B08_Attach 1 Specs LAKE 158678_FINAL CD_Div 1.pdf

LAKE - 158678 TOC-1

TABLE OF CONTENTS

DIVISION 01 – GENERAL REQUIREMENTS

01 11 00 Summary of Work

Structural Flood Mitigation at Cottonwood Cove: Geotechnical Investigation & Engineering Report (235 pages); Government Furnished Permits (Nevada Division of Environmental Protection 401 Certification (1 page); U.S. Army Corps of Engineers Individual 404 Permit (36 pages); Cottonwood Cove Developed Area Flood Response Plan (73 pages)

01 26 01 Contract Modification Procedures 01 27 00 Definition of Contract Line Items 01 31 00 Project Management & Coordination 01 32 16 Construction Schedule 01 33 23 Submittal Procedures 01 35 05 Environmental Protection and Special Controls 01 35 13.22 Archeological Protection 01 35 23 Safety Requirements 01 40 00 Quality Requirements 01 42 00 Reference Standards 01 50 00 Temporary Facilities and Controls 01 57 19.12 Noise & Acoustics Management 01 57 23 Temporary Storm Water Pollution Prevention 01 73 40 Execution 01 74 19 Construction Waste Management and Disposal 01 77 00 Closeout Procedures

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091015 SUMMARY OF WORK

SECTION 01 11 00 - SUMMARY OF WORK

PART 1 - GENERAL

1.1 SUMMARY

A. This Section includes the following:

1. Work covered by the Contract Documents.

2. Work phases.

3. Work under other contacts.

4. Contractor use of site.

5. Public use of site.

6. Conduct of operations.

7. Work Restrictions.

8. Special Construction Requirements.

9. Soils Investigation Report.

10. Government Furnished Permits

11. Flood Response Plan

1.2 DEFINITIONS

A. Contracting Officer: Includes the Government Contracting Officer (CO).

1.3 WORK COVERED BY CONTRACT DOCUMENTS

A. Project Location: The Cottonwood Cove structural flood mitigation project is located within Lake Mead National Recreation Area (LAKE) approximately 13 miles east of Searchlight, Nevada. The project site is northwest of Cottonwood Cove Road and the developed area (trailer park village, National Park Service maintenance facility, and marina).

LAKE - 158678 01 11 00 - 2

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B. The Work consists of the following:

1. Construction of an earthen berm and channel diversion system designed to control up to the 500 year flood event occurring upstream within the highly braided ephemeral stream known as Ranger Wash and other unnamed ephemeral tributaries. Portions of the berms and channels will be lined with soil cement for protection from erosion and scour.

2. Restoration for construction and staging areas of disturbance.

C. Project will be constructed under a single prime contract.

1.4 WORK PHASES

A. The work shall be conducted in a single phase, consisting of the following general activities:

1. Mobilize to site, set-up Contracting Officers office space, and establish site access.

2. Set up pumping station for non-potable construction water use.

3. Perform earthwork.

4. Place soil cement.

5. Site restoration and demobilization.

1.5 WORK UNDER OTHER CONTRACTS

A. The Federal Highway Administration Central Federal Lands Highway Division (FHWA- CFLHD), in coordination with LAKE, plans to realign and rehabilitate approximately 6.8 miles of the paved access road to Cottonwood Cove. The timing of this project is unknown.

1.6 CONTRACTOR USE OF SITE

A. General: Contractor shall have limited use of the site for construction operations during the construction period. Limit use of premises to areas within the Contract limits indicated on the Contract Drawings. Do not disturb portions of Project site beyond areas in which the Work is indicated. Closure of Cottonwood Cove Road shall not be permitted.

1. Limits: Confine construction operations to the Contract limits associated with the construction of the earthen berm and channel diversion system.

2. Limit site disturbance to the maximum extent practicable.

B. Storage of Materials: Confine storage of materials to the construction staging area adjacent to the LAKE Maintenance Facility at the end of Rattler Road or other areas within construction limits of disturbance approved by Contracting Officer.

C. Preservation of Natural Features:

1. The Contractor shall prevent damage to natural surroundings. The Contractor shall restore damaged areas, repairing or replacing damaged trees and plants, at no additional expense to the Government. This refers to any area outside the limits of disturbance. If any damage to Park resources outside the limits of disturbance occurs, the Contracting Officer should be notified immediately. Restoration will be done at no additional expense to the Government, but it will be the Government's choice whether the contractor does the restoration or pays the Government to do the restoration.

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2. Do not remove, injure, or destroy trees or other plants without prior approval. Consult with Contracting Officer and remove agreed-on roots and branches that interfere with construction.

3. Do not fasten ropes, cables, or guys to existing trees.

4. Carefully supervise excavating, grading, filling, and other construction operations near trees to prevent damage.

D. Driveways and Entrances: Keep driveways, Rattler Road, Cottonwood Cove Road, and entrances serving premises clear and available to Government, Government's employees, emergency vehicles, and general public at all times. Do not use these areas for parking or storage of materials.

1. Schedule deliveries to minimize use of driveways and entrances.

2. Schedule deliveries to minimize space and time requirements for storage of materials and equipment on-site.

E. Construction Camp: Establishment of a camp within the park will not be permitted.

F. Hauling Restrictions: Comply with all legal load restrictions in the hauling of materials. Load restrictions on park roads are identical to the state load restrictions with such additional regulations as may be imposed by the Park Superintendent. Information regarding rules and regulations for vehicular traffic on park roads may be obtained from the Office of the Park Superintendent. A special permit will not relieve Contractor of liability for damage which may result from moving of equipment. As per Paragraph 1.6-A, closure of Cottonwood Cove Road shall not be permitted. Written permission from the Park Superintendent is required for any roadway closures.

1.7 PUBLIC USE OF SITE

A. The impacted portions of the project site will be restricted by the Contractor to the public during construction. Contractor at all times shall conduct operations to ensure the least inconvenience to the public.

1.8 CONDUCT OF OPERATIONS

A. At all times the Contractor shall conduct his operations in conformance with the rules and regulations promulgated by the Secretary of the Interior for the National Park Service, and applicable park rules and regulations prescribed by the Park Superintendent.

B. No signs or advertisements (except those specified herein) shall be displayed on the construction site or within the park unless approved by the Contracting Officer.

1.9 WORK RESTRICTIONS

A. On-Site Work Hours: Work shall be generally performed during normal business working hours of 7:00 a.m. to 6:00 p.m., Monday through Friday, unless alternate hours are approved by the Contracting Officer. Requests for changes shall be submitted to the Contracting Officer.

Park quiet hours are from 10:00 p.m. to 6:00 a.m.

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B. Work on Saturdays, Sundays, Federal holidays or at night may not be performed without prior consent from the Contracting Officer. Submit requests two (2) business days in advance of the work to the Contracting Officer for approval.

C. The risk of flash flooding from storm events at the site is higher during the monsoon season or warm season months generally July through September. While precipitation still occurs outside the monsoon season during cooler months, the storms that occur between October and June are generally not of the duration or intensity to produce significant flooding.

D. Existing Utilities

1. Existing Utilities: Notify Contracting Officer and utility companies of proposed locations and times for excavation.

2. Contractor shall be responsible for locating and preventing damage to known utilities. If damage occurs, repair utility at no additional expense to the Government.

3. If damage occurs to an unknown utility, repair utility. An equitable adjustment will be made in accordance with the Changes clause of the contract.

E. Existing Utility Interruptions: Do not interrupt utilities serving facilities occupied by Government or others unless permitted under the following conditions and then only after arranging to provide temporary utility services according to requirements indicated:

1. Notify Contracting Officer not less than two (2) days in advance of proposed utility interruptions.

2. Do not proceed with utility interruptions without Contracting Officer’s written permission.

3. Hours for Utility Shutdowns: Utility outages are not anticipated for this project. If required, the Contracting Officer will determine timing and length of outages.

1.10 SPECIAL CONSTRUCTION REQUIREMENTS

A. Project Website: A project website administered by the NPS or by means as directed by the Contracting Officer will be used for purposes of managing communication and documents during the construction stage.

1. See Section 01 31 00 - Project Management and Coordination for requirements on using the Project Website.

B. All construction motor vehicles and equipment will have mufflers conforming to original manufacturer specifications that are in good working order to prevent excessive or unusual noise, fumes, or smoke.

C. Should construction unearth cultural resources, work will be stopped in the area of any discovery and the NPS Cultural Resources Branch Chief, Staffan Petersen, Ph.D. (702-293-8859), or other designated representative will be notified immediately. In the unlikely event that human remains are discovered during construction, work will stop and the NPS Cultural Resource Branch Chief will be notified immediately. All personnel who work on the project will be informed of the penalties for illegally collecting artifacts or intentionally damaging archeological sites or historic properties. Construction personnel will also be instructed on procedures to follow in case previously unknown archeological resources are uncovered during construction.

D. Contractor shall provide an onsite Authorized Desert Tortoise Biologist (Authorized Biologist) during construction activities to ensure that construction activities will not harm desert

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tortoises. The Authorized Biologist shall also ensure construction activities will not harm gila monsters, burrowing owls, and other migratory birds.

1. See Section 01 35 05 - Environmental Protection and Special Controls for additional requirements related to the Authorized Biologist.

1.11 SOILS INVESTIGATION REPORT

A. A soils investigation report entitled Structural Flood Mitigation at Cottonwood Cove:

Geotechnical Investigation & Engineering Report (April 2, 2020) has been prepared by HDR Engineering, Inc.

B. A copy of the report is provided as an attachment to this specification.

C. If conflicts occur between the report and drawings or specifications, the drawings and specifications govern.

1.12 GOVERNMENT FURNISHED PERMITS

A. NPS has obtained the following State and Federal permits required for the construction of this project:

1. Clean Water Act 401 Water Quality Certification: Permit Number NV401-19-038

2. Clean Water Act Section 404 (Department of the Army Permit): Permit Number SPK-

2019-00870

B. Copies of each government furnished permit are provided as attachments to this specification.

1.13 FLOOD RESPONSE PLAN

A. A Flood Response Plan (FRP) for the Cottonwood Cove Developed Area at Lake Mead National Recreation Area was developed by NPS in 2018 to provide emergency operations for flood related hazards. The FRP supports emergency management planning and incident response in order to reduce risk to the public, property, and environmental/cultural resources.

B. A copy of the FRP is attached to this specification.

PART 2 - PRODUCTS (Not Used)

PART 3 - EXECUTION (Not Used)

END OF SECTION 01 11 00

National Park Service | Structural Flood Mitigation at Cottonwood Cove Geotechnical Report hdrinc.com 1670 Broadway, Suite 3400, Denver, CO 80202-4824

(303) 764-1520 i

Table of Contents 1 Introduction

1.1 Project Description

1.2 Background

1.3 Purpose and Objectives

2 Geologic Setting

2.1 Regional Geology

2.1.1 Site Geology

2.1.2 Topography

2.1.3 Climate

3 Site Investigation Program

3.1 Overview

3.2 Site Access

3.3 Geotechnical Drilling

3.4 Test Pits

3.5 Geophysical Survey

3.6 Soil Cement Samples

3.7 Laboratory Testing

4 Site Investigation Results

4.1 Geotechnical Drilling Results

4.2 Test Pit Results

4.3 Geophysical Survey Results

4.4 Laboratory Testing Results

5 Geotechnical Considerations for Design

5.1 Excavations

5.2 Channel

5.2.1 Channel Excavation

5.2.2 Channel Rippability

5.3 Embankment

5.3.1 Embankment Excavation

5.3.2 Embankment Foundation Rippability

5.4 Embankment Design

ii

5.4.1 Embankment Materials

5.4.2 Filter/Drain Material

5.4.3 Material Handling

5.4.4 Corrosivity

5.5 Embankment Settlement

5.6 Surface Drainage

6 Seismic Hazards 7 Seepage and Slope Stability Analysis

7.1 Model Development

7.2 Seepage Analysis

7.2.1 Hydraulic Parameters

7.2.2 Boundary Conditions

7.2.3 Analysis Results

7.3 Slope Stability Analysis

7.3.1 Stability Analyses Results

8 Soil-Cement 9 Field Observations 10 Limitations 11 References

Tables

Table 2.1. Average Climate Data for Searchlight, NV (WRCC, 2018)

Table 3.1. Summary of Geotechnical Borings and Test Pits

Table 3.2. Laboratory Testing Summary

Table 4.1. Borings Moved Due to Refusal

Table 4.2. Boring Samples Laboratory Test Results Summary

Table 4.3. Test Pit Laboratory Test Summary

Table 7.1. Hydraulic Parameters used in the Seepage Analyses

Table 7.2. Material Properties used in Stability Analyses

Table 7.3. Slope Stability Results

Figures

1.1 – Cottonwood Cove Vicinity iv ft/s Feet per Second

H Horizontal in Inches

LAKE Lake Mead National Recreation Area

LiDAR Light Detection and Ranging

LL Liquid Limit m/s Meters per Second

NPS National Park Service

NV Non-Viscous

NP Non-Plastic pcf Pounds Per Cubic Foot psf Pounds Per Square Foot

Psi Pounds per Square Inch

PGA Peak Ground Acceleration

PI Plasticity Index

QSI Quantum Spatial Inc.

ReMi Refraction Microtremor

SD Schematic Design

SPT Standard Penetration Test

sq. mi.

Sta.

Square Miles

Station

USACE United States Army Corps of Engineers

USGS United States Geological Survey

V Vertical

Vs Shear Wave Velocity

WMK Wallace Morris Kline Surveying

1 Introduction

1.1 Project Description

In February 2018, the National Park Service (NPS) contracted HDR to perform Schematic

Design (SD) services for structural flash flood mitigation for the Cottonwood Cove developed area located in Lake Mead National Recreation Area (LAKE) shown on Figure 1.1.

Figure 1.1. Cottonwood Cove Vicinity (Google Earth, 2020)

A preferred alternative was selected by NPS from four potential alternatives presented at a

Value Analysis Workshop in August 2018 in Boulder City, NV. The preferred alternative is a diversion system of interconnected berms and channels. The diversion system is designed to block the floodwater in the braided channels of Ranger Wash and then divert those flows into an undeveloped tributary north of the developed area, which discharges into Lake Mohave north of

Cottonwood Cove. These components were sized and designed to convey and withstand a 500-year flood event.

Details of the SD development are presented in the Structural Flood Mitigation at Cottonwood

Cove, Basis of Design Report (BODR), dated December 7, 2018 (HDR, 2018). The design has progressed through the Design Development (DD) phase and was finalized during the

Construction Documents (CD) phase.

1.2 Background

The Cottonwood Cove developed area is located on the western bank of Lake Mohave and is one of three access points to the lake. It is approximately 36 miles south of the Hoover Dam and

13 miles east of Searchlight, NV. It was constructed at the downstream end of a highly braided ephemeral stream that is subject to flash flooding from convective thunderstorm events. Flood flows carry water and sediment from Black Mountain, which is 3.5 miles east through a drainage area of 4.7 square miles (sq. mi.) to discharge into Lake Mohave through the developed area of

Cottonwood Cove. Over the last five years, visitation at Cottonwood Cove has averaged

260,000 visitors per year, making it one of the most highly visited locations within LAKE. The busiest months for visitation are mid-May through September, which also coincides with flash flood season creating an elevated risk to park visitors.

1.3 Purpose and Objectives

To further advance the understanding of the subsurface conditions at the proposed project site, a geotechnical site investigation including borings, test pits, geophysical surveys, and laboratory testing program was performed. The objectives of the geotechnical investigation were:

Evaluate engineering properties of on-site materials.

Develop geotechnical properties for use in design.

Asses the depth to bedrock or groundwater, if encountered.

Develop seismic design criteria.

Evaluate the potential presence and rippability of carbonate cemented soils, also known as caliche.

Once the geotechnical investigation was completed, the information gathered was used to inform geotechnical analyses. The objectives of the geotechnical analyses included:

Evaluate stability of channel and embankment slopes under proposed loading conditions.

Develop recommendations for soil-cement design.

Provide recommendations for design and construction.

This report will present the results of the geotechnical investigation and design recommendations.

2 Geologic Setting

2.1 Regional Geology

LAKE lies within the Basin and Range physiographic province. The Basin and Range covers approximately 300,000 sq. mi. and is surrounded by the Sierra Nevada and Cascade mountains on the west, the Columbia Plateau on the north, and the Colorado Plateau and Wasatch Front of the Rocky Mountains on the east. South of Nevada, the Basin and Range province extends into Mexico and parts of Arizona, New Mexico, and Texas. This entire region is tectonically active, characterized by down-dropped desert basins separated by many uplifted, predominantly north-south trending mountain ranges. Most of the peaks are less than 10,000 ft in elevation, although a few top 13,000 ft. About half of the Basin and Range province is occupied by the

Great Basin, a large area of isolated internal drainages that covers most of Nevada. Because the Great Basin is slightly dome-shaped with the highest valleys in the middle, all the lakes and all but one of the major rivers are near the western and eastern edges of the basin, and are fed by snow that falls in the Sierra Nevada or Rocky Mountains. However, almost all valley floors throughout the basin contain unvegetated playas, dry remnants of former lakes that existed in wetter times (Brussard, 2009).

Based on a review of the Nevada Bureau of Mines and Geology Preliminary Geologic Map of the Spirit Mountain NW Quadrangle, Clark County, Nevada and Mohave County, Arizona

(House and Faulds, 2009), the project site is located within piedmont alluvial deposits which range from early Pleistocene (oldest) to Holocene (most recent) in age. Piedmont is the non-genetic term for a typically broad, generally low-relief area extending from the base of a mountain range toward the center or axis of a valley, in this case the Colorado River.

Piedmonts, typical of those in the area of the subject site, are composed mostly of alluvial sediment shed from adjacent highlands by stream flows and debris flows that form complexly coalescing and overlapping deposits and landforms of alluvial fans. They may also include complex mixtures of eroded bedrock and other kinds of surficial geologic deposits, including well-defined washes, inactive alluvial fan remnants, river terraces, sand dunes, and lacustrine beach forms. The adjacent mountains to the west are generally composed of monzonite, monzodiorite, dikes of various compositions, and various gneiss units (Hinz et al., 2012) which form the parent rock for the piedmont alluvium.

2.1.1 Site Geology

Figure 2.1 shows a geology map of the site from House and Faulds (2009). The mapped surficial geologic deposits in the area of the proposed flood diversion system include “Young piedmont alluvium” (Qay) located within the most recently active alluvial channels and fans, which are generally incised into narrow or broad channels below the elevation of older piedmont surfaces. The alluvium deposits located on the channel banks/side slopes and inter-channel terraces generally consist of “Piedmont alluvium” (Qai1, Qai2 and Qai3), which are known to contain carbonate soil or caliche. Older deposits consisting of early Pliocene “Colorado River sediments” (Tcb) are exposed in the channel banks/side slopes of the channels within the northern portion of the project site.

Figure 2.1. Geology Map of Project Area (House and Faulds, 2009)

Caliche is a soil unit in which the particles are cemented together by the precipitation of mineral matter in their interstitial spaces and is often found in arid and semiarid areas, including Nevada

(King, 2019). Occasional zones and layers of caliche, on the order of several in to several ft thick, were observed during the geotechnical investigation along the channel banks near the project area. The observed zones of caliche appeared to occur throughout the height of the channel banks and were not confined to a particular elevation or horizon. No caliche zones or layers were observed in the channel cut slopes during the geotechnical investigation based solely on a brief visual observation. The geologic units near the excavation are generally known to contain caliche (King, 2019) and it may be encountered during excavation. The strength of the cementation appeared to be variable based on observation and some manual manipulation.

The piedmont alluvial deposits, especially those associated with high energy alluvial processes like floods and debris flows, typically consist of silt- to boulder-sized particles and may occur in well-sorted layers or massive beds depending on the depositional process. The Colorado River alluvium may also consist of silt- to boulder-sized particles similar to the piedmont alluvium, but may also contain concentrations of clay.

Groundwater at the project site is at an unknown depth beneath the ground surface.

Groundwater was not encountered in the deepest boring of 100 ft bgs, which was drilled to an elevation of approximately 940 ft. Lake Mohave is less than 1.5 miles to the east at an elevation of 640 ft, therefore the water table at the project site is most likely somewhere between an elevation of 940 ft and 640 ft.

2.1.2 Topography

In March of 2018, Quantum Spatial Inc. (QSI) collected high resolution Light Detection and

Ranging (LiDAR) data over an approximate area of 4,460 acres. HDR performed a review of the data and determined that it met United States Geological Survey (USGS) Quality Level (QL) 1 standards as well as Federal Emergency Management Agency (FEMA) specifications for 1-foot contours in flat and open areas. Both the QSI data report and HDR review are included in the

BODR (HDR 2018).

LAKE lies in a region characterized by alternating northward trending mountain ranges and intervening wide basins with low relief. The Colorado River has cut deep canyons through the mountain ranges where the river channel is bordered by steep, high-relief walls composed primarily of Precambrian to Tertiary igneous and metamorphic rocks. The dry climate and topography create a variety of landscapes including alluvial fans, playas, mud flats, salt flats, lakes, sand dunes, and canyons.

The overall gradient from east to west across the project site is 4% to 5%, which is steep enough to create high velocity flows to cut into the older piedmont deposits, creating alluvial channels with steep side slopes up to 1.3H: 1V (horizontal: vertical) (77% slope) and near-vertical in areas, as shown on Photo 2.1. Some north-facing channel slopes are as shallow as

5H: 1V, but not all north-facing slopes are shallow. The height of channel slopes varies from about 8 ft, as shown on Photo 2.2, to 35 ft from the floor of the middle wash to the north ridge near Test Pit P-1. Most channel slopes are roughly 20 ft high and at about 2H: 1V, as shown on

Photo 2.3. The tops of the ridges are very flat and the piedmont alluvium forms what is referred to as desert pavement with tightly packed cobbles and gravel, as shown on Photo 2.4. The younger channel alluvium is less tightly packed and forms a more hummocky channel floor, as shown on Photo 2.5. The down-cutting fluvial forces can migrate, creating terraces below the ridges and mid-channel landforms as shown on Photo 2.6.

Photo 2.1. Near vertical slope of cemented soils, south slope of middle wash near Test Pit P-2

Photo 2.2. Eight-foot high terrace with 5H: 1V slopes at the south end of the south embankment

Photo 2.3. North slope of south wash, about 20 ft high with a 2H:1V slope, looking east down channel

Photo 2.4. North ridge desert pavement, looking west near Boring B-3

Photo 2.5. South wash alluvium looking down channel to the east

Photo 2.6. Looking northeast up the middle wash, showing terraces and mid-channel landforms

Terrace Landform

2.1.3 Climate

Cottonwood Cove is situated along the western shore (Nevada side) of the Colorado River in the very arid region of extreme southern Nevada at an elevation of approximately 680 ft. The climate of this region is characterized by a hot, dry season that extends from May to September with the majority of the minimal annual precipitation (7.70 in annually) occurring during the winter months of November through March. Monthly temperatures peak around July with daytime temperatures averaging about 97 degrees (deg). The minimum monthly temperatures occur in January and average (avg) highs are about 54 deg with lows averaging about 36 deg.

The region experiences impacts from the Southwest Monsoon during the months of July, August, and September, as isolated thunderstorms can rapidly build and produce short-duration, high-intensity periods of rainfall. Storms early within the monsoon season tend to be dry, consisting primarily of lightning and blowing dust. Later in the monsoon season, storms tend to have more precipitation.

The town of Searchlight, NV, 13.1 miles to the west of Cottonwood Cove, is the closest meteorological reporting station with a long period of record. This station collected meteorological data in the region between 12/01/1913 and 06/09/2016. The Western Regional

Climate Center (WRCC, 2018) provided the average (avg) climate data from this location as shown in Table 2.1, which is assumed to be representative of the climate at Cottonwood Cove.

Table 2.1. Average Climate Data for Searchlight, NV (WRCC, 2018)

Month Avg Max Temp (F)

Avg Min Temp (F)

Avg Total Precipitation (in)

Avg Total Snowfall (in)

Avg Snow Depth (in)

Annual Averages

75.2 51.9 7.7 1.3 0

Jan 53.7 35.6 0.92 0.7 0

Feb 58.4 38.3 0.96 0 0

Mar 66 41.8 0.77 0.1 0

Apr 73.1 48 0.4 0 0

May 82.5 55.9 0.2 0 0

Jun 92.7 64.8 0.11 0 0

Jul 97.6 71.4 0.91 0 0

Aug 95.4 69.6 1.08 0 0

Sep 89 63.9 0.61 0 0

Oct 77 53.9 0.52 0 0

Nov 63.6 43 0.43 0.1 0

Dec 54.4 36.4 0.79 0.4 0

3 Site Investigation Program

3.1 Overview

Prior to the commencement of the Geotechnical Investigation, a site visit was conducted by

HDR personnel on October 30, 2018 to coordinate with the subcontractor, Geotechnical &

Environmental Services, Inc. (GES), performing the geotechnical investigation. This coordination included finalizing logistics for the investigation such as access routes, staging areas, water supply, and schedule. Wallace Morris Kline Surveying (WMK) established permanent survey control monuments and staked out boring and test pit locations. WMK also performed utility locates to avoid damage to utilities. The borings and test pit locations were modified slightly during the investigation to accommodate access; this will be discussed in

Section 3.2, and the borings are shown in Table 3.2. The final locations of the borings and test pits were recorded using a hand held Global Positioning System (GPS) in the field.

The Geotechnical Investigation was performed December 10-20, 2018. A site plan of the geotechnical investigation is shown on Figure 3.1. Eagle Drilling (a subsidiary of GES) performed the drilling and sampling of nine geotechnical boreholes. GES provided an excavator to dig four test pits. GES also performed laboratory testing on disturbed samples taken from both the borings and test pits to establish material properties for analysis, design, and construction specifications.

A refraction microtremor (ReMi) survey was conducted by GES in December of 2018 with a depth of focus to a depth of 100 feet (ft) to evaluate the seismic hazard site class according to

American Society of Civil Engineers (ASCE) 7-10 (ASCE, 2010). Seismic refraction surveys were performed along the proposed embankment and channel alignments, totaling approximately 2,100 linear ft of survey length. These surveys were used to evaluate the indicated compression wave (p-wave) velocities to assess rippability of the subsurface layers. A separate site visit was conducted by HDR in June 2019 to collect soil samples for use in laboratory soil-cement mix design.

Figure 3.1. Geotechnical Site Investigation Plan

3.2 Site Access

The site is accessed via Rattler Road, which runs north from Cottonwood Cove Road, shown on

Figure 1.1. An open gravel lot behind the park buildings was used as a staging and unloading area for the drilling equipment. A gravel two-track through an east-west trending wash channel extends from Rattler Road for approximately one mile up the wash before it disappears, and is generally accessible only by four wheel drive pickup truck. This gravel road was the main access route for the geotechnical investigation work.

The hard desert gravel was suitable for both rubber-tired and tracked heavy equipment such as an excavator and drill rig. However, the steep wash channel slopes that exist between borings posed a challenge for accessing all the borings and test pits that were not in the main wash.

During the October 30 site visit, an access route to each boring and test pit was found to be suitable, with low enough grades, for the drill rig by walking the site with the drill rig operator.

Borings B-1 through B-3 and Test Pit P-1 were located on a ridge with high and steep side slopes that required a circuitous route to access. The original access plan was reviewed by NPS

LAKE staff and an alternate route to shorten the total distance and lessen the disturbance to the natural surfaces was proposed. On the first day of the investigation, Monday December 10th, 2018, the access route proposed by NPS was walked with HDR, Eagle Drilling, and NPS LAKE staff to confirm suitability for equipment travel and the least disturbance to the natural area.

Prior to any equipment mobilizing to the site, all equipment, including personal vehicles, was inspected by NPS LAKE staff to confirm that no invasive seeds were transported to the site.

Additionally all HDR, GES, and Eagle Drilling staff involved in the geotechnical investigation field work participated in endangered desert tortoise training to protect the local wildlife.

3.3 Geotechnical Drilling

Nine geotechnical borings were advanced by Eagle Drilling using a Diedrich D-50 Turbo track rig from December 10-19, 2018. Borings B-1 through B-9 and Test Pits P-1 through P-4 are shown on Figure 3.1 and are summarized in Table 3.1. The elevations and coordinates on Table

3.1 are approximate. Groundwater was not encountered in any of the borings or test pits during the investigation.

HDR personnel directed the drilling operations and also recorded field logs for each boring.

These boring data included: sample recovery, standard penetration tests (SPT) blows per 6 inches (in), soil descriptions and general classification estimates, and remarks on drilling. Field boring logs are included in Appendix A.

Table 3.1. Summary of Geotechnical Borings and Test Pits

Boring / Test Pit

Approxim ate

Easting1

(ft)

Approximate Northing1 (ft)

Approximate Elevation2

(ft)

Total Depth (ft)

Sampling Method

B-1 917233.77 26518200.49 1000 60 SPT/Bulk

B-2 916988.57 26518087.29 1015 70 SPT/Bulk

B-3 916794.24 26517945.79 1025 60 SPT/Bulk

B-4 916675.30 26517728.87 988 70 SPT/Bulk

B-5 916401.05 26517525.30 1015 57 SPT/Bulk

B-6 916137.80 26517307.68 1045 40 SPT/Bulk

B-7 915907.21 26517156.91 1055 60 SPT/Bulk

B-8 915739.97 26516846.23 1040 100 SPT/Bulk

B-9 915388.63 26516580.68 1063 42 SPT/Bulk

P-1 916739.34 26517925.64 1027 10 Bulk

P-2 916364.60 26517573.15 1002 10 Bulk

P-3 915985.30 26517158.95 1051 10 Bulk

P-4 915574.45 26516710.08 1048 9 Bulk Notes:

1. Coordinates taken during drilling with handheld GPS in NAD83 Nevada State Plane, East Zone

2. Elevations from LiDAR data surface

The SPTs were performed in general accordance with American Society for Testing Materials

(ASTM) D1586-11. In the SPT, an 18-inch-long, 2 inch-outside-diameter, 1.375-inch-inside-diameter, split-spoon sampler is driven with an automatic 140-pound hammer, falling freely from a height of 30 in. The number of blows required to achieve each of three 6-inch increments of sampler penetration is recorded. The number of blows required to advance the last 12 in of penetration is termed the Standard Penetration Resistance, or N-value. When penetration resistances exceeded 50 blows for 6 in or less of sampler penetration (refusal), the test was terminated and the number of blows along with the penetration distance was recorded on the borehole log. The presence of gravels or cobbles larger than the sampler may have impacted the indicated blow counts.

Split spoon samples were taken at 5-foot depth intervals to the borehole termination depth. Bulk samples of drilling cuttings were obtained at select locations for the borings. The borings were advanced using 8-inch outer diameter hollow-stem augers. Borings were backfilled to the surface with cuttings upon completion of drilling.

3.4 Test Pits

A total of four test pits were excavated using a CAT 420F-2 backhoe with a 2-foot wide bucket.

Test Pits P-1 through P-4 were dug at the locations shown on Figure 3.1 and backfilled on

December 11, 2018. The operator was instructed to make separate spoils piles for the material dug from depths of zero to 5 ft and from 5 ft to the bottom of the test pit. Bulk samples were collected in 5-gallon buckets. Three of the four test pits were excavated to an approximate depth of 10 ft, which was the maximum reach of the excavator arm. The other encountered practical refusal at a depth of 9 ft below ground surface (bgs) and could not be advanced further. All four test pits measured approximately 10 ft by 3 ft at the surface. The walls of all the test pits remained vertical and stable for the duration of the excavation and logging, but were not safely accessible for detailed logging.

HDR personnel photographed and recorded a field log of each test pit by describing the soil in the separate spoil piles and making any observations at a safe distance from the pit edge. The test pit logs are included with the boring logs in Appendix A. Additionally, photos of the test pits are provided in Appendix A. Each test pit was left open for approximately 30 minutes before being backfilled with the spoils and compacted by a few rolling passes of the excavator.

3.5 Geophysical Survey

The locations of the geophysical survey lines are shown on Figure 3.1. An initial geophysical survey was performed by GES concurrent with the drilling investigation. Upon review of the report submitted by GES, HDR determined that additional data was needed to evaluate the potential presence of high velocity subsurface layers that may indicate caliche, and also to assess soil excavatability/rippability. Therefore, GES remobilized to the site in March 2019 to perform additional seismic refraction surveys, which were processed by HDR to present tomographic profiles along the survey alignments. The HDR seismic refraction survey report is included in Appendix B.

At the time of drilling, GES also performed a ReMi survey to evaluate seismic site class. Details of the ReMi survey were described in a letter report from GES, which is included in Appendix C.

The full report from GES is included in Appendix C, but only the ReMi data was used by HDR.

The complete report from GES is provided for completeness, despite portions not being used.

The other geophysical information and analysis used by HDR is included in the HDR seismic refraction survey report provided in Appendix B.

3.6 Soil Cement Samples

In June 2019, soil samples were collected from the potential soil-cement borrow areas for laboratory testing of the proposed soil-cement mix design. The sample locations are shown on

Figure 2.1. The sample holes were excavated with a shovel to a depth of around two ft and had an approximate diameter of one foot. Nine 5-gallon buckets were each filled for the west and east sample areas for a total of 18 buckets.

3.7 Laboratory Testing

Table 3.2 presents a summary of the assigned laboratory tests. Samples consisted of both SPT samples from drilling and bulk samples collected either from drill cuttings or 5-gallon buckets from the tests pits. Laboratory results are included in Appendix D.

Table 3.2. Laboratory Testing Summary

Test Description ASTM Standard

Sample Type and Number of Tests

SPT Bulk Sieve Analysis D6913 12 3 Hydrometer Analysis D422 4 - Atterberg Limits D4318 4 2 Moisture Content D2216 8 - Corrosion Suite with Resistivity NA - 2 Sieve Analysis (Aggregate) C136 - 3 Hydraulic Conductivity D5856 - 3 1-D Consolidation D2435 - 2 Direct Shear D3080 - 3 Laboratory Compaction (Modified Proctor) D1557 - 3

Soil-Cement Tests

Sieve Analysis D6913 - 4 Laboratory Compaction (Standard Proctor) D558 - 4 Soil Cement Compressive Strength D1633 - 12

4 Site Investigation Results

4.1 Geotechnical Drilling Results

The boring and test pit logs are included in Appendix A. Nearly all the soils encountered at the project site are classified as gravel or sand with varying amounts of silt. It is evident from the ground surface and from test pit excavations that a significant amount of particles greater than approximately 3 in size exist throughout the project site, as shown on Photos 3.1 to 3.6 and the test pit photos in Appendix A.

Because the geologic processes that deposited the soil at the ground surface are the same that deposited the soil at depth, it is assumed that the presence of cobbles and boulders with depth is consistent with what is shown at the surface. The auger pushes oversized material outward during the drilling process and occasionally encounters auger refusal when a boulder or cobble is directly beneath the auger bit, or potentially when strongly to very strongly cemented soil is encountered. When auger refusal was encountered, the boring was moved approximately 20 ft from the original location and re-drilled to the depth of refusal. The refusal borings are listed in

Table 4.1. The locations shown on Figure 3.1 and Table 4.1 are the final locations.

Table 4.1. Borings Moved Due to Refusal

Boring No.

Depth of

Refusal (ft) Distance

Moved (ft) Direction

Moved

B-1 9.5 20 South

B-2 9.5 20 East

B-3 12 20 North

The Unified Soil Classification System (USCS) provides a naming convention for soils that are listed in the “Description” column of the boring and test pit logs included in Appendix A.

However, the USCS only accounts for material that is considered gravel or smaller, which is less than 3 in in size. Therefore, it is important to keep in mind the presence of larger particles, i.e. cobbles and boulders, when reviewing the boring logs and lab results. In general, the soil at the project site is granular and has a well-graded representation of all size material ranging from silt to boulders.

With the exception of Borings B-7 and B-8, the soils encountered below a depth of about 4 ft bgs were dense based on sampler penetration blow counts (N-values greater than 50 blows per foot), and remained dense to depth. At Borings B-7 and B-8, the sampler penetration blow counts suggest dense soil conditions below a depth of approximately 9 ft bgs. Because of the gravels, cobbles, and boulders noted in the soils, some of the high blow counts recorded in the borings could indicate refusal on or interference from the coarse-grained materials and may not be representative of the soil’s relative density.

Sample recovery was challenging due to the granular and cohesionless nature of the soils and the tendency of the soil to flow out of the sampler when extracted, even when using a sand catcher. Further challenging recovery was the coarse size of the grains relative to the inside diameter (1.375 in) of the split-spoon samplers, which frequently caused plugging of the sampler tip and limited recovery. Multiple drive samples (split-spoon samples) resulted in no recovery from the borings. When several sequential samples had no recovery, an approximate gallon-size bag sample of drill cuttings was taken as they were brought to the surface by the auger flights.

The dominant USCS soil types logged in the borings were sand (SW/SP), sand with silt

(SW/SP-SM), and silty sand (SM). A small amount of high plasticity clay was encountered at the very bottom of Boring B-5 at a depth of about 54 ft bgs, which is well below the depth zone of influence of the proposed embankment at that location. With the exception of the upper few ft of

Boring B-5, frequent concentrated layers of gravel were only encountered in Boring B-8 from a depth of about 24 ft bgs to the bottom of the boring at about 100 ft bgs. The remaining borings

(B-1 to B-3, B-5 to B-7 and B-9) were all drilled into the Piedmont ridges and tended to have a higher percentage of silt than Borings B-4 and B-8 that were drilled in the channels.

Cementation is apparent in some of the exposed channel slopes and can be seen in the areas of near-vertical slope faces. However, none of the soils recovered from the cuttings or from the boring samples appeared to be cemented due to the disturbance during sampling. It was difficult to ascertain from the borings and sampling alone the presence of cemented soils (caliche).

Though auger refusal or slower drilling and drill chatter was encountered in Borings B-1, B-2 and B-3 at depths ranging from about 9.5 to 12 ft bgs, the drilling behavior was interpreted to be typical for encountering cobbles/boulders because of the lack of evidence of heavily cemented soils or fragments of caliche in the recovered cuttings. However, the possibility remains that the drilling conditions encountered in Borings B-1, B-2 and B-3 at the noted depths were in part due to cemented soils. Evidence of caliche layers was not observed in the recovered boring samples and cuttings, but this could be due to drilling and sampling disturbance.

Groundwater was not encountered in any of the borings at the time of drilling, and piezometers were not installed in any of the borings. Fluctuations in the groundwater level may occur with time or may be transient following storms. Significant evidence of previous groundwater, such as iron staining, was not observed in the samples recovered from the borings.

4.2 Test Pit Results

The materials encountered in the test pits were similar to the soils encountered in the borings

(the logs are included in Appendix A). The soils were visually classified in the field as gravel with cobbles and boulders (GW/GP) while the laboratory classifications (which only include material smaller than 3 in) indicated silty sand (SM) and sand with silt (SP-SM), which occur as infill between the coarser particles.

Three of the four test pits were advanced to a depth of 10 ft bgs, which was the practical reach of the excavator. Test Pit P-4 encountered practical refusal at a depth of 9 ft bgs and could not be advanced further. Refusal was most likely due to an increased boulder fraction or cemented soils. Cobbles were present in significant proportions in all test pits, but boulders were only present in Test Pits P-1, P-4 and the uppermost portion of P-2. Boulders were not encountered in Test Pit P-3, which is at the top of a narrow ridge near Boring B-7. The walls of the test pits did not display any cross bedding or bedding planes. The test pit walls remained stable during the duration of observations and logging, about a 30-minute period for each pit. Groundwater was not encountered in any of the test pits during excavation and logging.

4.3 Geophysical Survey Results

Objectives of the seismic surveys were to:

Obtain velocities of the materials within the uppermost 40 to 50 ft bgs to assess rippability and excavatability.

Produce p-wave cross-sectional velocity tomograms to aid in extrapolating geotechnical information beyond boring location.

Help identify high velocity layers which could represent possible caliche layers in the subsurface.

The results of the data collection and processing are further described in Appendix B.

In order to evaluate the site-specific seismic Site Class, a ReMi survey was performed by GES at the project site at the location shown on Figure 3.1. The survey consisted of an array of 24 vertical geophones spaced 15 ft apart to record ambient noise. The data was processed using

SeisOpt ReMi software by Optim Software to produce a shear wave velocity (Vs) profile to a depth of 100 ft bgs (GES, 2019). The Vs over the 100-foot survey depth was 1,372 feet per second (ft/s) (418 meters per second, m/s) which indicated a Site Class C (very dense soil and soft rock) based on the criteria in ASCE 7-10 (ASCE, 2010). Additional details of the ReMi survey are included in Appendix C.

Surface seismic data collection was conducted along two survey sections for a cumulative length of approximately 2,100 ft along the general alignments of the proposed diversion structure. The seismic data was collected by HDR along eight overlapping seismic line segments; a small offset was located between the two sections where the bank of one of the channels was too steep to safely collect data. The seismic line locations are shown on Figure

3.1 along with the locations of the geotechnical borings and test pits. Two-dimensional (2D) compression wave (p-wave) velocity profiles were produced from the refraction tomography data processing and are shown on Figures 4.1 and 4.2. The original (non-annotated) figures are provided in Appendix B.

Along the northern seismic refraction profile (see Figure 3.1 for location), the profile generally identified increasing p-wave velocities with depth and showed less variability as compared with the southern seismic profile. The results of the seismic refraction suggest that the soils within approximately the upper 10 to 15 ft bgs have a p-wave velocity of approximately 1,000 to 3,000 ft/s. Below those depths p-wave velocities up to approximately 4,000 ft/s were measured above the approximate channel excavation limit, see Figure 4.1.

Borings B-1 and B-2 encountered practical auger drilling refusal at a depth of about 9.5 ft bgs, and Boring B-3 encountered slower drilling rates and drill chatter at depths of 21 ft and 40 ft bgs.

These depths and locations of auger refusal, slower drilling rates and drill chatter do not correlate well to discrete zones of higher velocity soils. They have a somewhat better correlation to areas of rapid changes in p-wave velocities, as identified by closely spaced velocity contours, see Figure 4.1. These zones could represent changes in density or layering in the soil as well as concentrated layers of gravels, cobbles or boulders.

Along the southern seismic refraction profile (see Figure 3.1 for the location) the p-wave velocity for the majority of the soils above the proposed depth of excavation of about 25 ft bgs for the nearby south channel cut was between approximately 1,500 ft/s and 3,000 ft/s.

There also appear to be higher velocity zones which contrast with the generally recognizable trend of increasing p-wave velocity with depth. One zone of material having a higher p-wave velocity was located near Boring B-7, see Figure 4.2. This zone indicates at an elevation of about 1030 ft, which is near the base of the proposed excavation for the south channel, p-wave velocity of approximately 4,500 ft/s. This zone of higher velocity materials correlates well with an elevation noted in Boring B-7 where slower drilling rates and drill chatter were encountered.

Figure 4.1. Northern Seismic Refraction Profile

Figure 4.2. Southern Seismic Refraction Profile

4.4 Laboratory Testing Results

The results of the laboratory testing are included in Appendix D. The laboratory testing samples recovered from borings included both SPT samples and bulk samples of auger cuttings. The boring sample test results are presented in Table 4.2. The soil-cement sample tests are also included in Appendix D.

Table 4.2. Boring Samples Laboratory Test Results Summary

Boring Sample No.

/ Type

Depth BGS (ft)

MC1

LL2 PI3 USCS4 Gravel

Sand

Fines

B-1 SPT8 34 1 - - - - - -

B-1 SPT8 34 - - - SM 20 61 19

B-2 SPT7 29 - - - SM 26 56 18

B-2 Bulk 42 - - - GP 64 32 4

B-3 SPT2 4 - - - SW-SM 21 68 11

B-3 SPT7 29 - - - SP-SM 5 83 12

B-4 Bulk 62 - NV5 NP5 SP-SM 30 62 8

B-4 SPT3 9 0.7 - - - - - -

B-4 SPT 12/13 59.0/64 0.7 NV NP SM 24 58 18

B-5 SPT12 54 12.6 66 46 CH 0 8 92

B-6 SPT7 29 - - - GW-GM 32 57 11

B-7 SPT1 1 1.7 NV NP SM 10 64 26

B-7 SPT6 24 1.4 - - SM 17 66 17

B-7 Bulk 41 NV NP GW-GM 46 45 9

B-8 SPT2 4 0.8 NV NP SW-SM 14 76 10

B-8 SPT6 24 0.7 - - GP-GM 46 44 10

B-9 SPT6 24 - - - SW-SM 29 62 9

Notes:

1. Moisture Content

2. Liquid Limit (LL)

3. Plasticity Index (PI)

4. Unified Soil Classification System

5. Non-viscous (NV) and Non-plastic (NP)

A total of three 5-gallon buckets of material were collected from each test pit performed during the site investigation.