TCWL_Geotechnical_Baseline_0004.pdf

Engineering from the ground down

GEOTECHNICAL BASELINE REPORT

Replace Trans-Canyon Water Distribution Pipeline

GRCA 190083

Grand Canyon, Arizona

July 6, 2018

1360 S Wadsworth Blvd, Suite 114 Lakewood, Colorado 80232

303.625.9502 www.LithosEng.com

July 6, 2018

Project No. 16066-1

HDR Engineering, Inc.

419 Canyon Avenue

Fort Collins, CO 80521

Attention: Mr. Rich Thornton, PE

Project Manager

Regarding: Geotechnical Baseline Report

Replace Trans-Canyon Water Distribution Pipeline

GRCA 190083

Grand Canyon, AZ

Mr. Thornton, Submitted herewith is the Geotechnical Baseline Report for the Project to Replace Trans-Canyon Water

Distribution Pipeline in Grand Canyon, Arizona. The project includes replacement of the existing waterline as well as construction of facilities to support the improved waterline. This study was conducted in general accordance with the contract between Lithos Engineering and HDR Engineering, Inc. Contained herein are discussions of the geotechnical data, geotechnical baselines, and construction considerations in support of the subject project.

If you have any questions regarding the contents of this report, please contact the undersigned.

Sincerely, Lithos Engineering

Amara Meier Nate Soule, PE

Geological Engineer Vice President

Robin Dornfest, PG

President

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TABLE OF CONTENTS

1 INTRODUCTION

1.1 Project Description

1.2 Description and Purpose of the GBR

2 GEOLOGY AND FIELD INVESTIGATION

2.1 Regional Geology

2.2 Waterline History

2.3 Field Investigation

3 GEOLOGIC CHARACTERISTICS AND GROUND BEHAVIOR

3.1 Geologic Units

3.2 Brahma and Rama Schist Bedrock

3.2.1 Index Properties

3.2.2 Behavior

3.3 Granite Bedrock

3.3.1 Index Properties

3.3.2 Behavior

3.4 Tapeats Sandstone Bedrock

3.4.1 Index Properties

3.4.2 Behavior

3.5 Bright Angel Shale Bedrock

3.5.1 Index Properties

3.5.2 Behavior

3.6 Alluvium

3.6.1 Index Properties

3.6.2 Behavior

3.7 Colluvium

3.7.1 Index Properties

3.7.2 Behavior

3.8 Groundwater

4 CONSTRUCTION CONSIDERATIONS

4.1 Pipeline reaches

4.1.1 Delta Reach

4.1.2 River Reach

4.1.3 Talus Reach

4.1.4 Cliff Reach

4.1.5 Plateau Reach

4.1.6 Bright Angel Reach

4.2 Proposed Structures

4.2.1 Phantom Ranch Treated Water Storage Tank

4.2.2 Phantom Ranch Delta Structures

4.2.2.1 Raw Water Storage Tank

4.2.2.2 Booster Pump Building

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4.2.2.3 Water Treatment Plant

4.2.3 Indian Garden Structures

4.2.3.1 Indian Garden Water Treatment Plant

4.2.3.2 Indian Garden Water Storage Tank

5 LIMITATIONS

6 REFERENCES

LIST OF FIGURES

Figure Number Title

1 Pipeline Alignment with Geologic Map

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REPORT ORGANIZATION

The Geotechnical Baseline Report (GBR) is organized as follows:

Section 1: Introduction

This section describes the project background and discusses the purpose and intended usage of the GBR.

Section 2: Geology and Subsurface Conditions

This section provides background on the regional geology and describes the investigation undertaken to evaluate ground conditions at the site.

Section 3: Subsurface Characteristics and Ground Behavior

This section describes the materials found onsite and provides baselines for the materials’ index properties.

Section 4: Construction Considerations

This section discusses structural foundation excavation and slope stability, as well as pipeline ground conditions. Additional considerations are given for typical construction scenarios that may arise during pipeline or structure construction, which the contractor should account for in their bid, designs, and performance.

Sections 5 and 6: Limitations and References

These sections describe limitations of the GBR and provide references for citations within the report.

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1 INTRODUCTION

1.1 Project Description

The Project to replace the Trans-Canyon Water Distribution Pipeline is intended to improve service and overall integrity of the existing Trans-Canyon Waterline (TCWL). Improvements include relocating the current water supply source from Roaring Springs Cave to Bright Angel Creek, and constructing a new treated water storage tank, raw water storage tank, booster pump station, and water treatment facility building in the Phantom Ranch area. A new water treatment facility building and water storage tank will also be constructed at Indian Garden. The existing water pipeline between the Phantom Ranch area and

Indian Garden also will be replaced. The National Park Service (NPS) for Grand Canyon National Park manages the existing waterline and facilities.

Pipeline installation will require a variety of construction methods due to changes in the geologic setting along the alignment. Relevant information included in this GBR highlights the different geologic settings and corresponding construction limitations along the alignment. Relevant information in this GBR also highlights the different geologic settings and corresponding construction limitations for each structure foundation.

The project is located within a valued cultural heritage site with corresponding environmental protections.

Therefore, special care should be taken to reduce construction impacts on the protected environment.

The project location poses unique challenges to the overall project. Site, resources, and equipment access are limited in the canyon, so transportation will rely on the use of helicopters where possible. Therefore, weight restrictions will be based on carrying capacities of available helicopters. Additionally, soil and rock sourcing as well as disposal of excavated material from construction activities will likely be contained to within the canyon. Access to water and power will also require special attention at more remote locations, primarily along the pipeline alignment.

1.2 Description and Purpose of the GBR

The main purpose of this Geotechnical Baseline Report (GBR) is to establish contractual baselines for anticipated ground conditions and behavior that will be encountered during construction of the pipeline and structure foundations. Geological conditions associated with the construction of the pipeline and structure foundations are represented in the Geotechnical Investigation Report: Project to Replace Trans-

Canyon Water Distribution Pipeline (Geotechnical Investigation Report, Lithos Engineering, 2018).

This GBR also summarizes geotechnical and construction considerations that form the basis of the project design and Contract Documents. Report preparation was performed in general accordance with an ASCE document entitled: “Geotechnical Baseline Reports for Construction, Suggested Guidelines” (Essex, 2007).

The GBR presents the anticipated ground conditions and is recommended to be used as the basis for developing bids and to help the Contractor evaluate means and methods. The GBR will also be used for evaluating potential differing site conditions (DSC) during construction.

Anticipated ground conditions presented in this GBR reflect the Design Team’s judgment of anticipated subsurface conditions and ground behavior based on assumed construction means and methods expected to be employed in the work. The baselines were established by considering

HDR Engineering, Inc. Replace Trans-Canyon Water Distribution Pipeline Page 2 of 15 available geologic and geotechnical data, together with previous construction experience in similar ground conditions.

2 GEOLOGY AND FIELD INVESTIGATION

2.1 Regional Geology

The geologic conditions in the area are characterized by coarse alluvium (water deposited) and coarse colluvium (gravity deposited) overlying schist, granitic intrusions, sandstone, siltstone, and shale bedrock.

The geology of the Grand Canyon has been extensively studied and is widely available. The very brief summary here provides basic information as it relates to the project. The geologic setting of the project site is the Grand Canyon, in which sedimentary rocks overlie metamorphosed crystalline basement rocks.

Uplift, faulting, weathering, erosion, and deposition over the last five to six million years has resulted in a canyon that is, on average, up to ten miles wide and one mile deep. The Colorado River flows through the base of the canyon and the canyon walls are comprised of slope and cliff-forming geologic units.

Weathering of rock units both upstream and upslope provide the source material for alluvial and colluvial deposits in the canyon. Almost 40 major bedrock units have been identified in the canyon, however, only five of those geologic units are pertinent to the pipeline alignment and proposed structure locations. They are, in decreasing age, the Rama Schist, Brahma Schist, Zoroaster Plutonic Complex (granitic intrusions), Tapeats Sandstone, and the Bright Angel Shale. For the purpose of this report, the Brahma and Rama

Schist will collectively be referred to as schist, and the Zoroaster Plutonic Complex will be referred to as granite. Groundwater in the region is influenced by the Colorado River and its contributing tributaries, as well as local aquifers.

2.2 Waterline History

The existing TCWL was built around fifty years ago and provides water to the South Rim of the Park. The existing pipeline has an intake at Roaring Springs, north of Phantom Ranch, and follows the North Kaibab

Trail down the canyon past Phantom Ranch and across the Colorado River via the Silver Bridge. From there, the pipeline continues up the canyon to Indian Garden and eventually all the way to the South Rim.

Sections of the pipeline follow the North Kaibab Trail, the Bright Angel Trail, and the Plateau Point Trail, while other sections are off trail.

Based on records, the pipeline manufacturer anticipated the original pipe would last thirty years.

Helicopters were used to transport materials and equipment into the canyon and specialized machines were designed to work within the constraints of the canyon and narrow trails. Regular failures of the pipeline occur annually and cost around $25,000 per repair. As recent as March 2018, a Level 3 water restriction was put in place due to an outage which forced significant conservation measures in the park.

The current system is also inefficient due to an inability to regulate flow and wastes water when demand is low.

2.3 Field Investigation

The field investigation for the pipeline and proposed structures was performed by Lithos, accompanied by HDR, between April 17th and April 19th, 2018. The investigation was intended to assess the feasibility of the pipeline alignment and proposed structure locations. Exploration data from this investigation are

HDR Engineering, Inc. Replace Trans-Canyon Water Distribution Pipeline Page 3 of 15 presented in the Geotechnical Investigation Report (GIR). Many of the terms used in this GBR are further described and summarized therein.

Sample collection was not permitted in the Park; therefore, a non-destructive field investigation was performed. In the absence of sample collection and laboratory testing, data was collected on intact rock and deposits at various locations throughout the project area. The locations of data collection are provided in the GIR. Details of the procedures used for conducting the field work and the factual results of the investigation for this project are summarized in the GIR.

3 GEOLOGIC CHARACTERISTICS AND GROUND BEHAVIOR

The soil and bedrock characteristics and ground conditions described in this section of the GBR constitute the baseline geotechnical conditions to be anticipated during construction. Baseline values and discussion pertinent to the geologic conditions are derived are provided below.

3.1 Geologic Units

The extent of relevant geologic units to the project area are shown in Figure 1. Geologic units that will be encountered during construction of the pipeline and structures consist of coarse alluvium, coarse colluvium, Bright Angel Shale, Tapeats Sandstone, granitic intrusions of the Zoroaster Plutonic Complex, Brahma Schist, and Rama Schist. The sections below discuss the geologic and geotechnical characteristics of these units.

3.2 Brahma and Rama Schist Bedrock

Schist bedrock to be encountered in open-cut pipeline installation is mafic to intermediate metamorphic rock comprised primarily of quartz, biotite, feldspar, amphibolite, and hornblende minerals. Schist bedrock is commonly intruded by granitic veins. It is reasonable to assume that the observed joint sets are pervasive at depth and the rock is more weathered along the outcrop surfaces than at depth.

3.2.1 Index Properties

Schist bedrock will be encountered during construction and generally consists of interbedded Rama and

Brahma Schist units with granitic intrusions. Schist encountered during the investigation is hard, slightly weathered, and slightly to highly fractured. Field measurements on this unit resulted in UCS values ranging from 500 to 14,000 psi and seismic velocity values ranging from 1,690 ft/s to 3,280 ft/s.

3.2.2 Behavior

Figure 1 shows the extents of the schist as observed from the ground surface. This material will exhibit stable conditions in an open excavation and is expected to hold a vertical face under long and short-term conditions. Schist will break along foliation, intrusion, and joint surfaces. Ripability of this rock, based on the geologic conditions and the minimum Caterpillar tractor size (DL8) with published data, is possible at a rate of up to 500 bank cubic yards (BCY) per hour. However, we do not believe this equipment will be feasible in the canyon. Therefore, blasting for rock excavation will mostly likely be necessary.

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3.3 Granite Bedrock

Granite bedrock to be encountered in open-cut pipeline installation and structure foundation construction is igneous rock comprised primarily of quartz, feldspar, and muscovite minerals. Granite intrudes the schist bedrock and is commonly offset by faulting and localized folding. It is reasonable to assume that the observed joint sets are pervasive at depth and the rock is more weathered along the outcrop surfaces than at depth.

3.3.1 Index Properties

Granite bedrock will be encountered during construction and generally consists of granitic intrusions of varying ages collectively referred to as the Zoroaster Plutonic Complex. Granite encountered during the investigation is hard, slightly to moderately weathered, and moderately to highly fractured. Field measurements on the granite resulted in UCS values ranging from 0 to 8,700 psi and a seismic velocity of

4,700 ft/s.

3.3.2 Behavior

Figure 1 shows the extents of granite bedrock as observed from the ground surface. This material will exhibit stable conditions in an open excavation and is expected to hold a vertical face under long and short-term conditions. Granite will break along crystalline structures and joint surfaces. Ripability of this rock, based on the geologic conditions and the minimum Caterpillar tractor size (DL8) with published data, is possible at a rate of up to 500 bank cubic yards (BCY) per hour. However, we do not believe this equipment will be feasible in the canyon. Therefore, blasting for rock excavation will mostly likely be necessary.

3.4 Tapeats Sandstone Bedrock

The Tapeats Sandstone overlies the schist and granite and will be encountered in open-cut pipeline installation and structure foundation construction. The Tapeats Sandstone is comprised primarily of cross-bedded, medium to coarse sand grains. Bedding planes in the sandstone are near horizontal. It is reasonable to assume that the observed joint sets are pervasive at depth and the rock is more weathered along the outcrop surfaces than at depth.

3.4.1 Index Properties

Sandstone bedrock will be encountered during construction and generally consists of bedding planes with spacing between one inch and four feet. Sandstone encountered during the investigation is hard, slightly to moderately weathered, and lightly fractured. Field measurements on the sandstone resulted in UCS values ranging from 1,500 psi to 10,000 psi and a seismic velocity of 2,100 ft/s.

3.4.2 Behavior

Figure 1 shows the extents of sandstone bedrock as observed from the ground surface. This material will exhibit stable conditions in an open excavation and is expected to hold a vertical face under long and short-term conditions. Sandstone will break along bedding and joint surfaces. Ripability of this rock, based on the geologic conditions and the minimum Caterpillar tractor size (DL8) with published data, is possible at a rate of up to 500 bank cubic yards (BCY) per hour. However, we do not believe this equipment will be feasible in the canyon. Therefore, blasting for rock excavation will mostly likely be necessary.

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3.5 Bright Angel Shale Bedrock

Shale, siltstone, and sandstone bedrock of the Bright Angel Shale overlying the Tapeats Sandstone will be encountered in open-cut pipeline installation and structure foundation construction. The Bright Angel

Shale is a sedimentary rock comprised primarily of shale, siltstone, and sandstone. Bedding planes are near horizontal. It is reasonable to assume that the observed joint sets are pervasive at depth and the rock is more weathered along the outcrop surfaces than at depth.

3.5.1 Index Properties

Shale, siltstone and sandstone bedrock will be encountered during construction and generally consists of bedding planes with spacing between 0.25 inches and 12 inches. The Bright Angel Shale encountered during the investigation is hard, slightly to moderately weathered, and lightly fractured. Field measurements on the rock unit resulted in UCS values ranging from 600 psi to 4,900 psi and seismic velocity values ranging from 1,850 ft/s to 3,100 ft/s.

3.5.2 Behavior

Figure 1 shows the extents of the Bright Angel Shale bedrock as observed from the ground surface. This material will exhibit stable conditions in an open excavation and is expected to hold a vertical face under long and short-term conditions. The bedrock unit will break along bedding and joint surfaces. Ripability of this rock, based on the geologic conditions and the minimum Caterpillar tractor size (DL8) with published data, is possible at a rate of up to 1,000 bank cubic yards (BCY) per hour. However, we do not believe this equipment will be feasible in the canyon. Therefore, blasting or alternative trenching methods for rock excavation will mostly likely be necessary.

3.6 Alluvium

Alluvium to be encountered in open-cut pipeline installation and structure foundation construction consists primarily of rounded cobble and boulders with fine sand. Grain size distribution approximations are based on surface observations. Due to intrinsic alluvial depositional conditions, it is reasonable to expect alluvium to be interbedded with variations in gradation occurring over depth. It is also reasonable to assume the grain size distribution observed at the ground surface would dominate and control the overall engineering characteristics of interbedded geologic intervals at depth.

3.6.1 Index Properties

Alluvium will be encountered during construction and generally consist of:

Poorly graded, fine sand (SP);

Rounded gravel, cobbles, and boulders.

The density of alluvium encountered during the field investigation was medium to loose. Apparent density is based on field observations.

3.6.2 Behavior

Figure 1 shows the extents of alluvium as observed from the ground surface. This material will exhibit slow raveling in an open excavation and is not expected to hold a vertical face under long or short-term conditions.

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3.7 Colluvium

Colluvium to be encountered in open-cut pipeline installation and structure foundation construction consists primarily of angular gravel, cobbles, and boulders, with fine to coarse sand. Grain size distribution approximations are based on surface observations. It is reasonable to assume the grain size distribution observed at the ground surface would dominate and control the overall engineering characteristics of the geologic material at depth.

3.7.1 Index Properties

Colluvium will be encountered during construction and generally consist of:

Poorly graded, fine to coarse sand (SP);

Angular gravel, cobbles, and boulders.

The density of colluvium encountered during the field investigation was loose to very loose. Apparent density is based on field observations.

3.7.2 Behavior

Figure 1 shows the extents of colluvium as observed from the ground surface. This material will exhibit slow raveling in an open excavation and is not expected to hold a vertical face under long or short-term conditions.

3.8 Groundwater

Observations of topography and surrounding water sources at proposed construction locations did not reveal the presence of groundwater. Therefore, proposed construction locations should be considered free of groundwater.

4 CONSTRUCTION CONSIDERATIONS

The following sections discuss the methods Lithos anticipates will be used by the Contractor during construction of the pipeline and structure foundations. Discussed considerations are not intended to dictate construction methods, but rather the discussion is intended to provide Lithos’ opinion of various challenges to reasonable construction methods based on our experience and general practice. Within the limitations provided in the Specifications, the Contractor is ultimately responsible for selecting foundation and pipeline excavation methods and foundation and pipeline support systems. Of primary importance is the integrity of the natural environment also including the trails, existing waterline, and other nearby structures. Damage to the existing waterline must be avoided as shown on the Construction Drawings.

The Contractor’s means and methods must be designed around protecting the natural environment and critical infrastructure while still meeting other project requirements such as safety and schedule.

4.1 Pipeline reaches

The pipeline alignment was divided into six reaches for clarity and discussion purposes. The individual reaches are shown on Figure 1. In this report, lengths and grades are based on Google Earth and supplementary documents provided by HDR.

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Reach Length

(ft) Approximate Surface Grade

Minimum Cover (ft)

Carrier Pipe

Delta Reach 1,050 1% 2 8 in. steel

River Reach 6,200 3% to 15% 2 8 in. steel

Talus Reach 4,000 15% to 45% 2 8 in. steel

Cliff Reach 180 80% N/A 8 in. steel

Plateau Reach 4,750 2% to 18% 2 8 in. steel

Bright Angel Reach 2,400 12% 2 8 in. steel

The follow sections description the engineering geologic conditions of each individual reach. Most reaches contain several geologic units. Due to alternating geologic settings along the pipeline alignment, lengths are combined values and may not be continuous.

4.1.1 Delta Reach

The Delta Reach is comprised of colluvium, schist and granite bedrock. The general topography along this reach of the pipeline alignment is relatively flat-lying and located in the established Bright Angel and North

Kaibab Trails adjacent to Bright Angel Creek and the Colorado River. The trail width is approximately four feet and the drop off on either side of the trail is up to ten feet. The Delta Reach is in near proximity to an established helicopter landing pad. Relevant baseline values for this reach are provided in the table below.

Geologic Setting

Length (ft)

% of Reach Length

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Boulder Maximum

Dimension (ft)

Colluvium 400 38% N/A N/A N/A N/A 7

Schist 150 14% 3,000 6,500 64 2,980 N/A

Granite 500 48% 1,300 3,600 24 4,700 N/A

Fracturing in the schist along the Delta Reach was controlled by foliation spaced 1 inch to 4 inches.

Fracturing in the granite was dominated by primary joint sets spaced 12 inches to 18 inches and secondary joint sets spaced 4 to 10 inches. Baseline average and maximum values for UCS for boulders are 4,500 psi and 10,000 psi, respectively. Colluvium along this reach can be defined as 30% fine sand, 40% gravel and cobbles, and 30% boulders ranging from one to seven feet in the maximum dimension.

4.1.2 River Reach

The River Reach is comprised of colluvium, alluvium, schist and granite bedrock. The general topography along this reach of the pipeline alignment is relatively flat-lying except for short sections where the pipe transitions in and out the established Bright Angel Trail. The alignment parallels the Colorado River along the entire River Reach. The trail width is three to four feet and the drop off on either side of the trail is up to 75 feet. The east end of the River Reach is in near proximity to an established helicopter landing pad.

Relevant baseline values for this reach are provided in the table below.

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Geologic Setting

Length (ft)

% of Reach Length

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Boulder Maximum

Dimension (ft)

Colluvium 1,720 28% N/A N/A N/A N/A 7

Alluvium 1,810 29% N/A N/A N/A N/A 7

Schist 2,000 32% 5,200 14,000 88 3,300 N/A

Granite 670 11% 2,900 5,900 88 3,300 N/A

Fracturing in the schist along the River Reach was controlled by foliation planes and primary joint sets spaced 1 inch to 12 inches, secondary joint sets spaced 3 inches to 12 inches, and tertiary joint sets spaced

12 inches to 18 inches. Fracturing in the granite along the River Reach was dominated by primary and secondary joint sets spaced 1 inch to 12 inches. Baseline average and maximum values for UCS for boulders are 4,500 psi and 10,000 psi, respectively. Colluvium along this reach can be defined as 20% fine sand, 50% gravel and cobbles, and 30% boulders ranging from one to seven feet in the maximum dimension. Alluvium along this reach can be defined as 40% fine sand, 30% gravel and cobbles, and 30% boulders ranging from one to seven feet in the maximum dimension.

4.1.3 Talus Reach

The Talus Reach is comprised of colluvium overlying schist and granite bedrock. The general topography along this reach of the pipeline alignment is steep with a grade up to 45%. The alignment parallels the

Colorado River for approximately 1,700 feet and then turns southwest to continue up a talus slope and away from the Colorado River. There is a rudimentary helicopter landing pad built into the talus slope at the point where the pipeline turns southwest. Due to the steep slope, special attention should be paid to this reach regarding fall protection, available staging areas, and material transport. The waterline alignment through the Talus Reach is located out of an established trail. Relevant baseline values for this reach are provided in the table below.

Geologic Setting

Length (ft)

% of Reach Length

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Boulder Maximum

Dimension (ft)

Colluvium 4,000 100% N/A N/A N/A N/A 7

Baseline average and maximum values for UCS for colluvial boulders are 4,500 psi and 10,000 psi, respectively. Colluvium along this reach can be defined as 15% coarse sand, 30% gravel and cobbles, and

55% boulders ranging from one to seven feet in the maximum dimension with one seven-foot boulder encountered every 20 feet.

4.1.4 Cliff Reach

The Cliff Reach is comprised of the Tapeats Sandstone bedrock. The general topography along this reach of the pipeline alignment is near-vertical with a grade up to 80%. The existing pipeline through this reach is anchored to a sandstone cliff face with rock anchors. Due to the steep slope, special attention should be paid to this reach regarding fall protection during installation and freeze protection to the exposed

HDR Engineering, Inc. Replace Trans-Canyon Water Distribution Pipeline Page 9 of 15 pipeline. The waterline alignment through the Cliff Reach is located out of an established trail. Relevant baseline values for this reach are provided in the table below.

Geologic Setting

Length (ft)

% of Reach Length

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Sandstone 180 100% 7,300 8,900 91 2,100

Fracturing in the sandstone along the Cliff Reach was controlled by bedding planes spaced 2 inches to 48 inches.

4.1.5 Plateau Reach

The Plateau Reach is comprised of the shale, siltstone, and sandstone of the Bright Angel Shale and the

Tapeats Sandstone. The general topography along this reach of the pipeline alignment is relatively flat-lying except where the alignment turns to the east and travels along a drainage channel with a grade up to 18%. At the base of the drainage channel the alignment crosses Garden Creek and intersects with the

Bright Angel Trail. In general, the trail width is three to five feet and either side of the existing alignment is relatively flat and vegetated. The nearest known helicopter access point is located at Indian Garden.

The waterline alignment through the Plateau Reach is located in and out of the established Plateau Point

Trail. Relevant baseline values for this reach are provided in the table below.

Geologic Setting

Length (ft)

% of Reach Length

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Sandstone 650 14% 6,000 10,000 91 2,100

Siltstone/shale 4,100 88% 2,700 4,900 0 3,100

Fracturing in the sandstone along the Plateau Reach was controlled by bedding planes spaced 1 inch to 4 inches, primary joint sets spaced 4 inches to 10 inches, and secondary joint sets spaced 10 inches to 18 inches. Fracturing in the shale and siltstone along the Plateau Reach was dominated by bedding planes spaces 0.5 inches to 3 inches.

4.1.6 Bright Angel Reach

The Bright Angel Reach is comprised of the shale, siltstone, and sandstone of the Bright Angel Shale and the Tapeats Sandstone. The general topography along this reach of the pipeline alignment is relatively flat-lying. The trail width is three to four feet with bedrock outcrop to the east and a drop off to the west up to 10 feet. The alignment is to the east of and parallels Garden Creek. The nearest known helicopter access point is located at Indian Garden. The waterline alignment through the Bright Angel Reach is located in the established Bright Angel Trail. Relevant baseline values for this reach are provided in the table below.

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Length (ft)

% of Reach Length

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Sandstone 1,075 45% 6,000 10,000 91 2,100

Siltstone/shale 1,325 55% 2,700 4,900 0 3,100

Fracturing in the sandstone along the Bright Angel Reach was controlled by bedding planes spaced 1 inch to 4 inches, primary joint sets spaced 4 inches to 10 inches, and secondary joint sets spaced 10 inches to

18 inches. Fracturing in the shale and siltstone along the Bright Angel Reach was dominated by bedding planes spaces 0.5 inches to 3 inches.

4.2 Proposed Structures

4.2.1 Phantom Ranch Treated Water Storage Tank

The general topography in this area is moderately steep with a grade up to 30%. The proposed tank is located off the established North Kaibab Trail. Special attention should be paid to the risk of rockfall from above the tank, slope stability, flood erosion, large boulder removal, and bedrock excavation at this location. The proposed tank location is approximately one-half mile from an established helicopter landing pad.

The geologic conditions at the proposed Phantom Ranch Treated Water Storage Tank location are comprised of colluvium and granite bedrock. The proposed tank location is on the eastern edge of the

Phantom Ranch area and positioned on a colluvial slope adjacent to a drainage channel. The thickness of colluvium overlying granite bedrock is up to 15 feet. Relevant baseline values for this location are provided in the table below.

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Boulder Maximum

Dimension (ft)

Colluvium N/A N/A N/A N/A 8

Granite 1,300 3,600 24 4,700 N/A

Fracturing in the granite at this location was controlled by primary joint sets spaced 12 inches to 18 inches and secondary joint sets spaced 4 inches to 10 inches. Baseline average and maximum values for UCS for boulders are 4,500 psi and 10,000 psi, respectively. Colluvium in this area can be defined as 20% sand, 60% gravel and cobbles, and 20% boulders from one to eight feet in the maximum dimension. Up to ten boulders between five and eight feet in the maximum dimension should be expected in excavations at this location.

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4.2.2 Phantom Ranch Delta Structures

Three structures are proposed at on the Phantom Ranch Delta: a raw water storage tank, a booster pump building, and a water treatment plant. The general topography in this area is relatively flat-lying. The geologic conditions for structures at the Phantom Ranch Delta are comprised of alluvium. The alluvial deposits likely originate from the Colorado River and the delta of Bright Angel Creek. The thickness of alluvium overlying bedrock in this area is unknown but should be assumed to be deeper than the proposed construction.

4.2.2.1 Raw Water Storage Tank

The proposed tank is located off the established Bright Angel Trail. Special attention should be paid to large boulder removal at this location. The proposed tank location is approximately 400 feet from an established helicopter landing pad. The proposed tank location is to the north of the Colorado River and east of the established North Kaibab Trail. Relevant baseline values for this location are provided in the table below.

Geologic Setting

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Boulder Maximum

Alluvium N/A N/A N/A N/A 8

Baseline average and maximum values for UCS for boulders are 4,500 psi and 10,000 psi, respectively.

Alluvium in this area can be defined as 40% sand, 15% gravel and cobbles, and 45% boulders from one to eight feet in the maximum dimension. Up to 25 boulders between four and eight feet in the maximum dimension should be expected within the foundation footprint at this location.

4.2.2.2 Booster Pump Building

The proposed building is located off the established Bright Angel Trail. The proposed tank location is approximately 400 feet from an established helicopter landing pad. The proposed building location is to the north of the Colorado River and east of the established North Kaibab Trail. Relevant baseline values for this location are provided in the table below.

Geologic Setting

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Boulder Maximum

Alluvium in this area can be defined as 40% sand, 15% gravel and cobbles, and 45% boulders from one to eight feet in the maximum dimension. Up to 25 boulders between four and eight feet in the maximum dimension should be expected within the foundation footprint at this location.

HDR Engineering, Inc. Replace Trans-Canyon Water Distribution Pipeline Page 12 of 15

4.2.2.3 Water Treatment Plant

The proposed tank is located off the established Bright Angel Trail. The proposed tank location is approximately 400 feet from an established helicopter landing pad. The proposed building location is to the north of the Colorado River and east of the established North Kaibab Trail. Relevant baseline values for this location are provided in the table below.

Geologic Setting

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Boulder Maximum

Alluvium in this area can be defined as 40% sand, 15% gravel and cobbles, and 45% boulders from one to eight feet in the maximum dimension. Up to 25 boulders between four and eight feet in the maximum dimension should be expected within the foundation footprint at this location.

4.2.3 Indian Garden Structures

Two structures are proposed in the area of Indian Garden: a water treatment plant and a water storage plant. The general topography in this area is moderately flat-lying. The geologic conditions at the proposed

Indian Garden Water Treatment Plant location are comprised of colluvium. The proposed building location is to the west of Garden Creek and the established Bright Angel Trail. The thickness of colluvium in this area is unknown but should be assumed to be deeper than the proposed construction.

4.2.3.1 Indian Garden Water Treatment Plant

The proposed building is located approximately 200 feet to the west of the Indian Garden Ranger Station.

The proposed building location is approximately 300 feet from an established helicopter landing pad. The geologic conditions for the structures at Indian Garden are comprised of colluvium. The proposed building location is to the west of Garden Creek and the established Bright Angel Trail. The thickness of colluvium in this area is unknown but should be assumed to be deeper than the proposed construction. Relevant baseline values for this location are provided in the table below.

Geologic Setting

Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Boulder Maximum

Colluvium N/A N/A N/A N/A 7

Colluvium in this area can be defined as 40% sand, 40% gravel and cobbles, and 20% boulders from one to seven feet in the maximum dimension. Up to 15 boulders between three and seven feet in the maximum dimension should be expected in excavations at this location.

HDR Engineering, Inc. Replace Trans-Canyon Water Distribution Pipeline Page 13 of 15

4.2.3.2 Indian Garden Water Storage Tank

The general topography of the ridge is moderately steep with a grade sloping down to the east up to 30% and a grade sloping down to the north and south up to 20%. The proposed tank is located approximately

350 feet to the northwest of the Indian Garden Ranger Station. The proposed tank location is approximately 600 feet from an established helicopter landing pad. The geologic conditions at the proposed Indian Garden Water Storage Tank location are comprised of colluvium, and interbedded shale, siltstone, and sandstone bedrock. The proposed tank location is to the west of Garden Creek and the established Bright Angel Trail. The proposed tank location is positioned on a colluvial ridge. The thickness of colluvium overlying bedrock is up to ten feet. Relevant baseline values for this location are provided in the table below.

Geologic Setting Avg.

UCS

(psi)

Max

UCS

(psi)

RQD

Seismic Velocity

(ft/s)

Boulder Maximum Dimension

(ft)

Colluvium N/A N/A N/A N/A 6

Shale/Siltstone/Sandstone 2,700 4,900 0 3,100 N/A

Colluvium in this area can be defined as 30% sand, 50% gravel and cobbles, and 20% boulders from one to six feet in the maximum dimension. Up to ten boulders between four and six feet in the maximum dimension should be expected in excavations at this location.

5 LIMITATIONS

This study was conducted in accordance with generally accepted geotechnical engineering and engineering geologic practices and principles; no warranty, express or implied is made. The geologic conditions described in this report were based on data obtained from widely spaced field data collection, information provided by the client, engineering judgement, and our experience with similar geologic conditions and projects.

This report has been prepared exclusively for our client for design, bidding, and construction purposes for the subject project. Lithos is not responsible for technical interpretations by others of the data presented in this report or use of this report by others for the subject project or other projects.

The baseline values presented in this report are only intended for the proposed design and construction as understood by Lithos at the time of issuing this report. If the proposed design and construction changes, Lithos should be notified immediately and given the opportunity to review the proposed changes and if necessary, modify our baseline values presented herein.

An environmental assessment was not included in Lithos’ scope of work for this project. Any statements regarding the absence or presence of hazardous and/or toxic substances presented herein are only intended for informational purposes. If the client is concerned about the environmental conditions at the

HDR Engineering, Inc. Replace Trans-Canyon Water Distribution Pipeline Page 14 of 15 site, Lithos recommends the client and/or owner retain a qualified environmental firm to conduct an environmental site assessment.

6 REFERENCES

References listed herein are included as information only. The contractor may not rely upon the provided references as baseline statements in any phase of the project.

Billingsley, George H., 2000, Geologic Map of the Grand Canyon 30' by 60' Quadrangle, Coconino and Mohave Counties, Northwestern Arizona: U.S. Geological Survey Geologic Investigation Series I-2688.

Essex, Randall J., 2007, Geotechnical Baseline Reports for Construction, Suggested Guidelines, ASCE Standards

Historic American Engineering Record; Trans-Canyon Waterline; HAER No. AZ-95; U.S.

Government, Department of the Interior, National Park Service.

Weaver, John M., 1975, Geological factors significant in the assessment of rippability. Civ Eng S

Afr. 17. 313-316.

FIGURES

RAMA SCHIST (Xr)

BRAHMA SCHIST (Xbr)

GRANITE (Xgr)

TAPEATS SANDSTONE (Ct)

BRIGHT ANGEL SHALE (Cba)

ALLUVIUM (Qa)

COLLUVIUM (Ql)

YOUNGER SEDIMENTARY

UNITS

LEGEND

PROPOSED STRUCTURES

DELTA REACH

TALUS REACH

PLATEAU REACH

BRIGHT ANGEL REACHRIVER REACH

CLIFF REACH

LOCAL FAULTS

BRIDGES

PHANTOM

RANCH

INDIAN

GARDEN

P

I

P

E

C

R

E

E

K

C

O

L

O

R

A

D

O

I

V

E

R

B R

I G

H T

A

N G

L

E

E K

G

A

R

D

N

E

E

K

NOTE: GEOLOGIC MAP IS MODIFIED FROM

BILLINGSLEY (2000) GEOLOGIC MAP OF THE

GRAND CANYON QUADRANGLE.

DELINEATIONS OF COLLUVIUM AND

ALLUVIUM HAVE BEEN UPDATED AND/OR

ADDED BASED ON FIELD OBSERVATIONS

PHANTOM RANCH TREATED

WATER STORAGE TANK

PHANTOM RANCH DELTA RAW

WATER STORAGE TANK

PHANTOM RANCH DELTA WATER

TREATMENT FACILITY BUILDING

PHANTOM RANCH DELTA

BOOSTER PUMP STATION

INDIAN GARDEN

WATER STORAGE TANK

INDIAN GARDEN WATER

TREATMENT FACILITY BUILDING

PHANTOM

RANCH

DELTA

Xgr

Xgr

X g r

Xgr

Xgr

Xgr

Xgr

Xgr

Xr

Xbr

Qa

Ql

Qa

Xbr

Xbr

Xbr

Ct

Cba

Ct

Cba

Cba

Ct

Ql

Ct

Xbr

Xbr

Xbr

Xbr

Ql

Ql

Ql

970.373.3195

PROJECT

FORT COLLINS, COLORADO 80526

2625 REDWING ROAD, SUITE 160

TITLE

DRAWING

TITLE

OWNER CLIENT

PROJECT NO.:

LOCATION:

DATE:

DRAWN BY:

DESIGNED BY:

CHECKED BY:

FIGURE NUMBER

NS

AM

AM

May 17, 2018

GRAND CANYON, AZ

16066-1 FIG.1

PIPELINE ALIGNMENT

WITH GEOLOGIC MAP

PROJECT TO REPLACE TRANS-CANYON

WATER DISTRIBUTION PIPELINE

00 1250' 2500'