B08_Att_04_GRCA257282_Geotechnical_Recommendation_TM_May2025.pdf

Technical Memorandum

Jacobs Government Services Company 240620104000_c797e258

Geotechnical Recommendation Report

Date: May 30, 2025 Jacobs Government Services Company

4 Embarcadero Center Suite 3800 San Francisco, CA 94111 United States

T +1.415.356.2040

F +1.415.356.2055 www.jacobs.com

Project Name: Replacement of South Rim Wastewater Treatment Plant (GRCA 257282)

Project No.: D3167666

Attention: Mike Ryan/NPS Christopher Carpenter/NPS

Client: National Park Service- Grand Canyon National Park

Prepared by: Maddie Heidari/Jacobs

Reviewed by: Nason McCullough, PE/Jacobs Kathy Rosinski, PE/Jacobs

1. Introduction This report was prepared for the GRCA 257282 Replace Wastewater Plant South Rim Village project. As part of the geotechnical evaluation, two geotechnical explorations were conducted for the project, one focused on wastewater treatment plant area, and one based on the access road improvement.

The Preliminary Geotechnical Recommendation Report for Replace Wastewater Plant South Rim Village was prepared by Shannon & Wilson in April 2022 (Attachment 1) for the wastewater treatment plant area.

The report summarizes:

Subsurface conditions encountered during the exploration program completed on January 17 and 18, Laboratory test results The geotechnical engineering recommendations

Shannon & Wilson completed the work as a subconsultant to Jacobs Government Services Company (Jacobs) under Professional Service Task Order 148027714 dated October 1, 2021.

The Preliminary Geotechnical Report (Shannon & Wilson 2022) was prepared during the early phase of the project. Because Jacobs is the engineer of record for the final design, Jacobs has reviewed the Preliminary Geotechnical Report and prepared this technical memorandum (TM) to document updates and design decision changes that affect the Preliminary Geotechnical Report.

The following items in the Preliminary Geotechnical Report have changed, and are documented herein:

The list of proposed new facilities in the Preliminary Geotechnical Report was updated to the current facility list documented in Table 1 and Figures 1 and 2.

The Construction Considerations - Earthwork recommendations of the Preliminary Geotechnical Report have been modified as discussed in Section 3.

All other engineering recommendations are as presented by Shannon & Wilson.

240620104000_c797e258

The Geotechnical Report for South Rim WWTP Access Road was prepared by Shannon & Wilson in January 2025 (Attachment 2) for the access road improvement. The report summarizes:

Subsurface conditions encountered during the exploration program completed on September 18 and 19, 2024

Laboratory test results The geotechnical engineering recommendations for the access road

Shannon & Wilson completed the work as a subconsultant to Jacobs Government Services Company (Jacobs) under Professional Service Task Order 148052738 dated May 20, 2024. Jacobs has reviewed the Geotechnical Report and confirms all recommendations as presented by Shannon & Wilson.

2. Proposed New Facilities The project includes the construction of 15 new facilities at the wastewater treatment plant site, and the construction of a new gravel access road that extends from the wastewater treatment plant to the existing Arizona Public Service (APS) Substation. All new facilities will be within the existing plant, except the drying beds (facility number 85) that will be constructed south of the existing plant fence and the access road constructed to the east of the plant. Table 1 provides a summary of the new facilities, the foundation type, approximate foundation depth and the approximate foundation elevation based on 90 percent design drawings. Figures 1 and 2 show the existing site plan and the proposed facilities plan, respectively.

240620104000_c797e258

Table 1. Proposed New Plant Facilities (to replace Table 2-1 in Shannon & Wilson’s Preliminary Geotechnical Report, dated April 2022)

New Facilities Facility Number

Foundation Type

Approximate Foundation Depth

Below Existing Grade (feet)

Approximate Foundation

Elevation (feet)

Administration Building 10 Strip footings for CMU walls with floating slab-on-grade

1.75 to 9.25 6,774.75

Generator and Fuel Tanks 11 Slab-on-grade 2.1 to 6.6 6,776.4

Maintenance Building 12 Strip footings for CMU walls with floating slab-on-grade

2 6,773

Maintenance Building – Covered Exterior Storage

12 Slab-on-grade with thicken footing 3 6,672

Receiving Station 18 Slab-on-grade

Precast concrete vault

2 feet (slab-on-grade)

12 feet (Vault)

6,786 to 6,787

6,778 (Vault)

Headworks 20 Strip footings for CMU walls with floating slab-on-grade

Mat slab 3 to 12 f 6,777 to 6,786

Odor Control 22 Mat slab 2 to 3 6,789.5

Process Tanks 25 Mat Slab 10 to 15 6,764.4 to 6,759.4

Process Building 32 Mat Slab (basement), Strip footings for CMU walls with floating slab-on-grade (ground floor)

20 feet

Up to 4.5 feet of fill

6,764.9 to 6,782.5

Reclaimed Water Tank 70 Mat slab 0 to 2 6,777

Digester Facility 80 Mat slab 1 to 6.5 6,782

Drying Beds 85 Slab-on-grade

5 feet

Up to 12.5 feet of fill

6,773.6 to 6,777.8

Plant Drain Pump Station 86 Precast manhole 15 6,751

Compost Facility 87 Mat slab 0 to 1 6,788.5

Covered Storage 88 Strip footings for CMU walls with floating slab-on-grade

2 to 4 6,787

CMU = concrete masonry unit

240620104000_c797e258

3. Geotechnical Design Recommendations The recommendations provided by Shannon & Wilson (2022 and 2025) have been reviewed and are applicable to the design of the facilities and access road and they will be used in the design of the foundations, slopes, and wall for the facilities and access road, with the following exceptions.

Revise and/or add the following construction considerations to the Earthwork Section (Section 7.2) of Shannon & Wilson’s Preliminary Geotechnical Report, dated April 2022:

The Use of explosive is not allowed for the project.

Soil and bedrock subgrade preparation should meet the requirements of Specification Section 31 23 13.

Foundation slab, slabs-on-grade and wall and column foundations should bear on a minimum of 8 inches of compacted granular fill or undisturbed bedrock. If foundations partially bear on undisturbed bedrock, the portion of foundation that is on soil shall bear on 18 inches of compacted granular fill above native soils. If undisturbed bedrock is shallower than 18-inches, then the thickness of compacted granular fill shall be equal to the depth to undisturbed bedrock.

Granular fill should consist of 1-inch minus crushed gravel and or crushed rock. Granular fill should be well-graded from coarse to fine and containing sufficient fines to bind material when compacted, but with maximum 8 percent by weight passing No. 200 sieve.

4. References Shannon & Wilson. 2022. Preliminary Geotechnical Report. National Park Services – Replace Wastewater Plant South Rim Village: GRCA – 257282. April.

Shannon & Wilson. 2025. Geotechnical Report. Grand Canyon National Park – South Rim WWTP Access Road. January.

240620104000_c797e258

Figure 1. Existing Site Plan

240620104000_c797e258

Figure 2. Overall Site Plan

Attachment 1

Preliminary Geotechnical Report –

Shannon & Wilson 2022

SUBMITTED TO:

Jacobs Engineering Group, Inc.

9191 Jamaica Street Englewood, CO 80112

BY:

Shannon & Wilson 1321 Bannock St., Ste. 200 Denver, CO 80204

(303) 825-3800 www.shannonwilson.com

PRELIMINARY GEOTECHNICAL REPORT

National Park Service - GRCA - 257282, Replace Wastewater Plant South Rim Village

GRAND CANYON VILLAGE, ARIZONA

April 2022

Shannon & Wilson No: 107528-001

National Park Service - GRCA - 257282, Replace Wastewater Plant South Rim Village

Preliminary Geotechnical Report

107528-001 April 2022 ii

CO

NT

EN

TS

CONTENTS

1 Introduction

2 Project and Site Description

3 Subsurface Explorations and Laboratory Testing

3.1 Field Investigation

3.2 Geotechnical Laboratory Testing

3.3 Previous Explorations

4 Regional Geology and Subsurface Conditions

4.1 Regional Geology

4.2 Subsurface Conditions

4.3 Groundwater

4.4 Subsurface Variations

5 Geologic Hazard Evaluation

5.1 Seismic Hazards

5.2 Corrosion

6 Preliminary Geotechnical Recommendations

6.1 Ground Motion Design Parameters

6.2 Foundations

6.2.1 Spread/Strip Footings

6.2.2 Mat Foundations

6.3 Lateral Earth Pressures and Lateral Resistance

6.4 Surface Drainage

7 Construction Considerations

7.1 Dewatering

7.2 Earthwork

7.2.1 Site Preparation

7.2.2 Excavation

7.2.3 Foundation and Slab Subgrade Preparation

7.2.4 Fill Placement and Compaction

7.2.5 Granular Fill

iii

CO

NT

EN

7.3 Temporary Slopes

8 Limitations

9 References

Exhibits Exhibit 2-1: Proposed New Facilities Exhibit 3-1: Boring Summary Exhibit 5-1: Corrosivity Ratings Based on Soil Resistivity Exhibit 5-2: Corrosivity Ratings Based on Water Soluble Sulfate Exposure Exhibit 6-1: Seismic Design Ground Motion Parameters Exhibit 6-2: Recommended Subgrade Reaction Moduli Exhibit 6-3: Recommended Lateral Earth Pressure (LEP) Values Exhibit 6-4: Recommended LEP Reduction Values for Narrow Backfill Zones

Figures Figure 1: Vicinity Map Figure 2: Site and Exploration Plan Figure 3: Recommended Surcharge Loading for Temporary and Permanent Walls

Appendices Appendix A: Subsurface Explorations Appendix B: Laboratory Test Results Appendix C: Previous Explorations Important Information

Preliminary Geotechnical Report

107528-001 April 2022

1 INTRODUCTION

This report presents the results of our subsurface exploration and testing program and preliminary geotechnical engineering recommendations for the proposed South Rim Wastewater Treatment Plant (WWTP) Project (the Project) in Grand Canyon National Park, Arizona (Figure 1).

Our conclusions and recommendations are based on:

Our understanding of the Project and information provided by Jacobs;

Subsurface conditions observed in the explorations; and

The results of testing performed on samples collected from the explorations.

The objective of our studies was to provide geotechnical recommendations and construction considerations, as presented herein, for the proposed new facilities. This report should not be used for other purposes without Shannon & Wilson’s review. If a service is not specifically indicated in this report, do not assume that it was performed.

This report is preliminary. It will be necessary for the design-build contractor to develop final geotechnical recommendations for the Project.

2 PROJECT AND SITE DESCRIPTION

The Project is located in Grand Canyon National Park in Coconino County, Arizona (Figure 1). The Project site is approximately 2.5 miles west-southwest of Grand Canyon National Park South Rim Visitors Center at the existing Wastewater Treatment Plant (WWTP). The Project includes the construction of 11 new facilities within the existing plant site. Exhibit 2- 1 provides a summary of the new facilities proposed for the Project, the proposed foundation type, approximate foundation depth and the approximate foundation elevation based on preliminary plans provided by Jacobs (2022) and email correspondence.

The existing WWTP facility sits on approximately 4.5 acres that gently slopes from east to west. We understand that the existing site grades were modified during the original construction of the treatment plant. It appears that fill for construction on west side of the site was placed, however no plans or as-builts were provided documenting the materials or placement methods used. The existing grades slope from approximate elevation 6,790 to 6,769. The site is generally surrounded by undeveloped land. Refer to Figure 2 for a Project map.

Preliminary Geotechnical Report

107528-001 April 2022

Exhibit 2-1: Proposed New Facilities

New Facilities Foundation

Type Approx. Foundation Depth below Existing Grade Approx. Foundation

Elevation

Administration Mat 2.5 ft 6774

Maintenance Mat 2.5 ft 6772

Vault Waste / Septage Receiving

Mat 2.5 ft, with adjacent 10-ft deep vault

Headworks Footings 4 to 11 ft 6778.5 to 6784.5

Odor Control Mat 2.5 ft 6779

Process Tanks Footings 12 to 16 ft 6764

Process Building Mat 2.5 ft (east and west sections) 15 to 20 ft (center section)

6761 to 6766

Reclaimed Water Tank Footings 2.5 to 5 ft 6780

Decant Thickened Digester

Mat 2.5 ft 6782

Dewatering and Reclaimed Water Pump Station

Mat 2.5 ft 6773

Composter Facility Mat 2.5 ft 6785

NOTES:

ft = feet

3 SUBSURFACE EXPLORATIONS AND LABORATORY

TESTING

3.1 Field Investigation

Shannon & Wilson conducted a field exploration program on January 17 and 18, 2022, to explore subsurface conditions at the Project site. The subsurface exploration program consisted of drilling and sampling 6 borings, designated as borings BH-01-22 to BH-06-22 to depths selected by Jacobs. Refer to Figure 2 for the approximate boring locations. Exhibit 3- 1 provides a summary of the borings completed for the Project.

Preliminary Geotechnical Report

107528-001 April 2022

Exhibit 3-1: Boring Summary

Boring Name Elevation

(ft) Depth

(ft)

BH-01-22 6,777.8 22

BH-02-22 6,783.7 9

BH-03-22 6,777.1 22

BH-04-22 6,775.7 26

BH-05-22 6,774.8 17

BH-06-22 6,769.3 13.5

Appendix A presents a discussion of the drilling and sampling procedures used to complete the borings. Appendix A also presents the individual exploration logs and an explanation of the symbols and terminology used to classify soil and rock samples recovered from the borings.

3.2 Geotechnical Laboratory Testing

Geotechnical laboratory tests were completed on selected samples retrieved from the borings. Index tests included natural water content, grain size analysis, and Atterberg limits. Engineering properties tests included corrosion and unconfined compressive strength. Laboratory test results and a discussion of the testing procedures are included in Appendix B. The natural water content and fines content are also shown on the individual boring logs included in Appendix A.

3.3 Previous Explorations

Existing subsurface data available for the site includes logs for 12 borings by Chen & Associates (1986) and associated laboratory testing. Appendix C includes these logs, laboratory testing results and a site plan showing the approximate boring locations.

4 REGIONAL GEOLOGY AND SUBSURFACE

CONDITIONS

4.1 Regional Geology

A regional geologic map of the Bright Angel quadrangle (Maxson, 1961) indicates that the near surface geology in the Project area is dominated by the limestone member of the Kaibab Formation (Permian) and consists of massive, fine-grained limestone containing

Preliminary Geotechnical Report

107528-001 April 2022 beds of sandstone, siltstone, and nodules of white chert. The Kaibab Formation forms the uppermost cliffs along the north and south rims of the Grand Canyon.

4.2 Subsurface Conditions

Borings BH-01-22 to BH-04-22, completed along the center and southern portions of the site, encountered 1 to 2 feet of overburden soil overlying limestone bedrock. The overburden soil consisted of clayey gravel with sand. The limestone bedrock was observed to be slightly weathered to fresh and medium strong to medium strong. Interbedded layers of weak, moderately to highly weathered limestone was encountered ranging in thickness from approximately 1 to 2.5 feet thick. Sandstone bedrock was encountered in BH-03-22 from approximately 18.7 to 19.7 feet and was observed to be fresh and medium strong.

Borings BH-05-22 and BH-06-22, completed along the western side of the existing drying beds, encountered 6 to 7 feet of undocumented fill soil overlying limestone bedrock. The undocumented fill soil consisted of loose to dense, clayey sand with gravel to clayey gravel with sand and sandy lean clay with gravel. The limestone bedrock was observed to be slightly weathered and medium strong.

The previous borings completed by Chen and Associates (1986), indicated 1 to 3 feet of overburden soil, consisting primarily of gravel with varying amounts of clay and sand, overlying limestone bedrock.

4.3 Groundwater

Groundwater was not encountered in any of our borings or in the previous borings (Chen & Associates, 1986). Groundwater was not encountered prior to coring in borings BH-01-22, BH-03-22, and BH-04-22; therefore, groundwater was not able to be identified if it was encountered. Groundwater fluctuations are possible and will depend on many factors, including seasonal variations, local precipitation, runoff, and snow melt.

4.4 Subsurface Variations

The explorations were performed to evaluate subsurface conditions beneath the Project site.

Our observations are specific to the locations, depths, and times noted on the logs and may not be applicable to all areas of the site. No amount of explorations or testing can precisely predict the characteristics, quality, or distribution of subsurface and site conditions.

Potential variation includes, but is not limited to:

The conditions between explorations may be different, especially due to the presence of boulders and cobbles, differences in densities or gradations of fill.

Preliminary Geotechnical Report

107528-001 April 2022

The passage of time or intervening causes (natural and manmade) may result in changes to site and subsurface conditions.

If conditions different from those described herein are encountered during construction, we should review our description of the subsurface conditions and reconsider our conclusions and recommendations.

5 GEOLOGIC HAZARD EVALUATION

5.1 Seismic Hazards

Based on a database by the U.S. Geological Survey (USGS), the nearest confirmed fault, to the Project, is the Bright Angel fault zone (undifferentiated Quaternary fault), approximately 0.2 miles to the northwest (USGS, 2021). The Bright Angel Fault is a normal fault that runs roughly parallel to Rowe Well Road and has movements of less than 0.2 mm per year (Pearthree, 1997). Although the Bright Angel Fault is close to the Project site, the location is well defined (Pearthree, 1997) and therefore, it is our opinion that the potential for ground surface fault rupture at the Project site is low.

5.2 Corrosion

The soil encountered at the Project site can be corrosive to substructure elements. Due to the prevalence of bedrock at the site, a single soil sample was tested for pH, resistivity, water soluble sulfates, and chlorides. The results are presented in Table B-1 in Appendix B.

The resistivity measured in the sample was 4,000 ohm-centimeters. Based on correlations developed by Roberge (2012) as shown in Exhibit 5-1, this value suggests corrosive subsurface conditions for metallic pipe in contact with subsurface materials across the site.

Exhibit 5-1: Corrosivity Ratings Based on Soil Resistivity

Soil Resistivity (ohm-cm)

Corrosivity Rating

>20,000 Essentially Noncorrosive

10,000-20,000 Mildly Corrosive

5,000-10,000 Moderately Corrosive

3,000-5,000 Corrosive

1,000-3,000 Highly Corrosive

<1,000 Extremely Corrosive

Preliminary Geotechnical Report

107528-001 April 2022

The concentration of water-soluble sulfates measured in the sample was 0.01% by weight.

Based on classifications as defined by ACI-318-19 (ACI, 2019), as shown in Exhibit 5-2, this test result suggests an exposure class S0 on concrete exposed to site soils.

Exhibit 5-2: Corrosivity Ratings Based on Water Soluble Sulfate Exposure

Water Soluble Sulfate in Soil (Percent by Weight)

Sulfate Severity (Class)

<0.10 Negligible (S0)

0.10-<0.20 Moderate (S1)

0.20-2.00 Severe (S2)

>2.00 Very Severe (S3)

The test results and the above discussion are provided to assist the designer in the selection of Project materials, concrete type, or other features with respect to corrosion. As appropriate, the designer should consider protective measures, such as coatings, upsizing for section loss, or using alternative materials to reduce the corrosion potential.

6 PRELIMINARY GEOTECHNICAL RECOMMENDATIONS

The preliminary recommendations presented in the following sections are based on our understanding of the Project, conversations with Jacobs, and our subsurface exploration and laboratory testing program.

6.1 Ground Motion Design Parameters

We understand that design ground motion parameters will be based on the requirements of the 2021 International Building Code (International Code Council, 2020), which has adopted the ASCE 7-16 design code for minimum design loads on buildings (ASCE, 2017). These design loads are in turn based on the USGS National Seismic Hazard Maps that were updated in 2008 (Petersen and others, 2008). We characterized the site class using Standard Penetration Test (SPT) N-values (blow counts) noted in our exploration logs and our characterization of geologic conditions at the site. Based on not having shear wave velocity data, we recommend using Site Class C. A site classification of A or B may be appropriate if direct shear wave velocity measurements are obtained. Seismic design parameters for Site Class C are provided in Exhibit 6-1.

Preliminary Geotechnical Report

107528-001 April 2022

Exhibit 6-1: Seismic Design Ground Motion Parameters

Parameter Value

Peak Ground Acceleration, PGA (g) (Site Class B) 0.169

Short-period Spectral Acceleration, SS (g) 0.374

Long-period Spectral Acceleration, S1 (g) 0.114

Site Class C

PGA Site Factor, Fpga 1.23

Short-period Site Factor, Fa 1.3

Long-period Site Factor, Fv 1.5

Site Modified Peack Ground Acceleration, PGAM (PGA x Fpga) (g) 0.208

Site Modified Spectral Acceleration - 0.2 s, SMS (SS x Fa) (g) 0.487

Site Modified Spectral Acceleration - 1.0 s, SM1 (S1 x Fv) (g) 0.17

Seismic Design Value - 0.2 s, SDS (2/3 x SMS) (g) 0.324

Seismic Design Value - 1.0 s, SD1 (2/3 x SM1) (g) 0.114

NOTES:

Calculated in accordance with IBC 2021 (2020) and ASCE 7-16 (2016).

g = gravity; PGA = peak ground acceleration, s = second

6.2 Foundations

We recommend that the proposed structures be supported by either spread/strip footings or mat foundations. Based on the available subsurface data, bedrock was generally encountered at a depth of 1 to 2 feet. Deeper soil, undocumented fill, on the order of 7 feet was encountered on the east side of the existing drying beds in borings BH-05-22 and BH- 06-22. The undocumented fill consisted of clayey sands and gravels and sandy clays. We do not recommend placing foundation elements on undocumented fill. Based on preliminary plans provided by Jacobs (2022) and email correspondence, we anticipate the structures will be generally founded on bedrock.

If structures will be founded above the bedrock elevation, we recommend that undocumented fill be removed to the competent bedrock depth and replaced with Granular Fill (Section 7.2.5). The overexcavated fill can be used for general grading purposes;

however, we do not recommend placing the material beneath structure foundations (see below).

6.2.1 Spread/Strip Footings

We recommend designing spread/strip footings for a net allowable bearing capacities of 10,000 pounds per square foot (psf) and 4,000 psf for foundations on bedrock and properly

Preliminary Geotechnical Report

107528-001 April 2022 compacted Granular Fill, respectively. These capacities can be increased by 33% for transient wind or seismic loads. Strip footings should have a minimum width of 2 feet and rectangular (spread) footings a minimum width of 4 feet. We recommend foundation elements be founded a minimum embedment of 30 inches below finished grade (Coconino County, 2016). If competent bedrock is encountered at a depth shallower than 30 inches below finished grade, the foundations or slab-on-grade may be founded at that depth We anticipate a potential total settlement of footings to be on the order of 1 inch and differential settlement on the order of 0.5 inch over a span of 30 feet on soil and half those settlements for foundations on bedrock. The majority of the settlement is expected to occur as the load is applied.

6.2.2 Mat Foundations

We recommend designing mat foundations for the bearing pressure discussed for spread footings. For the bearing values discussed in Section 6.2.1, we anticipate a settlement of about 1 inch for mats on compacted Granular Fill and 0.5 inch for mats on bedrock.

However, we do not anticipate that bearing capacity will control the mat foundation design.

Instead, we anticipate that the design will be governed by soil-structure interaction and the evaluation of calculated mat settlement (deflections), shears, and moments. Geotechnical information required for this analysis is the subgrade reaction modulus, which is analogous to a spring that can be applied in the structural model to represent the soil/rock response to applied stress. This value is a function of the dimensions of the mat and the stiffness of the underlying soil. Recommended values for subgrade reaction moduli (k) are provided in Exhibit 6-2.

Exhibit 6-2: Recommended Subgrade Reaction Moduli

Subgrade Material Value

Competent Limestone Bedrock 100 - 250 pci

Compacted Granular Fill 25 - 75 pci

NOTES:

pci = pounds per square inch

We recommend evaluating a range of k values and designing for the worst-case conditions to account for potential variability of the bedrock strength and granular fill thickness.

6.3 Lateral Earth Pressures and Lateral Resistance

The lateral earth pressures acting on structure walls depend on many factors, including surcharge loads, the backfill soil type/consistency, and whether the top of the wall is free to yield or deflect laterally during and after excavation. If the top of the wall is free to yield a

Preliminary Geotechnical Report

107528-001 April 2022 minimum of 0.1% of the wall height (i.e., 0.001 times the height [H]), the soil pressures will generally be less (i.e., active condition) than if the wall is not able to yield this amount due to stiffness or resistance of the wall (i.e., at-rest condition). We anticipate that at-rest earth pressures will be appropriate for the structures. Our static earth pressure recommendations for soil backfill are presented in Exhibit 6-3. The static lateral earth pressures assume the structure walls are backfilled with properly compacted granular material in a 1 horizontal to 1 vertical (1H:1V) zone extending upward from the base of the structure from a point 1.5 feet behind the wall. These pressures also assume a vertical wall face and a flat backslope.

As discussed previously, onsite undocumented fill materials are not suitable for reuse as backfill.

Seismic active lateral earth pressure coefficients were determined based on the Mononabe- Okabe method (AASHTO, 2020), and seismic at-rest earth pressure coefficients were determined based on methods developed by Zhang and others (1998). Per AASHTO (2020), the pressure distribution shape for dynamic active earth pressures is triangular, with the resultant force (PAE) acting at the lower third of the wall height (h/3). The parameters are provided in Exhibit 6-3.

Exhibit 6-3: Recommended Lateral Earth Pressure (LEP) Values

Parameter Coefficient

Drained Equivalent Fluid Pressure

(pcf)1,2

Undrained Equivalent Fluid Pressure

(pcf)3 Static Active Earth Pressure KA = 0.28 36 80 Static At-rest Earth Pressure Ko = 0.44 56 90 Static Allowable Passive Earth Pressure4

Kp = 3.3 410 270

Dynamic Active Earth Pressure KAE = 0.34 43 85 Dynamic At-rest Earth Pressure Koe = 0.59 74 100 Dynamic Passive Earth Pressure Kpe = 3.1 390 250

NOTES:

Based on granular soil with an assumed unit weight of 125 pcf and a friction angle of 34 degrees for the retained soil.

Drained equivalent fluid pressure parameters assume no hydrostatic pressure.

Undrained equivalent fluid pressure parameters assume hydrostatic pressures behind wall.

Static Passive Earth Pressure coefficient includes a factor of safety of 2.

pcf = pounds per cubic foot

If narrow backfill zones are utilized between structure walls and the limestone bedrock, updated earth pressures should be evaluated during final design:

If flow fill is utilized as structure backfill, the flow fill may need to be placed incrementally and the walls should be designed for hydrostatic pressures associated with the maximum incremental flow fill lift height.

Preliminary Geotechnical Report

107528-001 April 2022

If Granular Fill can be utilized within a narrow backfill zone, the earth pressures could also be reduced for bin conditions and should be evaluated during final design.

Exhibit 6-4 provides recommended lateral earth pressure (LEP) reduction values based on the backfill aspect ratio (b/H, with b = backfill width and H = backfill height). The reduction values can be applied directly to the drained equivalent fluid pressure from Exhibit 6-3. For undrained conditions (i.e., with hydrostatic pressures behind wall), the reduction values should be applied to only the soil portion of the undrained equivalent fluid pressure (i.e.

[Value - 62.4 pcf]*[Reduction Value] + 62.4 pcf) from Exhibit 6-3. The reduction values can be linearly interpolated between the listed values.

Exhibit 6-4: Recommended LEP Reduction Values for Narrow Backfill Zones

Aspect Ratio (b/H)

Reduction Value

≥ 0.50 1.0

0.40 0.95

≤ 0.25 0.75

NOTES:

b = fill width, H = fill height

Surcharge loads from vehicles/traffic and construction equipment will induce additional lateral loads on structure walls. The pressures provided above do not account for surcharge loads. Lateral loads due to various types of surcharges may be calculated by multiplying the surcharge by the provided pressure coefficient. Surcharge loads should be applied as recommended in Figure 3.

Lateral loads can be resisted by friction along the base of the foundation using an allowable coefficient of sliding resistance of 0.35 for granular fill and 0.45 for bedrock. This allowable value for coefficient of sliding resistance includes a factor of safety of 1.5. In addition, we recommend an allowable passive pressure as provided in Exhibit 6-3. The allowable passive earth pressure coefficient includes a factor of safety of 2 to account for uncertainty in soil properties and to limit the lateral deflection necessary to mobilize the passive resistance.

Passive resistance should be ignored in the upper 30 inches; however, the equivalent fluid pressure line may be projected down from the ground surface.

6.4 Surface Drainage

Surface drainage control is critical in reducing the potential for hydrostatic pressures and soil movements. The ground surface around the structures should be sloped to provide positive drainage away from foundations and structures. We recommend providing a slope of at least 10% for the first 5 feet surrounding the structures. Roof downspouts should

Preliminary Geotechnical Report

107528-001 April 2022 discharge into the storm drain system. If this is not possible, roof downspouts should discharge beyond the limits of foundation backfill or a minimum of 5 feet. We recommend providing splash blocks and downspout extenders, or tightlining downspouts away from the building. Roof downspouts should not be connected into a perimeter foundation drain system.

7 CONSTRUCTION CONSIDERATIONS

The applicability of the design recommendations provided in this report is contingent on good construction practice. Poor construction techniques may alter conditions from those on which our recommendations are based, resulting in reduced foundation capacity and increased settlement. The following sections present construction considerations for this Project.

7.1 Dewatering

Groundwater was not encountered during our subsurface exploration program. Should dewatering be required for some of the deeper facilities, we recommend that a dewatering designer and contractor be obtained for the Project design.

7.2 Earthwork

7.2.1 Site Preparation

We recommend that pavement, brush, and other vegetation be cleared, and roots and stumps be removed from all areas to be improved. Any existing surficial organic topsoil and any soil containing organics also should be stripped and removed. The depth of this removal is anticipated to vary over the site. Pavement, topsoil, and organic-rich soils are not considered suitable for reuse as fill and should be removed from the site or stockpiled for reuse in landscaping areas.

As discussed previously, undocumented fill soils may exist below the facilities. We recommend that all undocumented fill soils be removed beneath all areas of the site where structures are to be constructed.

7.2.2 Excavation

Excavations on the order of 30 feet are expected at the site. In general, excavations greater than 3 feet will encounter bedrock material. Excavation of bedrock material using conventional excavating equipment is anticipated to be limited due to the unconfined

Preliminary Geotechnical Report

107528-001 April 2022 compressive strengths and RQD. Other forms of rock excavation, such as ripping, jackhammer or impact hammer, and blasting will likely be required at the Project site. The chosen method of excavation will largely be dependent on available space and impacts on adjacent structures.

Jackhammers or impact hammers may be used to breakup and chip away the rock with minor impact to adjacent structures. Although mechanized equipment may expedite the work, this method is still relatively slow and may be best for detailed excavation work.

Blasting is likely the most efficient way to break up the bedrock sufficiently for conventual excavation methods. Blasting is also the most likely to have an impact on surrounding structures. We recommend that an experienced blasting contractor be retained to evaluate the use of explosives at the site.

7.2.3 Foundation and Slab Subgrade Preparation

Subgrade excavations should be cleaned of all undocumented fill, debris, or loose/soft material prior to concrete placement and should be kept free of water at all times. All undocumented fill beneath proposed structures should be overexcavated to the bedrock depth and replaced with compacted Granular Fill (Section 7.2.5) to establish adequate foundation support.

Excavations for mat or shallow foundations should be observed by a geotechnical engineering representative familiar with the subsurface conditions to evaluate the adequacy of the bearing stratum and confirm that the subsurface conditions at and below the bearing elevations are consistent with design assumptions and all undocumented fill has been removed.

7.2.4 Fill Placement and Compaction

Fill materials should be placed in horizontal lifts, with the loose lift thickness not to exceed 12 inches for heavy equipment compactors and 6 inches for hand-operated compactors.

Compaction of backfill adjacent to walls can result in higher lateral earth pressures against the wall. As such, small equipment that is hand-operated shall only be used within a line extending upward from the base of the structure at 0.5H:1V, or at least 3 feet from the wall, whichever is greater.

All fill materials shall be compacted to a dense/hard and unyielding condition. Granular Fill should be compacted to a minimum of 95% of its Modified Proctor maximum dry density (ASTM D1557 (ASTM International, 2021)). The moisture content of Granular Fill should be within plus or minus 2% of the optimum moisture content.

Preliminary Geotechnical Report

107528-001 April 2022

For soil subgrades, the compacted surface should be proof-rolled with a fully-loaded, tandem-axle, 10-yard dump truck or equivalent. Areas that are identified as being loose, soft, or yielding during proof-rolling should be recompacted in place. Care should be taken during proof-rolling and subgrade preparation to avoid disturbing subgrade soils and supporting soils that will remain in place, as they can rut under repeated construction traffic.

7.2.5 Granular Fill

Granular Fill should consist of material that is free of organics, contaminants, debris, and rock fragments larger than 3 inches, and have a plasticity index (PI) of less than 10. We recommend that Granular Fill contain a maximum fines content of 20%. It should be noted that as the amount of fines (portion of soil particles passing a U.S. Standard No. 200 sieve, based on the minus ¾-inch fraction) increases, soil becomes more sensitive to small changes in moisture content, and adequate compaction becomes more difficult to achieve. Based our laboratory testing the onsite fill will not meet these requirements. Excavated bedrock, that has been crushed and process to meet the standards in this section, may be used as Granular Fill.

7.3 Temporary Slopes

Temporary excavations will be required to construct the proposed structures. The Contractor will be responsible for excavation stability during construction. As such, the Contractor should evaluate the stability of temporary slope and excavation configurations that may be required during construction.

The safe slope for the excavation of subsurface materials depends on many factors, including: (1) the presence of groundwater; (2) the type, density, and shear strength of the subsurface materials; (3) the depth of excavation; (4) the presence of adjacent structures;

(5) surcharge loading adjacent to the excavation (including excavated material, existing dead or live loads, and construction equipment); and (6) time of construction.

To the extent that temporary excavation slopes are feasible, the following slope conditions are for cost estimating and planning purposes only and limited to slopes up to 20 feet in height. We anticipate that temporary excavations can be made at slopes of 1.5H:1V in granular cohesionless soils. We anticipate that vertical or near vertical excavations can be made in the bedrock material. If temporary slopes will be made, they should be consistent with the Occupational Safety and Health Administration (OSHA) guidelines contained in 29 CFR 1926, Subpart P (OSHA, 1999).

Preliminary Geotechnical Report

107528-001 April 2022

Consistent with conventional practice, the Contractor should be responsible for the actual temporary excavation slopes and shoring, including methods, sequence, and schedule of construction. The Contractor is able to observe the nature and conditions of the subsurface materials encountered and should evaluate the factors discussed above. If instability is observed, slopes should be flattened or shored. All excavations should be accomplished in accordance with local, state, and federal safety regulations.

8 LIMITATIONS

This preliminary report was prepared for the exclusive use of Jacobs and the National Park Service specific application to their design of the Project at this site as it relates to the geotechnical aspects discussed herein. The purpose of this report was to provide information on factual data only, and it should not be construed as a warranty of subsurface conditions, such as those interpreted from the logs and discussions of subsurface conditions in this report. This report is preliminary and is not suitable for final design. It will be necessary for the design-build contractor to develop final geotechnical recommendations for the Project, including completing additional explorations, as necessary.

The conclusions and recommendations presented in this report are based on the site conditions as they presently exist. These opinions further assume that explorations are representative of the subsurface conditions beneath the site; that is, the subsurface conditions everywhere are not significantly different than those disclosed by the explorations.

Within the limitations of the scope, schedule, and budget, the analyses, conclusions, and recommendations presented in this report were prepared in accordance with generally accepted professional geotechnical engineering principles and practice in this area at the time this report was prepared. We make no other warranty, either express or implied.

Shannon & Wilson has prepared the attached "Important Information About Your Geotechnical Report," to assist you and others in understanding the use and limitations of our reports.

Preliminary Geotechnical Report

107528-001 April 2022

9 REFERENCES

American Concrete Institute (ACI), 2019, Building code requirements for structural concrete and commentary, Farmington Hills, Mich., ACI 318-19.

American Association of State Highway and Transportation Officials (AASHTO), 2020, AASHTO LRFD bridge design specifications, Customary U.S. units, 9th edition:

Washington, D.C., American Association of State Highway and Transportation Officials.

American Society of Civil Engineers (ASCE), 2017, Minimum design loads and associated criteria for buildings and other structures: Reston, Va. American Society of Civil Engineers, ASCE Standard ASCE/SEI 7-16, 2 v.

ASTM International, 2021, Standard test methods for laboratory compaction characteristics of soil using modified effort (56,000 ft-lbf/ft3 (2,700 kN-m/m3)), D1557-12(2021):

West Conshohocken, Pa., ASTM International, Annual book of standards, v. 04.08, soil and rock (I): D420 - D5876, 13 p., available: www.astm.org.

Coconino County Arizona, 2016, Community Development - Design Criteria, Building Division, https://www.coconino.az.gov/DocumentCenter/View/8134/Design- Criteria-?bidId=, accessed on 2/23/2022.

Chen & Associates, 1986, Grand Canyon National Park Wastewater Treatment and Disposal Facilities, Work Directive No. 4-001-85-13, South Rim Village, Arizona, Job Number 4 406 85, January 10.

International Code Council, Inc., 2020, International building code 2021: Country Club Hills, Ill., International Code Council, Inc., 1 v.

Jacobs, 2022, Civil Site Improvement, Grand Canyon, South Rim, Plan Set, Drawing No. 113, February.

Maxson, J.H., 1961, Geologic map of the Bright Angel quadrangle, Grand Canyon National Park, Arizona, Grand Canyon Association, 1:48,000.

Occupational Safety & Health Administration (OSHA), 1999, 29 CFR 1926, Subpart P.

Pearthree, P.A., compiler, 1997, Fault number 991, Bright Angel fault zone, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, https://earthquakes.usgs.gov/hazards/qfaults

Preliminary Geotechnical Report

107528-001 April 2022

Petersen, M.D., Frankel, A.D., Harmsen, S.C., and others, 2008, Documentation for the 2008 Update of the United States National Seismic Hazard Maps: U.S. Geological Survey Open-File Report 2008-1128, 61p., https://pubs.er.usgs.gov/publication/ofr20081128

Roberge, P.R., 2012, Handbook of Corrosion Engineering (2nd ed.): N.Y. McGraw-Hill.

United States Geological Survey (USGS), 2017, Geologic Provinces of the United States: Basin and Range Province. Accessed at:

https://geomaps.wr.usgs.gov/parks/provice/basinrange.html.

United States Geological Survey (USGS), 2021, U.S. Quaternary Faults, accessed at https://usgs.maps.arcgis.com/apps/webappviewer/index.html?id=5a6038b3a168456 1a9b0aadf88412fcf.

Zhang, J.-M.; Shamato, Yasuhiro; and Tokimatsu, Kohji, 1998, Seismic earth pressure theory for retaining walls under any lateral displacement: Soils and Foundations, v. 38,

no. 2, p. 143-163.

https://geomaps.wr.usgs.gov/parks/provice/basinrange.html https://usgs.maps.arcgis.com/apps/webappviewer/index.html?id=5a6038b3a1684561a9b0aadf88412fcf https://usgs.maps.arcgis.com/apps/webappviewer/index.html?id=5a6038b3a1684561a9b0aadf88412fcf

Herm it

R d

Her m it R d

M a rk e t P la z a R d

S Entrance

R d

S E n tra nce R d

Havasup a i S t

A lbright Ave

H e rm it

R d

C en te r

R d

Vill age Loop R d

S E n tr an ce

Rd

Grand Canyon Village

Las Vegas

Arizona

Phoenix

Project Location

0 0.5 1

Miles

National Park Service - GRCA-257282 Replace Wastewater Plant South Rim Village

Grand Canyon Village, Arizona

April 2022

VICINITY MAP

FIG. 1

107528-001

N

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants

Site Location

County of Yavapai, Esri, HERE, Garmin, 0 100 200

Approximate Scale In Feet

National Park Service - GRCA-257282 Replace Wastewater Plant South Rim Village

Grand Canyon Village, Arizona

SITE AND EXPLORATION PLAN

FIG. 2

April 2022 107528-001

SHANNON & WILSON, INC.

Geotechnical and Environmental Consultants

HOLE 3

HOLE 4

HOLE 5

HOLE 6

HOLE 7

HOLE 8

HOLE 9

HOLE 10

HOLE 11

HOLE 12

HOLE 13 HOLE 14

BH01-22

BH02-22

BH03-22

BH04-22

BH05-22

BH06-22

Maxar, Microsoft

N

1. Existing borings based on Chen & Associates (1986)

NOTESLEGEND

Chen & Associates 1986 Geotechnical Boring Designation and Approximate Location

!> Shannon & Wilson 2022 Geotechnical Boring Designation and Approximate Location

Future

Facilities Legend 10 - Administration 12 - Maintenance 18 - Vault Waste / Septage Receiving 20 - Headworks 22 - Odor Control 25 - Process Tanks 32 - Process Building 70 - Reclaimed Water Tank 80 - Decant Thickened Digester 85 - Dewatering and Reclaimed Water Pump Station 87 - Composter Facility

For m ≤ 0.4: s H

= 0.28 (psf) (see Note 3)

W a l l

PLAN VIEW

2.0 q

1.5

D e p t h

F a c t o r

Z

B

1.0

0.0

0.5

W a l l

Z

Wall Line

UNIFORM SURCHARGE

a b

EARTH BERM

(see Note 4)

Note:

H z=nH

Bottom of

Excavation x = mH

Point Load in Pounds s H

(psf)

ELEVATION VIEW

x = mH

H

Bottom of

Excavation

W a l l z=nH s H

(psf)

Line Load in

Pounds/Foot

B) LATERAL PRESSURE DUE TO LINE LOAD

i.e. NARROW CONTINUOUS FOOTING

PARALLEL TO WALL

C) LATERAL PRESSURE DUE TO STRIP LOAD

W a l l

W a l l

W a l l

A) LATERAL PRESSURE DUE TO POINT LOAD

i.e. SMALL ISOLATED FOOTING OR WHEEL LOAD y

D) LATERAL PRESSURE DUE TO EARTH BERM

OR UNIFORM SURCHARGE

Bottom of

Excavation

Bottom of

Excavation

E) LATERAL PRESSURE DUE

TO ADJACENT FOOTING

(see Notes 5 and 6)

0 0.5 1.0

L

B

W a l l

Bearing

Pressure q (psf)

1.

2.

3.

4.

5.

6.

I p

, Influence Factor s H

= 2(I p

) q s

Lateral Footing

Pressure on Wall

(derived from NAVFAC DM 7.02, 1986; and Sandhu, Earth Pressure on Walls Due to Surcharge, 1974)

(derived from Poulos and Davis, Elastic Solutions for

Soil and Rock Mechanics, 1974; and Terzaghi and

Peck, Soil Mechanics in Engineering Practice, 1967)

(NAVFAC DM 7.02, 1986)

(derived from Fang, Foundation

Engineering Handbook, 1991)

(NAVFAC DM 7.2, 1986)

Point Load in Pounds g = Unit Weight of Earth Berm

Bearing

Pressure

Earth

Berm s H

= Lateral Pressure in radians

ELEVATION VIEW

(see Note 3)

(see Note 3) q s

L

2B

Q p

H n

(0.16 + n

For m > 0.4: s H

= 1.77 (psf)

Q p

H m n

(m

+ n

Q p s H s'

H

= s H cos

(1.1q) (psf) s'

H s'

H

For m ≤ 0.4: s H

= 0.20 (psf) (see Note 3)

Q l

H n

(0.16 + n

For m > 0.4: s H

= 1.28 (psf)

Q l

H m n

(m

+ n

Q l

Q p y ≤ 33°

H s

≤ 15 Feet

(K)(g)(H s s H

H s s H

= (K)q s

(see Note 4) q s

(psf) s H

= (b - sin b cos2a) (psf)

2q p

L

= 0.25

= 0.5

= 1 s H

L

2B

L

2B

L

2B

RECOMMENDED SURCHARGE

LOADING FOR TEMPORARY AND

PERMANENT WALLS

FIG. 3

107528-001April 2022

NOTES

Figures are not drawn to scale.

Applicable surcharge pressures should be added to appropriate temporary and permanent wall lateral earth and water pressure.

If point or line loads are close to the back of the wall such that m £ 0.4, it may be more appropriate to model the actual load distribution (i.e., Detail E) or use more rigorous analysis methods.

See text for recommended K values.

The stress is estimated on the back of the wall at the center of the length, L, of loading.

The estimated stress is based on a Poisson's ratio of 0.5.

National Park Service - GRCA-257282

Grand Canyon Village, Arizona

National Park Service – GRCA – 257282, Preliminary Geotechnical Report

107528-001 April 2022 4/28/2022-107528-001_R1_AA.docx A-i

AP

PE

ND

IX

A : S

UB

SU

RF

AC

E

EX

PL

OR

AT

IO

NS

Appendix A: Subsurface Explorations

Appendix A

Subsurface Explorations

CONTENTS

A.1 Introduction ........................................................................................................................... A-1

A.2 Explorations ........................................................................................................................... A-1

A.2.1 Soil Classification System ........................................................................................ A-1

A.2.2 Rock Classification System ..................................................................................... A-1

A.2.3 Standard Penetration Test (SPT) ............................................................................ A-2

A.2.4 Rock Core Sampling ................................................................................................ A-2

Figures Figure A-1: Soil Description and Log Key Figure A-2: Rock Description and Log Key Figure A-3 to A-8: Log of Borings BH-01-22 through BH-06-22 Figure A-9 to A-11: Rock Core Photographs: BH-01-22, BH-03-22, and BH-04-22

National Park Service - GRCA – 257282, Preliminary Geotechnical Report

107528-001 April 2022 A-1

AP

PE

ND

IX

A : S

UB

SU

RF

AC

E

EX

PL

OR

AT

A.1 INTRODUCTION

Shannon & Wilson’s field exploration program was conducted from January 17 to January 19, 2022 and consisted of drilling six borings at the locations shown on Figure 2. The methods used to conduct the field exploration program are described below.

A.2 EXPLORATIONS

The borings were coordinated (including subcontractor coordination and utility locates) and observed by Shannon & Wilson. The boring logs are presented in Figures A-3 through A-8.

The exploration logs represent our interpretation of the contents of the field logs and select results of laboratory testing.

The borings were drilled by Vine Laboratories of Commerce City, Colorado (under subcontract to Shannon & Wilson) using a buggy-mounted CME 750X drill rig. The borings were advanced to depths ranging from 9 to 26 feet below existing site grade. The borings were advanced utilizing solid-stem auger, hollow-stem auger, and NQ rock coring methods.

Groundwater was not encountered during drilling in any of the borings. On completion of drilling, the borings were backfilled with drill cuttings and bentonite chips.

A.2.1 Soil Classification System

During exploration, our representative collected samples and prepared field logs of the explorations. Soil classification for this project was based on ASTM D2487, Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), and ASTM D2488, Standard Practice for Description and Identification of Soils (Visual-Manual Procedure). The Unified Soil Classification System is summarized in Figure A-1.

A.2.2 Rock Classification System

The Shannon & Wilson representative classified rock samples in general accordance with the International Society of Rock Mechanics (ISRM) classification method. According to this system, rocks are classified based on the stratigraphic structure, rock strength, degree of weathering, and other properties. The rock classification system is summarized in Figure A-2.

National Park Service - GRCA – 257282, A-2

AP

PE

ND

IX

A : S

UB

SU

RF

AC

E

EX

PL

OR

AT

A.2.3 Standard Penetration Test (SPT)

Disturbed samples were obtained in general accordance with the Standard Penetration Test (SPT) (ASTM Designation: D1586). The SPT consists of driving a 2-inch outside diameter (O.D.), 1.375-inch inside diameter split-spoon sampler a distance of 18 inches with a 140-pound hammer…