B08_Attach_09_GRCA_318719_GISR_20260331.pdf

Geologic Interpretive Summary Report

GRCA 318719: Rehabilitate North Rim Utility Infrastructure

Waterline Construction from the North Rim Ballfield Site to

Roaring Springs Pump House

Grand Canyon North Rim, Arizona

Submitted to:

HDR Engineering, Inc.

419 Canyon Avenue Fort Collins, CO 80521

Submitted by:

GEI Consultants, Inc.

350 Indiana Street, Suite 750 Golden, CO 80401 303.625.9502

March 31, 2026 Project No. 2305987

Nate C. Soule, P.E., P.G.

Principal Engineer

Matt P. Olson, P.E.

Project Manager www.geiconsultants.com GEI Consultants, Inc.

350 Indiana Street, Suite 750

Golden, CO 80401

303.625.9502

March 31, 2026

Project No. 2305987

VIA EMAIL: matt.gough@hdrinc.com

Matt Gough, P.E.

HDR Engineering, Inc.

419 Canyon Avenue

Fort Collins, CO 80521

Re: Geologic Interpretive Summary Report

Waterline Construction from the North Rim Ballfield Site to Roaring Springs Pump House

GRCA 318719: Rehabilitate North Rim Utility Infrastructure

Grand Canyon North Rim, Arizona

Mr. Gough:

Submitted herewith is the Geologic Interpretive Summary Report for the Waterline Construction from the North Rim Ballfield Site to the Roaring Springs Pump House, a component of the GRCA 318719

Rehabilitate North Rim Utility Infrastructure project. This report was prepared in general accordance with the Agreement between GEI Consultants, Inc. and HDR Engineering, Inc. The Geologic Interpretive

Summary Report includes discussions of the geological conditions, geotechnical data, and interpretations for the subsurface conditions that are anticipated to be encountered during the proposed construction, 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, GEI Consultants, Inc.

Rob D. Johanson, P.E.

Project Engineer

Matt. P. Olson, P.E.

Project Manager

Nate C. Soule, P.E., P.G.

Principal Engineer http://www.geiconsultants.com/

Grand Canyon North Rim, Arizona

GEI Consultants, Inc. i

Table of Contents

Report Organization iv

1. Introduction 1

1.1. Project Description 1

1.2. Description and Purpose of the GISR 1

2. Project Background 3

2.1. Project Overview 3

2.1.1. Existing System 3

2.1.2. Proposed Improvements 3

2.2. Subsurface Investigations 4

2.2.1. North Rim Investigation 4

2.2.2. Inner Canyon Investigation 5

2.2.3. Geophysical Investigation 5

2.3. Literature Review 6

2.4. Historic Projects 6

2.4.1. Transcanyon Water Transmission System Improvements Project 6

2.4.2. Offset Wells 8

3. Geology 10

3.1. Regional Geology 10

3.2. Site Geology 11

3.2.1. Kaibab Formation 11

3.2.2. Toroweap Formation 12

3.2.3. Coconino Sandstone 13

3.2.4. Hermit Formation 14

3.2.5. Supai Group 14

3.2.6. Redwall Limestone 16

3.2.7. Temple Butte Formation 17

3.2.8. Tonto Group 18

4. Anticipated Geologic Conditions and Ground Behavior 20

4.1. General 20

4.2. Geologic Formation Characteristics 20

4.2.1. Kaibab Formation 20

4.2.2. Toroweap Formation 21

4.2.3. Coconino Sandstone 22

4.2.4. Hermit Formation 22

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4.2.5. Supai Group 23

4.2.6. Redwall Limestone 24

4.2.7. Temple Butte Formation 26

4.2.8. Tonto Group 26

4.3. Rock Properties 27

4.4. Anticipated Hydrogeologic Conditions 28

4.4.1. Groundwater 28

4.4.2. Hydraulic Conductivity and Cement Take 28

5. Construction Considerations 30

5.1. General 30

5.2. Anticipated Drilling Conditions 30

5.3. Casing Pipe Design 31

5.4. Drill Bit Considerations 32

5.5. Cementing 32

6. Limitations 34

7. References 35

List of Tables Table 1-1. Project Roles 1

Table 2-1. South Rim Bore Problems and Solutions 8

Table 4-1. Estimated Rock Type Percent by Volume of Fossil Mountain Member 21

Table 4-2. Estimated Rock Type Percent by Volume of Woods Ranch Member 21

Table 4-3. Estimated Rock Type Percent by Volume of Brady Canyon Member 21

Table 4-4. Estimated Rock Type Percent by Volume of Seligman Member 22

Table 4-5. Estimated Rock Type Percent by Volume of Coconino Sandstone 22

Table 4-6. Estimated Rock Type Percent by Volume of Hermit Formation 22

Table 4-7. Estimated Rock Type Percent by Volume of Esplanade Sandstone 23

Table 4-8. Estimated Rock Type Percent by Volume of Wescogame Formation 23

Table 4-9. Estimated Rock Type Percent by Volume of Manakacha Formation 24

Table 4-10. Estimated Rock Type Percent by Volume of Watahomigi Formation 24

Table 4-11. Estimated Rock Type Percent by Volume of Horseshoe Mesa Member 25

Table 4-12. Estimated Rock Type Percent by Volume of Mooney Falls Member 25

Table 4-13. Estimated Rock Type Percent by Volume of Thunder Springs Member 25

Table 4-14. Estimated Rock Type Percent by Volume of Whitmore Wash Member 26

Table 4-15. Estimated Rock Type Percent by Volume of Temple Butte Formation 26

Table 4-16. Estimated Rock Type Percent by Volume of Muav Formation 26

Table 4-17. Estimated Rock Type Percent by Volume of Bright Angel Formation 27

Table 4-18. Estimated Strength and Abrasivity Parameters by Rock Type 27

Table 4-19. Estimated Hydraulic Properties 29

Table 5-1. Anticipated Drilling Conditions 31

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Table 5-2. Estimated Cement Take by Formation 32

List of Figures Figure 2-1. Site Vicinity and Layout 9

Figure 5-1. Interpreted Geologic Profile 33

Appendices Appendix A Tunnelman’s Ground Classification Chart

RCM/NCS/AH

B:\Working\HDR\2305987 21186 GRCA North Rim Water Supply LR\Design\Reports\GISR\GRCA 318719 GISR FINAL.docx

GEI Consultants, Inc. iv

Report Organization

The Geologic Interpretive Summary Report (GISR) is organized as follows:

Section 1: Introduction

Includes the project description and discusses the purpose and intended usage of the GISR.

Section 2: Project Background

Provides an overview of the project in relation to the proposed construction, a description of the geologic and subsurface investigations undertaken to evaluate ground conditions at the site, and a summary of relevant historic projects.

Section 3: Geology

Provides an in-depth description of the regional and site-specific geology in the project site vicinity.

Section 4: Anticipated Geologic Conditions and Ground Behavior

Provides anticipated formation characteristics and material properties of each rock type. Additional properties are provided for hydrogeological conditions.

Section 5: Construction Considerations

Briefly discusses relevant construction considerations for anticipated drilling conditions, casing pipe, drill bits, and cementing.

Sections 6 and 7: Limitations and References

Describes limitations of the GISR and provides references for citations within the report.

GEI Consultants, Inc. 1

1. Introduction

1.1. Project Description

The National Park Service (NPS) is currently planning infrastructure improvements to the existing water and wastewater systems for its North Rim and Inner Canyon facilities located in Grand Canyon National

Park, Arizona as part of the GRCA 318719: Rehabilitate North Rim Utility Infrastructure Project (Project).

The Project includes the construction of a new water treatment plant on the North Rim, upgrades to the existing wastewater treatment plant, open cut pipeline construction, and the replacement of the existing

North Rim Waterline between North Rim and the Roaring Springs Pump House (RSPH) using directional drilling methods. Table 1-1 below lists organizations and their respective roles for the Project.

Table 1-1. Project Roles

Organization Role

National Parks Service (NPS) Owner

HDR Engineering, Inc. (HDR) Prime Engineer

GEI Consultants, Inc. (GEI) Geotechnical and Trenchless Design Engineer

Geostock Sandia (GKS) Directional Drilling Consulting Engineer

Collier Geophysics (Collier) Geophysical Investigations

This report summarizes ground conditions that are anticipated to be encountered during directional drilling required to construct the North Rim Waterline from the North Rim to the RSPH. For the purposes of this report, directional drilling refers to the drilling practice commonly used in the oil and gas industry in which a hole is drilled through soil and rock with a vertical entry with the ability to steer the drill string using various bottom hole assembly configurations. A summary of the report organization is provided at the beginning of this report. Section 1.2 provides the description and purpose of this Geologic

Interpretive Summary Report (GISR).

1.2. Description and Purpose of the GISR

The main purpose of this GISR is to summarize interpreted ground conditions and behavior that are anticipated to be encountered during directional drilling between the entry point on the North Rim and the exit location at the RSPH. Geological and subsurface conditions observed through site visits, geotechnical and geophysical field explorations, laboratory analyses of collected samples, and literature review are summarized herein and presented for informational purposes only.

The interpretations presented in this GISR for the anticipated subsurface conditions may be used for informational purposes and to help the Contractor evaluate allowed means and methods. This GISR also summarizes geological, geotechnical, and construction considerations that form the basis of the directional drilling portion of the Project design and Contract Documents. The GISR is prepared in tandem with the applicable Contract Documents.

The interpreted subsurface conditions presented in this GISR reflect the design team’s judgment of anticipated subsurface conditions and ground behavior based on assumed construction means and

GEI Consultants, Inc. 2 methods expected to be employed in the work. Interpretations were established by considering available geological and geotechnical data, and previous construction experience in similar subsurface conditions. Development of the Project design required interpretation, extrapolation, and interpolation between data obtained for the Project including aerial imagery, geophysical profiles, geologic mapping, geotechnical test boreholes (i.e., borings), and laboratory tests. This report has been prepared exclusively for our client for design, bidding, and construction planning for the subject project. GEI 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 interpreted geology and estimated values presented in this report are only intended as supplemental information for the proposed design and construction as understood by GEI at the time of issuing this report.

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2. Project Background

2.1. Project Overview

2.1.1. Existing System

The North Rim waterline was originally constructed in 1928 to supply potable water to the Grand Canyon

Lodge on the North Rim. The existing waterline conveys water from the Roaring Springs Cave to the

North Rim by means of a pump house located below Roaring Springs and several sections of surface mounted pipelines. Water exiting the Roaring Springs cave is conveyed through a 12-inch steel pipe from the cave entrance to an existing diversion/spill box followed by approximately 700-feet of aluminum pipe where it is fed by gravity to the pump house. Raw water from the Roaring Springs Cave is treated at the pump house and pumped through an approximately 12,500-foot long 3.5-inch steel pipeline to the

North Rim water storage tanks. Treated water stored in the North Rim water tanks is distributed throughout the facilities located on the North Rim.

The existing, surface mounted pipeline is susceptible to environmental hazards including rockfall, treefall, and freeze/thaw cycles. These hazards in combination with the age of the pipeline result in frequent damage to the pipeline. Repairs to the pipeline are dangerous, challenging, and costly due to the remote location and steep, rough terrain along the pipeline. Additionally, the susceptibility to freezing temperatures requires the park service to drain the pipeline in the winter months during which the park must operate exclusively on water stored within the North Rim water tanks.

2.1.2. Proposed Improvements

Proposed improvements include upgrades to the existing RSPH and replacement of the existing North

Rim waterline between the RSPH and North Rim Water Tanks with 4.5-inch raw and finished waterlines, The raw waterline will bring water from the RSPH to the North Rim for treatment, while the finished waterline will return potable water to the RSPH and other Inner Canyon facilities.

The waterlines are planned to be constructed in three segments including the following as shown in

Figure 2-1:

1. Segment 1 - Roaring Springs Cave to the RSPH

2. Segment 2 - RSPH to the North Rim Ballfield Site

3. Segment 3 - North Rim Ballfield Site to the North Rim Water Tank

This GISR addresses only the second segment of the alignment between the RSPH and the North Rim

Ballfield Site as described above. This segment will include the 4.5-inch raw waterline and the 4.5-inch finished waterline, installed using directional drilling methods in separate cased bores which will parallel each other and enter/exit the ground near each other. Therefore, the anticipated geologic conditions with depth at each bore are assumed to effectively be the same. The bores will each include identical telescoped casing, excluding the final casing, which differs slightly between the two bores. Telescoped casings include an 80-foot long 20-inch diameter conductor casing, 1,350-foot long 13 3/8-inch diameter

GEI Consultants, Inc. 4 surface casing, 8,800-foot long 9 5/8 -inch diameter intermediate casing, and a 9,293 foot long 7-inch diameter final casing for bore B and a 9,304 foot long 7-inch diameter final casing for bore A. The bores will have vertical lengths or true vertical depths (TVD) of approximately 3,314 feet for bore B and 3,319 feet for bore A, horizontal lengths or displacements of approximately 7,200 feet for both bores, total measured depths along the bore path (MD) of approximately 9,293 feet for bore B and 9,304 feet for bore A, and will both exit the side of the canyon at a near horizontal angle.

Directional drilling was determined to be the preferred construction method during the cost and scope validation phase due to the success of a previous and similar bore conducted at the South Rim of the

Grand Canyon, reduced construction costs, reduced hazards to construction workers, and reduced environmental impact in comparison to other alternatives. Horizontal Directional Drilling (HDD), often used in municipal or near surface pipeline construction, is not feasible due to the length of the bore, major vertical relief of the canyon walls, and limited equipment staging and access to the lower elevation

Inner Canyon side of the alignment.

2.2. Subsurface Investigations

2.2.1. North Rim Investigation

GEI performed a geotechnical subsurface investigation at the North Rim for the proposed water treatment plant, improvements to the existing wastewater treatment plant, and raw water pipeline alignment between October 2022 and November 2023. The first phase of investigation was completed in

October 2022 and included percolation testing and a test pit investigation at the existing wastewater treatment plant. The second phase of investigation was conducted in November 2022 and consisted of

17 geotechnical borings drilled at the existing wastewater treatment plant, proposed water treatment plant, proposed raw water pipeline alignment between the North Rim Water Tanks and North Rim

Ballfield Site, and proposed bore entry locations. The third phase of investigation was completed in

November 2023 and consisted of 15 additional geotechnical borings at the existing wastewater treatment plant, proposed water treatment plant, and proposed raw water pipeline between the North

Rim Water Tanks and North Rim Ballfield Site. During the second and third phases of investigation, GEI collected split spoon and Modified California samples of the onsite residual soils and HQ core samples of the Kaibab Formation bedrock. A geotechnical laboratory testing program was performed on representative samples of the soil and bedrock and the results assisted in classification and assessment of applicable engineering properties for encountered subsurface materials.

Details of the procedures used for conducting the field work and laboratory testing are summarized in the North Rim Geotechnical Investigation Report (GIR) (GEI, 2025). Though the primary purpose of the

North Rim investigation was to characterize the subsurface conditions for the proposed North Rim water and wastewater treatment facility improvements, core samples obtained during the investigation were used for determination of Kaibab Formation properties included herein. Geotechnical data collected during the North Rim investigation relevant to directional drilling are summarized within this GISR.

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2.2.2. Inner Canyon Investigation

GEI and GKS performed a geological and geotechnical field investigation for the directional drilling design and proposed Inner Canyon infrastructure improvements in November 2023. The investigation consisted of visual rock and soil classification along the North Kaibab Trail, hand excavation of test pits, in situ rock strength tests, and visual observation of the existing Inner Canyon infrastructure. During the investigation along the North Kaibab Trail, GEI and GKS collected rock samples, performed Schmidt

Hammer rebound testing, and noted geologic formational contact elevations as observed hiking along the North Kaibab Trail. Geotechnical laboratory testing and a thin section analysis were performed by

Metarock Laboratories on rock samples collected during the Inner Canyon investigation. The laboratory testing program was developed by GKS with input from GEI.

Details of the procedures used for conducting the field work and laboratory testing are summarized in the Inner Canyon GIR (GEI, 2025) and the North Rim Bore Drilling Plan (GKS, 2026). The Inner Canyon GIR focuses on the proposed improvements to the Inner Canyon facilities while the North Rim Drilling Plan provides an indicative drilling plan for directional drilling based on the results of the field investigation.

Geotechnical data collected as part of the Inner Canyon investigation relevant to directional drilling are summarized within this GISR. All bedrock testing was performed on samples collected from the surface and were therefore subject to weathering. Weathering of surface rocks typically results in lower rock strength. As such, rock strength was conservatively estimated based on literature values for each lithology, with bedrock testing used for approximative confirmation of selected values.

2.2.3. Geophysical Investigation

Collier was retained by GEI to scope and design a multi-phase geophysical investigation to help characterize the subsurface geology for the proposed water treatment plant, bore entry locations, and bore exit locations, and to inform the design and completion of the water transmission bores. The geophysical survey was completed in two phases which included the “shallow phase” Electrical

Resistivity Tomography (ERT) survey for imaging the upper 100-200 feet below ground surface and the

“deep phase” Seismic Reflection survey for imaging depths ranging from 200 feet to over 3,500 feet below ground surface.

Descriptions of the procedures and results for the geophysical investigation are presented in the North

Rim Geophysical Studies Summary Report and Appendices (GEI, Collier, GKS 2025). Relevant findings of the geophysical investigation are accounted for in the geologic and hydrogeologic interpretations summarized in Section 4. The ERT methods used in the geophysical investigation are limited to depths of approximately 100-feet to 200-feet and are only indicative of relatively near surface formations, while 3D seismic reflection methods were employed to image depths to 3,500 feet below ground surface. The purpose of the additional geophysical investigations was to confirm the presence and approximate location of contacts between geologic formations, identify the presence of groundwater and preferential flow pathways, and characterize potential karst features, fractures, and anomalous rock zones at greater depths along the bore path.

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2.3. Literature Review

In addition to the subsurface investigation, GEI performed a review of available literature including available Geologic Maps and LiDAR data from the United States Geological Survey (USGS) and other publications pertaining to geological and hydrogeological conditions at the Grand Canyon. Specific documents reviewed for relevant data include:

⚫ Aerial imagery through Google Earth. Images dating from the 1980s through present were reviewed and showed little evidence of recent surficial geologic activity or observable disturbance of exposed geologic units near the North Rim bore site since the earliest available imagery.

⚫ Available literature from the South Rim bore including feasibility study from McLaughlin Water

Engineers (1984), hydrogeologic study from Hargis and Montgomery, Inc. (1984), and summary article from Lattimore et al. (1987). Relevant information from the South Rim bore is summarized in Section 2.4.1.

⚫ Available USGS Geologic Maps covering the bore path area. Maps were used to identify the bedrock formations and structural features which aided in characterizing the rock mass and identifying geologic contacts.

⚫ Available USGS LiDAR imagery of the Grand Canyon. LiDAR imagery with resolution less than one meter was used to identify surface weathering patterns that are indicative of changes in lithology for the determination of geologic contact elevations.

⚫ Available literature pertaining to rock strength and hydraulic characteristics by rock type including Atwell and Farmer (1976) and Freeze and Cherry (1979).

⚫ Geophysical CSAMT survey by Zonge International (2015) and hydrogeologic study by Yeh and

Associates (2015).

⚫ The geologic interpretations presented in this report are derived from USGS geologic unit descriptions, literature from published books and academic papers, as well as unpublished literature from the South Rim Bore.

Relevant observations from the literature review are noted in the GISR text where findings were applicable, and geologic interpretations were developed accordingly.

2.4. Historic Projects

2.4.1. Transcanyon Water Transmission System Improvements Project

Located approximately ten miles south of the North Rim bore site at the South Rim of the Grand Canyon, the Transcanyon Water Transmission System Improvements project is the only other known project to have included the installation of a utility pipeline by means of directional drilling. As such, GEI has relied on data, observations, direct involvement from participants of the project, and design elements from this project in developing this GISR.

GEI Consultants, Inc. 7

The Transcanyon Water Transmission System Improvements project was originally conceived in 1983 following an NPS study indicating that the demand for water at the South Rim was rapidly outpacing the capacity of the existing South Rim water supply system. Despite the relatively young age of the existing system, the NPS proposed to add a second transmission pipeline from Havasupai Gardens (then called

Indian Gardens) to the South Rim to increase water supply. A 1984 feasibility study was completed to assess the feasibility of directional drilling methods to install the new pipeline (McLaughlin Water

Engineers, 1984). The report concluded that directional drilling was preferable to alternative construction methods due to lower cost, reduced environmental impact, and fewer hazards to construction workers. The feasibility report noted that risks associated with directional drilling could have serious impacts on the project, but that those same risks are associated with alternative construction methods. With the directional drilling alternative these risks were considered to have a lower probability of occurrence and could be mitigated with careful drilling management and operation.

Drilling operations to construct the waterline were summarized in an SPE/IADC paper written following completion of the South Rim bore (Lattimore et al. 1987). Directional drilling was completed in 1986 and required 49 days to drill from spud (entry) to the total depth of 5,075 feet. Drilling mud was used to drill the conductor hole to 80 feet and the surface hole to 250 feet. No circulation loss of the drilling mud was encountered while drilling the conductor hole and the surface hole to the 250-feet depth. Due to the proximity to the cliff face and the risk of surface contamination, drilling mud was not considered a viable circulation medium for the remainder of the bore. Rather, drilling was completed using air and mist to circulate cuttings to the surface. However, circulation was lost with the mist and only intermittently returned while drilling the rest of the South Rim bore. Much of the circulation losses were attributed to regional northeast- and northwest-trending fracture systems and solution cavities in the limestone formations. During drilling, directional measurements were completed using magnetic single-shot instruments and confirmed with several comparison gyro runs. The bore was completed using three runs of casing pipe telescopically installed to progressively greater bore depths. Installed casing pipe included a 66-foot section of 26-inch conductor casing, a 245-foot section of 20-inch surface casing, and a 10 3/4-inch casing run to exit the canyon wall. The 8 5/8-inch steel waterline was run through the final casing before releasing the hole to the NPS for connection to the Havasupai Gardens pump station.

Geology encountered during directional drilling consisted of a Paleozoic sedimentary sequence from

Permian to Cambrian age. Geologic formations from oldest to youngest included the Muav Formation, Temple Butte Formation, Redwall Limestone, Supai Group, Hermit Formation, Coconino Sandstone, Toroweap Formation, and Kaibab Formation. No major faults or other structural features were encountered during drilling and all formation top elevations as projected from outcrops at the South Rim were consistent with a dip of approximately one to two degrees to the southwest as documented in

USGS geologic maps. Several of the limestone units exhibited karst features such as dissolution cavities and voids, particularly in the Kaibab, Toroweap, and Redwall Limestone Formations.

Several issues were encountered during the drilling process. Table 2-1 describes the major problems encountered during drilling and the solutions employed in the field.

GEI Consultants, Inc. 8

Table 2-1. South Rim Bore Problems and Solutions

Problem Solution

Severe drill string damage/loss of Bottom Hole Assembly (BHA) components

Fishing and/or cementing section of hole and sidetracking

Loss of air and mist circulation due to fractures and dissolution cavities

Continue drilling, monitor torque and drag to infer degree of hole cleaning

Anticipated difficulty setting casing due to severe doglegs resulting from sidetracks and drilling through dissolution cavities

Preemptive lubrication of hole using polymer, foam, and air was used but unknown whether this was necessary

Hole cleaning issues causing the hole to become sticky near the end

The motor run was aborted and the last directional correction was not completed causing the directional bore to exit the canyon wall in a slightly different location

Cement losses to formation due to fractures and dissolution cavities during cementing

Field testing developed to ensure fluids were able to travel through annular space between the casing and bore wall from top to bottom

2.4.2. Offset Wells

Other comparable wells completed in the vicinity of the North Rim were drilled for the purposes of oil and gas exploration and are located over 30 miles north of the project site. Additional details regarding these offset wells are provided in North Rim Drilling Plan (GKS, 2026). Large variation between geologic formation composition and thickness have been observed over these distances. Therefore, data from offset wells was not used in the interpretations summarized within this report.

SEGMENT 3:

NORTH RIM BALLFIELD SITE TO

NORTH RIM WATER TANKS

(NOT ADDRESSED BY THIS REPORT)

NORTH RIM WATER TANKS

NORTH RIM

BALLFIELD SITE

SEGMENT 2:

RSPH TO NORTH RIM

BALLFIELD SITE

(SEE FIGURE 5.1)

RSPH

BORE ENTRY

BORE EXIT

SEGMENT 1:

ROARING SPRINGS

CAVE TO RSPH

(NOT DISCUSSED

IN THIS REPORT)

© 2024 Microsoft Corporation © 2024 Maxar ©CNES (2024) Distribution Airbus DS © 2024 TomTom

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

INTERSTATE

Apache

Santa Cruz

La Paz

Yavapai

Mohave

Graham

Gila

Coconino

Cochise

Pima

Maricopa

Greenlee

Navajo

Pinal Yuma

SEGMENT 3:NORTH RIM BALLFIELD SITE TONORTH RIM WATER TANKS(NOT ADDRESSED BY THIS REPORT)

NORTH RIM WATER TANKS

NORTH RIMBALLFIELD SITE

SEGMENT 2:RSPH TO NORTH RIMBALLFIELD SITE(SEE FIGURE 5.1)

RSPH

BORE ENTRY

BORE EXIT

SEGMENT 1:ROARING SPRINGSCAVE TO RSPH(NOT DISCUSSEDIN THIS REPORT)

MAGILL, CHARLIE B:\Working\HDR\2305987 21186 GRCA North Rim Water Supply LR\00_CAD\Figures\GBR\GRCA_Site_Vicinity.dwg - 7/9/2025

Fig. 2-1

Geologic Interpretive Summary Report GRCA 318719 Rehabilitate North Rim Utility Infrastructure

Grand Canyon North Rim, Arizona

HDR Engineering, Inc.

Fort Collins, Colorado

SITE VICINITY AND LAYOUT

July 2025Project 2305987 Consultants

LEGEND:

PROPOSED PIPELINE ALIGNMENTS

NOTES:

1. ALL LOCATIONS ARE APPROXIMATE. SEE

CONTRACT DRAWINGS FOR EXACT

LOCATIONS.

2. ANTICIPATED GEOLOGIC PROFILE FOR

BORE ALIGNMENT SHOWN IN FIGURE 5-1.

SCALE, FEET

200010000

SITE

GEI Consultants, Inc. 10

3. Geology

3.1. Regional Geology

The Grand Canyon is located in the southwestern corner of the Colorado Plateau Physiographic Province, which spans the four corners region of Arizona, New Mexico, Colorado, and Utah. The Colorado Plateau is a region of thick continental crust which has remained largely resistant to significant tectonic deformation since the end of the Precambrian (544 million years before present (Ma)). A 325-million-year period of net subsidence and deposition during the Paleozoic was followed by Laramide-era uplift

75-55 Ma, and subsequent downcutting of the canyon in the last 5 million years (Huntoon, 2003). This has resulted in the prominently exposed geologic units within the present-day Grand Canyon which are both well preserved and readily observable.

The sedimentary units which form the Grand Canyon are founded on Precambrian basement rocks. In the eastern portion of the Grand Canyon sedimentary rocks of the Cambrian Tonto Group (Tapeats

Sandstone, Muav Formation, and Bright Angel Formation) rest on tilted beds of the Proterozoic (1.4- to

1.1-billion-year-old) Grand Canyon Supergroup, along the “Great Unconformity”, which represents an approximate 600-million-year gap in time of the geologic record at this location. The pre-existing topography formed by the Precambrian rocks which the Tonto group is founded on included irregular rolling hills, with alternating peaks and valleys of resistant bedrock separated by intermediate lowlands.

The Tonto Group constitutes the foundation of the Paleozoic stratigraphic sequence forming the canyon walls, which are typically capped by the Permian Kaibab Formation (Beus and Morales, 2003).

Major faults in the region are of Precambrian age (>544 Ma), generally trend northeast, north, and northwest, and have undergone periodic reactivation from cycles of regional compressive and tensional tectonic stresses (Huntoon, 2003). Faults near the site mapped on a 1:100,000 scale USGS quadrangle include the Roaring Springs Fault and the Bright Angel Fault (USGS, 2000). The bore entry point is located approximately 0.6 miles southwest of Roaring Springs Fault which is a reverse fault trending northwest-southeast along Roaring Springs Canyon. Based on the USGS quadrangle, the proposed bore alignment may cross the Roaring Springs Fault approximately 1.2 miles southeast of the entry point, within the

Bright Angel Formation (USGS, 2000). The precise location of the Roaring Springs Fault is difficult to locate in the area in which the bore is anticipated to cross it per the USGS geologic map. The Roaring

Springs Fault terminates in the Bright Angel Fault approximately 1.7 mi southeast of the bore entry point.

Although it is not anticipated to cross the proposed bore path, the Bright Angel Fault is a major northeast-trending structural feature which crosscuts the Grand Canyon and forms the primary structural control for Bright Angel Creek.

Throughout the Paleozoic and Mesozoic era, the Grand Canyon has generally not been subject to significant brittle deformation from faulting, but has instead undergone broad, ductile deformation and variable cycles of regional subsidence and uplift (Huntoon, 2003). Deformation since the Precambrian has typically been marked by reactivation of the pre-existing faults, resulting in the formation of regional monoclines during the Laramide Uplift. The Kaibab Plateau where the site is located is one such

Laramide-era monocline, thrusted upward from regional compressive stresses and reactivation of northwest-trending Precambrian faults (Huntoon, 2003). Because movement of crustal blocks has

GEI Consultants, Inc. 11 typically occurred along major pre-existing Precambrian faults, smaller scale secondary faulting in the vicinity of the site is not anticipated to be encountered.

3.2. Site Geology

The proposed bore entry point is in the southern portion of the Kaibab Plateau along the North Rim of the Grand Canyon, directly south of the North Rim Campground. A 1:100,000 scale USGS quadrangle published in 2000 titled, Geologic Map of the Grand Canyon 30’ x 60’ Quadrangle (USGS, 2000) was used to determine occurrence and aerial coverage of major stratigraphic units anticipated to be encountered along the proposed bore path. These include (in descending stratigraphic order): Kaibab Formation, Toroweap Formation, Coconino Sandstone, Hermit Formation, Supai Group Units, Redwall Limestone, Temple Butte Formation, Muav Formation, and Bright Angel Formation. Though not anticipated to be encountered along the proposed bore path, the Tapeats Sandstone is also present on the USGS geologic map and may outcrop near the bore exit location. A supplementary pamphlet provided with the USGS map also provides summary descriptions of each unit, which are referenced below. The geology described here is generally applicable to the Kaibab Plateau region of the Grand Canyon. A cross section illustrating the geologic profile interpretation along the bore path is provided in Figure 5-1.

3.2.1. Kaibab Formation

The Lower Permian Kaibab Formation is a light tan to dark gray limestone, with variable bedding thickness (Hargis & Montgomery, 1984). It is a sandy dolomitic limestone, heavily jointed, and contains chert. The Kaibab was reported by Hargis & Montgomery to range in total thickness from about 250 to

300 feet near the historic south rim bore location.

The surface of the Kaibab Plateau and much of the Grand Canyon is capped by the Kaibab Formation.

Generally, it is composed of both carbonate and siliciclastic sediments deposited throughout a complex cycle of marine transgressions and regressions (Hopkins and Thompson, 2003).

The Kaibab Formation is identifiable as gray cliffs formed over the vegetated slope of the underlying

Toroweap Formation. Based on an isopach map provided in Hopkins and Thompson (2003), the Kaibab is between 300 to 400 feet thick throughout the Kaibab Plateau. It includes the upper Harrisburg member and the underlying Fossil Mountain member, separated by a distinct chert horizon. Based on the geologic investigation, only the Fossil Mountain Member of the Kaibab Formation will be encountered in the bore.

3.2.1.1. Fossil Mountain Member

The Fossil Mountain Member is a calcareous unit which forms the prominent cliffs and pinnacles along the canyon rim. USGS (2000) describes the Fossil Mountain Member as “light-gray, cliff-forming, fine- to medium-grained, thin- to medium- bedded [1-6 ft], fossiliferous, sandy, cherty limestone.” Thickness of the Fossil Mountain Member has been reported ranging from 230 to 250 feet (USGS, 2000), or up to 250 to 300 feet (Hopkins and Thompson, 2003). The composition of this member transitions from predominantly limestone in the western Grand Canyon to increasingly siliceous to the east. Along the

Hermit Trail approximately 10 miles southwest of the North Rim bore site, the unit is approximately 50% siliciclastic sandstone or sandy dolomite. This member is known to contain chert nodules throughout, GEI Consultants, Inc. 12 which typically occur as thin, continuous layers parallel to bedding about 2 inches thick (Huntoon, 1968;

Hopkins and Thompson, 2003). The upper portion contains brecciated chert beds 4-10 feet thick where it forms the contact with the overlying Harrisburg Member (USGS, 2000).

The Fossil Mountain member forms an unconformable contact with the underlying Toroweap Formation, which can be attributed to erosive solutioning and channeling of the upper Toroweap. Localized infilling of these channels with sandy cherty limestone is typical (USGS, 2000).

3.2.2. Toroweap Formation

Generally, the Lower Permian Toroweap Formation includes pale orange to white fine-grained sandstone and siltstone separated by a limestone member, buff in color (Hargis & Montgomery, 1984). This

Formation typically forms a vegetated slope and includes, in descending stratigraphic order, the Woods

Ranch Member, Brady Canyon Member, and Seligman Member. Significant variability in lithology is characteristic of the Toroweap, with east-west lateral facies transitions occurring throughout the Grand

Canyon and regionally (Turner, 2003). The total vertical thickness of the Toroweap Formation at the

North Rim bore site is anticipated to be 310 feet based on available literature and evaluation of topographic slope breaks.

Solution tubes formed within limestone and gypsum beds, particularly along discontinuities within the

Toroweap, result in a high secondary permeability which permits downward transmission of groundwater. Less permeable units within the Toroweap Formation cause lateral migration and formation of seeps typically on west-facing slopes (Huntoon, 1968).

3.2.2.1. Woods Ranch Member

The Woods Ranch Member consists of “gray and light-red, slope forming [gypsum-bearing] siltstone and silty sandstone, interbedded with white laminated gypsum and gray thin-bedded limestone” (USGS, 2000). Although USGS indicates gypsum beds up to 10 feet thick within the unit, a map of facies distribution provided in Turner (2003) suggests these evaporite beds are generally restricted to a region far northwest of the project area. Along the South Kaibab Trail, near the North Rim bore site, this member consists primarily of cross-bedded sandstone with wavy bedforms and brecciated carbonate beds at the base (Turner, 2003). This lithology has an overall lower occurrence of the carbonate and evaporite beds found further to the north and northwest.

USGS (2000) notes a unit thickness of about 65 ft in the southeastern region of the Grand Canyon. This unit is interpreted to have formed from transgressive inundation of the underlying Brady Canyon carbonates.

The gradational contact between the Woods Ranch member and the underlying Brady Canyon member consists of a dolomite bed with distinct desiccation cracks (Turner, 2003). The contact is defined topographically at the top of the limestone cliff of the Brady Canyon Member (USGS, 2000).

3.2.2.2. Brady Canyon Member

The Brady Canyon Member consists of “gray, cliff-forming, thin- to medium-bedded [1-5 ft] fine- to coarse-grained, fetid, fossiliferous limestone” with chert nodules comprising less than 8 percent of the

GEI Consultants, Inc. 13 unit (USGS, 2000). The Brady Canyon member is a distinct cliff-forming carbonate unit which separates the Woods Ranch and Seligman Members. Towards the east near the North Rim bore site, dolomitic composition is typical. Deposition of this unit occurred in a shallow marine environment (Turner, 2003).

A map of lateral facies transitions in the Brady Canyon member, from Turner (2003), indicates “sandy dolomite” as the primary lithology throughout the Kaibab Plateau where the site is located. Unit thickness ranges from about 40 ft in the eastern portion of the USGS (2000) quadrangle thickening to about 130 feet at the western edge.

The contact between the Brady Canyon Member and the underlying Seligman Member is marked by a gradational transition from the thick carbonate beds of the Brady Canyon member to the heterogeneous interbeds of the Seligman Member (Turner, 2003). The contact is defined topographically at the base of the limestone cliff of the Brady Canyon Member (USGS, 2000).

3.2.2.3. Seligman Member

The Seligman Member consists of “gray, light-purple, and yellowish-red, slope-forming, thin-bedded dolomite, sandstone, and gypsum” (USGS, 2000). The eastern portion of the USGS quadrangle in particular consists primarily of calcareous sandstone with thin limestone interbeds.

Despite the prevalence of evaporites northwest of the Grand Canyon within the Toroweap, a map of facies distribution provided in Turner (2003) shows a primary facies of “irregular-bedded sandstone” within the Seligman member on the Kaibab Plateau. This lithology has a lower occurrence of the carbonate and evaporite beds found further to the north and northwest. Thickness of the Seligman

Member is about 30 feet in the eastern portion of the Grand Canyon increasing to about 55 feet to the west (USGS, 2000). Deposition of this unit occurred in a tidal flat environment (Turner, 2003).

The base of the Seligman member marks a conformable contact with underlying Coconino Sandstone and forms a sharp gradational boundary where the absence of cross bedding and/or presence of evaporites distinguishes the Seligman from the Coconino (USGS, 2000; Turner, 2003).

3.2.3. Coconino Sandstone

The Lower Permian Coconino Sandstone consists of “tan to white, cliff-forming, fine-grained, well-sorted, cross-bedded quartz sandstone” (USGS, 2000). Minor amounts of potassium feldspar are also present

(Middleton et al., 2003). Hargis & Montgomery (1984) reported a thickness at the south rim of about

500 feet and indicated the unit is brittle and friable. The unit is well-lithified with siliceous cement and large-scale cross-stratified beds up to 66 feet thick. Uniform sorting and siliceous mineralogy provide evidence of an eolian depositional environment (Middleton et al., 2003).

The Coconino Sandstone forms a sharp planar disconformity with the underlying Hermit Formation

(Blakey, 2003). This contact is marked by infilled desiccation cracks in the upper surface of the Hermit

Formation (USGS, 2000).

Due to its lithology, the Coconino is a major aquifer throughout much of northern Arizona. Within the

Grand Canyon region, however, it tends to bear water only where heavily fractured and where the underlying Hermit Formation forms an aquitard (Hargis & Montgomery, 1984).

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3.2.4. Hermit Formation

The Lower Permian Hermit Formation, historically referred to as the Hermit Shale, consists of “red, slope-forming, fine-grained, thin-bedded siltstone and sandstone” (USGS, 2000). Blakey (2003) further specifies “reddish-brown siltstone, mudstone, and very fine-grained sandstone,” with cyclically interbedded silty sandstone and sandy mudstone comprising the bulk of the unit. The Hermit Formation is about 260 feet thick in the eastern Grand Canyon and thickens to the west (USGS, 2000). Beds of silty sandstone form ledges approximately 3 feet on average and may contain calcareous nodules. Conversely, the interbedded sandy mudstone / platy siltstone is friable and forms slopes. A minor component of conglomerate is also present, with clasts largely consisting of calcareous concretions (Blakey, 2003).

Hargis & Montgomery (1984) reported a thickness at the south rim of about 250 feet. They also noted the difficulty of discerning the Hermit Formation from the underlying Supai Group in boring samples.

This unit forms an unconformable contact with the underlying Esplanade Sandstone where it infills erosion channels up to 60 feet deep, but typically less than 10 feet (USGS, 2000).

The Hermit Formation behaves as an aquitard, which often results in perched groundwater conditions at the base of the overlying Coconino Sandstone (Hargis & Montgomery, 1984).

3.2.5. Supai Group

The Supai Group spans the Permian, Pennsylvanian, and Mississippian periods, and includes alternating slopes and benches of red siltstone and mudstone, light-brown fine-grained sandstone, and occasional limestone beds, some containing chert. Hargis & Montgomery (1984) reported a thickness at the south rim of about 930 feet. It includes, in descending stratigraphic order, the Esplanade Sandstone, Wescogame Formation, Manakacha Formation, and Watahomigi Formation.

3.2.5.1. Esplanade Sandstone

The Lower Permian Esplanade Sandstone consists of an upper “light-red and pinkish-gray, cliff-forming, fine- to medium-grained, medium-bedded [3-10 ft], well-sorted calcareous sandstone” with a lower slope-forming unit consisting of dark-red thinly-bedded siltstone (USGS, 2000). The Esplanade Sandstone is emplaced between the steep ledges and slopes of the underlying Wescogame and the more continuous slopes of the Hermit Formation above. Of all the Supai group units, the Esplanade contains the highest fraction of sandstone. In the eastern Grand Canyon, the Esplanade ranges from 200 to 250 feet thick, although measured sections along the Kaibab Trail are about 300 ft (Blakey, 2003). The lithology comprising the Esplanade is dominated by cross-stratified sandstone exhibiting evidence of eolian deposition. Thinly bedded limestone may also occur in the lower slope-forming portion (USGS, 2000). Clean surfaces appear pale grayish orange to reddish orange, although outcrops are typically stained red from the overlying mudstone (Blakey, 2003).

The contact with the underlying Wescogame Formation is unconformable and demarcated by channels infilled with limestone conglomerate which average about 35 feet deep (USGS, 2000).

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3.2.5.2. Wescogame Formation

USGS (2000) describes the Upper Pennsylvanian Wescogame Formation as “light-red, pale-yellow, and light-gray upper slope unit and lower cliff unit.” The upper slope-forming subunit consists primarily of fine-grained siltstone and mudstone with heterogeneous interbeds of calcareous sandstone and conglomerate. The lower subunit consists primarily of cross-bedded sandstone and calcareous sandstone, which forms cliffs up to 40 ft thick (USGS, 2000).

Total thickness of the Wescogame ranges from about 100 to 200 feet in the Grand Canyon and is about

130 feet thick along the Kaibab Trail (Blakey, 2003). The lithology of the Wescogame is predominately sandstone throughout much of the central Grand Canyon, with mudstone becoming more prevalent to the east.

The boundary between the Wescogame and Manakacha can be poorly defined, although basal conglomerate in the Wescogame often demarks the contact (Blakey, 2003). Topographically, the transition from the Wescogame can be determined by locating the end of the slope at the top of the

Manakacha. The contact is unconformable and often consists of erosion channels infilled with limestone and chert conglomerate (USGS, 2000).

3.2.5.3. Manakacha Formation

USGS (2000) describes the Middle Pennsylvanian Manakacha Formation as “light-red, white, and gray upper slope unit and lower cliff unit of sandstone, calcareous sandstone, dark-red siltstone, and gray limestone.” The slope-forming unit consists of primarily siltstone and mudstone with some interbeds of limestone and sandstone. The cliff-forming unit consists of cross-bedded calcareous sandstone, dolomite, and sandy limestone. The upper unit is approximately 100 feet thick, and the lower cliff-forming unit is about 60 feet thick in the eastern Grand Canyon (USGS, 2000).

Within the Manakacha, three distinct types of sandstone are recognized by Blakey (2003). The first consists of variably thick cross-stratified bedding sets with indications of eolian deposition. Another type of sandstone consists of, “horizontally laminated to very low-angle, cross-stratified, fine-grained, calcareous and silty units up to 20 feet thick.” The third type of sandstone is grayish-orange to bright reddish-orange and consists of very fine-grained sands. The uppermost portions of the unit may have undergone significant chemical alteration resulting in the replacement of the original rock fabric via crystallization of calcite and dolomite (Blakey, 2003). The unconformable contact between the

Manakacha and Watahomigi is demarcated by conglomerate containing fragments of the Watahomigi with the bedding surface exhibiting scour and channeling (USGS, 2000).

3.2.5.4. Watahomigi Formation

The Lower Pennsylvanian to Upper Mississippian Watahomigi Formation consists of “gray and purplish-red, slope-forming limestone, siltstone, mudstone, and conglomerate” within a 70-feet thick upper unit consisting of thin interbeds of cherty limestone, siltstone, and mudstone (USGS, 2000). The lower unit predominately forms slopes containing mudstone and siltstone with thin interbeds of limestone and red chert veins (USGS, 2000). Carbonates in this unit within the eastern Grand Canyon tend to be very fine-grained, with some larger fragments of fossils and pellets (Blakey, 2003). Mudstones within this

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Formation tend to lack structure and have occasional interbeds of bright-orange calcareous sandstone.

Blakey (2003) indicated two units of red slope-forming mudstone, separated by a ledge of carbonates.

The Watahomigi averages about 100 feet thick in the eastern Grand Canyon (USGS, 2000; Blakey, 2003).

The Watahomigi forms an abrupt, unconformable contact with the underlying Redwall Limestone demarcated by interbedded conglomerates which infill erosion channels (USGS, 2000; Blakey, 2003).

3.2.6. Redwall Limestone

The Mississippian Redwall Limestone is light-gray and grayish-blue cliff-forming,…