Contract 2_Lewisville_GDR.pdf

FOR OFFICIAL USE ONLY

GEOTECHNICAL DATA REPORT

LEWISVILLE DAM SAFETY MODIFICATION

SPILLWAY, HAUL ROUTE AND BORROW AREA

DENTON COUNTY, TEXAS

US ARMY CORPS OF ENGINEERS

SWD DAM SAFETY PRODUCTION CENTER

STATUS: 100% DESIGN

DATE: May 2021

Final Version

GEOTECHNICAL DATA REPORT STATUS: 100% DESIGN

LEWISVILLE DAM SAFETY MODIFICATION – CONTRACT 2 DATE: May 2021

For Official Use Only

THIS PAGE INTENTIONALLY LEFT BLANK

GEOTECHNICAL DATA REPORT STATUS: 100% Design LEWISVILLE DAM MODIFICATION DATE: May 2021

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DISCLAIMER AND LIMITATIONS

Disclaimer

This Geotechnical Data Report (GDR) contains near-surface and subsurface information collected at or adjacent to the Site by the Government for use in preparing the Contract Documents. The Technical Data contained in this report upon whose accuracy the Contractor may rely are logs of borings, logs of trenches/test pits, field test results, laboratory test results, construction photos, rock core photos, original construction-era documents, recorded measurements of subsurface water levels, and contractor-reported optical televiewer data. The GDR does not include any interpretation of the data. If opinions, or interpretive or speculative non-factual comments or statements appear in the GDR, such opinions, comments, or statements are not operative parts of the GDR and do not have contractual standing.

This GDR is a summary of the full-text non-interpretive documents included within the attached non-interpretive appendices. Bidders must review the information in the GDR and draw their own conclusions in bid preparation. A separate Geotechnical Interpretive Report (GIR) and appendices are also being provided, which contain interpretive information.

Limitations

The information presented is limited to the conditions at the locations of the borings, test pits/trenches, or other field data collection locations at the time that the data were collected. Each bidder must form their own opinion of the character of the work and of the materials to be excavated, make their own interpretations, and satisfy themselves by their own interpretations and research regarding all conditions affecting the work to be performed. The Contractor must assume all responsibility for deductions and conclusions as to the nature or condition of all earth, rock and other materials to be excavated and the difficulties of making and maintaining the required excavations, and of performing other work affected by the geology and subsurface conditions at the Site.

The Contractor must assume that various rock and soil conditions may be encountered in excavations, including materials that are difficult to handle.

Limited Reliance by the Contractor on Technical Data Authorized: The Contractor may rely upon the general accuracy of the Technical Data contained in the GDR. However, the contractor should not rely on the GDR with respect to:

• the completeness of this report for the Contractor’s purposes, including but not limited to, any aspects of the means, methods, techniques, sequences, and procedures of construction to be employed by the Contractor, and safety precautions and programs incident thereto, or

• any interpretations and opinions contained in this report.

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GDR REPORT FUNCTION

This report, the Geotechnical Data Report (GDR), functions as a summary of non-interpretative data that have been collected for this project in separate reports at different times. Some of the information within and attached was created by USACE, some by Contractors working for

USACE.

For more information, please see the full-text appendices that contain more detailed information in each report. They are referenced within the report.

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TABLE OF CONTENTS

DISCLAIMER AND LIMITATIONS

GDR REPORT FUNCTION

PART 1 - GENERAL

1.1 Project Description

1.2 Embankment

1.3 Spillway

1.4 Historical Modifications

1.4.1 Spillway Apron

PART 2 - GEOLOGIC SETTING

2.1 Regional Geology

2.2 Site Geology

2.2.1 Soils

2.2.2 Bedrock Formations

2.2.3 Local Geologic Mapping

2.2.4 Eagle Ford Formation

PART 3 - GEOTECHNICAL INVESTIGATIONS

3.1 1947 Embankment Investigation

3.2 1951 Design Memorandum

3.3 1970’s and 1980’s Investigations

3.4 2015 Spillway Investigation

3.5 2017 Spillway Investigations

3.6 2018 Spillway Investigations

3.7 2018 Spillway Vibrating Wire Piezometer Installation

3.8 2018-2019 Spillway Anchor Test Program

3.9 2019 Spillway Training Wall Piezometer Installation

3.10 2015 Borrow Area Investigation

3.11 2017 Borrow Area Test Pit Investigation

3.12 2020 Haul Road Foundation Investigation

PART 4 - SUBSURFACE CONDITIONS

4.1 Spillway Area

4.1.1 Spillway Concrete

4.1.2 Spillway Soils

4.1.3 Spillway Bedrock

4.1.4 Spillway Weir Piezometers Time History

4.1.5 Spillway Training Wall Piezometers

4.1.6 Spillway Test Anchor Strain Gauge Strain History

4.2 Borrow Area

4.2.1 Borrow Area Index Testing – Untreated

4.2.2 Borrow Area Moisture Content Testing - Untreated

4.2.4 Borrow Area Atterberg Limits testing – Untreated & Lime-Treated

4.2.5 Borrow Area Gradation Testing

4.2.6 Borrow Area Compaction testing – Untreated & Lime Treated

4.2.7 Borrow Area Standard Proctor Testing - Untreated

4.2.8 Borrow Area Triaxial Shear Strength Testing – Untreated & Lime Treated

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4.2.9 Borrow Area Unconfined Compressive Strength & Undrained Shear Strength – Lime Treated

4.2.10 Borrow Area Direct Shear Testing - Untreated

4.2.11 Borrow Area Soluble Sulfate Testing - Untreated

4.2.12 Borrow Area Dispersion Testing - Untreated

4.2.13 Borrow Area Salt Testing - Untreated

4.3 Haul Road Alignment

4.3.1 `Haul Road 2020 Index Testing

4.3.2 Haul Road 2020 Sieve and Hydrometer

4.3.3 Haul Road 2020 UC Strength Testing & Dry Unit Weight Testing

4.3.4 Haul Road 2020 Modified Proctor Results

4.3.5 Haul Road 2020 California Bearing Ratio (CBR) Test Results

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Figures

Figure 1-1 Lewisville Dam, Project Location Map Figure 1-2 Significant Project Features Figure 1-3 Typical Embankment Section Figure 1-4 Typical Uncontrolled Spillway Weir Cross-Section Figure 2-1 Geology of Texas (State of Texas, 1992) Figure 2-2 Soil Map of Denton County with Key (USDA 1979) Figure 2-3 Geologic Map of Lewisville Dam Area (Geologic Atlas of Texas, 1991) Figure 2-4 Preconstruction Geologic Mapping (USACE, 1947, App. 3, Plate 1) Figure 3-1 Map of Spillway Boring Locations (USACE, 1947 ‘Definitive Project Report’, Appendix III, Plate 2) Figure 3-2 Borings in the Vicinity of the Spillway (USACE, 1952, Plan Drawing 43, entitled “Subsurface Exploration Location Plan) Figure 3-3 Core Boring Locations entitled “Core Borings Location Plan” (USACE, 1951, Design Memo., Plate 1) Figure 3-4 Historical Borings around Spillway Structure (USACE, 1952, sheet 270-8) Figure 3-5 Map of 2015 & Historical Borings Figure 3-6 Map of 2017 Borings Figure 3-7 Map of 2018 Investigation Borings Figure 3-8 Map with Close-up of the 2018 spillway borings within the concrete structure Figure 3-9 Spillway Vibrating Wire Piezometer Location Map (circled) Figure 3-10 Map of 2018-2019 Anchor Test Program borings Figure 3-11 Map with Close-up of 2018-19 Anchor Test Borings in/near the Concrete Structure Figure 3-12 Location Map of Training Wall Piezometers (2019) Figure 3-13 Borrow Area General Location Map Figure 3-14 2015 Borrow Area Boring Locations Figure 3-15 GPS Locations of Haul Route Borings (2020) Figure 4-1 1951 Eagle Ford Unit Dry Weight versus Moisture Content for Shales, Holes 6D-82, 6D-83 & 6D-84 (USACE, 1951, Design Memo., Plate 10) Figure 4-2 Eagle Ford 1951 Hole 6D-82 Lab Test Results (USACE, 1951, Design Memo., Plate 6) Figure 4-3 Eagle Ford 1951 Boring 6D-83 Lab Test Results (USACE, 1951, Design Memo., Plate 7) Figure 4-4 Eagle Ford 1951 Boring 6D-84 Lab Test Results (USACE, 1951, Design Memo., Plate 8) Figure 4-5 Eagle Ford 1951 Shearing Strength of Shales, Holes 6D-82, 6D-83 & 6D-84 (USACE, 1951, Design Memo., Plate 9) Figure 4-6 Eagle Ford 2017 & 2018 UC Strength Testing Results Figure 4-7 Piezometer Time History of Spillway PZs - 2018-2020 Figure 4-8 Strain Gauge Time History, Anchor 318, 2019-2020 Figure 4-9 Strain Gauge Time History, Anchor 320, 2019-2020

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Tables

Table 1-1 Lewisville Pertinent Data Table 3-1 Summary of 1947 Spillway Borings (USACE, 1947, Plates 5 &6) Table 3-2 Summary of 1951-1952 Core Borings (USACE, 1952, Plates 3-5) Table 3-3 Summary of 2015 Borings Table 3-4 2017 Investigational Borings Table 3-5 2018 Investigational Borings Table 3-6 Summary of Spillway V.W. Piezometers Table 3-7 Anchor borings 2018-19, Phase 1 Table 3-8 Anchor Test Program, 2018-19, Phase 2 Table 3-9 Anchor Test Program, 2018, Weir Phase 2 Table 3-10 Training Wall Standpipe Piezometer Details Table 3-11 2015 Borrow Area Boring Details Table 3-12 2017 Borrow Area Test Pit Details Table 3-13 Haul Route Investigation Boring Details, 2020 Table 4-1 Spillway Concrete Unit Weight Results 2018 Table 4-2 Spillway Concrete Compressive Strength Results Table 4-3 Spillway Concrete Direct Shear Results Table 4-4 Spillway Soil Laboratory Testing – Moisture (from SPT samples) Table 4-5 Eagle Ford 1947 Moisture Content Results Table 4-6 Eagle Ford 2017 Moisture Content Results Table 4-7 Eagle Ford 2018 Moisture Content Test Results Table 4-8 Eagle Ford 1947 Atterberg Limits Results Table 4-9 Eagle Ford 2017 Atterberg Limits Results Table 4-10 Eagle Ford 2018 Atterberg Limits Results Table 4-11 Eagle Ford 2015 Index Tests Table 4-12 Eagle Ford 2015 Sieve Analysis Table 4-13 Eagle Ford 2015 Hydrometer Analysis Table 4-14 Eagle Ford 1947 Unconfined Compressive Strength Table 4-15 Eagle Ford 2017 Unconfined Compressive Strength Test Results Table 4-16 Eagle Ford 2018 Unconfined Compressive Strength Test Results Table 4-17 Eagle Ford 2018 Direct Shear Test Results Table 4-18 Eagle Ford 2018 Natural Fracture Direct Shear Test Results Table 4-19 Eagle Ford 2015 Consolidation Test Results Table 4-20 Eagle Ford 2017 Elastic Modulus & Poisson’s Ratio Test Results Table 4-21 Eagle Ford 2018 Elastic Modulus & Poisson’s Ratio Test Results Table 4-22 Eagle Ford 2017 U-U Triaxial Compression Test Results Table 4-23 Eagle Ford 2018 U-U Triaxial Compression Test Results Table 4-24 Eagle Ford 2017 Laboratory Anchor Pullout Test Results Table 4-25 Eagle Ford 2018 Laboratory Anchor Pullout Test Results Table 4-26 Eagle Ford 2018 Fully Softened Shear Strength Test Results Table 4-27 Eagle Ford 1947 Compaction Tests Table 4-28 Falling Head Test Results, 2018 Table 4-29 Water Pressure Testing Results 2018 Table 4-30 Borrow Area 2017 Index Testing Results (NRCS-USDA) Table 4-31 Borrow Area 2015 Moisture Content Testing (TEAM Consultants) Table 4-32 Borrow Area 2017 natural moisture content sample results (NRCS-USDA) Table 4-33 Borrow Area 2015 Atterberg Limits (TEAM Consultants)

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Table 4-34 Borrow Area 2017 Index Tests on untreated and lime-treated samples (NRCS-

USDA)

Table 4-35 Borrow Area 2015 Gradation Test Results (TEAM Consultants) Table 4-36 Borrow Area 2017 Standard Proctor Compaction Test Results (NRCS-USDA) Table 4-37 Borrow Area 2015 Standard Proctor Testing (TEAM Consultants) Table 4-38 Borrow Area 2017 Consolidated Undrained Triaxial (NRCS-USDA) Table 4-39 Borrow Area 2017 Unconfined Compressive Strength & Undrained Shear Strength

(NRCS-USDA)

Table 4-40 Borrow Area 2015 Direct Shear Test Results (TEAM Consultants) Table 4-41 Borrow Area 2015 Soluble Sulfate Testing Results (TEAM Consultants) Table 4-42 Borrow Area 2017 Dispersion Testing Results (NRCS-USDA) Table 4-43 Haul Road 2020 Moisture Contents, Unit Weights and Att. Limits Table 4-44 Haul Road 2020 Sieve and Hydrometer Table 4-45 Haul Road 2020 UC Strength of Tube Samples (standard Proctor) Table 4-46 Haul Road 2020 Moisture-Density (ASTM D 1557) Results (modified proctor) Table 4-47 Haul Road 2020 California Bearing Ratio

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Non-Interpretive Appendices

USACE Pre-Construction Spillway Investigation – 1950’s -Preconstruction Map of borings and Boring Logs– 1952 USACE Borrow Area Investigation – 2010’s -Map of Borrow Area Boring Locations - 2015 -Borrow Area Boring Logs - 2015 -Borrow Area Lab Testing Results (TEAM Consultants) – 2015 -Borrow Area Test Pit Logs - 2017 -Borrow Area Laboratory Testing Results (USDA-NRCS) - 2017 CDM-Smith Spillway Investigation - 2017 -CDM Boring Locations Map

-CDM-Smith Boring Logs -CDM Pressure Testing Results -CDM Investigation laboratory Results -CDM SPT & Core Photos -CDM Anchor Pull-out Laboratory Test Results -CDM gINT database Stantec Spillway Investigation – 2017-2018 -Stantec Boring Logs -Stantec gINT database -Stantec Core and SPT photos -Stantec Lab Testing -Stantec Anchor Pull-out Laboratory Test Results -Stantec Boring Location Map -Stantec Downhole Geophysics -Stantec Falling Head Tests and Pressure Tests Results -Stantec Piezometer Installation Details -Stantec Boring Location Coordinates Nicholson/Stantec Spillway Anchor Study - 2019 -Field Anchor Boring Locations Map -Field Anchor Boring Logs

-Field Anchor Study Excel Files (zipped) -Field Anchor Study Videos (available by request—large files, roughly 8 GB)

USACE Spillway Training Wall Investigation - 2019 -USACE Boring Logs for PZs installed behind-the-training-walls -Spillway Time History for automated PZs Haul Route Borings (USACE & TEAM Consultants) -2020 -Haul Route Boring Locations Map (USACE) -Haul Route Boring Logs (USACE) -Haul Route Laboratory Test Results (TEAM Consultants)

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PART 1 - GENERAL

1.1 Project Description

Lewisville Dam is located at river mile 30.0 on the Elm Fork of the Trinity River, about 1 mile north of Lewisville, Texas, and about 22 miles northwest of Dallas, Texas, as shown in Figure 1-1. The project consists of an earthen embankment, an uncontrolled concrete ogee weir spillway, and a gated outlet works.

A smaller dam and reservoir on the Elm Fork called the Garza Dam-Lake Dallas was built before Lewisville Lake. Garza Dam was built by the City of Dallas for water supply. Construction began in 1927 and impoundment began in 1928. Lake Dallas was the primary municipal water supply source for the City of Dallas until it was breached in 1957. In 1945, Congress authorized a larger project known as Garza-Little Elm Dam and Reservoir, slightly downstream that would impound Clear, Little Elm, Stewart, Pecan and Hickory Creeks in addition to the Elm Fork of the Trinity River. Garza Dam-Lake Dallas was breached in 1957 and became part of the larger project. The project was renamed Lewisville Dam in 1955 and Lewisville Reservoir in 1960.The title Lewisville Reservoir reverted to Garza-Little Elm Reservoir in 1961. The reservoir title was changed again in the mid-1970s to Lewisville Lake. Since then the dam and lake have been called Lewisville Dam-Lewisville Lake.

Construction of the Lewisville Dam began in November 1948, impoundment of the reservoir began November 1954 and completion in August 1955. The conservation pool of elevation

515.0 feet NAVD88 was first reached in May 1957 (NGVD29 and NAVD88 are approximately equal at the project). Once Ray Roberts Dam was constructed upstream of Lewisville Lake, the conservation pool elevation of Lewisville Lake was raised to Elevation 522 feet NAVD88 for enhancement of water supply. The pool raise was officially authorized in November 1988 and was achieved in the spring of 1989. Two (2) municipal water supply intakes constructed by local sponsors are also significant project features. The project features are shown in Figure 1-2.

Pertinent data is shown in Table 1-1.

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Figure 1-1 Lewisville Dam, Project Location Map

Lewisville Dam

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Figure 1-2 Significant Project Features

Table 1-1 Lewisville Pertinent Data

Physical Data (feet, NAVD88) Dam Type Homogeneous Earthen Embankment

Dam Length 32,328 FT (excluding spillway)

Top of Dam Elevation 560.0 FT (Design), 559.4 FT (Surveyed Low Point)

Crest Width 20 FT

Maximum Height Above Streambed 125 FT

Embankment Upstream Side Slopes 1V:2.5H above Elevation 520-feet, and 1V:3H below Elevation 520-feet

Embankment Downstream Side Slopes 1V:2.5H above Elevation 520-feet, and 1V:3H below Elevation 520-feet

Uncontrolled Spillway Location Station 282+25, near Left Abutment

Spillway Crest Elevation 532.0 FT

Spillway Type Uncontrolled Ogee

N

Spillway

Outlet Works Municipal

Water Intakes

Embankment

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Spillway Width 560 FT

Capacity at PMF Elevation 237,000 CFS

Controlled Outlet Works Location Station 149+16

Outlet Structure Description 16 FT Round Conduit

Control Three 6.5 FT x 13 FT Broome-type Sluice Gates

Low Flow Control Two 5 FT Steel Conduits

Hydrology Drainage Area 1,660 SQ MI

PMF Pool Elevation 552.1FT

Max. Historic Release - Spillway 21,000 CFS

Max. Historic Pool Elevation 536.9 FT (30 May 2015)

Elm Fork Channel Capacity 7,000 CFS (Before Damages*)

Datum adjustment from NGVD29 to NAVD88** + 0.00

*If flows exceed 7,000 CFS, property damages begin to occur. Damages increase with increased flow.

**At the location of Lewisville Dam the conversion from vertical datum NGVD29 to vertical datum NAVD88 ranges from +0.03 to -0.02 feet along the length of the dam as determined using Corpscon 6.0.1. This study assumes that NGVD29 and NAVD88 are equivalent with a

0.0 foot conversion at Lewisville Dam.

Feature Elevation (feet)

Cumulative Storage1

(AC-FT)

Outlet Works2 Capacity

(CFS)

PMF Pool Elevation 552.1 2,111,000 N/A Top of Flood Pool (Spillway Crest)

532.0 940,000 11,100

Top of Conservation Pool 522.0 599,000 10,200 Streambed 435.0 N/A N/A 1 Cumulative storage based on the elevation-capacity curve developed from the September 2007 survey.

2 Outlet works capacity based on PLATE 2-10B in the 1997 Lewisville Water Control Manual.

1.2 Embankment

The embankment is 32,328 feet-long with a maximum height of 125 feet and a crest width of 20 feet at elevation 560 feet NAVD88. The embankment was constructed of approximately 13,208,400 cubic yards of impervious material obtained from onsite borrow areas and excavations. The impervious homogenous structure was built under multiple contracts.

An inspection trench with a 20-foot bottom width and 2H:1V side slopes was incorporated into the dam design between Station 79+00 and Station 163+70. The trench was to be excavated through the foundation soils to the top of shale except at the ends where it transitioned up to

For Official Use Only Page 14 of 85 natural ground. Also incorporated into the design of the dam was a 3 to 4-foot thick poorly graded sand drainage blanket underneath the downstream section of the embankment. The drainage blanket has a maximum width (as measured from upstream to downstream) of 200 feet and was constructed between Stations 79+07 and 177+70 and Stations 210+70 and 241+30 utilizing onsite borrow materials. A typical cross-section of the embankment is shown in Figure 1-3.

Figure 1-3 Typical Embankment Section

1.3 Spillway

An uncontrolled concrete ogee weir spillway, shown in Figure 1-4 (below), is located near the left abutment. The structure consists of an approach channel, a 560-foot wide concrete ogee weir with crest elevation of 532 feet NAVD88, two 90-foot long concrete gravity sections (non-overflow), a concrete paved apron, training walls, and wing walls. The reinforced concrete apron slab approximately 209-feet long and 560 feet wide, and was built with a 10-foot deep turn-down wall at the end of the original apron slab. The reinforced concrete cantilever training walls are about 13-feet high and extend the length of the concrete apron. Twenty-eight (28) foot high wingwalls are located at the downstream end of each training wall. A 1985 spillway modification described in Paragraph 1.2.1 extended the spillway apron slabs 60 feet downstream. The spillway does not have a stilling basin nor is the channel downstream of the apron lined.

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Figure 1-4 Typical Uncontrolled Spillway Weir Cross-Section

1.4 Historical Modifications

1.4.1 Spillway Apron

Erosion occurred immediately downstream of the apron during the 1981 flow event. In response, a 1985 modification extended the apron 60 feet downstream. The extension is about 3 feet lower than the original apron and is constructed with 18-inch thick, reinforced and anchored concrete slabs. A 10-foot deep cutoff wall and a band of riprap was installed at the downstream end of the extension to protect against future scouring.

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PART 2 - GEOLOGIC SETTING

The geology indicated in this section was taken from published literature and only indicate general conditions in the greater project area. Thicknesses and depths of deposits indicated are approximate only and should be expected to vary significantly.

2.1 Regional Geology

Lewisville dam is located near the northwest boundary of the major Coastal Plain Province, specifically in the West Gulf Coastal Plain, a physiographic subdivision of the Coastal Plain Province. The West Gulf Coastal Plain is further subdivided into belts having general northeast-southwest trends. These subdivisions are based upon the underlying geologic formations and upon the consequent variation of vegetation found within the various belts.

The dam extends from a point coincident with the boundary of the Eastern Cross Timbers and the Blackland Prairie, across the alluvium of recent origin in the stream valley and onto the Eagle Ford Prairie on the east abutment. The reservoir area extends from the Grand Prairie soil group at the western edge of the reservoir over the East Cross Timbers and onto the Blackland Praire soils on the east.

The bedrock of North Texas is generally composed of Cretaceous age sedimentary deposits that are mostly marine in origin. Approximately 100 Million Years Ago (MYA) the Western Interior Seaway (WIS) expanded as sea levels rose, flooding the North American continent from the present day Gulf of Mexico northward to the Arctic Circle. The depth of the ocean rose and fell many times. In doing so, the sediments that were deposited varied from higher energy sandier/coarser grained materials near shoreline and deltaic complexes, to lower energy, deeper water and finer grained deposits of silt and clay. After the Cretaceous Period the area tilted slightly resulting in a ½ to 1-degree dip east-southeast. The tilting of the strata, combined with more recent erosion, formed bands of exposed bedrock that strike generally north-south, as seen in Figure 2-1.

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Figure 2-1 Geology of Texas (State of Texas, 1992)

Location of Lewisville Dam

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2.2 Site Geology

2.2.1 Soils

Residual soils of the upland areas in the vicinity of the site are derived from the Woodbine and Eagle Ford formations from the Upper Cretaceous. The soils in the Stewart’s Creek flood plain are predominantly a highly plastic, clay residuum of Eagle Ford shale, while those to the west in the Elm Fork flood plain are sandy, silty, and clayey residual soils of the Woodbine Group. The valley floor contains alluvial materials composed chiefly of sand, silt, and clay. The depth of overburden at the dam site varies from an estimated 50 to 60 feet at the stream banks to a minimum of approximately 10 feet on the abutments. Much of the overburden throughout the flood plain area of the river can be classified as pervious material. The overburden in the area of high relief and east of the valley section is composed of impervious clay residuum of the Eagle Ford formation, with soils east of the Elm Fork being either reworked or residual clays from the Eagle Ford shale. The valley of Stewart’s Creek has been filled with approximately 42 feet of reworked clay. East of Stewart’s Creek and on the left abutment of the stream, the overburden decreases to a thickness of about 35 feet. Continuing west, the mantle of residual material becomes thinner and decreases to about 25 feet. See Figure 2-2 for a USDA soil map of the area in the vicinity of the dam.

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Figure 2-2 Soil Map of Denton County with Key (USDA 1979)

2.2.2 Bedrock Formations

Primary bedrock formations occurring at the dam site are the Eagle Ford and Woodbine groups of Upper Cretaceous age. The Cretaceous rocks in the reservoir area dip southeastward at a gradient of 50 to 60 feet per mile. This is greater than the slope of the land surface, and results in the encounter of progressively younger beds when proceeding in a southeastward direction.

Historically, the Eagle Ford group was not subdivided into various member formations at the dam site and, for project purposes, was originally considered to be a single entity. However, based on more recent mapping in the region of north central Texas, the Eagle Ford Shale is divided into three (3) ascending units: the Tarrant, the Britton, and the Arcadia Park formations.

At the dam site, the Woodbine formation has been segregated into the upper Lewisville beds and the lower Dexter Sands. No major structural faulting or folding is known at the dam site or in the reservoir area. Original design reports described the eastward dip of the primary strata in

For Official Use Only Page 20 of 85 the area as favorable in that the waters which might infiltrate into the pervious strata exposed within the reservoir would find no outlet below the embankment. However, regional groundwater availability modeling and the related report produced for the Texas Water Development Board (Hardin & Associates, 2004), as well as multiple historical geologic references such as Dr.

Robert T. Hill’s 1900 Map of the Paluxy Artesian Reservoirs of the Black and Grand Prairies of Texas, clearly indicate that seeps and springs as well as artesian wells have historically been noted in the regions surrounding the dam. Artesian pressures were significantly reduced following the development and use of groundwater. However, after the construction of multiple surface water reservoirs, and increased surface water supply options, the reduced use of groundwater has resulted in a partial return of higher water levels and artesian pressures in the Woodbine. The Woodbine aquifer is confined to semi-confined beneath the Eagle Ford Shale.

2.2.3 Local Geologic Mapping

Geologic Mapping from the ‘Sherman Sheet’ of the Geologic Atlas of Texas (1967, revised 1991) shows that the spillway region is underlain by Eagle Ford Formation Rocks, with Quaternary-Age alluvium covering the bedrock in the spillway area (Figure 2-3). During construction of the spillway, all overburden was removed within the immediate area of the spillway itself.

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Figure 2-3 Geologic Map of Lewisville Dam Area (Geologic Atlas of Texas, 1991)

In addition, USACE conducted pre-construction bedrock geologic mapping in the region of the dam. Figure 2-4 shows the map produced as part of the pre-construction efforts.

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Figure 2-4 Preconstruction Geologic Mapping (USACE, 1947, App. 3, Plate 1)

2.2.4 Eagle Ford Formation

Lewisville Dam Alignment

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The Eagle Ford formation is found on the left abutment and flood plain east of the Elm Fork. The Eagle Ford lies unconformably upon the Woodbine and is 450 to 500 feet thick. At the dam site, the unweathered Eagle Ford is considered to be a firm, massive, somewhat silty, dark, impervious clay-shale with some thin bentonite seams. In north central Texas, the Eagle Ford Shale is divided into three (3) ascending units: the Tarrant, the Britton and the Arcadia Park formations of the Eagle Ford Group. Bedrock at the project appears to correlate with the upper portions of the Britton formation, which is composed of a 200-feet thick sequence of dark gray clay shale with minor amounts of quartz silt and large numbers of small, flattened, reddish-brown clay iron-stone nodules and light gray limestone concretions. The Arcadia Park formation is approximately 100 feet thick with the basal 10 to 30 feet consisting of dark gray calcareous shale, shaly chalk, and hard beds of gray-orange calcarenite. The remainder of the Arcadia Park formation consists of soft dark olive gray shale (USGS, 1982).

Because of its high montmorillonite content, the Eagle Ford Shale is dissimilar to typical shales in the eastern part of the United States. Weathered clay-shale rapidly slakes when submerged in water and rapidly desiccates when exposed. The weathered Eagle Ford Shale is susceptible to swell and significant volume change potential. It is similar to a very hard clay found in other parts of the country. In place Eagle Ford Clay Shale is competent below the weathered zone.

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PART 3 - GEOTECHNICAL INVESTIGATIONS

3.1 1947 Embankment Investigation Geotechnical investigations at the dam site began with the definitive project report in 1947. Four

(4) borings, numbered 6C-11, 6C-12, 6C-13, and 6C-19, were drilled along the spillway centerline, perpendicular to the dam axis, as shown on Figure 3-1. A summary of the boring logs is shown as Table 3-1. Samples were collected and analyzed for moisture content, Atterberg limits, unconfined compressive strength, and direct shear strength. Results of the investigation and testing are summarized in Part 4, and laboratory reports are located in the Non-Interpretive Appendices.

Figure 3-1 Map of Spillway Boring Locations (USACE, 1947 ‘Definitive Project Report’, Appendix III, Plate 2).

Table 3-1 Summary of 1947 Spillway Borings (USACE, 1947, Plates 5 &6)

Hole #

Coordinates (NAD83 Texas State Plane, North Central, feet)

Inclined or

Vertical

Surface Elevation

(NAVD88)

Top of Rock Depth (feet)

Bottom of Hole

Depth (feet) Northing Easting

6C-11 unknown unknown Presumed vertical 546.1 6.0 31.2

6C-12 “ “ “ 548.1 24.3 61.4 6C-13 “ “ “ 520.9 9.4 44.7

N

Borings highlighted for emphasis

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Coordinates (NAD83 Texas State Plane, North Central, feet)

Inclined or

Vertical

Surface Elevation

(NAVD88)

Top of Rock Depth (feet)

Bottom of Hole

Depth (feet) Northing Easting

6C-19 “ “ “ 540.7 21.0 85.4

3.2 1951 Design Memorandum Further studies for the design of the spillway took place in 1951 and later published in 1951 and 1952. A total of twenty-three (23) borings were drilled in the (then-future) spillway vicinity; this includes the four borings from 1947, described earlier. Figure 3-2 shows all the borings, and Figure 3-3 shows just the rock core borings, which are a subset of the total borings. Figure 3-4, is a zoomed-in view of the core borings, in the vicinity of the (then-future) spillway. A summary of the borings is shown as Table 3-2. The original drawings can be found in the Non- Interpretive Appendices. Samples were collected and analyzed for moisture content, Atterberg limits, dry unit weight, unconfined compressive strength, direct shear, and consolidated-undrained triaxial tests. Results of the investigation and testing are discussed in Part 4, and laboratory reports and boring logs are in the Non-Interpretive Appendices.

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Figure 3-2 Borings in the Vicinity of the Spillway (USACE, 1952, Plan Drawing 43, entitled

“Subsurface Exploration Location Plan)

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Figure 3-3 Core Boring Locations entitled “Core Borings Location Plan” (USACE, 1951, Design Memo., Plate 1)

Table 3-2 Summary of 1951-1952 Core Borings (USACE, 1952, Plates 3-5)

Coordinates (NAD83 Texas State Plane, North Central, feet)

Inclined or

Vertical

Surface Elevation

(NAVD88)

Top of Rock Depth (feet)

Bottom of Hole

Depth (feet) Northing Easting

6C-31 unknown unknown Presumed vertical 546.7 10.0 51.2

6C-32 “ “ “ 548.0 9.0 58.0 6C-33 “ “ “ 544.1 10.0 91.7 6C-34 “ “ “ 545.3 12.5 89.7 6C-35 “ “ “ 543.7 12.6 91.5 6C-36 “ “ “ 484.1 12.7 15.4 6D-48 “ “ “ 499.3 - 14.5

8A-6C-59 “ “ “ 556.9 30.0 45.5 8A-6C-60 “ “ “ 556.7 26.0 41.7 8A-6C-61 “ “ “ 556.0 17.6 44.7

8A-71 “ “ “ 552.9 - 34.0 8A-6C-72 “ “ “ 555.4 16.5 55.5 8A-6C-73 “ “ “ 552.3 18.6 52.0

For Official Use Only Page 28 of 85

Coordinates (NAD83 Texas State Plane, North Central, feet)

Inclined or

Vertical

Surface Elevation

(NAVD88)

Top of Rock Depth (feet)

Bottom of Hole

Depth (feet) Northing Easting

8A-6C-74 “ “ “ 553.6 15.0 55.6 8A-6C-75 “ “ “ 554.5 16.0 57.0 8A-6C-76 “ “ “ 556.4 8.0 48.0

6D-82 “ “ “ 535.6 29.8 43.4 6D-83 “ “ “ 532.1 17.2 30.3 6D-84 “ “ “ 524.7 18.8 30.6

Figure 3-4 Historical Borings around Spillway Structure (USACE, 1952, sheet 270-8)

Borings highlighted for emphasis N

For Official Use Only Page 29 of 85

3.3 1970’s and 1980’s Investigations

In October 1976 Modification of the Embankment Design Memorandum (#3) addressed embankment slides, an April 1979 Supplement 1, and a November 1982 Supplement 2. None of these documents list or show any holes or test pits in the vicinity of the spillway. The closest boring is at roughly embankment Station 248+00, which is distant from the spillway; the spillway starts at embankment Station 276+00. These memorandums are not included in the appendices since they do not apply to this contract work.

3.4 2015 Spillway Investigation

A total of ten borings were drilled in 2015 to determine the foundation potential to support anchors, determine if foundation shales are contributing to heaving of the spillway slabs, and determine the integrity of the foundation clay shales and if voids are present underneath the ogee or apron slabs. Three (3) of these borings were drilled on an incline of 15˚ from vertical.

Samples were collected and analyzed for Atterberg Limits, gradation, moisture content, intact peak and residual direct shear, pre-split direct shear, consolidation, and specific gravity. A map of the boring locations is shown as Figure 3-5, and a table of the borings is shown as Table 3-3.

Results of the investigation and testing are discussed in Part 4, and laboratory reports and boring logs are located in the non-interpretive documents appendix.

For Official Use Only Page 30 of 85

Figure 3-5 Map of 2015 & Historical Borings

Table 3-3 Summary of 2015 Borings

Coordinates (NAD83 Texas State Plane, North Central, feet)

Inclined or

Vertical Surface

Elevation

Top of Rock Depth (feet)

Bottom of Hole

Depth (feet) Northing Easting

15-L300 Not Surveyed

Not Surveyed 105° Not

Surveyed 5.4 50.0

15-L301 “ “ 105° “ 6.0 100.0 15-L302 “ “ 105° “ 6.0 50.0 15-L303 “ “ Vertical “ 1.5 50.0 15-L304 “ “ Vertical “ 1.4 50.0 15-L305 “ “ Vertical “ 1.7 50.0 15-L306 “ “ Vertical “ 1.6 24.3 15-L307 “ “ Vertical “ 1.7 25.0 15-L308 “ “ 105° “ 2.0 50.0 15-L309 “ “ Vertical “ 1.0 81.0

3.5 2017 Spillway Investigations

For Official Use Only Page 31 of 85

In January and February of 2017, USACE directed a geophysical and geotechnical investigation of the spillway, which included ground penetrating radar (GPR) surveys, hollow stem auger and rotary coring and sampling, and downhole geophysics. This work was lead by CDM-Smith, Inc.

A map of these borings is shown as Figure 3-6, and a table of the boring is shown as Table 3-4.

Figure 3-6 Map of 2017 Borings

Table 3-4 2017 Investigational Borings

Hole

Surveyed Coordinates (NAD83 Texas State Plane, North Central, feet) Inclination

(degrees)

Ground Surface Elevation

(NAVD88,

feet)

Top of Rock Elevation

(NAVD88,

feet)

Bottom of Hole Elevation

(NAVD88,

feet) Northing Easting

B-310 7074579.85 2451420.04 Vertical 524.0 517.2 398.9 B-313 7074489.96 2451414.17 Vertical 523.5 512.0 399.1 B-314 7074539.27 2452022.04 Vertical 524.5 517.7 399.1 B-317 7074449.33 2452016.14 Vertical 523.4 513.7 397.3 B-329 7074512.83 2451517.85 Vertical 510.1 508.6 493.1 B-330 7074466.71 2451742.03 Vertical 509.4 507.9 492.4 B-331 7074454.28 2451928.78 Vertical 510.8 509.3 493.8

Results of 2017 investigations are summarized in Part 4, and laboratory reports and boring logs are located in the non-interpretive documents appendix.

3.6 2018 Spillway Investigations There were two periods of drilling in 2018 by Stantec within the greater spillway region. The first round was from January to May, the second round was in September.

For Official Use Only Page 32 of 85

From January to May of 2018, Stantec, Inc. performed exploratory drilling within and adjacent to the spillway, on the upstream side of the spillway. A total of seventeen (17) holes were drilled.

Some of the holes were drilled along the crest of the spillway, requiring the use of work platform.

Other holes were drilled along the toe of the spillway weir and on the apron.

In September 2018, additional exploratory drilling was performed in two (2) locations, also by Stantec, Inc. Selected cores were preserved in wax and tested later in a laboratory. All holes were surveyed by an optical televiewer and a three-armed physical caliper.

The first location was on the lower spillway apron where three (3) holes were drilled. The purpose of these holes was to gather information for a proposed end-of-spillway cutoff wall.

These holes were cored.

The second location was downstream of the spillway. Four (4) holes were drilled along the alignment of a possible future cutoff wall roughly 500 feet downstream of the existing ogee spillway. Each of the four (4) holes was augered to below the top of rock, and then cored.

Selected cores from all of the drilling were preserved in wax and tested later in a laboratory. All holes were observed by an optical televiewer and a three-armed physical caliper. The primary purposes of the exploration were to characterize the bedrock and obtain samples for laboratory testing. A listing of the investigation borings is shown in Table 3-5, and maps of the boring locations are shown in Figure 3-7 and Figure 3-8.

Table 3-5 2018 Investigational Borings

Surveyed Coordinates (NAD83 Texas State Plane, North Central, feet) Inclination (degrees)

Azimuth (degrees)

Ground Surface

Elevation

(NAVD88,

feet)

Top of Rock

Elevation

(NAVD88,

feet)*

Bottom of Hole

Elevation

(NAVD88,

feet) Northing Easting B-321 7074651.63 2451527.12 Vertical -- 531.2 503.1 380.0 B-322 7074646.29 2451606.54 Vertical -- 531.4 503.0 380.1 B-323 7074640.95 2451686.76 Vertical -- 531.4 503.4 380.3 B-324 7074636.21 2451766.38 Vertical -- 531.6 503.2 380.2 B-325 7074631.88 2451846.90 Vertical -- 531.6 503.2 380.2 B-326 7074625.54 2451927.03 Vertical -- 531.5 503.3 380.2 B-327 7074608.72 2451626.43 20 30 512.2 507.1 410.1 B-328 7074595.62 2451827.62 30 330 512.2 506.7 425.2 B-332 7074609.55 2451603.64 Vertical -- 512.2 506.7 504.7 B-333 7074598.69 2451763.71 Vertical -- 512.2 507.1 505.0 B-334 7074588.46 2451924.40 Vertical -- 512.1 506.8 504.7 B-335 7074586.69 2451494.82 Vertical -- 511.5 509.9 441.0 B-336 7074570.15 2451719.20 Vertical -- 511.5 510.0 4cross b B-337 7074555.04 2451948.97 Vertical -- 511.5 509.7 441.2 B-400 7074403.33 2451483.01 Vertical -- 506.5 504.9 351.1 B-401 7074391.47 2451704.09 Vertical -- 505.0 503.3 349.6 B-402 7074374.46 2451948.83 Vertical -- 506.7 504.2 351.4 B-403 7073691.05 2451177.25 Vertical -- 544.2 520.9 348.8

For Official Use Only Page 33 of 85

Surveyed Coordinates (NAD83 Texas State Plane, North Central, feet) Inclination (degrees)

Azimuth (degrees)

Ground Surface

Elevation

(NAVD88,

feet)

Top of Rock

Elevation

(NAVD88,

feet)*

Bottom of Hole

Elevation

(NAVD88,

feet) Northing Easting B-404 7073664.44 2451498.34 Vertical -- 507.2 506.2 351.7 B-405 7073651.63 2451790.87 Vertical -- 507.0 507.0 351.7 B-406 7073705.12 2452094.26 Vertical -- 547.4 522.0 351.6 B-501 7074615.82 2451517.46 Vertical -- 512.3 507.2 492.2 B-502 7074599.74 2451740.55 Vertical -- 512.3 507.3 492.2 B-503 7074586.06 2451949.99 Vertical -- 512.2 507.2 492.1

Figure 3-7 Map of 2018 Investigation Borings

~500-ft D/S of Spillway holes

Upper Spillway holes

Lower Spillway Apron holes

For Official Use Only Page 34 of 85

Figure 3-8 Map with Close-up of the 2018 spillway borings within the concrete structure

Results of 2018 investigations are summarized in Part 4, and complete laboratory reports are located in the non-interpretive documents appendix. Boring logs and downhole geophysical surveys are also found in the non-interpretive documents appendix.

3.7 2018 Spillway Vibrating Wire Piezometer Installation

As part of the 2018 investigation, nine (9) vibrating wire piezometers were installed in the weir.

The locations are shown in Figure 3-9, and the details of the spillway piezometers are presented in Table 3-6.

For Official Use Only Page 35 of 85

Figure 3-9 Spillway Vibrating Wire Piezometer Location Map (circled)

Table 3-6 Summary of Spillway V.W. Piezometers

Hole # Location

Elevation (NAVD88, feet)

Concrete Surface

Top of Filter Pack

Bottom of Filter Pack

PZ Tips

321 Weir Crest 531.2 505.2 499.0 502.2 322 Weir Crest 531.4 505.5 496.6 502.4 323 Weir Crest 531.4 505.4 496.6 502.4 324 Weir Crest 531.6 505.2 500.6 502.6 325 Weir Crest 531.6 505.2 501.0 502.6 326 Weir Crest 531.5 505.5 501.2 502.5 332 Weir Toe 512.2 506.8 504.7 505.7 333 Weir Toe 512.2 507.2 505.0 506.1 334 Weir Toe 512.1 506.9 504.7 505.8

3.8 2018-2019 Spillway Anchor Test Program A total of 21 borings were drilled as part of the 2018-2019 spillway anchor test program, which was performed by Nicholson under the direction of Stantec. Lists of the borings are provided in Table 3-7, Table 3-8, and Table 3-9. Maps of the boring locations are shown in Figure 3-10 and Figure 3-11.

Vibrating Wire Piezometers (2018) [Circled]

For Official Use Only Page 36 of 85

Table 3-7 Anchor borings 2018-19, Phase 1

A nc ho r # um be r o f S tr an ds

B on d D ia m et er

(in

A s-bu ilt

B on d (ft

Fr ee

L en gt h

(ft

Ja ck in g

Ta il

Le ng th (f t)

To ta l A nc ho r

Le ng th T es te d (ft

To ta l D ril l L en gt h

(ft

M ax im um

A ct ua l

Lo ad

(k ip

M ax

B on d St re ss

A ch ie ve d

D ur in g

Te st in g ps i)

D es ig n

Lo ad

(k ip

To ta l A ct ua l

D ef le ct io n

(in ch es

C le an in g M ed iu m

In st al la tio n fo

311 7 5.875 10.9 136.1 4.5 151.5 149 12 5.0 247 Failed air tremie grout

312 7 5.875 11.1 115.9 4.5 131.5 129 20 8.1 247 Failed air tremie grout

315 7 5.875 8.6 138.4 4.5 151.5 149 20 10.5 247 Fail Pulled out air tremie grout

316 7 5.875 7.7 119.3 4.5 131.5 129 17 10.0 247 Failed air tremie grout

BH-

BAR

1.25" 4.50 18.40 4.20 3.00 25.6 25 25 8.0 100 .56 at

28% DL auger tremie grout

BH-

BAR

1.25" 4.50 13.30 4.30 3.00 20.6 20 20 8.9 100 .77 at

23% DL auger tremie grout

BH-

BAR

1.25" 6.00 17.30 5.30 3.00 25.6 25 30 7.7 100 .72 at

34% DL auger tremie grout

BH-

BAR

1.25" 6.00 13.10 4.50 3.00 20.6 20 25 8.4 100 .89 at

27% DL auger tremie grout

BH-

BAR

1.25" 6.00 12.20 5.40 3.00 20.6 20 10 3.6 100 .34 at

13% DL auger tremie grout

BH-

BAR

1.25" 6.00 17.80 4.80 3.00 25.6 25 29 7.2 100 .22 at

29% DL auger tremie grout

BH-

BAR

1.25" 4.50 13.00 4.60 3.00 20.6 20 20 9.1 100 .61 at

21% DL auger tremie grout

BH-

BAR

1.25" 4.50 17.50 5.10 3.00 25.6 25 25 8.4 100 .64 at

27% DL auger tremie grout

BH-

BAR

1.25" 6.00 17.70 4.90 3.00 25.6 25 29 7.2 100 .58 at

32% DL auger tremie grout

BH-

BAR

1.25" 4.50 17.50 5.10 3.00 25.6 25 20 6.7 100 .32 at

21% Dl auger tremie grout

BH-

BAR

1.25" 6.00 12.70 4.90 3.00 20.6 20 26 9.1 100 .34 at

29% DL auger tremie grout

BH-

BAR

1.25" 4.50 12.50 5.10 3.00 20.6 20 20 9.4 100 .72 at

22% DL auger tremie

**For failed anchors the maximum load noted in summary is the estimated failure load.

For Official Use Only Page 37 of 85

Table 3-8 Anchor Test Program, 2018-19, Phase 2

A nc be r o f S tr d D ia m

A s-bu ilt

B on d (ft

Fr ee

L en gt h

(ft

Ja ck in g

Ta il

Le ng th (f t)

To ta l A nc ho r

Le ng th T es te d (ft

To ta l D ril l L en gt h

(ft

M ax im um

A ct ua l

Lo ad

(k ip

M ax

B on d St ie ve d

D ur in g

Te st in g ps i)

D es ig n

Lo ad

(k ip

C le an in g M ed al la tio n

425 4 8.375 15 100 7.5 122.5 117 180 38.0 141 water

Post Grouted with TAM Pipe (17.5 gal). Water entering hole at 25' deep.

426 4 8.375 15 100 8 123 117 187 39.5 141 water

Post Grouted with Boston Method (5 gal top 7' BZ) Water cleaned 2nd day. Water entering hole at 25'.

427 12 16 16 100 8.2 124.2 136 563 58.3 422 air Underream to 16".

Tremie grout

428 BAR

1.25" 16 10 29 9.5 48.5 49 150 24.9 100 air Underream to 16".

Tremie grout

429 BAR

1.25" 16 10 29 10 49 49 150 24.9 100 air Underream to 16".

Tremie grout

430 BAR

1.25" 16 10 29 9 48 49 150 24.9 100 air Underream to 16".

Tremie grout

Table 3-9 Anchor Test Program, 2018, Weir Phase 2 nc ng le D eg re e fr om

Ve rt ic al be r o f S tr d D ia m

A s-bu ilt

B on d (ft

To ta l D ril l L en gt h

(ft

M ax im um

A ct ua l

Lo ad

(k ip

M ax

B on d St ie ve d

D ur in g

Te st in g ps i)

D es ig n

Lo ad

(k ip

C le an in g M ed al la tio n

318 20 12 16 16 145 563 58.3 422 air Underream to 16". Tremie

320 35 12 16 16 167 563 58.3 422 air Underream to 16". Tremie

For Official Use Only Page 38 of 85 nc ng le D eg re e fr

Ve rt ic al be r o f S tr d D ia m

A s-bu ilt

B on d (ft

To ta l D ril l L en gt h

(ft

M ax im um

A ct ua l

Lo ad

(k ip

M ax

B on d St ie ve d

D ur in g

Te st in g ps i)

D es ig n

Lo ad

(k ip

C le an in g M ed al la tio n

Figure 3-10 Map of 2018-2019 Anchor Test Program borings

For Official Use Only Page 39 of 85

Figure 3-11 Map with Close-up of 2018-19 Anchor Test Borings in/near the Concrete

Structure

3.9 2019 Spillway Training Wall Piezometer Installation

Four (4) piezometers were installed in 2019. All four (4) of these piezometers are located outside of the spillway training walls. These are screened PVC standpipe piezometers and are not automated. The approximate location of these piezometers is shown in Figure 3-12. Details are listed in Table 3-10.

For Official Use Only Page 40 of 85

Figure 3-12 Location Map of Training Wall Piezometers (2019)

Table 3-10 Training Wall Standpipe Piezometer Details

Hole # GPS Coordinates (NAD83 Texas State Plane, North Central, feet)

Inclined or Vertical

Surface Elevation

Top of Rock Depth (feet)

Bottom of Hole Depth (feet)

Northing Easting 311 7074594.0 2451434.2 Vertical Not

Surveyed

10.0 16.1

312 7074499.2 2451426.4 Vertical “ 9.5 11.6 315 7074547.8 2451998.6 Vertical “ 10.0 15.4 316 7074467.8 2451996.7 Vertical “ 7.5 9.6

3.10 2015 Borrow Area Investigation

The borrow area selected for this project is located approximately one (1) mile downstream of Lewisville Dam. See for Figure 3-13 the location of the borrow area.

Training-Wall Piezometers (2019)

For Official Use Only Page 41 of 85

Figure 3-13 Borrow Area General Location Map

The location of the borrow area borings are shown on Figure 3-14. Details of the borings are listed in Table 3-11.

Since 2015, there has been periodic episodes of significant active excavation in the borrow area for construction borrow. This borrow has been used at the dam, but not in the vicinity of the spillway. The ground surface shown for the boring logs may no longer be the ground surface at that location. Please see the contract drawings, specifically sheet CG-101, for the most recent topographic survey of the borrow area.

For Official Use Only Page 42 of 85

Figure 3-14 2015 Borrow Area Boring Locations

Table 3-11 2015 Borrow Area Boring Details Hole # GPS Coordinates

(NAD83 Texas State Plane, North Central, feet)

Inclined or Vertical

Rough Surface Elevation (not surveyed)

Bottom of Hole Depth (feet)

Northing Easting 401 7071142.8 2441512.6 Vertical 461 +/- 25.0 402 7071043.0 2442792.1 Vertical 462 +/- 23.0 403 7070388.3 2442167.2 Vertical 461 +/- 25.0 404 7069874.0 2441587.4 Vertical 460 +/- 23.0 405 7069952.1 2442715.9 Vertical 461 +/- 23.0

3.11 2017 Borrow Area Test Pit Investigation

Test pits were dug using an excavator in March of 2017 in the borrow area. For the general location of the borrow area, see the previous figure, Figure 3-13. The test pits were dug to a depth of 9 feet. Both jar samples and bucket samples were taken from the pit. The general

For Official Use Only Page 43 of 85 locations are known; the test pits are located near the 2015 borings with the same numbers (see previous Figure 3-14 for locations of these holes). The exact locations and elevations could not be found; it is unknown if they were surveyed or not. The information summary for these test pits is shown as Table 3-12. The test pit logs for these test pits are found in the Non- Interpretive Appendices.

Table 3-12 2017 Borrow Area Test Pit Details Test Pit

GPS Coordinates (NAD83 Texas State Plane, North Central, feet)

Generalized Location

Inclined or Vertical

Surface Elevation

Bottom of Test Pit Depth (feet)

Northing Easting A-403 unknown unknown Near 2015 boring 403 Vertical unknown 9

A-404 unknown unknown Near 2015 boring 404

Vertical unknown 9

A-405 unknown unknown Near 2015 boring 405

Vertical unknown 9

Since 2017, there has been periodic episodes of significant active excavation in the borrow area for construction borrow. This borrow has been used at the dam, but not in the vicinity of the spillway. The ground surface shown for the boring logs may no longer be the ground surface at that location. Please see the contract drawings, specifically sheet CG-101, for the most recent topographic survey of the borrow area.

3.12 2020 Haul Road Foundation Investigation

In October of 2020, eight (8) borings were drilled along a haul route which will be utilized in the spillway remediation contract. Total depths varied slightly, from 7.5 to 8.5 feet. Drilling consisted of augering, with continuous sampling using SPT, thin-wall-tube methods, as well as bulk sample collection from auger cuttings. The boring information is shown on Table 3-13.

Table 3-13 Haul Route Investigation Boring Details, 2020

GPS Coordinates (NAD83 Texas State Plane, North Central, FIPS 4202, feet)

Inclined or Vertical

Rough Surface Elevation* (not surveyed)

Bottom of Hole Depth (feet) Northing Easting

B-01-20 7074232.554 2450685.129 Vertical 520.0 +/-** 8.5 B-02-20 7074185.07 2451111.067 Vertical 525.4 +/- 7.5 B-03-20 7073665.671 2447682.845 Vertical 531.1 +/- 8.5 B-04-20 7073743.199 2448466.737 Vertical 535.2 +/- 7.5 B-05-20 7073755.985 2449123.967 Vertical 537.3 +/- 8.5 B-06-20 7073765.605 2449724.168 Vertical 545.3 +/- 7.5 B-07-20 7073950.227 2449973.772 Vertical 545.3 +/- 7.5 B-08-20 7074299.616 2450261.059 Vertical 547.6 +/- 7.5

* Elevation determined from LIDAR data using GPS coordinates **Outside LIDAR coverage, best estimate

For Official Use Only Page 44 of 85

After the investigation, laboratory samples were sent off and tested. The results of the laboratory testing are described in Section 4.

The locations of the holes are…