B08_Attach_(2)_Geotech_Report_from_Kleinfelder_19106_005_-_FINAL_Revised.pdf

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GEOTECHNICAL INVESTIGATION REPORT

TASK ORDER NO.: 140P8520F0034

TITLE II – DESIGN DEVELOPMENT SERVICES

DESIGN TO EXTEND PUBLIC LAUNCH RAMPS

DUE TO LOWERING LAKE LEVELS

PMIS 264151 HEMENWAY HARBOR

PMIS 264588 ECHO BAY

PMIS 364593 CALLVILLE BAY

KLEINFELDER PROJECT NO. 20212055.001A

FEBRUARY 9, 2021

REVISED MARCH 9, 2021

Copyright 2021 Kleinfelder All Rights Reserved

ONLY THE CLIENT OR ITS DESIGNATED REPRESENTATIVES MAY USE THIS DOCUMENT AND ONLY FOR THE SPECIFIC

PROJECT FOR WHICH THIS REPORT WAS PREPARED.

http://www.kleinfelder.com/

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A Report Prepared for:

Mr. Ryan Mitchell, PE, PLS (MT) Robert Peccia and Associates PO Box 5100 Kalispell, Montana 59903

GEOTECHNICAL INVESTIGATION REPORT

TASK ORDER NO.: 140P8520F0034

TITLE II – DESIGN DEVELOPMENT SERVICES

DESIGN TO EXTEND PUBLIC LAUNCH RAMPS

DUE TO LOWERING LAKE LEVELS

PMIS 264151 HEMENWAY HARBOR

PMIS 264588 ECHO BAY

PMIS 364593 CALLVILLE BAY

KLEINFELDER PROJECT NO. 20212055.001A

Prepared by:

Kelli Ogborn, PE Geotechnical Engineer

Reviewed by:

Marc Moncilovich, PG Adam Williams, PE Project Manager II Senior Geotechnical Engineer

KLEINFELDER

6280 South Valley View Boulevard, Suite 500 Las Vegas, Nevada Phone: 702 736 2936

February 9, 2021

Kleinfelder Project No. 20212055.001A

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TABLE OF CONTENTS

SECTION PAGE

1 INTRODUCTION

1.1 GENERAL

1.2 PROJECT DESCRIPTION

2 FIELD EXPLORATION

2.1 GENERAL

2.1 FIELD GEOLOGIC RECONNASSAINCE

2.2 SUBSURFACE CONDITIONS

2.2.1 Echo Bay

2.2.2 Callville Bay

2.2.3 Hemenway Harbor

3 LABORATORY TESTING

4 GEOLOGY

4.1 REGIONAL GEOLOGIC SETTING

4.2 REGIONAL SEISMICITY, FAULTING AND SUBSIDENCE

4.3 FIELD GEOLOGIC RECONAISSANCE

4.3.1 Echo Bay

4.3.2 Callville Bay

4.3.3 Hemenway Harbor

5 BOAT LAUNCH RAMP RECOMMENDATIONS

5.1 SITE PREPARATION AND GRADING

5.1.1 Precast Concrete Panels

5.1.2 Engineered Fill (Aggregate Base)

5.1.3 Sub Base for Stabilization

5.1.4 Ramp Terminations (Riprap)

5.2 SOIL CORROSION

5.3 CONSTRUCTION CONSIDERATIONS

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6 CLOSING

6.1 LIMITATIONS

6.2 ADDITIONAL SERVICES

7 REFERENCES

FIGURES

1 Project Vicinity Map 2 Exploration Location Map Callville Bay 3 Exploration Location Map Echo Bay 4 Exploration Location Map Hemenway Harbor

APPENDICIES

A “Geophysical Surveys of Lake Mead National Park Service Boat Launch Ramps:

Hemenway Harbor, Callville Bay, Echo Bay and Temple Bar,” prepared by TEG Oceanographic Services, dated November 16, 2020

B Laboratory Test Results, Plates B-1 through B-3 C Chemical Test Results (9 pages) D Geoprofessional Business Association (GBA) Document

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GEOTECHNICAL INVESTIGATION REPORT

BOAT LAUNCH RAMP EXTENSIONS

CALLVILLE BAY, ECHO BAY, AND HEMENWAY HARBOR

LAKE MEAD NATIONAL RECREATION AREA

CLARK COUNTY, NEVADA

1 INTRODUCTION

1.1 GENERAL

This report presents the results of our geotechnical exploration for ramp extensions at three public boat launch facilities at Lake Mead National Recreation Area. The launch facilities include Callville Bay, Echo Bay, and Hemenway Harbor, located in Clark County, Nevada. The approximate locations of the sites are shown on Figure 1, Project Vicinity Map. The Temple Bar launch ramp located in Mohave County, Arizona, is covered in a separate report.

The purpose of this exploration was to provide information regarding the subsurface soil conditions and general site geology. This report presents geotechnical recommendations for site preparation and grading, including excavation and removal of unsuitable materials and subgrade preparation, and construction considerations. The services included geologic site reconnaissance, subsurface exploration, soil sampling, field and laboratory testing, engineering analyses, and preparation of this report, as presented in our proposal dated March 27, 2020 (Kleinfelder Document No. FRE20P109581).

Based on our explorations, laboratory testing and geotechnical analyses, it is our professional opinion that the proposed boat launch improvements are feasible provided the recommendations in this report are implemented in the design and construction for the project. If during construction, the site conditions or proposed design differs from that described in this report, Kleinfelder should be notified to verify that our geotechnical recommendations remain valid or provide updates to these where needed.

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The recommendations contained in this report are subject to the limitations presented in the

CLOSING section of this report. In addition, a brochure prepared by Geoprofessional Business

Association (GBA) has been included in Appendix D that provides additional information regarding data interpretation and industry-standard limitations of a geotechnical investigation. We recommend that all individuals using this report read the limitations along with the attached brochure.

1.2 PROJECT DESCRIPTION

It is our understanding that the project consists of extending launch ramps at the existing public boat launch facilities at Echo Bay, Callville Bay, and Hemenway Harbor in the Lake Mead National Recreation Area due to lowering lake levels. We understand the extensions will consist of 6-inch thick, tongue and grooved, precast concrete planks supported by compacted layers of aggregate base with 2-foot-wide by 1.5-foot-deep shoulders of compacted aggregate base and rip rap at termination of the ramp. Placement of the launch ramp extensions will be progressive as lake levels drops over time. Extensions planned are:

• Callville Bay: approximately 60 linear feet (LF) of ramp extension at 100 feet in width.

• Echo Bay: approximately 160 LF of ramp extension at 100 feet in width.

• Hemenway Harbor: approximately 1,500 LF of ramp extension at 100 feet in width.

Two options are under consideration; one to extend the existing launch ramp along the existing alignment (5% grade), and a second to move the launch ramp north onto an existing peninsula; however, we understand the latter option is not being considered any longer.

The scope of the exploration and engineering evaluation for this study, as well as the conclusions and recommendations in this report, were based on our understanding of the project described above. If pertinent details of the project have changed or otherwise differ from our descriptions, we must be notified and engaged to review the changes and modify our recommendations, if needed.

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2 FIELD EXPLORATION

2.1 GENERAL

The site was explored by performing limited sub-bottom surveys, diver-supported geo-probe studies, and vibracore soil sampling within the areas of the proposed launch ramp extensions.

SITE DESCRIPTIONS

Callville Bay

The proposed approximately 60 LF boat ramp extension is located within the northwestern Lake

Mead National Recreation Area, and in the northern portion of Boulder Basin of Lake Mead. The many washes that drain into Callville Bay originate from the Gale Hills and Muddy Mountains to the north. There are campground facilities, commercial, and residential buildings, and Callville

Bay Resort located west of the project. The marina (boat docks, rental and fueling facility) accessible from an inactive boat ramp to the northwest. There is one main paved access road

(Callville Bay Road), along with paved parking lots for the marina and current boat launch ramp

(completed in 2010). The land adjacent the boat ramp extensions consisted of loose lake shore sands and gravels. The topography consisted of loose steep hills and deep (approximately 15 to

20 feet) washes. Bedrock outcroppings are located to the south of the extension. Sparse to moderate vegetation covers the site with increasing vegetation in the low lying wash areas. The overall surface drainage direction is to the northeast. Review of aerial and satellite photography indicates the project Site has remained underwater over the last 20 years.

Echo Bay

The proposed approximately 160 LF boat ramp extension is located within the northern Lake

Mead National Recreation Area, on the west side of the Overton Arm of Lake Mead. Echo Bay is located north of the Black Mountains, east of the Muddy Mountains of southern Nevada and west of the South Virgin Mountains of northwest Arizona. The many washes that drain into Echo Bay originate from the Muddy Mountains to the west and Black Mountains to the south. There are campground facilities, commercial, paved airstrip and residential buildings, and Echo Bay Resort located northwest of the project. There is one main paved access road (Echo Bay Road), along with paved parking lots for the inactive marina. A helicopter landing pad, gravel parking lot and current boat launch ramp is accessed along a gravel road east of the Resort.

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The peninsula the boat ramp extensions is located on consisted of loose lake shore sands and gravels. The topography consisted of loose steep hills and deep (approximately 10 to 15 feet) lake shore coves. Bedrock outcroppings are located to the north and east of the extension. Sparse vegetation covers the site with increasing vegetation in the low-lying cove areas. The overall surface drainage direction is southwest to south-southwest and is northwest to north along the peninsula. Review of aerial and satellite photography indicates the project Site has remained underwater over the last 20 years.

Hemenway Harbor

The proposed approximately 1,500 LF of ramp extension is located within the western Lake Mead

National Recreation Area, and in the southern portion of Boulder Basin of Lake Mead. Hemenway

Harbor is located in between River Mountains to the west and the Black Mountains to the east of southern Nevada and northwestern Arizona. The many washes that drain into Boulder Basin including those near Hemenway Harbor originate from the River and Muddy Mountains to the west and east respectively and Promontory Point to the south. There are campground facilities and residential buildings located west of the project. The Las Vegas Boat Harbor (café, boat docks, boat rental and fueling facility) are located to the southeast. There is one main paved road

(Hemenway Rd), that provides access to the project site and facilities in Hemenway Harbor. of them run through north of the project site, the other one running southwest across the site. Rough graded parking is located along the shoreline to the south of the boat ramp extension. The land adjacent the boat ramp extensions consisted of loose lake shore sands and gravels. The topography to the southwest consisted of a loose gently sloping shoreline. To the northwest the topography consisted of loose steep hills and deep lake shore coves (approximately 10 to 15 feet) lake shore coves. Bedrock outcroppings are located to the southeast and west of the extension.

Sparse vegetation covers the site with increasing vegetation in the low-lying areas close to the shoreline. The overall surface drainage direction is to the northeast. Review of aerial and satellite photography indicates the project Site has remained underwater over the last 20 years.

2.1 FIELD GEOLOGIC RECONNASSAINCE

A field geologic reconnaissance was performed in the vicinity of each proposed launch ramp extension area. A Kleinfelder geologist traversed the exposed outcrops present above the current lake water level to characterize the geologic conditions at the site and to obtain limited

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© 2021 Kleinfelder www.kleinfelder.com geomechanical information on the geologic units exposed nearby. The results of our Field Geologic Reconnaissance are summarized in Section 4 below.

2.2 SUBSURFACE CONDITIONS

Bathymetric geophysical soundings along the proposed ramp alignments were used to identify sediment layers at the lake bottom. A detailed report of the field exploration and findings, prepared by TEG Oceanographic Services, is presented in Appendix A.

The subsurface conditions were explored using vibracore sampling and diver-supported jet probing at each boat launch location, as summarized in Table 4-1. Vibracore and jet probing sample locations were determined by Robert Peccia and Associates based on bathymetric surveys.

TABLE 4-1: Method of Exploration and Depth of Penetration

Sample

Designation Method of Exploration

Depth of Penetration into

Lake Bottom (Feet)

Echo Bay

EB-Core-3 Vibracore 1.5

EB-JP-4 Jet Probe 1.0

EB-JP-5 Jet Probe 3.0

Callville Bay

CB-Core-2 Vibracore 2.0

CB-JP-7 Jet Probe 2.0

Hemenway Harbor

HH-Core-1 Vibracore 2.0

HH-JP-1 Jet Probe 2.0

HH-JP-2 Jet Probe 2.5

HH-JP-3 Jet Probe 2.0

Vibracore sampling involved the use of an aluminum core barrel secured to a vibrohead that was lowered to the desired depth of penetration or depth of refusal to obtain a core sample. Physical samples were obtained at this time and transported to our laboratory for additional testing.

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Diver-supported jet probing was also performed. The approximate locations of the vibracore and jet probing samples are shown on Figure 2 through Figure 4, Exploration Location Maps for Echo

Bay, Callville Bay, and Hemenway Harbor.

A detailed report of the field exploration and findings, prepared by TEG Oceanographic Services, is presented in Appendix A.

2.2.1 Echo Bay

One vibracore and two jet-probing explorations were performed within Echo Bay. One to three feet of sediment consisting of loose sand, gravel and silt were encountered. Refusal was met at depths ranging from 1 to 3 feet on a layer of dense gravel. A physical sample of loose sediment was obtained from EB-JP-5. Based on the results of our laboratory testing, the material consists of non-plastic sandy silt.

2.2.2 Callville Bay

Vibracoring and diver-supported jet probing was performed at two locations within Callville Bay.

Soils encountered were one to 2 feet of sediment, then refusal on gravel. Laboratory testing of a sample of sediment indicates this material consists of non-plastic sandy silt.

2.2.3 Hemenway Harbor

One vibracore and three jet-probing explorations were performed within Hemenway Harbor. The core barrel was able to penetrate through approximately 2 feet of soft sediment and encountered refusal on what appeared to be a layer of dense gravel. Similar results were determined during jet probing methods and refusal was met at depths ranging from 2 to 2.5 feet. Physical samples of sediment were obtained from HH-JP-2 and HH-JP-3. Laboratory testing indicates this material consists of non-plastic silt.

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3 LABORATORY TESTING

Soil samples from the borings were tested in the laboratory to provide information regarding engineering characteristics and properties of the subsurface soils. The laboratory testing program consisted of:

• Four (4) gradation analyses tests (ASTM D1140) and three (3) Atterberg limits tests (ASTM

D4318) performed to characterize the subsurface soils.

• Three (3) solubility (SM 2540C), water-soluble sulfate (SM 4500-S04E), water-soluble sodium

(EPA 6010B), and sodium sulfate (calculation) tests performed by Veritas Laboratories.

The results of the laboratory tests are presented on the laboratory test data sheets in Appendix B.

Analytical testing was performed on recovered samples for determination of water-soluble sulfate, and total dissolved solids. The results of chemical analytical testing are presented in Appendix C.

Tabulated below is a summary of the test data:

TABLE 3-1: Summary of Analytical Test Data

Sample

ID

Sample

Depth

(inches)

Soluble

Sodium

(percent)

Soluble

Sulfate

(percent)

Soluble

Sodium

Sulfate

(percent)

Solubility

(Total

Solids)

(percent)

EB-JP-5 25.0 0.0087 0.028 0.027 0.087

CB-JP-7 25.0 0.0077 0.064 0.024 0.075

HH-JP-2 23.5 0.011 0.052 0.033 0.14

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4 GEOLOGY

4.1 REGIONAL GEOLOGIC SETTING

The subject sites are located in the Basin and Range Physiographic Province, a region characterized by north-south trending, faulted mountains and flat valley floors. The proposed launch ramp extension areas are currently submerged and are likely underlain by recent Lake

Mead deposits which were formed within the last 70 years when Lake Mead was filled. These deposits could also contain alluvial material which originated in washes that flow into each launch ramp site and have since been reworked by wave action from Lake Mead. Bedrock outcroppings of various older geologic material are present below the shore and alluvial deposits. The geologic conditions observed from our field reconnaissance are described for each boat ramp location in the following sections.

4.2 REGIONAL SEISMICITY, FAULTING AND SUBSIDENCE

The Lake Mead is an area of relatively low to moderate seismicity and earthquake risk. Historic earthquakes in the area are associated with the filling of Lake Mead beginning in the mid-1930s.

The largest of these were the Hoover Dam Earthquake of May 4, 1939, M 5.0 (Bausch and Brumbaugh, 1997). This seismicity has since decreased in intensity and frequency. No tectonic Quaternary-age (1.8 million years ago to Present) faults are mapped in any of the boat launch ramp areas. A mapped fault is indicated on the Callville Bay Quadrangle Geologic map at the eastern end of the project site. This fault is shown offsetting the Tertiary-age volcanic rocks. The nearest mapped Quaternary fault is the Mead Slope fault mapped approximately 3.5 miles south of the Callville Bay project site. This short, 7-kilometer fault is located along the eastern side of Lake Mead (U.S. Geological Survey website, 2020).

4.3 FIELD GEOLOGIC RECONAISSANCE

Prior to field work, Kleinfelder examined geologic features documented in aerial photographs and published geologic maps. During the field reconnaissance on December 7th and 8th, 2021.

Kleinfelder examined exposed bedrock outcrop features at Echo Bay, Callville Bay, and

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Hemenway Harbor. The geologic exposures at each site (above the current lake water level) were observed and, in consideration of our review of existing geologic maps and previous geotechnical reports, the interpolated geologic units anticipated to be encountered during ramp construction are provided below.

4.3.1 Echo Bay

Echo Bay is located within the northern Lake Mead National Recreation Area, on the west side of the Overton Arm of Lake Mead. Based on the results of our geologic reconnaissance and the results of our field exploration, the proposed Echo Bay boat ramp extension areas are likely covered by a surficial veneer, approximately 1 to 3 feet thick, of lake deposits composed of loose silt, sand, gravel, with cobbles and boulders. These deposits were laid down by Lake Mead by current action as the lake level fluctuated through time. A review of core logs from our previous exploration in 2010 (Kleinfelder, 2010), and observations during our geologic reconnaissance indicates excavations below the surficial veneer is likely to encounter coarse-grained Muddy Creek Formation (Tmc) underlain by Fine-grained Muddy Creek Formation (Tmf).

Coarse-grained Muddy Creek Formation (Tmc) The Tmc generally consists of very weak to weak, light gray to brownish gray, subrounded gravel and cobbles in a sandy matrix with nearly equal proportions in areas of interlayered gravelly sandstone. This unit may contain localized resistant zones with well-developed cementation but is overall more soil-like than rock-like where exposed on the site and as described in our previous borings in 2010 (Kleinfelder, 2010). The bedding in the Tmc is gently south-dipping, discontinuous and roughly parallel. The Tmc ranges from matrix-supported to clast-supported and matrix-free (open), but generally exhibits a sandy matrix. The matrix-free portion of the unit generally appears to be present in the upper portions of the profile and occurs as a clean, partially cemented deposit of rounded gravel to cobble-sized material.

Fine-grained Muddy Creek Formation (Tmf) The fine-grained facies of the Muddy Creek Formation underlies the Tmc and generally consists of pale pinkish or yellowish brown, very weak to weak, thinly-bedded siltstone and fine-grained sandstone with lesser amounts of interbedded conglomerate. This unit is typically weathered to a silty, sandy, and gravelly soil to depths of two to more than 10 feet where exposed at the surface.

The bedding in the Tmf dips shallowly at approximately 10 degrees to the south and east.

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The soils overlying the Tmf, where exposed at the surface, are likely a combination of alluvium deposited prior to filling to Lake Mead, and soils from deposits laid down after Lake Mead was filled, and soils generated from weathered in-place Muddy Creek deposits.

4.3.2 Callville Bay

Callville Bay is located along the extreme northwestern portion of the Black Mountains of southern Nevada and northwestern Arizona. Black and Callville Mesa are to the west of the site. The many washes that drain into Boulder Basin including those near Callville Bay originate from the Gale Hills and Muddy Mountains to the north.

Based on the results of our geologic reconnaissance and the results of our field exploration, the proposed Callville Bay boat ramp extension area is likely covered by a surficial veneer, approximately 0 to 2 feet thick, of lake deposits composed of loose silt, sand, gravel, with cobbles and boulders. These deposits could also be composed of similar alluvial material originating from washes north of the site and have since been reworked by current action from Lake Mead. Our review of published geologic maps (Anderson, 2003), and observations during our geologic reconnaissance indicates excavations below the surficial veneer is likely to encounter Sidestream Alluvium (Ts) underlain by Coarse-grained Muddy Creek Formation (Tmc).

Sidestream Alluvium (Ts) Sidestream Alluvium (Ts) outcrops were observed in the vicinity of the site and generally consisted of weak to medium strong sandstone, siltstone, and conglomerate layers. The conglomerate layers are generally matrix-supported and included fine- and coarse-grained gravels with cobbles and boulders. The conglomerate, siltstone, and sandstone layers were observed to be weakly to strongly cemented with calcium carbonate (caliche).

Coarse-grained Muddy Creek Formation (Tmc) Exposed outcrops of Tmc were difficult distinguish between the Ts. Our review of published geologic literature indicates these two units are frequently interbedded. The Tmc generally consists of weak to moderately strong, light gray to brownish gray, subrounded gravel and cobbles in a sandy matrix with nearly equal proportions in areas of interlayered gravelly sandstone. This unit may contain localized resistant zones with well-developed cementation (caliche).

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During our geologic field reconnaissance, we observed Tertiary Volcanic Rocks (Tsv) generally exposed as a “cap” on top of the Ts and Tmc bedrock outcrops nearby to the launch ramp extension area. Based on observations made during vibracore and diver operations, and the typical geologic occurrence of this unit, it is unlikely that these volcanic rocks will be encountered during construction.

4.3.3 Hemenway Harbor

Hemenway Harbor is located in between River Mountains to the west and the Black Mountains to the east of southern Nevada and northwestern Arizona. The many washes that drain into Boulder Basin, including those near Hemenway Harbor, originate from the River Mountains and Muddy Mountains to the west and east respectively and Promontory Point to the south.

Based on the results of our geologic reconnaissance and the results of our field exploration, the proposed Hemenway Harbor boat ramp extension area is likely covered by a surficial veneer, approximately 0 to 2.5 feet thick, of lake deposits composed of loose silt, sand, gravel, with cobbles and boulders. These deposits could also be composed of similar alluvial material originating from the wash west of the site and have since been reworked by current and wave action from Lake Mead. Our review of the Geologic Map of the Boulder Beach Quadrangle, Nevada (Smith, 1984), and observations during our geologic reconnaissance indicates excavations below the surficial veneer is likely to encounter Quaternary Alluvium (Qa) and/or Pediment and Fan Deposits of the Eldorado Mountains (Qe).

Quaternary Alluvium (Qa) During our geologic field reconnaissance, we observed Qa outcroppings approximately 130 feet north of the boat ramp. The exposed Qa near the launch ramp site is generally composed of light reddish brown fine grained, very weak to weak, cemented, silty and clayey sand, with fine to coarse gravels, cobbles, and boulders. This unit may contain localized resistant zones with poorly developed weak cementation layers and is overall more soil-like.

Pediment and Fan Deposits of the Eldorado Mountains (Qe) We observed Qe outcrops nearby the launch ramp area. The Qe is generally vary similar in lithologic composition to the Qa deposits. However, Qe pediments typically contain a higher degree of calcium carbonate cementation (caliche).

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The Qe observed during our field reconnaissance was composed of weak to strong, cemented, fine to coarse-grained sand with lesser but variable amounts of silt and clay, fine to coarse-grained gravel, and cobbles and boulders.

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5 BOAT LAUNCH RAMP RECOMMENDATIONS

5.1 SITE PREPARATION AND GRADING

We understand that in-water cutting, and filling methods will be used to construct the boat launch ramp extensions. For below-water grading, it will not be feasible to observe the subgrade conditions directly. Therefore, the geotechnical engineer or their representative will need to observe the ease/difficulty of excavation, methods of fill placement and compaction, and composition of spoils.

Based on the subsurface conditions, we anticipate loose to very loose lake sediments up to 4 feet exist over the more dense pre-lake sediments. The loose lake sediment should be removed prior to placing the aggregate base. The subgrade preparation and fill placement should be observed by the geotechnical engineer of record or their representative. Where the boat launch ramp embankments are placed on slopes inclined at a ratio steeper than 5H:1V, the base fill materials should be placed in approximate 8-foot-wide nearly level benches.

Our geotechnical scope did not include soil borings or slope stability analysis of the proposed cut and fill slopes. Therefore, the geotechnical engineer or their representative should observe the construction of the cut and fill slopes to verify the assumptions considered in our preliminary review remain valid. Geotechnical conditions that vary from the assumed conditions may require further analysis.

We understand Echo Bay and Callville Bay will require cut slopes oriented at an inclination of 2Horizontal to 1Vertical (2H:1V) or less that range up to 18 feet. From preliminary review assuming the 2H:1V cut slopes are constructed within dense, granular alluvial sediments or bedrock, the proposed cuts are feasible and should satisfy global static and pseudo-static slope stability factors of safety of 1.3 and 1.0, respectively. Our analyses assume the natural soil has a minimum internal friction angle of 30 degrees, a cohesion of 50 pounds per square foot, and a unit weight of 120 pounds per cubic foot. Similarly, fill slopes constructed from engineered fill as recommended below and oriented at a ratio of 3H:1V or less up to 8 feet are feasible.

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Provided these are constructed on the dense, granular alluvial sediments or bedrock, such fill slopes should satisfy global static and pseudo-static slope stability factors of safety of 1.3 and 1.0, respectively. For pseudo-static analysis, we consider a design event corresponding to 7 percent exceedance in 75 years (975-year return period) as appropriate for the boat launch ramp facility. The horizontal coefficient (kh) applied in our preliminary slope stability analysis was 0.10.

Our analyses considered gradual drawdown of the lake level from the existing elevation of about +1,082 down to an elevation of about +1,072 feet.

Where slopes are adjacent to the launch ramps, the National Park Service should anticipate surficial erosion or raveling of exposed soil surfaces. Continued maintenance may be required, due to the accumulation of sediment eroded from the adjacent cut slopes.

We understand only minor grading is necessary for the proposed Hemenway Harbor launch ramp extension (i.e., cut and fill areas generally less than 5 feet high)

5.1.1 Precast Concrete Panels

Based on communications with the Robert Peccia and Associates, the extension of the existing ramps in areas that are presently underwater will be constructed using engineered fill, leveling pipes, and precast concrete panels with locking connections. We understand the panels are lowered into place using a crane.

5.1.2 Engineered Fill (Aggregate Base)

We recommend the precast concrete panels be supported using a minimum of 6 inches of aggregate base. The aggregate base should meet the gradation and other requirements summarized in Tables 5-1 and 5-2.

Table 5-1. Aggregate Base Gradation Standard Sieve Size Percent Passing y Weight

1-½ inch 100

1 inch 80-100

No. 4 30-65

No. 16 15-40

No. 200 ≤ 8

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Table 5-2. Aggregate Base Quality Control

Test Nev. Test Method

(AASHTO Test Method)

Requirement

Particle Size Gradation Nev. T206

(AASHTO T27)

See Table 5-1

Sampling Aggregate Nev. T200

(AASHTO T2)

N/A

Fractured Faces Nev. T230

(ASTM D5821)

35% Minimum

Plasticity Index Nev. T212

(AASHTO T90)

6 Maximum

Liquid Limit Nev. T210

(AASHTO T89)

35 Maximum

Resistance Value or

Resilient Modulus

Nev. T115

(AASHTO T307)

70 Minimum

(35,000 psi minimum)

Percentage of Wear N/A

(AASHTO T96)

45% Maximum

We recommend the use of a geotextile (e.g., Mirafi 140N or equivalent) for soil separation between the aggregate base and underlying or adjacent materials [i.e., lake sediment, and/or ramp termination (rip rap) material.]

The aggregate base should be placed in maximum 8-inch lifts starting above the water line (i.e., from the shoreline) and moving down grade. The aggregate base should be compacted by tamping the material with an excavator bucket until it has achieved a firm and unyielding condition.

5.1.3 Sub Base for Stabilization

Where required for stabilization of soft subgrade conditions, clean, angular crushed rock (ballast) with a maximum particle size of 4 inches, a nominal particle size of 2 to 4 inches, and less than 5 percent passing the No. 4 Sieve (4.75 millimeters) may be placed and compacted into the subgrade until a firm and unyielding condition is achieved. A geotextile should be placed to separate the sub base from the overlying aggregate base and adjacent materials. The sub base should be placed in maximum 8-inch lifts starting at the water line and moving down grade.

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© 2021 Kleinfelder www.kleinfelder.com

The sub base should be compacted by tamping the material with an excavator bucket until it has achieved a firm and unyielding condition.

5.1.4 Ramp Terminations (Riprap)

To protect the launch ramps from undermining or erosion and to help support the precast concrete panels at the termination of the ramps, a minimum 2-foot-wide by 2-foot-deep shoulder of riprap should be constructed. We recommend Class 550/700 riprap as summarized in Table 5-3 and 5- 4 below be used to construct the ramp termination. Riprap should be placed individually and not be end dumped. Rock with appreciable amounts or layers of clay, such as shale, mudstone, siltstone, claystone, etc., are not acceptable for use as riprap.

Table 5-3. Class 550/700 Riprap Gradation Sieve Size Percent Passing by

Weight

250 mm (10 in.) 100

225 mm (9 in.) 70-85

150 mm (6 in.) 35-0

50 mm (2 in.) 5-15

25 mm (1 in.) 0-5

Table 5-4. Riprap Quality Control

Test Nev. Test Method

(Other Test Method)

Requirement

Percentage of Wear N/A

(AASHTO T96)

45% Maximum

Specific Gravity Nev. T104

(ASTM D6473)

2.5 Min

5.2 SOIL CORROSION

Based on the corrosion testing performed on near surface soils obtained from the site, the soils are classified as providing Sulfate Exposure Class S0 as defined in Table 19.3.1.1 of the 2019

American Concrete Institute (ACI) Manual 318; however, based on our experience locally, we recommend that all concrete in contact with the on-site soils be formulated with an appropriate

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© 2021 Kleinfelder www.kleinfelder.com cement type, water-cement ratio, and an appropriate minimum compressive strength to resist

Sulfate Expose Class S2, as outlined in Table 19.3.1.1 of the 2019

American Concrete Institute (ACI) Manual 318. Underwater concrete may require additional formulation and should be confirmed by the precast concrete designer.

5.3 CONSTRUCTION CONSIDERATIONS

We anticipate that excavation of the near surface on-site materials can generally be performed using conventional, heavy-duty excavation equipment; however, the contractor should review the site conditions presented in this report and determine the earthwork equipment required for this project.

All excavations should be planned and executed in accordance with current OSHA recommendations (Federal Register 29 CFR Part 1926) and applicable local governing agency standards and procedures. Safety of construction personnel is the sole responsibility of the

Contractor.

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© 2021 Kleinfelder www.kleinfelder.com

6 CLOSING

6.1 LIMITATIONS

This work was performed in a manner consistent with that level of care and skill ordinarily exercised by other members of Kleinfelder’s profession practicing in the same locality, under similar conditions, and at the date the services are provided. The subsurface data presented in this report was obtained sub-bottom profiling, vibracoring, and diver-supported jet probing during the field exploration. Our conclusions, opinions, and recommendations are based on a limited number of observations and data. It is likely that conditions vary between or beyond the data evaluated. If conditions are encountered at this site which is different from those described in this report, our firm should be notified so that we may make any necessary revisions to this report.

Kleinfelder makes no other representation, guarantee, or warranty, express or implied, regarding the services, communication (oral or written), report, opinion, or instrument of service provided.

The work performed was based on project information provided by Robert Peccia and Associates.

If the Owner does not retain Kleinfelder to review any plans and specifications, including any revisions or modifications to the plans and specifications, Kleinfelder assumes no responsibility for the suitability of our recommendations. In addition, if there are any changes in the field to the plans and specifications, the Owner must obtain written approval from Kleinfelder’s engineer that such changes do not affect our recommendations. Failure to do so will vitiate Kleinfelder’s recommendations.

This report may be used only by the Client and the registered design professional in responsible charge and only for the purposes stated for this specific engagement within a reasonable time from its issuance, but in no event later than one year from the date of the report.

Recommendations contained in this report are based on our field observations and subsurface explorations, limited laboratory tests, and our present knowledge of the proposed construction.

If soil, rock, or groundwater conditions are encountered during construction that differ from those described herein, the Owner is responsible for ensuring that Kleinfelder is notified immediately so that we may reevaluate the recommendations of this report. If the scope of the proposed construction, including the design depths or locations of the improvements changes from that described in this report, the conclusions and recommendations contained in this report are not

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© 2021 Kleinfelder www.kleinfelder.com considered valid unless the changes are reviewed, and the conclusions of this report are modified or approved in writing, by Kleinfelder.

This report, and any future addenda or reports regarding this site, may be made available to bidders to supply them with only the data contained in the report regarding subsurface conditions and laboratory test results at the point and time noted. Bidders may not rely on interpretations, opinions, recommendations, or conclusions contained in the report. Because of the limited nature of any subsurface study, the contractor may encounter conditions during construction which differ from those presented in this report. In such event, the contractor should promptly notify the owner so that Kleinfelder’s geotechnical engineer can be contacted to confirm those conditions.

We recommend the contractor describe the nature and extent of the differing conditions in writing and that the construction contract include provisions for dealing with differing conditions.

Contingency funds should be reserved for potential problems during earthwork and construction.

6.2 ADDITIONAL SERVICES

The recommendations provided in this report are based on the assumption that an adequate program of tests and observations will be performed prior to and during construction to verify compliance with these recommendations. These tests and observations should include, but not necessarily be limited to, the following:

• Review project plans and specifications.

• Observation during construction of cut slopes, excavations and subgrade preparation.

• Observation and testing of structural fill and foundation subgrade.

• Consultation as may be required during construction.

Additional information concerning the scope and cost of these services can be obtained from our office. We appreciate the opportunity to be of service on this project. Should you have any questions regarding this report or wish to discuss additional services, please do not hesitate to contact us.

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7 REFERENCES

Anderson, (2003). Geologic Map of the Callville Bay Quadrangle, Clark County, Nevada and Mohave County, Arizona. Nevada Bureau of Mines and Geology.

Anderson, R. E. (1973). Large-magnitude late Tertiary strike-slip faulting north of Lake Mead, Nevada, Professional Paper. doi:10.3133/pp794

ACI 318 (2019). “Building Code Requirements for Structural Concrete,” American Concrete

Institute (ACI 318-19).

ASTM, Annual Book of Standards, Volume D.

Beard, (2007). Preliminary Geologic Map of the Lake Mead 30’ and 60’ Quadrangle, Clark County, Nevada and Mohave County, Arizona. USGS.

Bausch, D.B.; Brumbaugh, D.S. Earthquake Hazard Evaluation, Mohave County, Arizona, July

30, 1997, Arizona Earthquake Information Center, Northern Arizona University

Kleinfelder Inc. (2009). Geotechnical Exploration Report, Proposed Rock and Slope Stability

Evaluation, Boat Launch Ramp and Roadway, Callville Bay, Lake Mead National

Recreation Area, Clark County, Nevada, December 30, 2009, Kleinfelder, Inc. Project

Number 94065

Kleinfelder Inc. (2010). Geotechnical and Geologic Assessment Report, New Boat Launch Ramp and Access Road, Echo Bay, Lake Mead Recreation Area, Clark County, Nevada, May

25, 2010, Kleinfelder, Inc., Project Number 109996.

Oregon State Marine Board. (2011). Design Guidelines for Recreational Boating Facilities, Third

Edition.

Smith, E.I. (1984). Geologic Map of the Boulder Beach Quadrangle, Nevada. Department of

Geosciences, University of Nevada Las Vegas.

U.S. Geological Survey. (2020). Interactive Quaternary Fault Database, accessed June 4, 2020, from USGS web site: https://www.usgs.gov/natural-hazards/earthquake-hazards/faults.

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Vigil, J.F., Pike, R.J., and Howell, D.G., (2000). A Tapestry of Time and Terrain, U.S. Geological Survey Geologic Investigations Series 2720, http://pubs.usgs.gov/imap/i2720/ http://www.kleinfelder.com/ http://pubs.usgs.gov/imap/i2720/

Fig u re s

202122055.001A/LAS21R121907_R1 February 9, 2021

© 2021 Kleinfelder www.kleinfelder.com

FIGURES

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ECHO BAY LAUNCH RAMP

CALLVILLE BAY LAUNCH RAMP

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EXPLORATION LOCATION MAP

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EXPLORATION LOCATION MAP

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A p p e n d ix

APPENDIX A

“GEOPHYSICAL SURVEYS OF LAKE MEAD NATIONAL PARK SERVICE BOAT LAUNCH

RAMPS: HEMENWAY HARBOR, CALLVILLE BAY, ECHO BAY AND TEMPLE BAR,”

PREPARED BY TEG OCEANOGRAPHIC SERVICES, DATED NOVEMBER 16, 2020

GEOPHYSICAL SURVEYS

OF LAKE MEAD

NATIONAL PARK SERVICE

BOAT LAUNCH RAMPS:

HEMENWAY HARBOR,

CALLVILE BAY, ECHO

BAY AND TEMPLE BAR

DRAFT REPORT

For:

KLEINFELDER, INC.

6280 South Valley View Blvd Suite 500 Las Vegas, NV 89118

By:

TEG Oceanographic Services 217 Florence Drive Aptos, CA 95003 831.684.2749

November 16, 2020

TABLE OF CONTENTS

List of Figures ...............................................................................................................ii

List of Tables ..…...........................................................................................................iii

PROJECT BACKGROUND

TIMING

SITE LOCATON

EQUIPMENT

Vessel

Navigation

Edgetech 3100 Sub-Bottom Profiling System

Diver Operated Jet-Probing System

Vibracoring

Water Level Variations

Planned Tracklines

RESULTS …

Sub-bottom Surveys …

Coring/Jetting Activities

CONCLUSIONS…

REFERENCE

APPENDIX A: Sub-bottom Waterfall Displays i

LIST OF FIGURES

Figure 1 Lake Mead Project Area Showing Boat Ramp Locations

Figure 2 Survey Boat Relentless

Figure 3 Vibrocore, Barrel and Core Catcher

Figure 4 Callville Bay Planned Survey

Figure 5 Echo Bay Planned Survey

Figure 6 Hemenway Harbor Planned Survey

Figure 7 Temple Bar Planned Survey

Figure 8 Temple Bar Sub-bottom Tracklines and Jet Probe Locations

Figure 9 Echo Bay Sub-bottom Tracklines and Core and Jet Probe Locations

Figure 10 Callville Bay Sub-bottom Tracklines and Core and Jet Probe Locations. .8

Figure 11 Hemenway Harbor Core and Jet Probe Locations ii

LIST OF TABLES

Table 1. Lake Mead Water Levels

Table 2. Sub-bottom File Information

Table 3. Core and Jet Probe Survey Data iii

PROJECT BACKGROUND

TEG Ocean Services, Inc. (TEG) was contracted by the Las Vegas, Nevada office of Kleinfelder, Inc.

to provide water-borne geophysical services at four public launch ramps located in the National Park Service's Lake Mead National Recreational Area (NRA). The launch ramps area are located at Callville Bay, Echo Bay, Hemenway Harbor and Temple Bar. The services included sub-bottom surveys, diver supported geo-probe studies, and vibrocoring. Information gathered by these techniques will inform the design of launch ramp extensions required to accommodate the anticipated lowering of lake water levels in the NRA.

TIMING

The project was conducted over 5 days from November 2nd through November 6th, 2020. TEG routinely arrived at the appropriate site at approximately 0800 hrs and worked til darkness which occurred around 1630 hrs. The first day was reserved for equipment testing at Callville Bay. Day 2 continued at Callville Bay. Subsequent days were allotted each to Echo Bay, Hemenway Harbor and lastly, Temple Bar.

SITE LOCATION

The Lake Mead National Recreational Area is located approximately 22 miles east of downtown Las Vegas, Nevada. It can be reached from the north via State Highway 147, from the west by State Highway 564 and from the south via U.S. Highway 93. Figure 1 presents the study area and identities the boat ramp locations.

EQUIPMENT

Vessel

TEG’s 24-foot survey boat, Relentless, conducted the survey. The Relentless is a fiberglass Grady white Offshore with a “walk around cabin” design with approximately 39 sq. ft. (6.5’ x 6’) of back deck (Figure 2).

Figure 1: Lake Mead Project Area Showing Boat Ramp Locations

For this project it was outfitted with a 500 lb-capable davit and capstan winch for vibrocoring and towfish support and a dive ladder for diving operations.