STA 1W Expansion #2 Final Geotechnical Engineering Design ...

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STA 1W Expansion #2 Final Geotechnical Engineering Design Report Deliverable 2.5.2 – Updated Geotechnical Design Report

South Florida Water Management District Project reference: STA 1W - Expansion No. 2 May 19, 2020

Quality information

Prepared by Checked by Verified by Approved by

T. Kristopher Wachtel, EITPh.D.Associate Dams Engineer

G. Michael McIntyre, PE

Dams Practice Leader, Southeast Region

Dennis J. Hogan, PE

Senior Project Engineer

Fernando Navarrete, PhD, PE

Sr. Project Manager

Revision History

Revision Revision date Details Authorized Name Position

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Geotechnical Engineering Design Report

Project reference: STA 1W - Expansion No. 2

Prepared for: South Florida Water Management District

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Prepared by: Dennis J. Hogan, PE Senior Project Engineer T: 215-869-9448 E: [email protected] T. Kristopher Wachtel, PhD, EIT Geotechnical Engineer T: 301-944-3466 E: [email protected] AECOM 2090 Palm Beach Lakes Blvd, Suite 600 West Palm Beach, FL 33409 aecom.com

Copyright © 2020 by AECOM

All rights reserved. No part of this copyrighted work may be reproduced, distributed, or transmitted in any form or by any means without the prior written permission of AECOM.




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List of Acronyms and Abbreviations

cfs cubic feet per second CERP Comprehensive Everglades Restoration Plan CIU Isotropically Consolidated Undrained strength test DCM Design Criteria Memorandum ECPM Engineering and Construction Project Manager EM Engineer Manual (USACE) ENR Everglades Nutrient Removal FAS Floridan Aquifer System FDEP Florida Department of Environmental Protection FEMA Federal Emergency Management Agency FERC Federal Energy Regulatory Commission FFE Finished Floor Elevation FGS Florida Geological Survey FPL Florida Power & Light Company FS Factor of Safety ft feet GBODM Geotechnical Basis of Design Memorandum GDR Geotechnical Data Report GEDR Geotechnical Engineering Design Report H Horizontal HPC Hazard Potential Classification Hz hertz IBC International Building Code ICU Intermediate Confining Unit in. inch NAD83 North American Datum of 1983 NAVD88 North American Vertical Datum of 1988 NEH National Engineering Handbook NFSL Normal Full Storage Level NRCS Natural Resources Conservation Service PGA peak ground acceleration psf/ksf pounds per square foot/ kilopounds per square foot psi pounds per square inch RADISE RADISE International, L.C. SAS Surficial Aquifer System SDC Seismic Design Categories SFWMD South Florida Water Management District SIR Subsidence Incident Report SPT Standard Penetration Test STA 1W Stormwater Treatment Area 1 West tsf tons per square foot USACE U.S. Army Corps of Engineers USBR U.S. Bureau of Reclamation USDA United States Department of Agriculture




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USGS United States Geological Survey V Vertical WCA-1 Water Conservation Area 1 WQBEL Water Quality Based Effluent Limit WSEL Water Surface Elevation




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Table of Contents

1. Organization of Report ......................................................................................... 1 2. Introduction ........................................................................................................... 2 2.1 Scope of Work ................................................................................................................................................. 3 3. Project Description ............................................................................................... 4 3.1 Background ...................................................................................................................................................... 4 3.2 Project Features .............................................................................................................................................. 5 3.3 Site Location .................................................................................................................................................... 7 3.4 Geologic Conditions ......................................................................................................................................... 7 3.4.1 Physiography ............................................................................................................................................... 7 3.4.2 Surficial Soils ................................................................................................................................................ 7 3.4.3 Geology ........................................................................................................................................................ 8 3.4.4 Hydrogeologic Conditions ............................................................................................................................ 8 3.5 Geologic Hazards ............................................................................................................................................ 9 3.5.1 Seismic Potential .......................................................................................................................................... 9 3.5.2 Sinkhole Potential......................................................................................................................................... 9 4. Design Criteria .................................................................................................... 10 4.1 Canal and Embankments ............................................................................................................................... 10 4.1.1 Design Water Levels .................................................................................................................................. 12 4.1.2 Material Parameters ................................................................................................................................... 13 4.1.3 Field Exploration Programs ........................................................................................................................ 13 4.1.4 Survey and Mapping .................................................................................................................................. 14 4.1.5 Laboratory Testing Programs ..................................................................................................................... 14 4.1.6 Generalized Site Stratigraphy .................................................................................................................... 14 4.1.7 Selection of Engineering Properties ........................................................................................................... 15 4.2 Structures Analyses ....................................................................................................................................... 16 4.2.1 Foundation Information .............................................................................................................................. 17 4.2.2 Structures Analyses Material Properties ..................................................................................................... 17 4.2.3 Structures Analyses Water Surface Elevations .......................................................................................... 18 4.2.4 Estimated Subsurface Profile ..................................................................................................................... 19 5. Geotechnical Analyses and Design .................................................................... 20 5.1 Canal and Embankments ............................................................................................................................... 20 5.1.1 Embankments Analyses Material Properties .............................................................................................. 20 5.1.2 Embankment Bearing Capacity .................................................................................................................. 21 5.1.3 Embankment Settlement ............................................................................................................................ 21 5.1.4 Seepage Analysis ....................................................................................................................................... 22 5.1.4.1 Hydraulic Conductivity ................................................................................................................................ 22 5.2 Boundary and Geometry Sensitivity Analysis ................................................................................................. 22 5.2.1 Limestone Hydraulic Conductivity Sensitivity Analysis ............................................................................... 23 5.2.2 Sensitivity Analysis of Embankment Fill and Foundation Seepage Engineering Properties ....................... 25 5.2.3 Sensitivity Analysis of Vertical Boundary Conditions .................................................................................. 26 5.2.4 Selected Hydraulic Conductivity Parameters ............................................................................................. 26 5.2.4.1 Uplift, Heave and Piping ............................................................................................................................. 27 5.2.4.2 Seepage Impact ......................................................................................................................................... 29 5.2.5 Slope Stability Analysis .............................................................................................................................. 30 5.2.5.1 Slope Stability Analysis Results ................................................................................................................. 31




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5.3 Structure Foundations.................................................................................................................................... 35 5.3.1 Settlement Analyses ................................................................................................................................... 35 5.3.2 Bearing Capacity Analyses ......................................................................................................................... 37 5.3.3 Recommendations ..................................................................................................................................... 38 5.3.3.1 Mat Foundations ........................................................................................................................................ 38 5.3.3.2 Spread Footings ......................................................................................................................................... 39 5.3.3.3 Floor Slabs ................................................................................................................................................. 40 5.3.3.4 Below Grade Walls ..................................................................................................................................... 40 5.3.3.5 Hydrostatic Uplift Design ............................................................................................................................ 40 5.3.3.6 Seepage Cut Off Walls ............................................................................................................................... 40 5.3.3.7 Sheet Piles ................................................................................................................................................. 41 5.4 Seismic Design .............................................................................................................................................. 42 6. Considerations for Construction and Future Activity ........................................... 43 6.1 Site Access and Preparation .......................................................................................................................... 43 6.2 Erosion Protection ......................................................................................................................................... 43 6.3 Embankment and Canal Construction ........................................................................................................... 44 6.4 Fill Materials and Fill Placement .................................................................................................................... 44 6.5 Foundation Subgrade Preparation ................................................................................................................. 45 6.6 Instrumentation and Monitoring ..................................................................................................................... 45 7. Summary ............................................................................................................ 46 8. Limitations .......................................................................................................... 47 9. References ......................................................................................................... 48

Figures Figure 1. Approximate STA 1W and Expansion Areas 1 and 2 Location ........................................................................ 2 Figure 2. Alternative 6 Configuration Schematic ............................................................................................................ 4 Figure 3. STA 1W Expansion Area 2 .............................................................................................................................. 5 Figure 4. STA 1W Expansion Area 2 Cross Section Locations..................................................................................... 11 Figure 5. Seismic Hazard Map Based on 2% Probability of Exceedance in 50 Years of PGA ..................................... 42

Tables

Table 3-1: Expansion 2 Anticipated Structures ............................................................................................................... 6 Table 4-1: Design Water Surface Elevations for XS-1, XS-2, and XS-3 (NAVD88) ...................................................... 12 Table 4-2: Design Water Surface Elevations for XS-4 (NAVD88) ................................................................................. 12 Table 4-3: Design Water Surface Elevations for XS-5 (NAVD88) ................................................................................. 12 Table 4-4: Design Water Surface Elevations for XS-6 (NAVD88) ................................................................................. 12 Table 4-5: Design Water Surface Elevations for XS-7 (NAVD88) ................................................................................. 12 Table 4-6: Design Water Surface Elevations for XS-8 (NAVD88) ................................................................................. 12 Table 4-7: Design Water Surface Elevations for XS-9 (NAVD88) ................................................................................. 13 Table 4-8: Design Water Surface Elevations for XS-10 (NAVD88) ............................................................................... 13 Table 4-9: Design Water Surface Elevations for XS-11 (NAVD88) ............................................................................... 13 Table 4-10: Design Water Surface Elevations for XS-12 (NAVD88) ............................................................................. 13 Table 4-11: Shear Strength Parameters for Connection Canal ..................................................................................... 16 Table 4-12: Shear Strength Parameters for STA Expansion 2...................................................................................... 16 Table 4-13: Foundation Information.............................................................................................................................. 17 Table 4-14: Material Properties for Settlement Analyses (North Inflow Pump Station and Connection Canal Energy Dissipation Structure) ................................................................................................................................................... 18




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Table 4-15: Material Properties for Settlement Analyses (Other Structure Foundations) ............................................. 18 Table 4-16: Structural Fill Properties used in Structures Bearing Capacity and Settlement Analyses .......................... 18 Table 4-17: Subsurface Profile Borings ........................................................................................................................ 19 Table 5-1: Organic/Peat Elastic Deformation Parameters ............................................................................................ 21 Table 5-2: Organic/Peat Consolidation Parameters ..................................................................................................... 21 Table 5-3: Embankment Settlement (with underlying Peats) Calculation Summary ..................................................... 22 Table 5-4: Field-Measured Horizontal Hydraulic Conductivity from Piezometer Constant Head Tests ......................... 23 Table 5-5: Cross Section XS-4 (Phase 1) Boundary Conditions .................................................................................. 23 Table 5-6: Cross Section XS-6 Boundary Conditions ................................................................................................... 24 Table 5-7: Cross Section XS-8 Boundary Conditions ................................................................................................... 24 Table 5-8: Cross Section XS-4 (Phase 1) Boundary Conditions for Existing Conditions .............................................. 25 Table 5-9: Sensitivity Analysis results for Vertical Boundary Conditions ....................................................................... 26 Table 5-10: Hydraulic Conductivity Parameters............................................................................................................ 27 Table 5-11: Uplift, Heave and Piping Analysis Parameters ........................................................................................... 28 Table 5-12: Uplift, Heave and Piping Analysis Results for Connection Canal .............................................................. 28 Table 5-13: Uplift, Heave and Piping Analysis Results for Expansion 2 ....................................................................... 29 Table 5-14: Comparison of Seepage Flow Rates with Existing Conditions .................................................................. 30 Table 5-15: Slope Stability Factors of Safety ................................................................................................................ 31 Table 5-16: Critical Slope Stability Factors of Safety Connection Canal ...................................................................... 33 Table 5-17: Critical Slope Stability Factors of Safety Expansion 2 ............................................................................... 34 Table 5-18: Estimated Structure Foundation Settlements ............................................................................................ 36 Table 5-19: Estimated Allowable Bearing Capacities of Structure Foundations ........................................................... 37 Table 5-20: Recommended Maximum Net Allowable Bearing Pressure for the Structures .......................................... 38 Table 5-21: Geotechnical Parameters for the Design of Restrained Walls ................................................................... 40 Table 5-22: Approximate Sheet Pile Refusal/Hard Driving Elevations .......................................................................... 41

List of Appendices

Appendix A – Overall Location Map and Site Plan, Boring Plan, and Piezometers Location Plan Appendix B – Summary of Laboratory & Field Tests Appendix C – Bearing Capacity Analyses (Embankments) Appendix D – Settlement Analyses (Embankments) Appendix E – Seepage Analyses Appendix F – Uplift, Heave and Piping Analyses Appendix G – Slope Stability Analyses Appendix H – Settlement Analyses (Structures) Appendix I – Bearing Capacity Analyses (Structures) Appendix J – Liquefaction Potential Analyses




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1. Organization of Report This Geotechnical Engineering Design Report (GEDR) is divided into nine sections as listed below:

• Section 1 describes the organization of the report.

• Sections 2 and 3 provide introduction and discussions on the scope work, project description and background information on: the project, the site geology and the physical geography.

• Section 4 discusses the design criteria utilized in the analyses, such as the design water levels considered, the material parameters employed in the analyses, the field exploration and laboratory testing programs performed, and the basis for the selection of the engineering properties in the design.

• Section 5 presents the geotechnical engineering evaluations and analyses performed for the design with regard to foundation considerations, seepage and slope stability, and construction recommendations. Information specific to the canal and embankment analyses is also presented. The canals were sized based on hydraulic computations, and the geometry is dependent on the cross-sectional area needed to convey the required flows.

• Section 6 provides information and considerations on future project construction and future activities.

• Section 7 provides a summary of the report.

• Section 8 includes the limitations to AECOM and the information contained herein.

• Section 9 lists the references used in the geotechnical engineering evaluation and design.

The appendices that provide additional design information, analyses and calculations are included at the end of this report.




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2. Introduction The Stormwater Treatment Area 1 West (STA 1W) Expansion #2 (Expansion 2) project is a component of the Restoration Strategies projects identified to work in conjunction with the existing Everglades STAs to meet the Water Quality Based Effluent Limit (WQBEL). These limits will achieve compliance with the State of Florida’s numeric phosphorus criterion for the Everglades outlined in Rule 62-302.540 of the Florida Administrative Code, enforced by the Environmental Protection Agency. The present work is part of Subtask 2.5.2 - Updated Geotechnical Design Report under WORK ORDER NO. 4600003992-WO2, for the Intermediate and Final Design of the Expansion 2 Project.

The Expansion 2 project is located within Palm Beach County positioned immediately west of the Arthur R. Marshall Loxahatchee National Wildlife Refuge, also known as Water Conservation Area 1 (WCA-1). The overall STA 1W Expansion Project (Expansion 1 and Expansion 2) consists of approximately 6,500 acres (5,900 acres of effective treatment area) of STA expansion to the existing STA 1W. STA 1W Expansion 1, in which construction was completed in September 2019, is approximately 4,300 acres, located just west of the existing STA 1W. The Expansion 2 area is approximately 2,185 acres, located approximately 5.5 miles south of the southern edge of the existing STA 1W complex. Expansion 2 will be connected to STA 1W with a new proposed north-south aligned connection canal that will be constructed parallel to the L-7 Levee and Canal. Figure 1 shows the existing STA 1W, Expansion 1 and Expansion 2 areas.

Figure 1. Approximate STA 1W and Expansion Areas 1 and 2 Location




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Based on the project layout that was included in the scope of work, AECOM and RADISE International, L.C. (RADISE) performed field investigations in the Fall of 2018 and Fall/Winter of 2019/20. The field investigations and subsequent laboratory testing are the basis of the material parameters described in this Geotechnical Engineering Design Report (GEDR).

2.1 Scope of Work This report was developed to detail the criteria, methodology, design parameters, material properties and Geotechnical Engineering Analyses results that were used for the geotechnical evaluation and design of the Expansion 2 project. The criteria are based on the applicable Design Criteria Memorandums (DCM) for CERP projects. This final report utilizes field geotechnical investigation and laboratory testing results performed by RADISE and presented in Deliverable 2.1.2 Geotechnical Data Report Technical Evaluation of STA 1W Expansion 2 (RADISE GDR, 2020). The parameters detailed in Deliverable 2.5.1 Geotechnical Basis of Design Memorandum (GBODM) prepared by AECOM dated April 3, 2020 were used herein to complete the Design Process for the Project features through the Final Design level.

This GEDR is a continuation of the project geotechnical engineering evaluation and design provided through the Preliminary Design and is also part of the ongoing development of documents suitable to advance the design through Intermediate and Final Design phases. AECOM, in consultation with the District Engineering and Construction Project Manager (ECPM), has provided the necessary support to the District, including engineering and decision-making process documentation to support the recommendations made herein.

The data generated during the geotechnical design was used for the following:

• Seepage system design • Perimeter embankment design • Interior divider embankment design • Canal conveyance improvements • Culverts • Inflow and Outflow structures • Flow-ways • Canal Extensions • Spreader Canals • Seepage Pump Station • Inflow and Outflow Pump Stations • Earthworks and regrading requirements

The appendices that provide additional design information, analyses and calculations are included at the end of this report.




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3. Project Description 3.1 Background

The proposed layout and features of the STA is shown in Figure 2. All three cells flow from north to south. Cells 9 and 10 are located between the L-7 levee and the existing north-south Florida Power and Light Company (FPL) road which provides maintenance access to transmission towers that bisect the site. Both cells extend from the northern limit of the Expansion 2 property, including the previously cultivated land, to the east-west FPL road and then continue to the southern extent of the Expansion 2 property on remnant Everglades wetland that has not had prior farming.

Figure 2. Alternative 6 Configuration Schematic




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Cell 9 is east of the proposed north-south levee, located slightly east of the third set of FPL towers which run east-west near the north property boundary. The levee dividing Cells 9 and 10 is located along elevation 10.5 feet-NAVD88. The location of the proposed levee was selected to better distribute the topographic differences between Cells 9 and 10, keeping the maximum topographic differences at around 1 foot. The north part of Cell 9 includes previously farmed land north of the existing east-west FPL road. The area south of the east-west FPL road lays in remnant Everglades wetland that has not had prior farming.

Cell 10 is located just west of Cell 9 and includes the land located between the new north-south levee from Cell 9 described above, and the existing north-south FPL road extended to the north to meet the south level of the inflow canal. The north part of Cell 10 includes previously farmed land north of the existing east-west FPL road. The area south of the east-west FPL road lays in remnant Everglades wetland that has not had prior farming.

Cell 11 is west of the existing north-south FPL road and transmission towers and extends from the northern to the southern limit of the Expansion 2 property, all of which has been previously farmed.

3.2 Project Features The undisturbed land known as the Snail Farm which consists of remnant Everglades wetland that has not had prior farming, is relatively high in topographically, and has a significant slope from southeast (high) to northwest (low). The second parcel is a previously farmed area known as the Sunset Farm that has a “pan-handle” shape and is lower in topography and flatter in comparison as shown Figure 3. The project design accommodates the inherent logistical complexities of the additional treatment cells located 5.5 miles from the existing STA-1W with considerable variation in topography.

Figure 3. STA 1W Expansion Area 2




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The additional infrastructure needed to transmit water to and distribute water into Expansion 2 is significant due to the topographic and spatial challenges. Table 3-1 on the following page summarizes the new structures associated with Expansion 2.

Table 3-1: Expansion 2 Anticipated Structures

No. Location Structure New Structure Name

1 Southeast Exp #1

(Connection Canal North) North Inflow Pump Station G-780 Pump Station

1.a Southeast Exp #1 (Connection Canal North)

North Inflow Pump Station Generator Building

G-780 Pump Station (Gen BLDG)

2 Northeast Exp #2

(Connection Canal South) South Inflow Pump Station G-781 Pump Station

2.a Northeast Exp #2 (Connection Canal South)

South Inflow Pump Station Generator Building


3 Southeast Exp #2 Outflow Pump Station G-782 Pump Station

3.a Southeast Exp #2 Outflow Pump Station Generator Building


4 Southeast Exp #1 (Connection Canal North)

Connection Canal Energy Dissipation Structure Energy Dissipator

5 Northeast Exp #2 Inflow Canal Divide Weir G-783 Divide Weir

6 Cell 9 (West) Inflow Control Structure 2 G-784 Control Structure

7 Cell 9 (East) Outflow Control Structure 1 G-787A Control Structure

8 Cell 9 (West) Outflow Control Structure 2 G-787B Control Structure

9 Cell 10 (East) Inflow Control Structure 1 G-785A Control Structure

10 Cell 10 (West) Inflow Control Structure 2 G-785B Control Structure



13 Cell 11 (East) Inflow Control Structure 1 G-786A Control Structure

14 Cell 11 (Middle) Inflow Control Structure 2 G-786B Control Structure



In addition to the structural requirements, the design includes the construction of over 5.5 miles of connection canal to the southern tip of the expansion, over 2 miles of northern inflow canal, over 4 miles of discharge canal, and over 2 miles of seepage management canals.

The north end of the new connection canal starts at the southeast corner of Expansion 1. The east project boundary is 150 feet west of the centerline of the L-7 levee extending south from the proposed location for the new north inflow pump station located just west of the existing G-251 and G-310 pump stations. The project east boundary runs along the L-7 levee from the STA 1W complex south to the proposed outflow pump station near the existing communication tower and S-6 pump station.




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To the west, the project boundary runs along the L-15 levee just outside of the Hillsboro Canal and Brown’s Farm Road. The north project boundary extends from the L-15 levee in the west to the southern end of the levee maintenance road and south end of the new connection canal just north of the proposed south inflow pump station. The treatment cells can run and operate independently of each other while maintaining different operating water levels through the STA cells as controlled with the proposed inflow and outflow gated water control structures.

3.3 Site Location The proposed Expansion #2 project of the existing STA 1W is located within Palm Beach County in the south-eastern portion of the State of Florida southeast of Lake Okeechobee and east of the City of Belle Glade. Specifically, the expansion is located approximately 5.5 miles south of the existing STA 1W complex at the approximate latitude and longitude of 26° 27' 40" North and 80° 28' 52" West. Expansion 2 consists of 1,800 acres of expansion area. The Overall Location Map and Site Plan(s) are included in Appendix A.

3.4 Geologic Conditions

3.4.1 Physiography The subject site is located in the southern or distal physiographic zone within the Everglades geomorphic province. The subject site is relatively flat with elevations ranging from 7 to 16 feet North American Vertical Datum of 1988 (NAVD88), as shown in Figure 2. The topography and geomorphology of Florida have been influenced by interactions of multiple sea-level changes, karst processes, and subtle tectonic forces. Within the Everglades geomorphic province, peat overlies the limestone. Peat growth is dependent on voluminous freshwater discharge from Lake Okeechobee and reflects recent and/or current swampy conditions. The subject site coincides with the Pamlico marine terrace, which closely parallels the modern Atlantic oceanic shoreline (Geotechnical Data Report; 2019, 2020).

3.4.2 Surficial Soils Soil data from the United States Department of Agriculture – Natural Resources Conservation Service’s (USDA-NRCS) Soil Survey of Palm Beach County and the Web Soil Survey website were reviewed as part of the investigation (RADISE Geotechnical Data Report; 2020).

The mapped soil units at the site were identified as Okeechobee muck, Pahokee muck, Terra Ceia muck, Udorthents, and Water-Udorthents complex. A brief description of the soil units are as follows:

Unit 23 – Okeechobee Muck: This soil is very poorly drained and occurs on 0 to 1 percent slopes. Typically, this soil consists of muck from 0 to 66 inches below surface. Areas of this soil are subjected to frequent ponding but not flooding. The available water capacity is very high. The seasonal high-water table is at the ground surface.

Unit 26 – Pahokee Muck: This soil is very poorly drained, frequently ponded, and occurs on 0 to 1 percent slopes. Typically, this soil consists of muck from 0 to 40 inches, and unweathered bedrock from 40 to 50 inches below surface. Areas of this soil are subjected to frequent ponding but not flooding. The available water capacity is high to very high. The seasonal high-water table is at the ground surface.

Unit 43 – Terra Ceia Muck: This soil is very poorly drained and occurs on 0 to 1 percent slopes. Typically, this soil consists of muck from 0 to 65 inches and unweathered bedrock from 65 to 69 inches below surface. Areas of this soil are subjected to frequent ponding but not flooding. The available water capacity is very high. The seasonal high-water table is at the ground surface.

Unit 47 – Udorthents: This soil is well drained and occurs on 2 to 65 percent slopes. Typically, consists of gravelly sand from 0 to 80 inches below the surface. The seasonal high-water table is at more than 80 inches below the ground surface.

Unit 89 – Water-Udorthents Complex: This soil is well drained and occurs on 0 to 35 percent slopes. Typically, consists of gravelly sand from 0 to 80 inches below the surface. Available water storage in profile is very low.

The USDA and NRCS soil classifications are based on an interpretation of aerial photographs and widely spaced hand auger borings. Borders between mapping units are considered approximate, and the transition between soil types may be very gradual. Areas of dissimilar soils can occur within a mapped unit. However, the soil survey provides a good




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basis for an initial evaluation of shallow soil conditions in the area and can provide an indication of changes that may have occurred due to land filling, excavation, and other activities at the site.

The soil and groundwater conditions reported by the USDA and NRCS have likely been modified by development activities associated with the adjacent farmlands, construction of farm roadways, excavation of drainage canals, and the construction of STA and WCA (RADISE Geotechnical Data Report; 2020).

3.4.3 Geology The geologic history of South Florida has been influenced by multiple transgressions and regressions of what was known as the Okeechobean Sea basin. These inundations by the sea occurred approximately 11 times, resulting in discrete marine environments identified as Subsea. During the mid-Pleistocene, the sea had receded causing the isolation of the interior sea from the marine environments, which allowed for the formation of a large freshwater environment, referred to as Lake Okeelanta.

Freshwater deposits from Lake Okeelanta are represented by the middle member of the Bermont Formation. Sea levels later rose and fell again; the final marine carbonate deposition of the Okeechobean Sea basin began with the flooding of the Lake Worth Subsea. Finally, as sea levels fell to the current level, the channels linking the Okeechobean Sea to the Atlantic Ocean and Gulf of Mexico were filled in and much of South Florida was blanketed by sand and peat of the Pamlico Formation, which contains fossils of mammals, reptiles, and freshwater fauna. Modern-day Lake Okeechobee and the Everglades are interpreted to represent the final landscape of the last retreat of the Okeechobean Sea (Geotechnical Data Report; 2019, 2020).

Existing academic and professional publications and journals were reviewed to determine the local and regional geology and hydrogeology of the project site and across Palm Beach County. Several publications address the overall county-wide geology of Palm Beach County but progressively lose geologic detail from east to west. The following are brief descriptions of the Quaternary and Tertiary deposits that comprise the formations common to western Palm Beach County:

Lake Flirt/Marl Formation: Relatively impermeable, primarily dense limestone. Underlies surface peat layer throughout most of the Everglades. Lithographic textures are consistent with deposition in freshwater lakes.

Fort Thompson Formation: Alternating beds of marine, brackish, and freshwater limestone. This formation overlies Caloosahatchee Marl. Formation covers greatest geographical expanse of all Quaternary formations in S. Florida. Discontinuity surfaces include well-indurated laminated crusts.

Anastasia Formation: Alternating beds of offshore bar, beach ridge, and dune system deposits. Formation encountered east of Everglades Nutrient Removal (ENR) study site and not likely to be encountered in the project area.

Bermont Formation: Sandy, molluscan-rich, unconsolidated lime mud, marl, and variably indurated limestone and limy sandstone.

Caloosahatchee Formation: Sandy marl, clay, and silt-sized particles interbedded with shell beds. Erosion and dissolution can make the formation appear thinner or it may be absented altogether from certain areas.

Tamiami Formation: Cream, white, and greenish-gray clayey marl, silty and shelly sands, and shell marl that may be hardened locally into limestone. This formation underlies the Caloosahatchee Formation. The Tamiami was identified only at ENR Well MP3.

Hawthorn Group: Phosphatic siliciclastic sediments of fine- to coarse-grained quartz sand, quartz and dolomitic silt and clay minerals. This group is identified as the base of the Surficial Aquifer. The Hawthorn was identified only at ENR Well MP3.

3.4.4 Hydrogeologic Conditions Two aquifer systems are found in the vicinity of the project site: The Surficial Aquifer System (SAS) and the deeper artesian Floridan Aquifer System (FAS). These aquifers are separated by sediments and rocks with low hydraulic conductivity forming the Intermediate Confining Unit (ICU). The SAS is the primary source of potable water in eastern




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Palm Beach County. The Pamlico Sand represents the upper portion of the SAS, while the Fort Thompson, Bermont, and Caloosahatchee Formations represent the lower portion of the SAS in the project area. The elevation near the project area varies from an approximate elevation of -135 feet to elevations deeper than -250 feet. The thickness of the SAS unit tends to increase from west to the east.

The ICU is located below the SAS and comprised of a relatively impermeable sequence of clay, silt, and limestone of the lower Tamiami Formation and the Hawthorn Group. It ranges in thickness from approximately 500 to 700 feet. The ICU is underlain by the confined artesian FAS at a depth of 800 to 1,000 feet below land surface, with an average thickness of approximately 3,000 feet in the project area. The hydraulic connection between the SAS and the FAS is restricted by this confining layer. Thick layers of limestone and dolomite comprise an intra-aquifer confining unit of FAS which separates the upper part of the system from the lower part of the system. Both upper and lower parts of the FAS are non-potable in the proximity of the project area due to high concentrations of dissolved solids, like salt (RADISE GDR, 2019).

3.5 Geologic Hazards

3.5.1 Seismic Potential The United States Geological Survey (USGS) Seismic Hazard Maps display earthquake ground motions for various probability levels. The maps indicate approximate peak ground accelerations (PGA) of 0.02g to 0.04g for the southern half of Florida for a 1 Hz spectral acceleration with a two percent in 50 years probability of exceedance at the site. This value is very low in comparison to seismically active areas in the U.S. No active faults are identified in the south eastern Florida region.

The Federal Emergency Management Agency (FEMA) and International Building Code (IBC) classify areas by Seismic Design Categories (SDC) which reflects the likelihood of experiencing earthquake shaking of various intensities. The southeast Florida area has a SDC ‘A’ classification which represents areas described as having a “very small probability of experiencing damaging earthquake effects”. The risk of an earthquake occurring nearby the project site large enough to cause structural damage is considered extremely low.

3.5.2 Sinkhole Potential A sinkhole is a landform that occurs due to the subsidence or collapse of sediment or rock as underlying limestone or dolostone layers are dissolved by slightly acidic groundwater. Sinkhole activity is common in some areas of peninsular Florida; however, sinkhole development is a rare geological event in Palm Beach County.

The Florida Department of Environmental Protection (FDEP) Florida Geological Survey (FGS) map series No. 110 (“Sinkhole Type, Development and Distribution in Florida”) maps out the four area types (Area I through Area IV) based on thickness of overburden, frequency of occurrence, and dominant type and morphology of sinkholes.

Area I Solution sinkholes are the dominant type within this area and occur in areas where limestone is exposed at the land surface or is covered by thin layers of soil and permeable sand. Solution is most active at the limestone surface and along joints, fractures or other openings in the rock that permit water to move easily into the subsurface. Dissolved limestone and some insoluble residue are carried downward by percolating water along enlarged openings as solution of the limestone progresses. Large voids commonly do not form because subsidence of the soil layer occurs as the limestone surface dissolves. The result is a gradual downward movement of the land surface and development of a depression that collects increasing amounts of surface runoff as its perimeter expands (RADISE GDR, 2020).

Geographic data from the FGS showing Subsidence Incident Reports (SIR) relatively close by the site were reviewed. Subsidence incidents include both sinkhole activity and other subterranean events formed by other mechanisms such as expansive clay, organic layers, and anthropogenic (environmental pollution) events. The data indicates that there has not been any SIR produced within a 10-mile radius of the subject site. The FGS subsidence incident data contain only those events reported to the FGS through its March 5, 2013 published date (RADISE GDR, 2020).

The probability of a sinkhole developing in the vicinity of the project site is considered very low.




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4. Design Criteria 4.1 Canal and Embankments

The locations of the ten evaluated cross sections are shown in Figure 4 below. The cross sections were selected based on the configuration of the project after the 1D modelling was performed. Therefore, the proposed north-south divide levee between Cells 9 and 10 was not included in the analyses.




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Figure 4. STA 1W Expansion Area 2 Cross Section Locations




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4.1.1 Design Water Levels The minimum and maximum water levels were based on the hydraulic analyses performed by AECOM and A.D.A. Engineering from 2D modelling and upon selection of an inflow rate for the connection canal by the District.

The AECOM team worked with the District to analyse the maximum capacity for the connection canal and assisted in choosing the best inflow rates for treatment purposes. The water levels were determined by modelling of the selected alternative configuration by A.D.A. Engineering. The design Water Surface Elevations (WSELs) for each cross section are provided in feet NAVD88 in Tables 4-1 to 4-10.

Table 4-1: Design Water Surface Elevations for XS-1, XS-2, and XS-3 (NAVD88)

Cross-Section L-7 Levee Connection Canal

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

XS-1 14.80 16.80 10.05 13.01 XS-2 14.80 16.80 9.09 11.61 XS-3 14.80 16.80 8.26 9.62

Table 4-2: Design Water Surface Elevations for XS-4 (NAVD88)

Cross-Section L-7 Levee Cell 9

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

XS-4 14.80 16.80 12.30 13.2


Cross-Section Inflow Canal Cell 9 Seepage Canal

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

XS-5 10.50 13.70 12.30 13.20 7.30 7.50



Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

XS-6 10.50 13.70 8.80 9.80 7.30 7.50


Cross-Section Cell 10 Cell 11

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

XS-7 11.40 12.40 8.80 9.80


Cross-Section Hillsboro Canal Outflow Canal Cell 11

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

XS-8 8.80 10.60 7.90 10.20 8.80 9.80




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Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

XS-9 8.80 10.60 7.90 10.20 11.40 12.40



Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool

Normal Pool (Ft)

Maximum Pool (Ft)

XS-10 8.80 10.60 7.90 10.20 12.30 13.2



Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

XS-11 10.50 13.60 11.40 12.40 7.30 7.50


Cross-Section Cell 10 Cell 9

Normal Pool (Ft)

Maximum Pool (Ft)

Normal Pool (Ft)

Maximum Pool (Ft)

XS-12 11.40 12.40 12.30 13.2

Seepage and slope stability analyses were performed using modelled phreatic surfaces based on piezometer field measurements and laboratory testing results. The operating water levels were applied in the evaluation of the embankment slopes under various conditions. The phreatic conditions related to the canal water surface elevations were used for required geotechnical design elements. The seepage and slope stability analyses are presented in Sections 5.1.4 and 5.2.5, respectively.

4.1.2 Material Parameters The Phase 1 and Phase 2 field investigations, including laboratory testing, was performed by RADISE. Detailed results of the geotechnical investigation were submitted in RADISE’s report (GDR, 2020) and summarized below in the subsequent sections. The findings of the geotechnical investigation were the foundation of the selected material properties previously transmitted in the GBODM.

4.1.3 Field Exploration Programs The scope of the field investigations was to collect and compile geotechnical site data to aid in development of design criteria for seepage and slope stability analyses of the project site. The field investigations included:

• 355 Muck probes

• 25 In-situ field vane shear tests

• 79 Standard Penetration Test (SPT) borings

• 22 Rock core borings

• 84 Undisturbed Shelby tube samplings

• 48 Piezometer and well installations

• 54 In-situ field permeability tests




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Further description of the subsurface exploration was provided in RADISE’s GDR, 2020.

4.1.4 Survey and Mapping Ground surface elevations at the core locations and boring locations were surveyed and provided by AECOM. Whidden Surveying & Mapping, Inc. provided the northing, easting, stationing, offsets and elevation information. Northings and eastings reference NAD 83. Stations and offsets reference the base line of the survey, and the topographic elevations reference NAVD88.

4.1.5 Laboratory Testing Programs Laboratory testing was performed on both disturbed and undisturbed soil samples acquired during the field subsurface investigation performed in the Fall of 2018 and Fall/Winter of 2019/20. Select samples were tested for index properties to aid in classification for engineering purposes. The following laboratory tests, along with the standard they were performed by, were as follows:

• (322) Standard Test Methods for Determination of Water Content of Soil and Rock by Mass (ASTM D2216).

• (130) Standard Test Methods for Determining the Amount of Material Finer than 75-μm (No. 200) Sieve in Soils by Washing Test (ASTM D1140).

• (104), Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis (ASTM D6913).

• (99) Standard Test Methods for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils (ASTM D2974).

• (31) Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils Test (ASTM D4318).

• (7) Standard Test Methods for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Test (ASTM D7928).

The results of the laboratory tests were included in RADISE’s Geotechnical Data Report (2020), and a summary of the laboratory tests is included in Appendix B.

4.1.6 Generalized Site Stratigraphy The general soil conditions observed included an upper layer of SAND and silty SAND fill material underlain by organic fibrous PEAT. The fibrous PEAT overlies the Limestone rock that is interbedded with SAND. The limestone varies from hard to soft. Below the thick limestone layer is a layer of deep SAND. For the purposes of this geotechnical engineering design report, the generalized strata have been consolidated into four units as described below:

Unit 1 FILL: Light gray, light brown to brown, sand with silt, fine to medium grained, some sand to gravel

sized shell and limerock fragments (SP, SP-SM), and light brown to gray silty sand to sandy silt with occasional varying amounts of organic fines and sand sized shell and limerock fragments (SM).

Unit 2 ORGANIC/PEAT: Black, dark brown, amorphous to fibrous, soft (PT). This unit contains localized elastic SILT (MH) and Organic SILT (OH).

Unit 3 LIMESTONE: This Unit consists of gray limestone, moderately to well cemented, moderately hard to hard, slightly weathered. This limestone can range from light gray to light brownish gray in color, and containing silty, sandy, very poorly to poorly cemented, soft to moderately hard, moderately to highly weathered, and with varying amounts of shell fragments.

Unit 4 LOWER SAND: This Unit consists of light gray, light brown to brown silty sand (or sand) to sand with silt, fine to medium grained, with varying amounts of sand to gravel sized shell and limestone fragments (SM, SP, SP-SM). This constitutes the lower sand layers identified below the PEAT materials identified in Unit 2 above.




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4.1.7 Selection of Engineering Properties Analyses of the geological investigation presented in the RADISE Geotechnical Data Report (2020) were utilized to determine the design soil parameters. The subject project site was separated into two sections (the Connection Canal and the STA 1W Expansion 2 site) to accurately represent actual field conditions based on laboratory and field tests. The design soil parameters were included in the GBODM prepared by AECOM dated April 3, 2020 and are summarized below.

Unit Weight

Unit weight parameters for the soil types and the Limestone were estimated based on laboratory testing, documentation, engineering judgement and experience with other similar STA projects. The United States Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS), National Engineering Handbook (NEH) Part 631 “Engineering Classification of Earth Materials” (2012), and the Principles of Geotechnical Engineering (Das and Sobhan, 2014) were also used as references.

Moist and saturated densities were estimated using natural moisture contents from laboratory testing on jar samples. These parameters are applicable to both the upper sand layer of Unit 1 and the lower sand layer of Unit 4. The dry and saturated unit weights of Peat are based on the unit weights obtained from the isotropically consolidated, undrained triaxial compression (CIU) laboratory testing results and the Limestone density was estimated based on the rock core test results.

Shear Strength Shear strength parameters for the material units were conservatively estimated based on field observations and laboratory test results during the geological investigation. Shear strength laboratory tests were obtained from CIU tests with pore pressure measurements (ASTM D 4767).

Undisturbed samples of fill material were not obtained during the geotechnical investigation as the material is generally non-cohesive and gravelly in nature. Shear strength parameters were estimated based on Standard Penetration Tests (SPT) and engineering judgement. The effective friction angle was estimated based on U.S. Army Corps of Engineers (USACE) EM 1110-1-1905 “Engineering and Design: Bearing Capacity of Soils” (1992) for SPT resistance values (N). The N values were adjusted to an average energy ratio of 60% (N60) based on methodology of Seed and Skempton (Das and Sobhan, 2014) and correlated for granular soil. For SPTs within Fill material above PEAT, only SPTs along existing canals along the exterior of the project site were utilized. This was to limit potential values from less dense original ground. For the other layers, all SPT samples, with the exception of transition samples, were utilized to estimate friction angle. Based on the N60 and USACE EM 1110-1-1905, the average effective friction angle for the Fill in the Connection Canal is 34 degrees and within Expansion 2 is 32 degrees. As the fill material is represented as SP, SP-SM, and SM, the effective and total cohesion of the soil was assumed to be 0 psf.

New fill material which will be utilized in construction of new embankments is assumed to be of similar material of existing fill. However, the material is expected to be densely compacted in lifts during construction. Therefore, for new Fill material a friction angle of 35 degrees is assumed. The new Fill is conservatively assumed to classify as sand, and therefore 0 psf cohesion is assumed.

The strength parameters for the Fibrous ORGANIC/PEAT were based on isotropically consolidated, undrained triaxial compression tests with pore pressure measurements (CIU tests) and in-situ vane shear tests performed as part of the geotechnical investigation. Fifteen triaxial shear strength laboratory tests were performed on undisturbed fibrous peat samples in Phases 1 and 2. In-situ vane shear tests were analysed to estimate cohesion based on undrained shear strength of fibrous organic PEAT at in-situ conditions. In-situ vane shear tests have an average cohesion of 660 psf (4.6) psi, assuming a zero-degree friction angle. However, vane shear tests may provide misleadingly high results if thin sand seams, shells, or roots are present (Tschebotarioff, 1973). Therefore, the organic/peat friction angle and cohesion were based on the CIU test results. For effective strength, the friction angle and cohesion are estimated to be 29 degrees and 150 psf, respectively. For total strength, the friction angle and cohesion are estimated to be 18 degrees and 250 psf, respectively.

Strength parameters for limestone were based on field SPT and laboratory unconfined compressive strength tests. The effective friction angle was estimated based on USACE EM 1110-1-1905 “Engineering and Design: Bearing Capacity of Soils” (1992) and N60 parameters as described prior in this section. The effective friction angle for limestone based on the average of SPT tests within limestone is 39 degrees for the Connection Canal and 38 degrees for Expansion 2.




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Cohesion of limestone was estimated based on the method described in “Estimating Mohr-Coulomb Friction and Cohesion Values from the Hoek-Brown Failure Criterion” by Hoek (1990). Using this method, cohesion was estimated based on 57 compressive strength laboratory tests, the friction angles as detailed above, and the rock material’s rock mass rating, which is estimated based on physical properties of the limestone. Fifteen (15) tests were performed on limestone samples taken from the Connection Canal and 42 samples were taken from limestone samples from Expansion 2. Using these input parameters, the cohesion was calculated to be 560 psf for the Connection Canal and 700 psf for Expansion 2.

The unit weight and shear strength parameters for the Connection Canal and Expansion 2 are presented in Table 4-11 and Table 4-12, respectively.

Table 4-11: Shear Strength Parameters for Connection Canal

Material Description Unit Weight (pcf) Shear Strength Parameters

Dry (pcf)

Moist (pcf)

Saturated (pcf)

Total Stress Effective Stress φ (degrees) c (psf) φ’ (degrees) c’ (psf)

Unit 1 Fill 105 120 135 34 0 34 0

Unit 2 Organic/Peat 14.4 50 69 18 250 29 150 Unit 3 Limestone 130 145 166 39 560 39 560 Unit 4 Lower Sand 105 120 135 33 0 33 0

Unit 5 Designed Embankment Fill 105 120 135 35 0 35 0

pcf= pounds per cubic feet φ= internal friction angle c=cohesion φ’=effective internal friction angle c’=effective cohesion

Table 4-12: Shear Strength Parameters for STA Expansion 2

Material Description Unit Weight (pcf) Shear Strength Parameters

Dry (pcf)

Moist (pcf)

Saturated (pcf)

Total Stress Effective Stress φ (degrees) c (psf) φ’ (degrees) c’ (psf)

Unit 1 Fill 105 120 135 32 0 32 0

Unit 2 Organic/Peat 13.3 50 69 18 250 29 150

Unit 3 Limestone 130 145 166 38 700 38 700

Unit 4 Lower Sand 110 125 135 33 0 33 0

Unit 5 Designed Embankment Fill 105 120 135 35 0 35 0

pcf= pounds per cubic feet φ= internal friction angle c=cohesion φ’=effective internal friction angle c’=effective cohesion

4.2 Structures Analyses The Expansion 2 project site, including the Connection Canal, is anticipated to include 11 flow control structures between cells and canals, three pump stations. Three generator buildings which will share a wall with their respective pump stations. Additionally, an energy dissipation structure in the connection canal and a divide weir in the inflow canal are anticipated. The locations of these structures are shown in Appendix A. The following sections present the information and parameters used for the analyses of the structure foundations.




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4.2.1 Foundation Information The information about structure foundations including anticipated foundation elevations, foundation dimensions, and anticipated bearing pressures are summarized in Table 4-13.

Table 4-13: Foundation Information

Structure Estimated Bottom

of Foundation Elevation (ft NAVD)

/ FFE* (ft NAVD)

Foundation Dimensions

(Length X Width) (ft)

Anticipated Bearing Pressure

(ksf)

North Inflow Pump Station -10.0 / +22.25 105X72 2.9

North Inflow Pump Station Generator Building +17.75 / +22.25

33X52 with 3-ft wide strip

footings 3.0

South Inflow Pump Station -11.5 / +20.75 125X72 3.0

South Inflow Pump Station Generator Building +16.25 / +20.75


footings 3.0

Outflow Pump Station -11.5 / +23.75 119X72 3.0

Outflow Pump Station Generator Building +19.25 / +23.75


footings 3.0

Connection Canal Energy Dissipation Structure +4.0 64X54 2.0

Inflow Canal Divide Weir -7.5 170X18 3.0

Cell 9 Inflow Control Structure +2.5 57.3X26.0 2.2

Cell 9 Outflow Control Structure 1 -1.0 57.3X26.0 2.4


Cell 10 Inflow Control Structure 1 +1.0 57.3X26.0 2.3

Cell 10 Inflow Control Structure 2 +1.0 57.3X26.0 2.3



Cell 11 Inflow Control Structure 1 -0.5 57.3X26.0 2.3

Cell 11 Inflow Control Structure 2 -0.5 57.3X26.0 2.3



*FFE = Finished Floor Elevation

4.2.2 Structures Analyses Material Properties The material properties provided in the Geotechnical Basis of Design Memorandum (GBODM) prepared by AECOM and dated April 2020 were used to analyse the bearing capacity, settlement and seepage conditions of the structure foundations. The shear strength parameters used for the Collection Canal and Expansion 2 structure bearing capacity




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analyses are presented in Table 4-11 and Table 4-12, respectively. Soil properties from Table 4-11 were used for the North Inflow Pump Station and Connection Canal Energy Dissipation Structure, and Table 4-12 was used for all other structures. The deformation parameters used for the structures’ settlement analyses are presented in Table 4-14 and Table 4-15. For the pump station settlement analyses, the modulus of elasticity was calculated based on the N-values of each layer using an equation from USACE EM 1110-1-1904, Engineering and Design, “Settlement Analysis”, (1990), with a maximum value of 500 tsf to be conservative.

It is understood that all structure foundations will bear on limestone or lower sand layers. Therefore, the properties of the peat and existing fill layers are not presented in the following tables. Typical conservative parameters were used for structural fill in the bearing capacity and settlement analyses, which are presented in Table 4-16.

Table 4-14: Material Properties for Settlement Analyses (North Inflow Pump Station and Connection Canal Energy Dissipation Structure)

Material Description Modulus of Elasticity (psf) Poisson’s Ratio (vs)

N/A Structural Fill 6.5E+05 0.3

Unit 3 Limestone 9.4E+05 0.25

Unit 4 Lower Sand 5.6E+05 0.3

psf= pounds per square foot

Table 4-15: Material Properties for Settlement Analyses (Other Structure Foundations)

Material Description Modulus of Elasticity (psf) Poisson’s Ratio (vs)

N/A Structural Fill 5.9E+05 0.3

Unit 3 Limestone 9.2E+-5 0.25

Unit 4 Lower Sand 5.2E+05 0.3

psf= pounds per square foot

Table 4-16: Structural Fill Properties used in Structures Bearing Capacity and Settlement Analyses

Material Description

Unit Weight (pcf) Shear Strength Parameters

Dry (pcf)

Moist (pcf)

Saturated (pcf)

Total Stress Effective Stress

φ (degrees)

c (psf)

φ’ (degrees)

c’ (psf)

N/A Structural Fill 105 120 135 30 0 30 0

Note: In some cases, a saturated unit weight of 125 pcf was used psf= pounds per square foot pcf= pounds per cubic feet φ= internal friction angle c=cohesion φ’=effective internal friction angle c’=effective cohesion

4.2.3 Structures Analyses Water Surface Elevations The groundwater elevations used in the bearing capacity and settlement analyses of structures were estimated from the groundwater levels observed in the Phase 1 and Phase 2 soil borings performed by RADISE International in the vicinity of the proposed structure locations, and also from the design water levels of the nearest canal or cell. In some cases, the groundwater level was assumed in order to be conservative.




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4.2.4 Estimated Subsurface Profile The subsurface profiles at the structures were estimated based on the soil borings performed in the vicinity of the proposed structure locations. Table 4-17 presents the soil borings used to estimate the subsurface profiles at the structure locations.

Table 4-17: Subsurface Profile Borings

Structure Subsurface Profile Boring

North Inflow Pump Station IPS1-2

South Inflow Pump Station IPS2-2

Outflow Pump Station DPS-3

Connection Canal Energy Dissipation Structure CC-11

Inflow Canal Divide Weir NIE-6

Cell 9 Inflow Control Structure NIE-6

Cell 9 Outflow Control Structure 1 SDE-9


Cell 10 Inflow Control Structure 1 NIE-2






Cell 11 Outflow Control Structure 1 WDE-2

Cell 11 Outflow Control Structure 2 WDE-1




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5. Geotechnical Analyses and Design Seepage and slope stability analyses were performed using GeoStudio SEEP/W and SLOPE/W 2016 computer modelling software in accordance with USACE EM 1110-2-1901 Engineering and Design “Seepage Analysis and Control for Dams” (1993) and USACE EM 1110-2-1902 Engineering and Design “Slope Stability” (2003). Allowable bearing capacity and settlement were computed in accordance with the USACE criteria contained in their engineering manuals, EM 1110-1-1905 and EM 1110-1-1904. The analyses were conducted based on the design and the geotechnical explorations effort.

5.1 Canal and Embankments The embankments, dikes, and canals located within the STA 1W Expansion 2 system were assumed to have a Low Hazard Potential Classification (HPC) similar to other STA projects in the regional area and the project was designed accordingly. The low hazard potential classification refers to dams and levees where failure would result in no probable human life loss and minimal economic or environmental impact. The model geometry of the canals and embankments was designed based on the project plans and District DCMs.

The following conditions were adhered to for the design:

• Per DCM-4, top design widths of the embankments are a minimum of 12 feet plus one-foot shoulder on either side (14 feet total minimum width).

• Exterior embankment (levee or dam) side slopes are 3H:1V or flatter for slope stability, erosion protection, and ease of maintenance.

• Levee embankment slopes were designed based on slope stability and erosion protection requirements. The 2.5H:1V slopes of the Connection Canal were designed with concrete linings to minimize Manning’s roughness coefficient (N) and to achieve the maximum flow requirement. In addition to reducing the roughness coefficient, the lining will provide wave protection and increase slope stability factors of safety above the minimum required.

• Canal side slopes above the normal pool levels will be 3H:1V or flatter for mowing and O&M activities.

• Turnouts for encircling embankments are at ½ mile intervals or 1-mile intervals for canal and STA levees. Access ramps are at 2-mile intervals.

• Exterior embankment crests are sloped towards the interior at a 2% grade to prevent erosion gullies on the interior slope surface.

• Turnaround areas at facility locations have a minimum 50-foot radius.

• Geotechnical slope stability analyses were based on typical embankment cross-sections.

5.1.1 Embankments Analyses Material Properties The material properties provided in the Geotechnical Basis of Design Memorandum (GBODM) prepared by AECOM dated April 2020 were used to analyse the bearing capacity, settlement, and seepage conditions of the proposed embankments. The shear strength parameters used for the embankment bearing capacity analyses are the same as those used in the structures analyses and are presented in Table 4-11 and Table 4-12. The deformation parameters used for the embankment settlement analyses are the same as those used in the structures analyses, presented in Table 4-14and Table 4-15, with the addition of the organic/peat parameters presented in Table 5-1. It is understood that the embankments subgrade will include up to four feet or organic/peat material, meaning that any areas with more than four feet of organic/peat material underlying proposed embankment fill will be cut until only four feet of organic/peat remains. The consolidation parameters for the organic/peat layer are presented in Table 5-2. The hydraulic conductivity values used for the seepage analyses are presented in Table 5-4.




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Table 5-1: Organic/Peat Elastic Deformation Parameters

Material Description Modulus of

Elasticity (Es) (psf)

Poisson's Ratio (νs)

Unit 2 Connection

Canal Organic/Peat 3.5E+05 0.4

Unit 2 Expansion 2 Organic/Peat 3.8E+05 0.4

Table 5-2: Organic/Peat Consolidation Parameters


Max Past Pressure, σp' (psf)

Estimated Overburden Pressure, σp' (psf)

Over-consolidation

Ratio, OCR Compression

Index, Cc Recompression

Index, Cr

Secondary Compression

Index, Cα

Coefficient of Consolidation,

Cv

Average psf Average psf

Unit 2 Connection

Canal 533 453 1.2133 1.6490 1.5830 0.0080 0.3633

Unit 2 Expansion 2 926 330 2.9748 2.4299 0.7832 0.051 0.329

5.1.2 Embankment Bearing Capacity The bearing capacity analyses of the foundation soils supporting the embankments and levees was performed in general accordance with USACE EM 1110-1-1905 (Engineering and Design “Bearing Capacity of Soils”, 1992) and are contained in Appendix C. The critical sections from the Connection Canal and Expansion 2 (XS-2 and XS-6, respectively) were selected for analysis based on anticipated loading conditions considering the placement of added fill material to reach design grades, as well as the underlying soil conditions based on nearby soil borings. The remaining sections were inferred to be acceptable by observation based on the worst-case scenario sections identified and the subsequent bearing capacity results. Bearing capacity analyses on the critical cross sections indicated acceptable factors of safety against bearing failure that were in excess of 3.

5.1.3 Embankment Settlement Up to approximately 9.6 feet of added fill will be required to reach the proposed embankment crest elevations. Soil borings drilled in the proposed embankment areas indicate the presence of approximately 4 feet of soft and compressible Peat layer underlaid by natural sandy soils. The weight of the new fill material will induce additional stresses onto the soft Peat layer, which will cause the material to consolidate and settle. The critical sections from the Connection Canal and Expansion 2 (XS-2 and XS-6, respectively) were analysed. The settlement analyses indicated that up to about 23 and 27 inches of total embankment settlement is anticipated in some areas during construction and after construction completion. Based on the analysis, primary settlement is anticipated to be between 22.4 inches and 25.9 inches. Although, the majority of this settlement is expected to occur during construction. Secondary settlement of the embankments is anticipated to be between 0.2 and 1.1 inches. Six inches of camber was included in the embankment design to account for settlement.

Based on the settlement calculations, a post embankment top-out settlement period of 180 days after construction of the embankments is recommended to allow for completion of primary consolidation to dissipate. Construction of the embankments should anticipate additional fill material required to compensate for approximately 23 to 27 inches of estimated primary and secondary consolidation of the Peat layer. Some regrading of the embankment crests will likely be required to re-establish level embankment after the waiting period.




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If a waiting period of 180 days is not feasible, the soft compressible Peat layer can be removed and replaced with new compacted fill material prior to construction of the embankments to eliminate the primary consolidation.

A summary of the anticipated embankment settlements is shown on Table 5-3. The embankment settlement analyses were performed in general accordance with USACE EM 1110-1-1904, Engineering and Design “Settlement Analysis”, 1990. The most critical sections (XS-2 and XS-6) were selected based on anticipated loading conditions and the underlying soil conditions. The remaining sections were inferred to yield less settlement and be acceptable based on the worst-case scenario sections identified and the resulting settlement values.

The settlement analyses are included in Appendix D of this report.

Table 5-3: Embankment Settlement (with underlying Peats) Calculation Summary

Embankment Section Immediate Settlement (in.)

Consolidation Settlement (in.) Total (in.) Long-term

(Primary) Secondary

XS-2 1.8 22.4 0.2 22.6 XS-6 2.4 25.9 1.1 27.0

5.1.4 Seepage Analysis The current standard of engineering practice is to perform seepage analysis by means of simplified two-dimensional analysis. For this site, a two-dimensional finite element seepage analysis was performed to estimate the porewater pressure distribution in the levee embankments and underlying foundation layer for use in the stability analysis under steady-state and maximum pool conditions.

The seepage analyses were performed using GeoStudio 2016 SEEP/W computer modelling software in accordance with USACE EM 1110-2-1901 Engineering and Design “Seepage Analysis and Control for Dams” (1993). The pool levels are based on the design operating levels of the canals and STA 1W expansion, along with normal pool levels at the levees.

5.1.4.1 Hydraulic Conductivity Hydraulic conductivity for soil and limestone rock at STA 1W Expansion 2 and the Connection Canal was obtained using in-situ permeability, laboratory testing, sensitivity analyses, and engineering judgement. In-situ testing was performed at 16 locations with three piezometers of varying depths clustered at each location. Constant head testing was performed by pumping water into the piezometers to obtain a constant head and measuring the pump flow rate. Laboratory tests were performed on fifteen undisturbed PEAT samples and one undisturbed Shelby tube Silty SAND sample by RADISE International, L.C. in accordance with ASTM D 5084 for flexible wall permeameter.

5.2 Boundary and Geometry Sensitivity Analysis Boundary conditions for seepage models to be utilized in design analysis were evaluated to determine the lateral and vertical extents required to reduce boundary effects. Three cross sections (XS-4 (Phase 1), XS-6, and XS-8) were analysed using proposed design elevations with pool levels at designed normal pool steady state conditions.

For lateral extent evaluations of the models, three model widths were evaluated; 250 feet, 500 feet, and 1000 feet. These offsets were measured from the centreline of the embankments located on either side of the cross-sections. This location was chosen as the origin for the offsets as it is the location of measurement of seepage via flux lines created within the seepage models.

From the analysis, the results show that the average difference in flow rates between lateral offsets of 500 feet and 1000 feet is 7.6 percent. Therefore, a distance of 500 feet was determined to be suitable for computer model lateral offsets.

Vertical sensitivity analysis was performed at various depths to determine the effect model depth had on seepage flow rates. Depths analysed were based on elevation. Four minimum elevations were evaluated; -50 ft, -100 ft, -150 ft, and -200 ft. As with the lateral analysis, flow rates were measured through the center-lines of the embankments, through the entire thickness of the model. The results of the analysis show that the difference between vertical elevations of -




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150 ft and -200 ft averaged 10.9 percent except for the inflow canal levee in Cross-Section XS-6. However, this showed a reduction in flow.

Flow rates were also measured to a depth of -50 ft EL for each of the modelled depths to verify seepage flow rates near the surface elevation. From -150 ft to -200 ft EL, only on measured flow had a difference greater than 1.2%. This was in XS-8 with flow measured beneath Brown’s Farm Road. The difference in flow was from 0.07 ft3/day to 0.02 ft3/day. Given the minimal flow rate and the location west of the Hillsboro canal, this was not considered a significant difference between the two model depths for analysis.

5.2.1 Limestone Hydraulic Conductivity Sensitivity Analysis Horizontal hydraulic conductivity was field tested using the constant head method which is utilized in measuring the horizontal hydraulic conductivity of soils. Twenty-four piezometers were drilled during the Phase 1 geotechnical investigation at various depths to measure the hydraulic conductivity within the embankment and foundation layers. During the supplemental investigation performed in Phase 2, an additional twenty-four piezometers were drilled and measured. Two clusters of piezometers were left open from Phase 1 and were remeasured during Phase 2. The results of the field tests are shown in Table 5-4.

Table 5-4: Field-Measured Horizontal Hydraulic Conductivity from Piezometer Constant Head Tests

Material Type

Horizontal Hydraulic Conductivity - Constant Head (Kh)*

Average cm / s

Average ft / day

Max ft / day

Min ft / day

Average Shallow Sand 2.99E-04 8.48E-01 8.48E-01 8.48E-01

Average Peat 1.45E-03 4.12E+00 6.39E+00 4.62E-01

Average Limestone 1.20E-02 3.41E+01 1.53E+02 1.22E-01

Average Lower Sand 7.27E-03 2.06E+01 9.24E+01 1.92E-01

Average Peat/Fill (transitional) 5.96E-04 1.69E+00 6.29E+00 2.29E-01

*Assumed Kh/Kv = 1 for Fill, Limestone, Lower Sand, and transitional (Peat/Fill) Layers. Assumed Kh/Kv = 10 for peat. As shown in Table 5-4, limestone hydraulic conductivity ranges from 0.12 feet/day to 153.49 feet/day with an average of 34.1 feet/day. Based on the client’s recommendations and prior studies performed locally to the project site, the horizontal hydraulic conductivity was suggested to be at least 100 feet/day. Seepage rates from prior studies showed a range of 0.95 to 2.0 cfs/mile/1-ft head. From Technical Publication WR-2014-004, Stormwater Treatment Area Water and Phosphorus Budget Improvements (SFWMD, 2014), STA projects use a seepage rate of 1.74 cfs/mile/1-ft head for water budget analysis. Therefore, a seepage sensitivity analysis was performed using various horizontal hydraulic conductivities for limestone at normal and maximum proposed pool levels to determine an appropriate value to be used for seepage and slope stability analysis. Three cross-sections (XS-4 (Phase 1), XS-6, and XS-8) were analysed for the sensitivity study. Boundary Conditions for each cross section analysed are shown in Table 5-5 through 5-7.

Table 5-5: Cross Section XS-4 (Phase 1) Boundary Conditions

Cross Section XS-4 (Phase 1)

Location Boundary Type Head Elevation (ft)

Normal Pool

Cell 9 Constant Head 12.3

Left Vertical Boundary (Cell 9) Constant Head 12.3

Right Vertical Boundary (East) Constant Head 14.8

Right Slope of L-7 Levee Constant Head 14.8




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Maximum Pool

Cell 9 Constant Head 12.9*

Left Vertical Boundary (Cell 9) Constant Head 12.9*



*Preliminary analysis, Maximum pool was revised to 13.2 ft for final design which was analysed to determine overall unit seepage rate.

Table 5-6: Cross Section XS-6 Boundary Conditions

Cross Section XS-6


Normal Pool

Left Vertical Boundary (North) Constant Head 5.65

Seepage Canal Constant Head 7.3

Inflow Canal Constant Head 10.5


Right Vertical Boundary (South) Constant Head 8.8

Maximum Pool

Left Vertical Boundary (North) Constant Head 5.65

Seepage Canal Constant Head 7.5

Inflow Canal Constant Head 13.6


Right Vertical Boundary (South) Constant Head 9.8

Table 5-7: Cross Section XS-8 Boundary Conditions

Cross Section XS-8


Normal Pool

Left Vertical Boundary (West) Constant Head 8.8

Hillsboro Canal Constant Head 8.8

Outflow Canal Constant Head 7.9



Maximum Pool


Hillsboro Canal Constant Head 10.6

Outflow Canal Constant Head 10.2






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Seepage was measured for the entire thickness of the embankment and foundation through existing and proposed levees. Each cross-section was analysed using the average field measured horizontal hydraulic conductivity of limestone at 34.1 ft/day, recommended 100 ft/day, 150 ft/day, and 200 ft/day. For each scenario, the unit seepage rate beneath each levee in ft3/day/ft was determined through a flux line and the flow rate in terms per mile per foot of head (cfs/mile/1-ft head) was determined through the hydraulic head difference. The results of these analyses are provided in Appendix E. The results of the limestone sensitivity analyses show that a horizontal hydraulic conductivity of 125 ft/day measured a Unit Seepage (ft3/mi/1-ft head) of 1.64 under normal pool conditions in the cross-sections analysed and a unit seepage (ft3/mi/1-ft head) of 1.88 under maximum pool conditions. This compares favourably to 1.74 ft3/mi/1-ft head used for water budget analysis in STA projects (SFWMD,2014). Therefore, horizontal hydraulic conductivity for Limestone was chosen to be 125 ft/day for this project. Further analysis of the cross-sections excluding XS-5 at normal pool conditions revealed an average unit seepage rate of 1.83 cfs/mi/1-ft head. Therefore, a horizontal hydraulic conductivity of 125 ft/day for limestone is conservative. XS-5 was excluded given the length of the North Perimeter Levee and Inflow Canal Levee benches which may not accurately represent the differential hydraulic head. The results of the analysis of the cross-sections are presented in Appendix E.

5.2.2 Sensitivity Analysis of Embankment Fill and Foundation Seepage Engineering Properties

Sensitivity Analysis was performed on Cross Section 4 (Phase 1) for STA 1W Expansion 2 in order to determine appropriate hydraulic conductivity and anisotropy of the material layers for seepage and slope stability analysis. Analysis was performed for normal pool conditions and the results were compared with phreatic surface measurements from borings obtained during the geotechnical investigation. Analysis was performed based on laboratory tested and assumed hydraulic conductivities for Embankment Fill, Peat, Limestone, and Lower Sand materials. Based on sensitivity analysis described in Section 5.2.1, Limestone hydraulic conductivity was assumed to be 125 feet per day. Therefore, the hydraulic conductivity of the limestone layer was not adjusted during sensitivity analysis of the Embankment Fill, Peat, and Lower Sand seepage parameters. Cross Section 4 (XS-4) was analysed based on availability of groundwater levels adjacent to the cross sections. The cross section is along the existing L-7 levee on the eastern side of Expansion 2. XS-4 (Phase 1) is located within the triangular section south of the Connection Canal and adjacent to the proposed Cell 9. XS-4 (Phase 1) was analysed under existing conditions at normal pool levels. Boundary conditions were developed based on known and assumed phreatic pool levels. The normal pool level at the L-7 Canal is assumed to be 14.80 ft. For XS-4 (Phase 1), the western portion of the cross-section contains an unnamed existing canal. This canal was assumed to be at approximate pool elevation of 8.12 ft. This elevation was based on groundwater elevation measured at Boring IEE-1 within the Expansion 2 project area. Boundary conditions are provided in Table 5-8.

Table 5-8: Cross Section XS-4 (Phase 1) Boundary Conditions for Existing Conditions

Cross Section XS-4 (Phase 1)

Location Boundary Type Head

Elevation (ft)

Normal Pool




Canal at Western Portion of Cross-Section Constant Head 8.12




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Initial hydraulic conductivities for Embankment Fill, Peat, and Lower Sand were based on laboratory test data with anisotropy estimated from US Bureau of Reclamation Design Standards No. 13, Embankment Dams Chapter 8: Seepage (USBR, 2014) and tested values. The corresponding phreatic surface was measured in the model beneath the bench located on the L-7 Levee, just west of the drainage ditch. This elevation was compared with the measured phreatic surface from Boring EIE-2, which was drilled on the bench adjacent to XS-4 (Phase 1). Each parameter was individually adjusted to a high and low value to determine the effect on the phreatic surface. The sensitivity analysis results are provided Appendix E. The analysis shows that the range of the model parameters analysed have a minimal impact on the seepage analysis results. This is likely due to the Limestone horizontal conductivity being the controlling factor for seepage. Two parameters tested showed results within 0.5 feet of Boring EIE-2. However, for the Embankment Fill material, the results are from a horizontal hydraulic conductivity that is abnormally high compared to measured embankment fill and embankment fill/peat in-situ tests. Therefore, a more conservative value of 1 ft/day was used for this layer. In addition, the Limestone horizontal hydraulic conductivity was varied to see the impact on phreatic surface through the exiting embankment. The results show that as the horizontal hydraulic conductivity of the limestone was reduced, the phreatic surface increased. However, between 200 ft/day and 20 ft/day the increased phreatic surface was 0.48 feet; showing a reduced limestone hydraulic conductivity increased the phreatic surface.

5.2.3 Sensitivity Analysis of Vertical Boundary Conditions Analysis was performed to determine what impact, if any, vertical seepage conditions would have on flow rates in a seepage model. Three cross sections were analysed comparing seepage flow rates with vertical and lateral boundary conditions with seepage flow rates using only lateral boundary conditions. The models were run with 500 feet lateral extents and vertical extent to -150 ft elevation as per prior sensitivity analyses described above. The results are provided in Table 5-9.

Table 5-9: Sensitivity Analysis results for Vertical Boundary Conditions

Normal Pool Seepage with Vertical and Lateral Seepage

Boundaries (ft3/day/1-foot length)

Seepage with Lateral Seepage Boundaries

only (ft3/day/1-foot-length)

CROSS SECTION Seepage Direction

XS-4 L-7 LEVEE TO CELL 9 25.12 24.60

XS-4 CELL 9 19.93 19.45

XS-6 INFLOW CANAL TO SPREADER CANAL 30.27 34.17

XS-6 INFLOW CANAL TO SEEPAGE CANAL 146.73 131.72

XS-8 HILLSBORO CANAL TO OUTFLOW CANAL 24.30 24.33

XS-8 COLLECTION CANAL TO OUTFLOW CANAL 30.32 29.88

The results show that there is an approximate 1% difference overall between the two methods. As vertical boundary conditions better represent actual field conditions, vertical boundary conditions were utilized for this project.

5.2.4 Selected Hydraulic Conductivity Parameters Horizontal hydraulic conductivity parameters for Fill, Peat, and Lower Sand were selected based on in-situ testing results and sensitivity analysis. As discussed in Section 5.2.1, Limestone hydraulic conductivity was estimated based on a sensitivity analysis to prior project sites. The hydraulic conductivity for the material types is presented in Table 5-10. Rather than separating seepage parameters for Connection Canal and Expansion 2, one value for hydraulic




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conductivity was selected for hydraulic conductivity, given the potential for localized variations in flow rate and anisotropy, which could reduce calculated seepage flow rates. The selected hydraulic conductivity values for the project design are shown in Table 5-10.

Table 5-10: Hydraulic Conductivity Parameters


Hydraulic Conductivity

kh (cm/s)

kh (ft/day)

kv (cm/s)

kv (ft/day)

Unit 1 Fill 3.53E-04 1.00E+00 8.82E-05 2.50E-01

Unit 2 Organic/Peat 1.45E-03 4.12E+00 1.45E-04 4.12E-01

Unit 3 Limestone 4.41E-02 1.25E+02 1.47E-02 4.16E+01

Unit 4 Lower Sand 7.27E-03 2.06E+01 2.42E-03 6.86E+00

Unit 5 Designed Embankment Fill 3.53E-04 1.00E+00 8.82E-05 2.50E-01

The anisotropic relationship between horizontal and vertical hydraulic conductivity for the soil and rock layers was estimated based on engineering judgement and typical values referenced in U.S. Department of Interior, Bureau of Reclamation Design Standards No. 13 “Embankment Dams, Chapter 8: Seepage” (2014). As the fill layer is classified as SAND with silt (SP, SM, SP-SM) the fill anisotropy that is used for analysis is 4kh:1kv, as the fine silt particles and horizontal layering will control the vertical hydraulic conductivity.

The organic PEAT layer anisotropy is based on field and laboratory testing. For this layer, anisotropy of 10kh:1kv was selected.

Limestone was assumed to have anisotropy similar to fractured rock as boring logs show discontinuities and thin sand deposits throughout the limestone. The anisotropy for limestone was selected as 3kh:1kv.

The lower SAND (SM, Unit 4), like the Unit 1 Fill layer, contains silt. However, based on comparison of particle size distribution for FILL and Lower SAND, the Lower SAND has significantly less fines content than the FILL. Therefore, the Lower SAND is assumed to have anisotropy of 3kh:1kv.

Seepage analysis of the STA 1W Expansion 2 site and the Connection Canal located between STA 1W Expansions 1 and 2 were performed using GeoStudio SEEP/W 2016 computer modelling software. SEEP/W is finite element software for modelling groundwater flow. The computer software is capable of simulating steady-state and transient conditions using 2D analysis. Seepage analysis was performed in accordance with USACE EM 1110-2-1901 Engineering and Design “Seepage Analysis and Control for Dams” (1993). The seepage analyses are contained in Appendix E.

5.2.4.1 Uplift, Heave and Piping Factors of safety for the critical hydraulic gradient along the canals, which causes uplift, heave and piping in soils, was evaluated in accordance with USACE EM 1110-2-1901 (1993). Vertical Exit (or Escape) gradients (ie) and critical gradients (icr) were evaluated to estimate factors of safety against piping. A gradient is the “rate of dissipation of head per unit length in the area where seepage is exiting the porous media”. If the gradient is too high, soil particle movement may occur which could initiate piping. The gradient in which particle movement begins is termed the critical gradient (icr).

Vertical critical gradient is determined based on specific gravity (GS) and porosity (n) of soils using the following equation (USACE, 1993):

𝑖𝑖𝑐𝑐𝑐𝑐 = (𝐺𝐺𝑠𝑠 − 1)(1 − 𝑛𝑛) For the case of cohesionless soils, the factor of safety (FS) with respect to vertical exit gradients against boiling or heave is generally defined as the ratio of the critical gradient to the predicted/measured exit gradient. This FS gives an indication of whether sand heave is probable or likely to occur. It is not an indication of piping or internal erosion.




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FS = 𝑖𝑖𝑐𝑐𝑐𝑐𝑖𝑖𝑒𝑒

Where: icr = critical gradient ie = exit (or escape) gradient

Seepage analyses indicate that if porewater pressures are excessive under embankment toe locations, especially if there are contact areas between the underlying peat and limestone rock, the peat layer could heave.

Analysis of critical gradients were limited to cohesionless soils based on USBR Design Standard 13 (2014). Values for Embankment Fill and Lower Sand were estimated based on observed soil materials, empirical correlations, and the laboratory test results presented in the RADISE Geotechnical Data Report, 2020 and presented in Table 5-11:

Table 5-11: Uplift, Heave and Piping Analysis Parameters

Material ϒd

(lb/ft3) ϒw

(lb/ft3) ϒsat

(lb/ft3) n Gs icr (V) icr (H)

Embankment Fill 105 62.4 135 0.367 2.66 1.050 0.735

Lower Sand 110 62.4 135 0.337 2.66 1.100 0.714 ϒd = dry unit weight ϒw = unit weight of water ϒsat = saturated unit weight n = porosity Gs = specific gravity icr = critical gradient

Vertical and horizontal exit gradients were obtained using GeoStudio SEEP/W software. Maximum gradients were conservatively calculated using 0.75 feet sections of the canal slopes. The average vertical gradients are provided for reference. The uplift, heave and piping evaluations are contained in Appendix F. The maximum vertical exit gradients obtained are provided in the Tables 5-12 and 5-13 below:

Table 5-12: Uplift, Heave and Piping Analysis Results for Connection Canal

Cross-Section Average Vertical

Gradient

Maximum Vertical

Gradient

Average Horizontal Gradient

Maximum Horizontal Gradient

XS-1 Embankment Fill 0.31 0.39 0.14 0.34

XS-1 Lower Sand N/A N/A N/A N/A

XS-2 Embankment Fill N/A N/A N/A N/A


XS-3 Embankment Fill N/A N/A N/A N/A


Given the proposed Connection Canal is to be concrete lined, analysis of soils was limited to the proposed swale located west of the Connection Canal. Based on the subsurface investigation, cohesionless soils were only located in the canals at XS-1.




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Table 5-13: Uplift, Heave and Piping Analysis Results for Expansion 2

Cross-Section Average Vertical

Gradient

Maximum Vertical

Gradient

Average Horizontal Gradient

Maximum Horizontal Gradient




XS-5 Lower Sand 0.15 0.44 0.019 0.18


XS-6 Lower Sand 0.076 0.18 0.031 0.079






XS-9 Lower Sand 0.081 0.084 0.027 0.034


XS-10 Lower Sand 0.17 0.23 0.072 0.16


XS-11 Lower Sand 0.28 0.49 0.057 0.15



The fill that intersects the swale adjacent to the Connection Canal has a maximum vertical gradient of 0.39. This corresponds to an exit gradient factor of safety within the Embankment Fill of 2.7 (FS = 𝑖𝑖𝑐𝑐𝑐𝑐

𝑖𝑖𝑒𝑒 = 1.05 / 0.39 = 2.7). The

Connection Canal is proposed to be lined with concrete which will add protection against particle transport and the initiation of piping.

For Expansion 2, the maximum vertical gradient was 0.60 for the Embankment Fill and 0.49 for sand material. For Expansion 2, the lowest factor of safety for vertical exit gradient is 1.74 (for XS-11 Embankment Fill). This was located in the swale just north of the Seepage Berm.

The horizontal critical gradient is based on the following equation:

𝑖𝑖𝑐𝑐𝑐𝑐ℎ𝑜𝑜𝑐𝑐𝑖𝑖𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 = 𝑖𝑖𝑐𝑐𝑐𝑐𝑣𝑣𝑣𝑣𝑐𝑐𝑜𝑜𝑖𝑖𝑐𝑐𝑜𝑜𝑜𝑜𝑥𝑥 tan(∅)

Where Φ is the angle of internal friction. Based on this correlation, the critical horizontal gradient for Embankment Fill is 0.74 and the critical horizontal gradient for Lower Sand is 0.71 for the Connection Canal. From the analysis, within the Connection Canal, the maximum horizontal gradient is 0.34 for Embankment Fill. Lower sand was not encountered within the swale. The lowest factor of safety for horizontal gradient is 2.2.

For Expansion 2, the maximum horizontal gradient for the Embankment Fill is 0.49 and for the Lower Sand is 0.18. The lowest factor of safety for horizontal gradient is 1.51 for Expansion 2. As with the vertical gradient, this was located in XS-11 Embankment Fill within the swale just north of the seepage berm.

5.2.4.2 Seepage Impact Analysis was performed to determine the potential seepage impacts on the proposed construction of the Expansion 2 STA and the Connection Canal on the surrounding areas outside of the project site. Seepage analyses with the project in operation show the flow paths from the L-7 and Hillsboro Canal systems flow into the project site. Therefore, construction of the project would not have a significant impact outside the project area at the L-7 and Hillsboro Canal systems locations. However, along the Connection Canal and North section of Expansion 2, analyses show seepage




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in the direction of the adjacent field. For the North section of Expansion 2 a seepage canal was included in the design to manage any fluctuations in groundwater levels. The canal water elevations will be maintained between a maximum of 7.5’ NAVD and a minimum of 6.5’ NAVD with an average elevation of 7.3’ NAVD. Groundwater elevation in the area varies between 5.0 to 8.0 ft. and the seepage to the field north of the seepage canal should not increase. If needed the average elevation for the seepage pump station can be lowered to control seepage.

Comparison between existing and proposed groundwater conditions along the Connection Canal was performed to determine the potential increase in seepage rates. Based on determined unit seepage rates measured in cfs/mi/1-ft head, XS-2 was analysed as the critical cross-section as it had the highest flow rates of the three typical cross sections for the connection canal. The results of the comparison are shown in Table 5-14. The detailed modelling results for areas adjacent to the Connection Canal are included in Appendix E.

Table 5-14: Comparison of Seepage Flow Rates with Existing Conditions

XS-2 Comparison of Seepage flow rates with Exiting Conditions (Overall)

Cross Section Location Existing

Conditions (ft3/day/ft)

Proposed Construction (ft3/day/ft)

Difference (ft3/day/ft)

Difference (%)

XS-2 West Field 108.21 108.04 -0.17 - 0.16

The first analysis was conducted with zero permeability for the concrete to simulate the actual field conditions. However, this generated high porewater pressures underneath the concrete-lined connection canal. This is not the actual load condition as there are 2” wide holes along the bottom of the connection canal every 50 ft. Therefore, the permeability of the concrete was adjusted and a head boundary condition equal to the normal operating pool level of the Connection Canal was introduced to simulate the equalization of the pressure head due to the designed weep holes. The results show that the proposed construction of Expansion 2 and the Connection Canal will have a minimal impact on the adjacent field with either of methods detailed. The analysis of XS-2 in Table 5-14 shows that the flow rate will decrease approximately 0.16 % into the field. The results of the comparison are presented in Appendix F.

5.2.5 Slope Stability Analysis Slope Stability analysis of the STA 1W Expansion 2 site and Connection Canal located between STA 1W Expansions 1 and 2 was performed using GeoStudio SLOPE/W 2016 computer modelling software. Slope stability analysis was performed in accordance with USACE EM 1110-2-1902, Engineering and Design, “Slope Stability”, 2003. The slope stability analyses of the embankments and canals were performed using Spencer’s method of slices for both shallow and deep critical failures. Spencer’s method of slices satisfies all conditions of static equilibrium for horizontal and vertical force equilibrium and moment equilibrium. Factors of safety for slope stability analysis were analyzed using a minimum slip surface depth of 5 feet. As each cross section has multiple proposed constructed or cut slopes, all proposed new slopes for each cross section were analyzed for slope stability.

Material properties used for the evaluation are presented in Section 4.1.7. As the Connection Canal, evaluated in cross-sections (XS) 1 through 3, is proposed to be lined with concrete, a cohesion of 1500 psi (216000 psf) was assumed for the concrete liner, based on one-half unconfined compressive strength of standard 3000 psi concrete compressive strength. However, as the concrete channel is designed primarily for flow, the Connection Canal was also conservatively analysed using a cohesion of 6.94 psf (1000 psf). The conservative evaluation results are presented in this section. Embankments and canals were analysed for both deep and shallow failures for the following conditions:

End of Construction

End of construction (“short-term”) analyses were performed using drained strengths in free-draining materials and undrained strengths for materials that drain slowly (USACE, 2003). The End of Construction case evaluates the condition that non-free draining materials may not drain sufficiently as loading conditions are applied, such as during the placement of fill material. The non-free draining soil may consolidate creating an undrained condition; for these soils, total stress strength parameters were applied in the analysis. As the organics in Peat may retain moisture during construction, evaluation of the Peat was performed using both drained and undrained parameters. Evaluation of End of Construction stability was performed for Steady-State seepage conditions at normal pool and drawn down water




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levels. The drawn down water level is to simulate the immediate conditions after construction where normal pool conditions would simulate initial filling of Expansion 2 and the Connection Canal.

Long-term Steady-State Seepage Conditions

Steady-State conditions were considered long-term and pore pressures within the embankments were assumed to reach relatively steady levels. This analysis uses effective stress parameters. The pool levels analysed for the Steady-State case included both the normal pool level and the maximum storage pool level that could potentially reach steady-state conditions.

Earthquake Loading

Earthquake loading conditions were analysed based on USACE ER 1110-2-1806 Engineering and Design “Earthquake Design and Evaluation for Civil Works Projects” (2016). The USGS (2009) shows that the Expansion 2 project site is in an area with an approximate peak ground acceleration (PGA) between 0.02g and 0.04g with a two percent probability of exceedance in 50 years (or a 2,475-year return period).

The earthquake loading case considers the stability of the embankments during potential seismic events, and a pseudo-static (horizontal inertial force) coefficient of kh 0.04 was used for the slope stability analyses for the canal slopes and embankments. Vertical seismic coefficients have little impact on the resulting factors of safety and not analysed.

Rapid Drawdown

The Rapid (or Sudden) drawdown case was evaluated for slope stability at the maximum rate the retained pool is expected to lower. During rapid drawdown, the pool could potentially lower at a rate faster than the internal pore pressures can fully drain in low permeability soils. For this condition, a rapid drawdown to the bottom of each canal at over 24-hour period was evaluated. For each cross section, the drawdown was analysed for two conditions; from normal pool conditions to minimum designed pool elevations to simulate pumping during normal operating conditions and; from normal pool to the bottom channel elevations to simulate an uncontrolled drawdown condition.

Minimum required factors of safety for the analyses were taken from USACE EM 1110-2-1902 (2003) shown in Table 5-15.

Table 5-15: Slope Stability Factors of Safety

Analysis Condition Required Minimum Factor of Safety 1

End-of-Construction 1.3 Long Term Steady Seepage (Normal Pool) 1.5 Maximum Surcharge Pool (Maximum Pool) 1.4 Rapid Drawdown 1.1 -1.4 Earthquake Loading 1.1

Note: 1 in accordance with Table 3-1 in USACE EM 1110-2-1902 (2003)

5.2.5.1 Slope Stability Analysis Results The slope stability analyses and a summary of all the calculated factors of safety are included in Appendix G of this report. For each cross section, the critical slope (lowest factor of safety) is presented in the Table 5-16 and 5-17 on the following pages.

Peat layers located directly beneath the Connection Canal were removed due to potential settling post-construction. For model development, the peat was assumed removed from the extents of the concrete, extending out at a 1H:1V slope to the surface.

Cross section 4 represents a typical cross section along the L-7 Levee on the eastern edge of Expansion 2. Borings drilled in this location indicate that subsurface Limestone and Lower Sand elevations may vary along this section. Therefore, Cross-section 4 was analysed based on representative borings from the northern and southern portions of




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the eastern edge of expansion 2. The analysis showed minimal variation between the two analyses. As the cross-section in XS-4 is located in the northern portion of Expansion 2, this analysis is presented in the results.




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Table 5-16: Critical Slope Stability Factors of Safety Connection Canal

Analysis Condition Required

Minimum Factor of Safety1

Calculated Minimum Factor of Safety (Min depth 5.0 ft)

XS-1 Connection Canal - North

End-of-Construction 1.3 1.9

Long Term Steady Seepage (Normal Pool) 1.5 1.9

Maximum Surcharge Pool (Maximum Pool) 1.4 1.8

Earthquake Loading 1.1 1.6

Rapid Drawdown from Normal Pool to Minimum 1.4 1.9

Rapid Drawdown from Maximum Pool to Channel Bottom 1.1 1.2

XS-2 Connection Canal - Middle







XS-3 Connection Canal – South







Note: 1 in accordance with Table 3-1 in USACE EM 1110-2-1902 (2003)




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Table 5-17: Critical Slope Stability Factors of Safety Expansion 2

Analysis Condition Required Minimum

Factor of Safety 1 Calculated Minimum Factor of Safety (Min depth 5.0 ft)

XS-4 East Perimeter/L-7 Levee – Cell 9





Rapid Drawdown from Normal Pool to Minimum Pool 1.4 3.1


XS-5 Inflow Canal – Cell 9














XS-7 Interior Levee – Cells 10 &11







XS-8 Outflow Canal – Cell 11

















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Analysis Condition Required Minimum

Factor of Safety 1 Calculated Minimum Factor of Safety (Min depth 5.0 ft)















XS-12 Interior Levee – Cells 9 & 10






Rapid Drawdown from Maximum Pool to Channel Bottom 1.1 1.9 Note: 1 in accordance with Table 3-1 in USACE EM 1110-2-1902 (2003)

5.3 Structure Foundations The project will require the construction of structures to convey, distribute, and discharge surface water flows to the treatment cells and canals. It is expected that all structures will be founded on mat foundations bearing on limestone or sand layers within the limestone, except for the generator buildings, which will be founded on shallow spread footings bearing on structural fill. The structure foundations should not be placed on soft or loose soils such as peat, existing fill or loose sand. This section presents the results of analyses performed to evaluate the structure foundations.

5.3.1 Settlement Analyses The structure foundation settlement analyses were performed in general accordance with USACE EM 1110-1-1904, Engineering and Design “Settlement Analysis”, 1990. USACE EM 1110-1-1904 recommends that a minimum of three methods be applied to estimate a range of settlements. Settlements were estimated using the Modified Terzaghi and Peck approximation, the Schultze and Sherif approximation, and the Schmertmann approximation, as described in USACE EM 110-1-1904. Only immediate settlements were calculated because the granular soils and limestone expected below the structure foundations will not experience long-term consolidation or creep settlements. Pump station and generator building settlement was analysed considering two loading scenarios: 1) The applied bearing pressure of the structure; and 2) The applied bearing pressure of the structure plus the pressure added by backfilling and filling around the structure foundations to proposed grade, taken conservatively as the FFE, (henceforth referred to as “considering the effect of fill”. The results of the settlement analyses are presented in Appendix H and are summarized in Table 5-18.




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Table 5-18: Estimated Structure Foundation Settlements

Structure

Anticipated Bearing

Pressure (ksf)

Estimated Settlement (inches)

Schmertmann Modified Terzaghi & Peck

Schultze & Sherif

North Inflow Pump Station 2.85 0.1 0.4 0.3

North Inflow Pump Station (considering the effect of fill) 4.5 1.0 0.7 0.6

North Inflow Pump Station Generator Building 3.0 0.3 0.7 0.2

North Inflow Pump Station Generator Building (considering the effect of fill) 3.4 0.3 0.7 0.2

South Inflow Pump Station 3.0 0.1 0.8 0.6

South Inflow Pump Station (considering the effect of fill) 4.4 0.9 1.2 0.9

South Inflow Pump Station Generator Building 3.0 0.3 0.7 0.2

South Inflow Pump Station Generator Building (considering the effect of fill) 3.4 0.3 0.7 0.2

Outflow Pump Station 3.0 0.3 0.7 0.5

Outflow Pump Station (considering the effect of fill) 4.5 1.2 1.1 0.7

Outflow Pump Station Generator Building 3.0 0.3 0.7 0.2

Outflow Pump Station Generator Building (considering the effect of fill) 3.4 0.3 0.7 0.2

Connection Canal Energy Dissipation Structure 2.0 0.9 0.4 0.3

Inflow Canal Divide Weir 3.0 0.7 0.5 0.2

Cell 9 Inflow Control Structure 2.21 0.5 0.2 0.2

Cell 9 Outflow Control Structure 1 2.35 0.3 0.2 0.1


Cell 10 Inflow Control Structure 1 2.28 0.4 0.3 0.2







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Structure

Anticipated Bearing

Pressure (ksf)

Estimated Settlement (inches)

Schmertmann Modified Terzaghi & Peck

Schultze & Sherif





Estimated settlements are considered acceptable.

5.3.2 Bearing Capacity Analyses The bearing capacity analyses were performed in general accordance with USACE EM 1110-1-1905 (Engineering and Design “Bearing Capacity of Soils”, 1992) and are included in Appendix I. USACE EM 1110-1-1905 recommends that a minimum of two methods be applied to estimate the foundation bearing capacities. The bearing capacities of structure foundations were estimated using the Terzaghi model and the Vesic model, as described in USACE EM 110-1-1905. The results of the bearing capacity analyses are summarized in Table 5-19 and indicate the anticipated foundation allowable bearing pressures on the foundations.

Table 5-19: Estimated Allowable Bearing Capacities of Structure Foundations

Structure

Anticipated Bearing

Pressure (ksf)

Allowable Bearing

Capacity – Vesic (ksf)

Allowable Bearing

Capacity – Terzaghi (ksf)

North Inflow Pump Station 2.9 26.0 22.7

North Inflow Pump Station Generator Building

3.0 4.1 4.3

South Inflow Pump Station 3.0 27.2 22.7

South Inflow Pump Station Generator Building

3.0 4.1 4.3

Outflow Pump Station 3.0 26.2 22.1

Outflow Pump Station Generator Building

3.0 4.1 4.3

Connection Canal Energy Dissipation Structure

2.0 18.5 17.2

Inflow Canal Divide Weir 3.0 12.9 10.4

Cell 9 Inflow Control Structure 2.2 9.1 7.0

Cell 9 Outflow Control Structure 1 2.4 9.1 7.0




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Structure

Anticipated Bearing

Pressure (ksf)

Allowable Bearing

Capacity – Vesic (ksf)

Allowable Bearing

Capacity – Terzaghi (ksf)


Cell 10 Inflow Control Structure 1 2.3 9.1 7.0








Allowable bearing capacities considered a minimum factor of safety of 3.0 and in all cases exceed the anticipated foundation bearing pressures.

5.3.3 Recommendations Based on the results of the analyses performed and the information provided to us, we have the following geotechnical recommendations for the proposed structures:

5.3.3.1 Mat Foundations

We understand that the proposed control structures and pump stations will be founded on mat foundations bearing on limestone or sand layers within the limestone. Mat foundations founded on limestone or firm sand material are considered suitable for support of the proposed control structures and pump stations. Mat foundations may be designed using net allowable bearing pressures as indicated in Table 5-20 on the following page:

Table 5-20: Recommended Maximum Net Allowable Bearing Pressure for the Structures

Structure Recommended Maximum Net Allowable Bearing Pressure (ksf)

North Inflow Pump Station 2.9

South Inflow Pump Station 3.0

Outflow Pump Station 3.0

Connection Canal Energy Dissipation Structure 2.0

Inflow Canal Divide Weir 3.0

Cell 9 Inflow Control Structure 2.3




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Structure Recommended Maximum Net Allowable Bearing Pressure (ksf)

Cell 9 Outflow Control Structure 1 2.4


Cell 10 Inflow Control Structure 1 2.3








Settlement of the mat slab foundations should not exceed about 1 inch and the differential settlement should not exceed approximately half this amount. Mat foundation subgrades should be observed and approved prior to placement of concrete, to ascertain that the mat foundations are bearing on suitable bearing material. Foundations should be excavated and poured the same day in order to avoid construction disturbance and to allow adequate time for placement of mat slab reinforcement. If foundations cannot be poured the next day after they are excavated, a 3-inch mud mat should be placed over the subgrade materials to protect the mat subgrades. Any existing fill, disturbed soils, or excessively soft subgrade soils should be removed prior to placing mat foundation concrete. Groundwater is expected to be above the bases of the completed mat foundations for the pump stations and the control structures.

Excavations to reach the proposed bottom of foundation elevations are expected to be up to about 23 feet below the existing ground surface. Excavations exceeding 5 feet in depth will require sloped excavations, shoring or bracing as per Occupational Safety and Health Administration (OSHA) regulations.

Groundwater is expected to be present at or above the foundation elevations. Therefore, the contractor should be prepared to provide construction dewatering consisting of submersible pumps in gravel sumps, collector trenches and well points. Due to the presence of cohesionless soils and groundwater in the excavations, sloughing or caving may occur that could create unstable conditions. The actual dewatering means and methods are the responsibility of the construction contractor.

5.3.3.2 Spread Footings Based on the information provided to us, we understand that the generator buildings at the three pump stations will be founded on spread footings. We understand that the existing soils in the generator building areas will be removed down to the limestone during construction of the pump stations. Therefore, the generator buildings will be placed on new structural backfill. It is our opinion that the generator buildings can be supported on new fill or crushed stone. The footings may be designed with a maximum net allowable soil bearing pressure of up to 3,000 psf. A coefficient of friction of 0.35 may be used for sliding resistance at the soil/concrete interface.

Shallow footings should bear at least 12 inches below the adjacent exterior finished grades to provide adequate confinement. The bases of all foundation excavations should be free of water, loose soil and any deleterious matter prior to the placement of concrete. A maximum allowable slope of 1.5H:1V should be maintained between the bottom edges of adjacent footings or underground utility trenches. Below grade walls adjacent to the footings must be designed




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to resist the lateral earth pressure imparted by the footings on the walls. Below grade wall recommendations are presented in Section 5.2.4.4.

The foundation subgrades should be observed and approved by the geotechnical Engineer of Record (EOR) or his designated qualified representative. Recommendations for footing subgrade preparation are presented in Section 6.5.

5.3.3.3 Floor Slabs We understand that the soils at the proposed generator building floor slab subgrades are expected to consist of compacted structural fill. These materials are generally considered suitable for direct floor slab support. It is important for the subgrades to be firm and unyielding before granular sub-base material is placed. The subgrades should be observed and probed by the geotechnical engineer to verify the suitability of the subgrades for slab support. Any excessively loose or yielding materials at the subgrades should be undercut and replaced with new compacted fill or crushed stone.

The ground-supported floor slabs should be placed over a minimum 4 inches of open graded granular material, such as American Association of State Highway and Transportation Officials (AASHTO) No. 57 stone or equivalent. The granular material will provide a capillary break between the subgrade and the concrete slab and will provide more uniform support for the floor slab. A vapor barrier consisting of a minimum 6-mil polyethylene sheeting, meeting ASTM E1745 standards should be placed on top of the granular layer before the placement of concrete to prevent intrusion of the concrete into the granular base and to provide an additional barrier against moisture migration. Underfloor drainage should not be necessary since groundwater was observed to be below the proposed generator building floor slab elevations. In order to minimize the development of any shrinkage cracks near the surface of the slabs, we recommend that wire mesh (fiber or welded wire fabric) reinforcement be included in the design of the floor slabs. The wire mesh should be in the top half of the slabs to be effective.

5.3.3.4 Below Grade Walls It is anticipated that below-grade non-yielding walls will be required for the pump stations. Below grade walls should be designed for at-rest earth pressures to resist the earth pressure loads. Assuming the new backfill around the walls consists of granular soils meeting the requirements of structural fill, the walls can be designed using the parameters mentioned in Table 5-21 below.

Table 5-21: Geotechnical Parameters for the Design of Restrained Walls

Backfill Moist Unit Weight (pcf)

Backfill Saturated Unit Weight (pcf)

Backfill Internal Friction Angle (degrees)

At Rest Earth Pressure Coefficient

120 125 30 0.5

The below grade walls should also be designed to resist the horizontal pressures due to any surcharge loads. Surcharge loads may include adjacent footing loads, live loads and construction equipment loads. For surcharge loads, 50 percent of any uniform areal surcharge placed at the top of the walls may be assumed to act as a uniform horizontal pressure over the entire height of the wall. In addition, the below-grade walls should also be designed to resist water pressures.

5.3.3.5 Hydrostatic Uplift Design Groundwater is expected to be above the bases of the mat foundations for the pump stations and the control structures. Therefore, these structures will need to be designed to resist the hydrostatic uplift pressures if the weight of the completed structure is not adequate to resist uplift water pressures on the bottom of the foundation mats. In addition, the below-grade walls should be designed to resist horizontal water pressures.

5.3.3.6 Seepage Cut Off Walls As discussed in Section 5.2.3, the average maximum exit gradients at the structure locations are relatively low and there are adequate factors of safety against the potential of piping due to exit gradients at the structure locations. In addition, the structures are expected to be founded on limestone which is generally not susceptible to piping. It is also understood that uplift at the structure locations will be resisted by structural means and will be analysed by the project structural engineer. Therefore, seepage cut off walls at the structure locations are not considered necessary as a protection against piping or against uplift.




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However, we understand that the owner’s standard details typically require installation of seepage cut off walls at the structure locations as a long-term piping protection safety measure. It is understood that the seepage cut off walls below the structures would extend to the same depths as the adjacent sheet pile retaining walls. According to US Bureau of Reclamations (USBR) design manual “Design of Small Canal Structures”, the structure cut off walls should, in general, be a minimum of 3 feet deep for water depths greater than 6 feet. The seepage cut off walls should extend laterally on either side of the structures. The lateral extent of the cut off walls should be at least equal to their embedment depths.

5.3.3.7 Sheet Piles It is understood that the proposed structures may utilize sheet pile walls as retaining walls and as seepage cut off walls. The design of the sheet pile walls will be completed as part of the Final Design phase. Boring logs drilled in the vicinity of the proposed structure locations indicate that limestone with varying degrees of cementation is present below the structure foundations. Limestone is also interbedded with the underlying lower sands. The sheet piles may encounter hard driving conditions or refusal if driven through the cemented limestone layers. Based on the review of the nearest available boring log, we have summarized approximate elevations at which the sheet piles may encounter refusal or hard driving conditions at the structure locations. This data is presented in Table 5-22 below. We have assumed that soil and limestone will be excavated down to the lowest structure invert elevations prior to sheet pile installation. It should also be noted that due to the variability in subsurface conditions, the actual refusal or hard driving elevations may be different during installation.

Table 5-22: Approximate Sheet Pile Refusal/Hard Driving Elevations

Structure Approximate Sheet Pile

Refusal/Hard Driving Elevation (ft NAVD88)

North Inflow Pump Station -22

South Inflow Pump Station -16

Outflow Pump Station -16

Cell 9 Inflow Control Structure -5

Cell 9 Outflow Control Structure 1 -2


Cell 10 Inflow Control Structure 1 0

Cell 10 Inflow Control Structure 2 -7










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5.4 Seismic Design Southern Florida, the location of the subject property, is located within a low seismic region as can be seen in Figure 5 showing the USGS Seismic Hazard Map (2014) for peak ground acceleration (PGA) with a 2% probability of exceedance in 50 years.

Figure 5. Seismic Hazard Map Based on 2% Probability of Exceedance in 50 Years of PGA

The foundation soils at the project site can potentially be affected by strength loss from seismic events and possible liquefaction of loose foundation sands that could lead to embankment slope failures. An initial screening of the liquefaction potential was conducted using the methodologies indicated in DCM-6 and is contained in Appendix J. The results of the liquefaction potential analyses resulted in all factors of safety greater than 1.5 indicating that the soils at the site are not likely to liquefy due to a probable earthquake load.




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6. Considerations for Construction and Future Activity The major construction work for Expansion 2 will include earthwork operations such as the transport of soils for stockpiling, regrading, excavating, and the placement of new compacted fill or rock/stone materials. Areas to be used as batch plants and staging areas for equipment, assembly, and material storage should be coordinated with the District and denoted on construction plans and documents. Cranes, lifts, pump trucks, etc. should be staged on level ground not adjacent to or on top the apex of embankment slopes.

The contractor will need to verify that the selected heavy construction equipment such as cranes will not have an adverse effect on the stability of any embankments, berms or levees especially in areas underlain by soft and compressible Peats. Excavated material will be used as backfill for the proposed structures, for grading purposes and for soil cover and topsoil application.

This section of the report addresses the construction of site design aspects of the project and includes discussions on erosion and sediment control, access roads, and other site amenities required for construction. The applicable earthwork specifications contained within the construction documents should include earthwork, quality control and testing, erosion and sediment control, disposal of waste, site amenities, and temporary facilities and controls.

6.1 Site Access and Preparation Site preparation activities will include preparation of embankment and canal areas and the potential construction of temporary access roadways to and from work areas. Accessing the site, preparing work surfaces to receive fill, the placement of fills, and the ability of construction equipment to traverse proposed canal and borrow excavation areas will present major access considerations to the earthwork contractor. Challenging surficial soil conditions, the presence of near-surface peats will create problems related to construction equipment mobility and activity.

The presence of surficial peats and wet soil conditions will hinder the movement of heavy construction equipment that will likely include compactors, excavators, bulldozers, cranes, etc. working in and around the Expansion 2 project site. The high groundwater levels will further complicate site access after significant rainfall events typical of the regional area.

Embankment and canal alignment preparation will include clearing and grubbing of existing vegetation and brush. Clearing by cutting at the ground surface will be required for dense vegetation, and any limbs or tree trunks will require removal and disposal. Cleared and grubbed areas should be cleaned of muck and silty or clayey materials. If any undercutting or clearing is performed at proposed embankments, the cut areas should be backfilled with compacted fill placed in accordance with Section 6.4 of this report.

In interior cell areas, it will be necessary to locally fill some existing drainage ditches or swales or relocate them to nearby flow conduits. This fill material should consist of either spoils from adjacent canal excavations or loose fill from offsite sources. After placement of the fills, they should be covered with a 2- to 3-inch layer of peat or topsoil to enable vegetation growth.

6.2 Erosion Protection Erosion protection should be compatible with the design embankment slopes, embankment soil types, surface water levels, and freeboard requirements and should be in accordance with the District’s Applicant’s Handbook Part IV: Erosion and Sediment Control. The District allows riprap as a means to reduce the force of waves and to protect land from erosion. Riprap should consist of predominantly angular unconsolidated boulders, rocks, or clean concrete rubble with no exposed reinforcing rods or similar protrusions. Erosion control measures (such as riprap and concrete lined channels) should provide proposed velocities that are non-erosive and sufficient to safely convey flows. Information on design and performance standards to achieve storage and conveyance requirements are in Volume II specific to the geographic area covered by each District. The stone size for the protection of embankment slopes and canals upstream and downstream of structures should be selected in accordance with District and/or USACE criteria (USACE EM 1110-2-1601 and USACE HDC Sheet 712-1).




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Where flow velocities are greater than 2.5 ft/sec or nearby control structures and at the inflow and discharge points for the pump stations, slope protection will be included that will consist primarily of rip rap. Other slope protection measures such as articulated concrete block could also be used.

6.3 Embankment and Canal Construction

Typical problems that may be encountered during embankment and canal construction could include unexpected weak or soft soils encountered during embankment foundation preparation to receive the placement of embankment fill materials; conflicts with utilities or other facilities. At the onset of site grading, the entire area should be stripped of vegetation, roots, topsoil, construction debris, and any deleterious materials. Following the removal of any unsuitable material, fill and pavement subgrades should be proof-rolled with a 10-ton loaded dump truck, construction roller, or construction equipment of equal weight. The geotechnical EOR or the EOR’s designated representative should be present to verify the suitability of the subgrades to receive fill or base course material. Existing fill and soft, compressible Peat soils were encountered in the borings drilled near the proposed embankments. These soils are soft and some undercutting, or removal of soft soils to more competent soils of these soils may need to be performed.

Fill subgrades may consist of soft and yielding soils in some areas. Where moisture conditioning and re-compaction do not create stable subgrades, removal of these soils may be necessary to stabilize the subgrades to achieve the structural fill compaction requirements. The depth of removal, if necessary, will vary depending on the actual soil conditions encountered and should be determined in the field by the Geotechnical Engineer. We recommend establishing a budget for the removal of soft and yielding existing fill and natural soils. All undercut or removal, if necessary, should be approved and performed under the observation of the geotechnical engineer.

6.4 Fill Materials and Fill Placement In accordance with South Florida Water Management District (SFWMD) Design Standards, a layer of topsoil should be added to the exterior face of any embankments prior to seeding. This topsoil material should be obtained from the local peat and muck that is expected to be available from the material removed from the embankment construction areas. The peat can be stockpiled adjacent to the location of the exterior toe of the embankments to reduce transport, handling and costs. Care should be taken, and construction phase drainage/dewatering provisions provided such that rainwater does not become ponded between stockpiled areas.

Based on the analysis, primary settlement is anticipated to be between 22.4 inches and 25.9 inches. Although, the majority of this settlement is expected to occur during construction. Secondary settlement of the embankments is anticipated to be between 0.2 and 1.1 inches. Six inches of camber was included in the embankment design to account for settlement.

The new embankment fill materials will generally consist of onsite material obtained from nearby canal excavations. Based on the subsurface investigations performed in 2018, this material will likely be a combination of sandy materials (SP, SM) and excavated limestone. Excavated peat and organic soil materials obtained from canal areas should be separated from the reusable granular materials and temporarily stockpiled on-site in relatively nearby areas for re-use on embankment slopes to facilitate vegetation. Refer to specification 02200 Earthwork for details on designed material properties.

Portions of the onsite natural granular soils encountered in the soil borings that meet classification requirements are generally expected to be suitable for reuse as compacted structural fill. The suitability of the onsite soils for reuse as fill and backfill should be verified by the geotechnical EOR or the EOR’s designated representative during construction. Some moisture conditioning of these soils will be required to achieve the compaction requirements. Soils classified as CH, MH, or OL/OH are not considered suitable for reuse as compacted embankment fill or backfill. Portions of the existing material encountered in the borings may be reused as compacted fill, provided they meet the above requirements and are free of organic matter and other deleterious matter.

Mechanical methods are expected to be required for limestone excavation. Excavations through the well cemented limestones will be difficult and required for the connection, inflow, spreader, seepage, collection and outflow canals, borrow areas, and for project structures such as pump stations and culverts. Blasting outside of FPL power line exclusion areas may be required and is allowed by design specifications to expedite excavation activities. It is noted that blasting will not be allowed for the excavation of rock materials within 500 feet of the FPL lines that run through the project site.




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Excavations into the in-situ limestone rock material by mechanical methods such as backhoes, hydraulic hoe rams, rippers, and other similar equipment, are expected to be very difficult but reportedly has been performed on nearby sites per recent discussions with local contractors.

Due to the high-water levels at the site, construction will require ground and surface water control. Water that collects in project excavations should be routed to local sumps by ditches and pumped into settling basins or tanks prior to discharge into nearby waterways. In some locations, well point systems may be needed to provide effective control of water during excavation.

6.5 Foundation Subgrade Preparation All footing excavations should extend to suitable bearing material, and final bearing subgrades should be observed and approved by a geotechnical EOR or the EOR’s designated representative prior to the placement of concrete to verify their suitability to provide foundation support, as recommended herein. Any localized soft or unsuitable existing fill material containing organics or deleterious matter at the footing subgrades should be removed and replaced with new compacted structural fill, lean concrete or crushed stone. If crushed stone is used, it should covered with geotextile cloth. The geotechnical EOR or the EOR’s designated representative should monitor and document all undercuts. We recommend establishing a budget for the undercutting of soft and yielding existing fill and natural soils. If foundations cannot be poured the same or following day they are excavated, a 3-inch mud mats should be placed over soil subgrades to protect the footing subgrade soils. Groundwater is expected to be present at or above the proposed footing levels. Therefore, the contractor should be prepared to provide localized construction dewatering consisting of submersible pumps in gravel sumps, collector trenches or well points. The actual means and method of dewatering should be left up to the contractor.

6.6 Instrumentation and Monitoring DCM-9 presents the guidelines for instrumentation and monitoring of CERP dams and was utilized as guidance in the design of instrumentations for STA-1W Expansion 2 facilities. Currently, the design of the STA classifies as a low hazard dam.

Instrumentation and monitoring of dams is an established practice and an important part of operating and maintaining the facilities. Instrumentation provides physical records of internal conditions within the embankments and foundations to supplement visual observation and regular safety inspections.

DCM-9 indicates that low HPC dams should include reservoir level gages and provisions for seepage monitoring and/or collection as minimum instrumentation for the structure. The instrumentation and monitoring systems should be installed to accomplish the following goals:

• To evaluate embankment behaviour during the first filling of the Connection Canal and Expansion 2,

• To monitor the ongoing performance of the embankments,

• To provide early warning of potential problems,

• To make rational decisions regarding remedial action, and

• To provide real-time information to on-site water managers.




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7. Summary This section presents a summary of the analyses performed based on the information obtained during the exploration effort and the results of the analysis present in the attached appendices and the RADISE report (2020). The conceptual design was utilized to determine the location of the exploration efforts. The bullets below present the summary of the analyses:

• Detailed results of the geotechnical field and laboratory investigations were submitted in the RADISE report (2020). The project geotechnical design soil parameters were included in the GBODM prepared by AECOM dated April 2020.

• Based on the modelled seepage analyses for the subject project, the proposed Expansion 2 project embankments will adequately control seepage through foundations and embankments with minimal to no impact to surrounding areas.

• The slope stability analysis for the proposed project embankment and canal slopes indicated adequate factors of safety against deep and shallow failures.

• Based on the soil borings, up to about 9 feet of Peat was encountered in certain project areas. This material is not considered suitable for use as structural fill and shall be excavated to a thickness of no more than 4 feet for embankments. The sandy materials present below the Peat layer are considered suitable for reuse as compacted fill.

• It is anticipated that some existing drainage ditches or swales will need to be filled or relocated to nearby flow conduits. The fill material should consist of either spoils from adjacent canal excavations or borrow fill from offsite sources. After placement of the fills, they should be covered with a 2-to-3-inch layer of peat or topsoil to enable vegetation growth.

• The control structures and the pump stations may be supported on mat foundations bearing on limestone or sand layers within the limestone. Mats can be designed for maximum allowable net bearing pressures as presented in Table 5-20.

• The generator buildings can be supported on shallow footings bearing on structural fill and can be designed for a maximum allowable net bearing pressure of 3,000 psf.

• Below grade walls for the pump stations must be designed to resist the lateral earth pressures, water pressures and surcharges due to adjacent footings, construction equipment, traffic and other loads.




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8. Limitations Interpretation of general subsurface conditions presented herein is based on the soil, rock and groundwater conditions encountered in the field and laboratory test results. Although representative portions of the samples taken were tested, subsurface conditions may vary outside of the exploration location. This report does not reflect any variations that may occur across the site in areas not sampled. The nature and extent of such variations may not become evident until construction. The Contractor shall conduct its own exploration to eliminate any potential concerns of soil conditions in areas where soil borings were not performed.

This report has been prepared for the specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranty, express or implied, is provided. In the event that any changes in the nature of the project as outlined in this report are planned, the conclusions contained in this report will not be considered valid unless the changes are reviewed, and the conclusions of this report are modified or verified in writing by AECOM.




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9. References Das, B. and Sobhan, K. (2014). “Principles of Geotechnical Engineering”. Cengage Learning. Stamford, CT.

Deere, D.U. and Miller, R.P. (1966). Engineering Classification and Index Properties of Intact Rock. Technical Report No. AFWL-TR-65-116. Urbana, IL.

Idriss and Boulanger, 2008. Soil Liquefaction During Earthquakes, Earthquake Engineering Research Institute, 2008.

Natural Resources Conservation Service. 2012. National Engineering Handbook, Part 631 Geology, Chapter 4: Engineering Classification of Soil Materials. U.S. Department of Agriculture.

RADISE International, L.C. Geotechnical Data Report for the SFWMD STA 1W Expansion #2 Project, Palm Beach County, Florida, April 2019.

Ranjan, G. and Rao, A. (2007). “Basic and Applied Soil Mechanics 2E”. New Age International. New Delhi, India.

South Florida Water Management District (2014). Technical Publication WR-2014-004 Stormwater Treatment Area Water and Phosphorus Budget Improvements

Tschebotarioff, Gary. (1973). “Foundations, Retaining and Earth Structures” 2E. McGraw-Hill Book Company. USA

United States Geological Survey. (2019). Seismic Hazard Maps. Retrieved from https://earthquake.usgs.gov

US Army Corps of Engineers. (2003). Engineering and Design: Slope Stability. EM 1110-2-1902.

US Army Corps of Engineers. (2016). Engineering and Design: Earthquake Design and Evaluation for Civil Works Projects. EM 1110-2-1806.

US Army Corps of Engineers. (1994). Engineering and Design: Hydraulic Design of Flood Control Channels.

US Army Corps of Engineers. (1993). Engineering and Design: Seepage Analysis and Control for Dams. EM 1110-2-1901.

US Army Corps of Engineers. (1992). Engineering and Design: Bearing Capacity of Soils. EM 1110-1-1905.

US Army Corps of Engineers. (1990). Engineering and Design: Settlement Analysis. EM 1110-1-1904.

US Army Corps of Engineers. (1997). Engineering Technical Letter. Engineering and Design: Design Guidance on Levees. ETL 1110-2-555.

US Bureau of Reclamation. (2014). Design Standards No. 13: Embankment Dams, Chapter 8: Seepage.

US Bureau of Reclamations (1974). Design of Small Canal Structures.

USSD 28th Annual USSD Conference, “The sustainability of experience--investing in the human factor”, Portland, Oregon, April 28 - May 2, 2008

Youd, T. L., Idriss, I.M., et al. (2001). "Liquefaction resistance of soils: Summary report from the 1996 NCEER and 1998 NCEER/NSF workshops of evaluation of liquefaction resistance of soils." Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 127, No. 4, pp. 297-313.




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Appendix A – Overall Location Map and Site Plan, Boring Plan, and Piezometers Location Plan




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Appendix B – Summary of Laboratory & Field Tests




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Appendix C – Bearing Capacity Analyses (Embankments)




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Appendix D – Settlement Analyses (Embankments)




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Appendix E – Seepage Analyses




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Appendix F – Uplift, Heave and Piping Analyses




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Appendix G – Slope Stability Analyses




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Appendix H – Settlement Analyses (Structures)




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Appendix I – Bearing Capacity Analyses (Structures)




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Appendix J – Liquefaction Potential Analyses




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Appendix K – Seepage Analyses (Structures)

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