-term and Max Surcharge Circular Exterior Spencer Pond B1, B2, B3 Section A-A Pond B1, B2, B3 Section A-A Seismic Circular Exterior Spencer Post-Earthquake Liquefaction Circular Exterior Spencer Pond B1, B2, B3 Section A-A Post-Earthquake Liquefaction with Fill Placement b Circular interior Spencer b a Calculated factor of safety is less than required. Refer to technical memorandum for discussion. bthis calculation was done as part of a sensitivity analysis. Conclusion, Discussion, and Recommendation Except for the post-earthquake liquefaction scenario, the calculated factors of safety exceed the minimum safety factors required by (e) of the CCR Rule. The factor of safety of less than 1 for the post-earthquake liquefaction scenario indicates that rotational failure of the embankment into the pond could occur following the design seismic event. EN BOI 7

8 SAFETY FACTOR ASSESSMENT, PONDS B1, B2, AND B3, REID GARDNER GENERATING STATION (SLOPE STABILITY) One potential method to increase the factor of safety for the post-earthquake liquefaction scenario would be to conduct a more detailed investigation and analysis. It is important to note that the low factor of safety for this scenario was calculated using somewhat conservative assumptions and shear strength values. A combination of lower bound shear strengths, a high groundwater elevation, and subsurface data gathered by hollow-stem auger drilling methods could all contribute to a lower the factor of safety. A more rigorous geotechnical exploration and testing program, possibly coupled with more detailed geotechnical calculations, could yield higher shear strengths and thus increase the factor of safety. A second potential method to increase the factor of safety for the post-earthquake liquefaction scenario would be by field mitigation. A sensitivity analysis calculation showed a layer of earthen fill material placed inside of the pond, approximately 4 feet thick, could be suitable mitigation to increase the factor of safety above the required value of 1.2. As stated in the background section, CCR and bottom-liner systems have been removed from Ponds B1, B2 and B3, and the conveyance pipelines that originally delivered water to the ponds have been rendered physically incapable of transmitting process wastewater or other CCR. Because the ponds no longer contain liquid or CCR, a release to the environment could not occur as the result of failure. Furthermore, the ponds are regulated and permitted as dams by the State Engineer, who, at the request of NV Energy, has lowered the hazard rating and revoked the legal authorization to impound liquid in the ponds. Due to this status, neither a more rigorous analysis nor field mitigation are recommended to improve the post-earthquake liquefaction factor of safety for Ponds B1, B2, and B3. It is recommended that closure operations for Ponds B1, B2, and B3 continue, meeting CCR Rule requirements for closure triggered by failing a safety factor assessment. Per (b)(2), within 6 months of failing a safety factor assessment the owner must cease placing CCR and non-ccr wastewater streams in the ponds and close the unit in accordance with The first part of that requirement was met when the ponds stopped receiving CCR and non-ccr waste on October 14, Closure began on December 14, 2015 when notifications of intent to initiate closure were placed in the Station s operating record, and completing closure in accordance with CCR Rule requirements will satisfy the second part of (b)(2). Professional Engineer Certification This section contains the written certification by a qualified professional engineer as required by Section (e)(2) of the CCR Rule. This initial safety factor assessment meets the requirements of Section (e) of the CCR Rule. 8 EN BOI

9 References SAFETY FACTOR ASSESSMENT, PONDS B1, B2, AND B3, REID GARDNER GENERATING STATION (SLOPE STABILITY) Kramer, S.L Evaluation of Liquefaction Hazards in ashington State, ashington State Department of Transportation, Report A-RD December. Rocscience, Inc Slide Computer Software. Version 7.009, Build date: March 29, Stanley Consultants Liquefaction Analysis: NV Energy Reid Gardner Station Coal Combustion aste Impoundments. December. U.S. Geological Survey (USGS). U.S. Seismic Design Maps. Accessed March 19, EN BOI 9

10 EN BOI Figure

11 E POND B1 D F B Figure_Ponds_B1_B2_B3.dgn PLOT DATE: POND B \04\11 PLOT TIME: APVD BY E C D BAR IS ONE INCH ON ORIGINAL DRAING. VERIFY SCALE DATE 1" PROJ DG P-BG:387230_NV ENERGY \ SHEET 10:51:42 AM NOT FOR c CH2M HI LL ALL RI GHTS RESERVED. APVD PRELIMINARY R E N L O I S T M I T R F NA U O R C R Y T IO N CONSTRUCTION REUSE OF DOCUM ENTS: THI S DOCUM ENT,AND THE I DEAS AND DESI GNS I NCORPORATED HEREI N,AS AN I NSTRUM ENT OF PROFESSI ONAL SERVI CE,I S THE PROPERTY OF CH2M HI LL AND I S NOT TO BE USED,I N HOLE OR I N PART,FOR ANY OTHER PROJECT I THOUT THE RI TTEN AUTHORI ZATI ON OF CH2M HI LL. CHK REVI SI ON DR A DSGN DRAFT I SSUE FOR CLI ENT REVI E DATE C 03/ 11/ 18 B 0 N Scale In Feet 300 NO. O 200 PRELI MI NARY NOT FOR CONSTRUCTI ON A 100 P 0 POND B1,B2 & B3 A POND B2 5 CROSS SECTI ONS LOCATI ON F TI TLE1 C N D B C 4 PHONE: HENDERSON, NEVADA VILLAGE VIE DRIVE, SUITE

12 EN BOI Attachment 1 Slide Output Plots

13 Safety Factor Material Name Color Unit eight (lbs/ 3) Cohesion (psf) Phi (deg) Fill (CL-CH) Clay (CL-CH) Lean Clay (CL) Silty Clay (CL-ML) Silt (ML) Silty Sand (SM) Sand (SP) Factor of Safety Fill (CL-CH) Clay (CL-CH) 1600 Lean Clay (CL) 1580 Silty Clay (CL-ML) Silt (ML) 1560 Silty Sand (SM) 1540 Sand (SP) Project CCR Pond B1 - Slope Stability Analysis Analysis Description Long-term Static Loading Drawn By L. Kinney Scale 1:300 Company Jacobs SLIDEINTERPRET Date 3/29/2018, 3:28:17 PM File Name Long-term Static - Circular - Interior

14 1720 Safety Factor Material Name Color Unit eight (lbs/ 3) Cohesion (psf) Phi (deg) Fill (CL-CH) Clay (CL-CH) Lean Clay (CL) Silty Clay (CL-ML) Factor of Safety 1.09 Silt (ML) Silty Sand (SM) Sand (SP) Fill (CL-CH) Clay (CL-CH) 1600 Lean Clay (CL) 1580 Silty Clay (CL-ML) Silt (ML) 1560 Silty Sand (SM) 1540 Sand (SP) Project CCR Pond B1 - Slope Stability Analysis Analysis Description Seismic Loading Drawn By L. Kinney Scale 1:300 Company Jacobs SLIDEINTERPRET Date 3/29/2018, 11:39:26 AM File Name Seismic - Circular - Interior

15 Safety Factor Material Name Color Unit eight (lbs/ 3) Cohesion (psf) Phi (deg) Fill (CL-CH) Clay (CL-CH) Lean Clay (CL) Silty Clay (CL-ML) Silt (ML) Factor of Safety 0.96 Silty Sand (SM) Sand (SP) Fill (CL-CH) Clay (CL-CH) 1600 Lean Clay (CL) 1580 Silty Clay (CL-ML) Silt (ML) 1560 Liquefied Zone Silty Sand (SM) 1540 Sand (SP) Project CCR Pond B1 - Slope Stability Analysis Analysis Description Post-Earthquake Liquefaction Drawn By L. Kinney Scale 1:300 Company Jacobs SLIDEINTERPRET Date 3/29/2018, 3:28:17 PM File Name Liquefaction - Circular - Interior

16 Safety Factor Factor of Safety 1.93 Material Name Color Unit eight (lbs/ 3) Cohesion (psf) Phi (deg) Fill (CL-CH) Clay (CL-CH) Lean Clay (CL) Silty Clay (CL-ML) Silt (ML) Silty Sand (SM) Sand (SP) Fill (CL-CH) Clay (CL-CH) 1600 Lean Clay (CL) 1580 Silty Clay (CL-ML) Silt (ML) 1560 Silty Sand (SM) 1540 Sand (SP) Project CCR Pond B1 - Slope Stability Analysis Analysis Description Long-term Static Loading Drawn By L. Kinney Scale 1:300 Company Jacobs SLIDEINTERPRET Date 3/29/2018, 3:28:17 PM File Name Long Term Static - Non-circular - Interior

17 Safety Factor Factor of Safety Material Name Color Unit eight (lbs/ 3) Cohesion (psf) Phi (deg) Fill (CL-CH) Clay (CL-CH) Lean Clay (CL) Silty Clay (CL-ML) Silt (ML) Silty Sand (SM) Sand (SP) Fill (CL-CH) Clay (CL-CH) 1600 Lean Clay (CL) Silty Clay (CL-ML) 1575 Silt (ML) Silty Sand (SM) 1550 Sand (SP) Project CCR Pond B1 - Slope Stability Analysis Analysis Description Seismic Loading Drawn By L. Kinney Scale 1:350 Company Jacobs SLIDEINTERPRET Date 3/29/2018, 11:39:26 AM File Name Seismic - Non-circular - Interior

18 Safety Factor Factor of Safety Material Name Color Unit eight (lbs/ 3) Cohesion (psf) Phi (deg) Fill (CL-CH) Clay (CL-CH) Lean Clay (CL) Silty Clay (CL-ML) Silt (ML) Silty Sand (SM) Sand (SP) Fill (CL-CH) Clay (CL-CH) 1600 Lean Clay (CL) Silty Clay (CL-ML) 1575 Silt (ML) 1550 Liquefied Zone Silty Sand (SM) Sand (SP) Project CCR Pond B1 - Slope Stability Analysis Analysis Description Post-Earthquake Liquefaction Drawn By L. Kinney Scale 1:350 Company Jacobs SLIDEINTERPRET Date 3/29/2018, 3:28:17 PM File Name Liquefaction - Non-circular - Interior

19 Safety Factor Material Name Color Unit eight (lbs/ 3) Cohesion (psf) Phi (deg) Fill (CL-CH) Clay (CL-CH) Lean Clay (CL) Silty Clay (CL-ML) Silt (ML) Silty Sand (SM) Sand (SP) Factor of Safety Fill (CL-CH) Clay (CL-CH) 1600 Lean Clay (CL) 1580 Silty Clay (CL-ML) Silt (ML) 1560 Silty Sand (SM) 1540 Sand (SP) Project CCR Pond B1 - Slope Stability Analysis Analysis Description Long-term Static Loading Drawn By L. Kinney Scale 1:300 Company Jacobs SLIDEINTERPRET Date 3/29/2018, 3:28:17 PM File Name Long Term Static - Circular - Exterior

20 Safety Factor Factor of Safety Material Name Color Unit eight (lbs/ 3) Cohesion (psf) Phi (deg) Fill (CL-CH) Clay (CL-CH) Lean Clay (CL) Silty Clay (CL-ML) Silt (ML) Silty Sand (SM) Sand (SP) Fill (CL-CH) Clay (CL-CH) 1600 Lean Clay (CL) 1580 Silty Clay (CL-ML) Silt (ML) 1560 Silty Sand (SM) 1540 Sand (SP) Project CCR Pond B1 - Slope Stability Analysis Analysis Description Seismic Loading Drawn By L. Kinney Scale 1:300 Company Jacobs SLIDEINTERPRET Date 3/29/2018, 11:39:26 AM File Name Seismic - Circular - Exterior

21 Safety Factor Material Name Color Unit eight (lbs/ 3) Cohesion (psf) Phi (deg) Fill (CL-CH) Clay (CL-CH) Lean Clay (CL) Silty Clay (CL-ML) Silt (ML) Factor of Safety 1640 Silty Sand (SM) Sand (SP) Fill (CL-CH) Clay (CL-CH) 1600 Lean Clay (CL) 1580 Silty Clay (CL-ML) Silt (ML) 1560 Liquefied Zone Silty Sand (SM) 1540 Sand (SP) Project CCR Pond B1 - Slope Stability Analysis Analysis Description Post-Earthquake Liquefaction Drawn By L. Kinney Scale 1:300 Company Jacobs SLIDEINTERPRET Date 3/29/2018, 3:28:17 PM File Name Liquefaction - Circular - Exterior

22 Safety Factor Material Name Color Unit eight (lbs/ 3) Cohesion (psf) Phi (deg) Fill (CL-CH) Clay (CL-CH) Lean Clay (CL) Silty Clay (CL-ML) Silt (ML) Factor of Safety Silty Sand (SM) Sand (SP) Fill 2 (CL-CH) Fill (CL-CH) Clay (CL-CH) Fill 2 (CL-CH) Approx. 4 ft. fill 1600 Lean Clay (CL) 1580 Silty Clay (CL-ML) Silt (ML) 1560 Liquefied Zone Silty Sand (SM) 1540 Sand (SP) Project CCR Pond B1 - Slope Stability Analysis Analysis Description Post-Earthquake Liquefaction Drawn By L. Kinney Scale 1:300 Company Jacobs SLIDEINTERPRET Date 3/29/2018, 3:28:17 PM File Name Liquefaction Left with Fill