25-81-201_Geotechnical report SB Co-parks~1.pdf

GEOTECHNICAL INVESTIGATION REPORT

THREE RESTROOM BUILDINGS REPLACEMENT AT MOJAVE RIVER FORKS REGIONAL PARK

17891 CA-173

City of Hesperia, San Bernardino County, California

CONVERSE PROJECT NO. 25-81-201-01

Prepared For:

COUNTY OF SAN BERNARDINO

PROJECT & FACILITIES MANAGEMENT DEPARTMENT

620 South “E” Street

San Bernardino, California 92415

Prepared By:

CONVERSE CONSULTANTS

2021 Rancho Drive, Suite 1

Redlands, CA 92373 909-796-0544

September 10, 2025

Converse Consultants Geotechnical Engineering, Environmental & Groundwater Science, Inspection & Testing Services

2021 Rancho Drive, Suite 1, Redlands CA 92373 Telephone: (909) 796-0544 ♦ Facsimile: (909) 796-7675 ♦ www.converseconsultants.com

September 10, 2025

Ms. Gloria Loofbourrow Project Manager ll County of San Bernardino Project & Facilities Management Department 620 South “E” Street San Bernardino, California 92415

Subject: GEOTECHNICAL INVESTIGATION REPORT Three Restroom Buildings Replacement at Mojave River Forks Regional Park

17891 CA-173

City of Hesperia, Riverside County, California Converse Project No. 25-81-201-01

Dear Ms. Loofbourrow:

Converse Consultants (Converse) is pleased to submit this Geotechnical Investigation Report to assist with the design and construction of the Three Restroom Buildings Replacement at the Mojave River Forks Regional Park in the City of Hesperia, San Bernardino County, California. This report was prepared in accordance with our proposal dated May 21, 2025, and your signed purchase order 780-26-PO dated July 16, 2025.

Based upon our field investigation, laboratory data, and analyses, the proposed project is considered feasible from a geotechnical standpoint, provided the recommendations presented in this report are incorporated into the design and construction of the project.

We appreciate the opportunity to be of service to the County of San Bernardino Project & Facilities Management Department. Should you have any questions, please do not hesitate to contact us at 909-474-2847.

CONVERSE CONSULTANTS

Hashmi S. E. Quazi, PhD, PE, GE Principal Engineer

Dist.: 1-Electronic-Pdf/ Addressee HSQ/AR/kvg

Geotechnical Investigation Report Restroom Buildings Replacement at Mojave River Forks Regional Park

17891 CA-173

City of Hesperia, San Bernardino County, California

September 9, 2025 Page ii

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PROFESSIONAL CERTIFICATION

This report has been prepared by the following professionals whose seals and signatures appear herein.

The findings, recommendations, specifications and professional opinions contained in this report were prepared in accordance with the generally accepted professional engineering and engineering geologic principle and practice in this area of Southern California. We make no other warranty, either expressed or implied.

Anthony Rosas Jason Bragg Staff Engineer Staff Geologist

Catherine Nelson, PG Hashmi S. E. Quazi, PhD, PE, GE Project Geologist Principal Engineer

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City of Hesperia, San Bernardino County, California

September 9, 2025 Page iii

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TABLE OF CONTENTS

1.0 INTRODUCTION ---------------------------------------------------------------------------------- 1

2.0 PROJECT DESCRIPTION --------------------------------------------------------------------- 1

3.0 SITE DESCRIPTION ----------------------------------------------------------------------------- 1

4.0 SCOPE OF WORK ------------------------------------------------------------------------------- 3

4.1 Project Set-up ----------------------------------------------------------------------------- 3

4.2 Subsurface Exploration ----------------------------------------------------------------- 3

4.3 Laboratory Testing ----------------------------------------------------------------------- 4

4.4 Analysis and Report Preparation ----------------------------------------------------- 4

5.0 SUBSURFACE CONDITIONS ---------------------------------------------------------------- 5

5.1 Subsurface Profile ----------------------------------------------------------------------- 5

5.2 Groundwater ------------------------------------------------------------------------------ 5

5.3 Expansive Soils --------------------------------------------------------------------------- 6

5.4 Collapse Potential ------------------------------------------------------------------------ 6

5.5 Excavatability ----------------------------------------------------------------------------- 7

5.6 Subsurface Variations ------------------------------------------------------------------ 7

6.0 ENGINEERING GEOLOGY -------------------------------------------------------------------- 8

6.1 Regional Geology ------------------------------------------------------------------------ 8

6.2 Local Geology ----------------------------------------------------------------------------- 8

7.0 FAULTING AND SEISMICITY----------------------------------------------------------------- 8

7.1 Faulting ------------------------------------------------------------------------------------- 8

7.2 CBC Seismic Design Parameters -------------------------------------------------- 10

7.3 Secondary Effects of Seismic Activity --------------------------------------------- 11

8.0 LABORATORY TEST RESULTS ---------------------------------------------------------- 12

8.1 Physical Testing ----------------------------------------------------------------------- 12

8.2 Chemical Testing - Corrosivity Evaluation --------------------------------------- 13

9.0 EARTHWORK AND SITE GRADING RECOMMENDATIONS --------------------- 13

9.1 General ----------------------------------------------------------------------------------- 13

9.2 Remedial Grading ---------------------------------------------------------------------- 14

9.3 Cut and Shallow Fill Below Building Pad Areas -------------------------------- 15

9.4 Cut/Fill Transition and Fill Differentials ------------------------------------------- 15

9.5 Engineered Fill -------------------------------------------------------------------------- 16

9.6 Compacted Fill Placement ----------------------------------------------------------- 16

9.7 Shrinkage and Subsidence ---------------------------------------------------------- 17

9.8 Site Drainage ---------------------------------------------------------------------------- 18

9.9 Utility Trench Backfill ------------------------------------------------------------------ 18

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10.0 DESIGN RECOMMENDATIONS ----------------------------------------------------------- 19

10.1 Shallow Foundation Design Parameters ----------------------------------------- 19

10.3 Slabs-on-Grade ------------------------------------------------------------------------- 21

10.4 Expansion Potential ------------------------------------------------------------------- 22

10.5 Settlement ------------------------------------------------------------------------------- 22

10.6 Soil Corrosivity -------------------------------------------------------------------------- 23

10.7 Pavement Recommendations ------------------------------------------------------- 25

10.8 Rigid Pavement Recommendations ----------------------------------------------- 26

10.9 Concrete Flatwork --------------------------------------------------------------------- 26

11.0 CONSTRUCTION RECOMMENDATIONS ----------------------------------------------- 27

11.1 General ----------------------------------------------------------------------------------- 27

11.2 Temporary Sloped Excavations ---------------------------------------------------- 28

12.0 GEOTECHNICAL SERVICES DURING CONSTRUCTION ------------------------- 28

13.0 CLOSURE ---------------------------------------------------------------------------------------- 28

14.0 REFERENCES ---------------------------------------------------------------------------------- 30

FIGURES

Following Page No.

Figure No. 1, Approximate Site Locations Map Figure No. 2, Approximate Boring Locations Map Figure No. 3, Geologic and Groundwater Map

TABLES

Page No.

Table No. 1, Summary of Borings Table No. 2, Summary of USGS Groundwater Depth Data Table No. 3, Collapse Potential Values Table No. 4, Summary of Regional Faults Table No. 5, CBC Seismic Design Parameters Table No. 6, Overexcavation Depths Table No. 7, Overexcavation Depths for Cut/Fill Transitions Table No. 8, Recommended Foundation Parameters Table No. 9, Active and At-Rest Earth Pressures Table No. 10a, Correlation Between Resistivity and Corrosion Table No. 10b, Correlation Between Sulfates and Corrosion Table No. 10c, Correlation Between Chlorides and Corrosion Table No. 10d, Correlation Between pH and Corrosion Table No. 11, Recommended Preliminary Flexible Pavement Sections Table No. 12, Recommended Preliminary Rigid Pavement Sections Table No. 13, Slope Ratios for Temporary Excavations

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City of Hesperia, San Bernardino County, California

September 9, 2025 Page v

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APPENDICES

Appendix A .............................................................................................. Field Exploration Appendix B ............................................................................ Laboratory Testing Program Appendix C .............................................................. Liquefaction and Settlement Analysis

17891 CA-173

City of Hesperia, San Bernardino County, California

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1.0 INTRODUCTION

This report presents the results of our geotechnical investigation performed for the Three Restroom Buildings Replacement at Mojave River Forks Regional Park in the City of Hesperia, San Bernardino County, California. The project location is shown in Figure No.

1, Approximate Site Locations Map.

The purpose of this investigation was to determine the nature and engineering properties of the subsurface soils, and to provide design and construction recommendations for the project.

This report is prepared for the project described herein and is intended for use solely by the County of San Bernardino Project & Facilities Management Department and their authorized agents for design purposes. It should not be used as a bidding document but may be made available to potential contractors for information on factual data only. For bidding purposes, the contractors should be responsible for making their own interpretation of the data contained in this report.

2.0 PROJECT DESCRIPTION

According to the information provided by Gloria Loofbourrow with the County of San Bernardino Project & Facilities Management Department the project includes the demolition and replacement of three existing restrooms. The buildings will be one-story, approximately 640 square feet. The buildings will be masonry block walls with shallow footing foundations.

3.0 SITE DESCRIPTION

The project site is located within the Mojave River Forks Regional Park in the City of Hesperia, San Bernardino County, California. The site is bounded on the north and west by State Route 173 (CA-173) and on the east and south by undeveloped land covered with natural vegetation. The site is used as a campground for recreational activities.

The proposed project location can be accessed by an existing secured gate that enters the Mojave River Forks Regional Park from 17891 CA-173. The restroom buildings can be accessed by following the paved road and the signs labelled “tent sites”. The proposed project area is relatively flat with surface elevations ranging from 3,150 to 3,175 feet above mean sea level (amsl).

Photograph Nos. 1 through 3 show the current conditions at the site.

Project No.

Figure No.

25-81-201-01

Approximate Site Locations Map

Project:

Location:

Three Restroom Buildings Replacement at

Mojave River Forks Regional Park

For: County of San Bernardino

Approximate Site Location

(Not to Scale)

Converse Consultants

Project No.

Figure No.

25-81-201-01

Approximate Site Locations Map

Project:

Location:

Three Restroom Buildings Replacement at

Mojave River Forks Regional Park

For: County of San Bernardino

Approximate Site Location

(Not to Scale)

17891 CA-173

City of Hesperia, San Bernardino County, California

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Photograph No. 1: Present site conditions at BH-01, facing southwest.

Photograph No. 2: Present site conditions at BH-02, facing southeast.

17891 CA-173

City of Hesperia, San Bernardino County, California

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Photograph No. 3: Present site conditions at BH-03, facing west.

4.0 SCOPE OF WORK

The scope of this investigation included project set-up, subsurface exploration, laboratory testing, engineering analysis, and preparation of this report, as described in the following sections.

4.1 Project Set-up

The project set-up consisted of the following tasks.

Prepared a boring locations map and submitted it to Gloria Loofbourrow with San

Bernardino County for review and approval.

Coordinated with Gloria Loofbourrow for site access.

Conducted a field reconnaissance and marked the boring locations such that the drill rig access to all locations was available.

Notified Underground Service Alert (USA) at least 48 hours prior to drilling to clear the boring locations of any conflict with existing underground utilities.

Engaged a California-licensed driller to drill exploratory borings.

4.2 Subsurface Exploration

Three exploratory borings (BH-01 through BH-03) were drilled at three different sites on August 5, 2025, to investigate the subsurface conditions at the site. The borings were drilled using an 8-inch diameter hollow stem auger to the maximum explored depth of

51.5 feet below existing ground surface (bgs).

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City of Hesperia, San Bernardino County, California

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The proposed and completed depths of the borings are presented in Table No. 1, Summary of Borings, below. The planned depths were achieved in all borings.

Table No. 1, Summary of Borings

Boring No. Boring Depth (ft, bgs) Groundwater Depth (ft. bgs)

Date Completed Proposed Completed

BH-01 50.0 51.5 43.8 8/5/25

BH-02 10.0 11.5 Not Encountered 8/5/25 BH-03 10.0 10.5 Not Encountered 8/5/25

Approximate boring and percolation test locations are indicated in Figure No. 2, Approximate Boring Locations Map. For a description of the field exploration and sampling program, see Appendix A, Field Exploration.

4.3 Laboratory Testing

Representative soil samples from the project site were tested in the laboratory to aid in the soils classification and to evaluate the relevant engineering properties of the soils. These tests included the following.

In-situ moisture contents and dry densities (ASTM D2216-19 and ASTM D2937-

24) Expansion index (EI) (ASTM D4829-21) R-value (R) (CT301) Soil corrosivity (CR) (California Tests 643, 422, and 417) Collapse potential (CL) (ASTM D4546-21) Passing Sieve No.200 (WA) (ATSM D1140-17) Maximum dry density and optimum-moisture content (CP) (ASTM D1557-12R21) Direct shear (DS) (ASTM D3080/D3080M-23)

For in-situ moisture and dry density data, see the Logs of Borings in Appendix A, Field Exploration. For a description of the laboratory test methods and test results, see Appendix B, Laboratory Testing Program.

4.4 Analysis and Report Preparation

Data obtained from the field exploration and laboratory testing program was assembled and evaluated. Geotechnical analyses of the compiled data were performed, followed by the preparation of this report to present our findings, conclusions, and recommendations for the project.

Project:

County of San Bernardino

Location: 25-81-201-0117891 CA-173

City of Hesperia, San Bernardino County, California

For:

Three Restroom Buildings Replacement at

Mojave River Forks Regional Park Project No.

Approximate Boring Locations Map

Figure No.

Number / Depth and Approximate Location of Exploratory Boring

Number / Depth and Approximate Location of Exploratory Boring

Number / Depth and Approximate Location of Exploratory Boring

BH-03 / 51.5'BH-03 / 51.5'

BH-01 / 51.5'

BH-02 / 11.5'

BH-03 / 10.5'

Project:

County of San Bernardino

Location: 25-81-201-0117891 CA-173

City of Hesperia, San Bernardino County, California

For:

Three Restroom Buildings Replacement at

Mojave River Forks Regional Park Project No.

Approximate Boring Locations Map

Figure No.

Number / Depth and Approximate Location of Exploratory Boring

Number / Depth and Approximate Location of Exploratory Boring

Number / Depth and Approximate Location of Exploratory Boring

BH-03 / 51.5'BH-03 / 51.5'

BH-01 / 51.5'

BH-02 / 11.5'

BH-03 / 10.5'

17891 CA-173

City of Hesperia, San Bernardino County, California

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5.0 SUBSURFACE CONDITIONS

A general description of the surface and subsurface conditions and various materials encountered during our field exploration are presented in this section.

5.1 Subsurface Profile

Based on the exploratory borings and laboratory test results, the subsurface soil at the site, to the depths explored, consist of alluvial fan deposits which are primarily alternating layers of sand, silty sand and sand with silt. The alluvium was generally fine to coarse grained, medium dense to very dense, moist and various shades of brown.

For a detailed description of the subsurface materials encountered in the exploratory borings, see Drawings No. A-2a and A-2b through A-4, Logs of Borings, in Appendix A, Field Exploration.

5.2 Groundwater

Groundwater was encountered at 43.8 feet bgs and stabilized at 39.5 feet bgs in BH-01 during the investigation to a depth of 51.5 feet bgs. For comparison, national and regional groundwater databases were accessed as detailed below.

For comparison, regional groundwater data from the GeoTracker database (SWRCB, 2025) was reviewed to evaluate the current and historical groundwater levels. No site with groundwater data was identified within a 1.0-mile radius of the project site.

The National Water Information System (USGS, 2025) was reviewed for current and historical groundwater data from sites within an approximately 1.0-mile radius of the proposed development and the results of that search are included in Table No. 2, Summary of USGS Groundwater Depth Data, below.

Table No. 2, Summary of USGS Groundwater Depth Data

Site Number Location Groundwater Depth Range

(ft. bgs) Date Range

342006117154801 Approximately 1,700 feet north 103-121 1957-1969

342000117160001 Approximately 4,200 feet northwest 82-145 1991-2025

341940117154801 Approximately 1,700 feet south 29 1957

341925117154901 Approximately 3,000 feet south 6 1957

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City of Hesperia, San Bernardino County, California

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The California Department of Water Resources database (DWR, 2025) was reviewed for historical groundwater data from sites within a 1.0-mile radius of the project site. No site with groundwater data was found within a 1.0-mile radius of the project site.

Based on the depth explored during our investigation, as well as current and historical data in the vicinity of the project site, groundwater is expected to be deeper than 48.3 feet bgs. Groundwater is not expected to be encountered during construction. It should be noted that the groundwater level could vary depending upon the seasonal precipitation and possible groundwater pumping activity in each site vicinity. Shallow perched groundwater may be present locally, particularly following precipitation or irrigation events.

5.3 Expansive Soils

Expansive soils are characterized by their ability to undergo significant volume changes (shrink or swell) due to variations in moisture content. Changes in soil moisture content can result from precipitation, landscape irrigation, utility leakage, roof drainage, perched groundwater, drought, or other factors and may result in unacceptable settlement or heave of structures or concrete slabs supported on grade. Depending on the extent and location below finish subgrade, expansive soils can have a detrimental effect on structures.

Based on the laboratory test results, the expansion index was between 1 and 2, corresponding to very low expansion potentials.

5.4 Collapse Potential

Soil deposits subjected to collapse/hydro-consolidation generally exist in regions of moisture deficiency. Collapsible soils are generally defined as soils that have potential to suddenly decrease in volume upon increase in moisture content even without an increase in external loads. Moreover, some soils may have a different degree of collapse/hydro-consolidation based on the amount of proposed fill or structure loads. Soils susceptible to collapse/ hydro-consolidation include wind-blown silt, weakly cemented sand, and silt where the cementing agent is soluble (e.g. soluble gypsum, halite), alluvial or colluvial deposits within semi‐arid to arid climate, and certain weathered bedrock above the groundwater table.

Granular soils may have a potential to collapse upon wetting in arid climate regions.

Collapse/hydro-consolidation may occur when the soluble cements (carbonates) in the soil matrix dissolve, causing the soil to densify from its loose/low density configuration from deposition.

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The degree of collapse of a soil can be defined by the collapse potential value, which is expressed as a percentage of collapse of the total sample using the Collapse Potential Test (ASTM D4546). According to the ASTM guideline, the severity of collapse potential is commonly evaluated by the following Table No. 3, Collapse Potential Values.

Table No. 3, Collapse Potential Values

Collapse Potential Value (%) Severity of Problem 0 None

0.1 to 2 Slight

2.1 to 6.0 Moderate

6.0 to 10.0 Moderately Severe >10 Severe

Three collapse tests were conducted for this project. Based on the laboratory test results a collapse potential between 0.4 and 1.6 percent, (slight collapse potential) is anticipated at the sight. Collapse potential distress is typically considered a concern when collapse potential is over 2% (LA County, 2013).

5.5 Excavatability

The surface and subsurface soil materials at the site are expected to be excavatable by conventional heavy-duty earth moving and trenching equipment. However, excavation will be difficult if concentration of gravel is encountered.

The phrase “conventional heavy-duty excavation equipment” is intended to include commonly used equipment such as excavators and trenching machines. It does not include hydraulic hammers (“breakers”), jackhammers, blasting, or other specialized equipment and techniques used to excavate hard earth materials. Selection of an appropriate excavation equipment model should be done by an experienced earthwork contractor and may require test excavations in representative areas.

5.6 Subsurface Variations

Based on the results of the subsurface exploration and our experience, some variations in the continuity and nature of subsurface conditions within the project site should be anticipated. Because of the uncertainties involved in the nature and depositional characteristics of the earth material, care should be exercised in interpolating or extrapolating subsurface conditions between or beyond the boring locations.

17891 CA-173

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6.0 ENGINEERING GEOLOGY

The regional and local geology within the proposed project area is discussed below.

6.1 Regional Geology

The project site is located in the Mojave Desert Geomorphic Province of Southern California.

The Mojave Desert is a broad interior region of isolated mountain ranges separated by wide desert plains. The area is roughly triangular shaped and bounded by the Garlock Fault on the north, the San Andreas Fault on the southwest, and the Colorado River on the east. The drainages are primarily closed and terminate in playas within the valley floors.

The province is a seismically active region primarily characterized by a series of northwest-southeast-trending strike-slip faults and east-west trending secondary faults. The most prominent of the nearby fault zones include the Helendale, Lenwood, Landers, and San Andreas Fault Zones, all of which have been known to be active during Quaternary time.

Extension of the region has resulted in exposure of basement rocks dating to the Precambrian age, deposition of young Holocene-aged and older Pleistocene-aged sedimentary basins, with eruptions of volcanic units.

6.2 Local Geology

The project site is underlain by early Holocene-aged Young Alluvial Fan Deposits. The young alluvial fan deposits primarily consist of sand, silt and gravel. (Dibblee and Minch, 2008).

For a map of mapped geology and groundwater see Figure No. 3, Geologic and Groundwater Map.

7.0 FAULTING AND SEISMICITY

The approximate distance and seismic characteristics of nearby faults as well as seismic design coefficients are presented in the following subsections.

7.1 Faulting

The proposed site is situated in a seismically active region. As is the case for most areas of Southern California, ground-shaking resulting from earthquakes associated with nearby and more distant faults may occur at the project site. During the life of the project, seismic activity associated with active faults can be expected to generate moderate to strong ground shaking at the site.

Project No.

Figure No.

25-81-201-01

Location:

Project: Three Restroom Buildings Replacement at

Mojave River Forks Regional Park

17891 CA-173

City of Hesperia, San Bernardino County, California For: County of San Bernardino For: County of San Bernardino

Legend

Approximate Project

Location

Qg Young Alluvial Fan

Deposits, Sand and

Gravel

Qa Young Alluvial

Fan Deposits, Sand

Qot Older Alluvial Fan

Deposits, Gravel

Approximate Project

Location

Location and depth

(ft, bgs) of shallowest groundwater measurement.

Dates ranging from 1957-2025.

Converse Consultants

Project No.

Figure No.

25-81-201-01

Geologic & Groundwater Map

Location:

Project: Three Restroom Buildings Replacement at

Mojave River Forks Regional Park

17891 CA-173

City of Hesperia, San Bernardino County, California For: County of San Bernardino For: County of San Bernardino

Legend

Approximate Project

Location

Qg Young Alluvial Fan

Deposits, Sand and

Gravel

Qa Young Alluvial

Fan Deposits, Sand

Qot Older Alluvial Fan

Deposits, Gravel

Approximate Project

Location

Location and depth

(ft, bgs) of shallowest groundwater measurement.

Dates ranging from 1957-2025.

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The project site is not located within a currently mapped State of California Earthquake Fault Zone for surface fault rupture. Table No. 4, Summary of Regional Faults, summarizes selected data of known faults capable of seismic activity within 100 kilometers of the site using the generalized coordinates of 34.33135° N, -117.26388° W.

The data presented below was calculated using the National Seismic Hazard Maps Database (USGS, 2008) and other published geologic data.

Table No. 4, Summary of Regional Faults

Fault Name and Section Closest

Distance (km)

Slip Sense Length (km)

Slip Rate (mm/year)

Maximum Magnitude

North Frontal (West) 0.89 reverse 50 1 7.2 Cleghorn 6.21 strike slip 25 3 6.8 S. San Andreas 15.32 strike slip 548 n/a 8.18 Cucamonga 23.37 thrust 28 5 6.7 Helendale-So Lockhart 29.35 strike slip 114 0.6 7.4 North Frontal (East) 42.69 thrust 27 0.5 7 San Jose 46.06 strike slip 20 0.5 6.7 Sierra Madre 49.57 reverse 57 2 7.2 Lenwood-Lockhart-Old Woman Springs 51.6 strike slip 145 0.9 7.5

Clamshell-Sawpit 54.52 reverse 16 0.5 6.7 Chino, alt 1 55.42 strike slip 24 1 6.7 Johnson Valley (No) 57.41 strike slip 35 0.6 6.9 Pinto Mtn 58.7 strike slip 74 2.5 7.3 Landers 62.53 strike slip 95 0.6 7.4 Elsinore 63.16 strike slip 241 n/a 7.85 Gravel Hills-Harper Lk 67.8 strike slip 65 0.7 7.1 Raymond 69.45 strike slip 22 1.5 6.8 So Emerson-Copper Mtn 70.09 strike slip 54 0.6 7.1 Puente Hills (Coyote Hills) 73.55 thrust 17 0.7 6.9 Calico-Hidalgo 77.1 strike slip 117 1.8 7.4 Blackwater 78.61 strike slip 60 0.5 7.1 Burnt Mtn 81.82 strike slip 21 0.6 6.8 Elysian Park (Upper) 82.38 reverse 20 1.3 6.7 Puente Hills (Santa Fe Springs) 82.5 thrust 11 0.7 6.7

Eureka Peak 83.35 strike slip 19 0.6 6.7 Verdugo 84.92 reverse 29 0.5 6.9 San Joaquin Hills 87.5 thrust 27 0.5 7.1

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Fault Name and Section Closest

Distance (km)

Slip Sense Length (km)

Slip Rate (mm/year)

Maximum Magnitude

Pisgah-Bullion Mtn- Mesquite Lk 88.17 strike slip 88 0.8 7.3

Puente Hills (LA) 89.09 thrust 22 0.7 7 Hollywood 92.09 strike slip 17 1 6.7 San Gabriel 93.55 strike slip 71 1 7.3 Santa Monica Connected alt 2 97.18 strike slip 93 2.4 7.4

Newport Inglewood Connected alt 1 99.2 strike slip 208 1.3 7.4

(Source: https://earthquake.usgs.gov/cfusion/hazfaults_2008_search/)

7.2 CBC Seismic Design Parameters

Seismic parameters based on the 2022 California Building Code (CBSC, 2022) are provided in Table No. 5, CBC Seismic Design Parameters. These parameters were determined using the generalized coordinates 34.33135°N, -117.26388°W and the ASCE Online Hazard Tool.

Table No. 5, CBC Seismic Design Parameters

Seismic Parameters

Site Coordinates 34.33135°N, -117.26388°W

Site Class D Risk Category II Mapped Short period (0.2-sec) Spectral Response Acceleration, SS 1.94g

Mapped 1-second Spectral Response Acceleration, S1 0.66g Site Coefficient (from Table 11.4-1), Fa 1.0 Site Coefficient (from Table 11.4-2), Fv 1.7 MCE 0.2-sec period Spectral Response Acceleration, SMS 2.15g MCE 1-second period Spectral Response Acceleration, SM1 1.70g Design Spectral Response Acceleration for short period SDS 1.44g Design Spectral Response Acceleration for 1-second period, SD1 1.13g Site Modified Maximum Peak Ground Acceleration, PGAM 0.80g

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7.3 Secondary Effects of Seismic Activity

In general, secondary effects of seismic activity include surface fault rupture, soil liquefaction, landslides, lateral spreading, and settlement due to seismic shaking, tsunamis, seiches, and earthquake-induced flooding. The site-specific potential for each of these seismic hazards is discussed in the following sections.

Surface Fault Rupture: The site is not located within a currently designated State of California or San Bernardino County Earthquake Fault Zone (CGS, 2007; San Bernardino County, 2025). There are no known active faults projecting toward or extending across the project site. The potential for surface rupture resulting from the movement of nearby major faults is not known with certainty but is considered low.

Liquefaction: Liquefaction is defined as the phenomenon in which a cohesionless soil mass within the upper 50 feet of the ground surface suffers a substantial reduction in its shear strength, due to the improvement of excess pore pressures. During earthquakes, excess pore pressures in saturated soil deposits may develop as a result of induced cyclic shear stresses, resulting in liquefaction.

Soil liquefaction generally occurs in submerged granular soils and non-plastic silts during or after strong ground shaking. There are several general requirements for liquefaction to occur, and they are as follows.

Soils must be submerged.

Soils must be loose to medium-dense.

Ground motion must be intense.

Duration of shaking must be sufficient for the soils to lose shear resistance.

Based on a site-specific liquefaction analysis presented in Appendix C, Liquefaction and Settlement Analysis, the potential for liquefaction of the site is expected to be negligible.

Seismic Settlement: Dynamic dry settlement may occur in loose, granular, unsaturated soils during a large seismic event. Based on a site-specific liquefaction analysis presented in Appendix C, Liquefaction and Settlement Analysis, the potential for dynamic dry settlement of the site is negligible.

Landslides: Seismically induced landslides and slope failures are common occurrences during or soon after large earthquakes. Due to the flat nature of the site, the potential for seismically induced landslides affecting the proposed site is considered to be low.

Lateral Spreading: Seismically induced lateral spreading involves primarily lateral movement of earth materials over underlying materials which are liquefied due to ground shaking. It differs from the slope failure in that complete ground failure involving large

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Lateral spreading is demonstrated by near-vertical cracks with predominantly horizontal movement of the soil mass involved. Due to the relatively flat nature of the site, the risk of lateral spreading is considered very low.

Tsunamis: Tsunamis are large waves generated in open bodies of water by fault displacement or major ground movement. Due to the inland location of the site, tsunamis are not considered to be a risk.

Seiche: Seiches are large waves generated in enclosed bodies of water in response to ground shaking. Due to the distance from any enclosed bodies of water, seiching is not considered to be a risk.

Earthquake-Induced Flooding: Dams or other water-retaining structures may fail as a result of large earthquakes. The project site is not located within the State of California or Riverside County designated dam inundation zone (CGS, 2007; Riverside County, 2025).

The risk of earthquake-induced flooding affecting the project site is considered low.

8.0 LABORATORY TEST RESULTS

Results of physical and chemical tests performed for this project are presented below.

8.1 Physical Testing

Results of the various laboratory tests are presented in Appendix B, Laboratory Testing Program, except for the results of in-situ moisture and dry density tests which are presented on the Logs of Borings in Appendix A, Field Exploration. The results are also discussed below.

In-situ Moisture and Dry Density: In-situ dry densities and moisture contents of the alluvium soils in the upper 10 feet bgs. were determined in accordance with ASTM Standard D2216-19 and D2937-24. Dry densities of onsite soils ranged from 107 to 122 pounds per cubic foot (pcf) with moisture content of 2 to 5 percent.

Expansion Index (EI): Two representative samples from the upper 10 feet soils were tested to evaluate the expansion potential in accordance with ASTM Standard D4829-21. The EI test results were 1 and 2.

R-Value (R): One representative bulk sample was tested in accordance with Caltrans Test Method 301 and ASTM d284 and D2844M-18e1. The R-value test result was 38.

Collapse Potential (CL): The collapse potential of three relatively undisturbed samples were tested under a vertical stress of up to 2.0 kips per square foot (ksf) in accordance with the ASTM Standard D4546-21 test method. The test results showed collapse potentials ranging from 0.4 to 1.6 percent.

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Percent Passing #200 Sieve (WA): Six representative soil samples were tested in accordance with the ASTM Standard D1140-17. The fine contents ranged from

11.1 to 48.0 percent.

Maximum Dry Density and Optimum Moisture Content (CP): Typical moisture-density relationship tests were performed on one representative sample in accordance with ASTM D1557-12R21. The result is presented in Drawing No. B- 1, Moisture-Density Relationship Results, in Appendix B, Laboratory Testing Program. The laboratory maximum dry density is 133.5 pounds per cubic feet (pcf), with optimum moisture content at 7.0 percent.

Direct Shear (DS): One direct shear test was performed on relatively undisturbed representative ring samples under soaked moisture conditions in accordance with ASTM Standard D3080/D3080M-23. The result is presented in Drawings No. B-2, Direct Shear Test Results in Appendix B, Laboratory Testing Program.

8.2 Chemical Testing - Corrosivity Evaluation

One representative soil sample was tested to determine minimum electrical resistivity, pH, and chemical content, including soluble sulfate and chloride concentrations. The purposes of these tests were to determine the corrosion potential of site soils when placed in contact with common pipe materials. These tests were performed by Keegan Labs (Pomona, CA) in accordance with California Tests 643, 422, and 417. The test results are presented in Appendix B, Laboratory Testing Program and summarized below.

The pH measurement of the tested sample was 7.8.

The sulfate content of the tested sample was 58 ppm.

The chloride concentration of the tested sample was 27 ppm.

The minimum electrical resistivity when saturated was 5,330 ohm-cm.

9.0 EARTHWORK AND SITE GRADING RECOMMENDATIONS

Recommendations for earthwork are presented in the following sections.

9.1 General

This section contains our general recommendations regarding earthwork and grading for the project. These recommendations are based on the results of our field exploration, laboratory tests, our experience with similar projects, and data evaluation as presented in the preceding sections. These recommendations may require modification by the geotechnical consultant based on observation of the actual field conditions during grading.

Prior to the start of construction, all existing underground utilities and appurtenances should be located at the project site. Such utilities should either be protected in-place or removed and replaced during construction as required by the project specifications. All

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All debris, surface vegetation, deleterious material, and surficial soils containing roots and perishable materials should be stripped and removed from the site.

The final bottom surfaces of all excavations should be observed and approved by the project geotechnical consultant prior to placing any fill. Based on these observations, localized areas may require remedial grading deeper than indicated herein. Therefore, some variations in the depth and lateral extent of excavation recommended in this report should be anticipated.

Observations and field tests should be performed by the project soils consultant to confirm that the required degree of compaction has been obtained. Where compaction is less than specified, additional compactive effort should be made with adjustment of the moisture content as necessary, until the specified compaction is obtained.

It should be the responsibility of the contractor to maintain safe working conditions during all phases of construction.

9.2 Remedial Grading

Building footings, slab-on-grade and pavements should be uniformly supported by compacted fill. In order to provide uniform support, structural areas should be overexcavated, scarified, and recompacted as follows.

Table No. 6, Overexcavation Depths

Structure/Pavement Minimum Overexcavation Depth

Foundation (Restrooms) 12 inches below footings or 4 feet below ground surface, whichever is deeper

Slab-on-grade 24 inches below slab bottom or 2 feet below ground surface, whichever is deeper

Pavement 12 inches below finished grade or 2 feet below ground surface, whichever is deeper

The change in depth of the overexcavation below the footings and slabs-on-grade should be transitioned by a gradual slope. Generally, overexcavation should extend to at least 5 feet beyond the footprint of the building foundation, at least 2 feet beyond the footprint of the slab-on-grade and at least 1 foot beyond the edge of pavement. The overexcavation bottom should be scarified and compacted as described in Section 9.6, Compacted Fill Placement.

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The final bottom surfaces of all excavations should be observed and approved by the project geotechnical consultant prior to placing any fill or structures. However, localized, deeper over-excavation could be required based observation made during grading of the final bottom surfaces of all excavations should be approved by the geotechnical consultant.

If isolated pockets of very soft, loose, eroded, or pumping soil are encountered, the unstable soil should be excavated as needed to expose undisturbed, firm, and unyielding soils.

The contractor should determine the best manner to conduct the excavations, such that there are no losses of bearing and/or lateral support to the existing structures or utilities (if any).

Areas to receive fill and/or other surface improvements should be scarified to a minimum depth of 6 inches, brought to a near-optimum moisture condition, and recompacted to at least 90 percent relative compaction (based on ASTM Test Method D1557-12R21).

9.3 Cut and Shallow Fill Below Building Pad Areas

Building pads with shallow cut and fill areas should be capped with a minimum of 4.0 feet of engineered structural fill, so that all footings for structures and walls are founded into engineered fill with a minimum of 2.0 feet of fill below footings for proposed structures and walls. Over-excavation should extend to the entire level portions of the building pad area with proposed structures or walls, to the depth of fill.

9.4 Cut/Fill Transition and Fill Differentials

To mitigate distress to structures related to the potential adverse effects of excessive differential settlement, cut/fill transitions should be eliminated from all level portions of the building pad areas. This should be accomplished by overexcavating the entire “cut” portion of the building pad area by at least 4.0 feet below proposed grade and replacing the excavated materials as properly compacted fill, so that all footings for structures and walls are founded into engineered fill with a minimum of 2.0 feet of fill below footings for proposed structures and walls. Recommended depths of over-excavation are provided in the following table.

Table No. 7, Overexcavation Depths for Cut/Fill Transitions

Depth of Fill (“Fill” Portion) Depth of Overexcavation (“Cut” Portion)

Up to 3.0 feet 3.0 feet

Greater than 3.0 feet One-third the maximum thickness of fill placed on the “fill” portion (15 feet maximum)

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9.5 Engineered Fill

No fill should be placed until excavations and/or natural ground preparation have been observed by the geotechnical consultant. The native soils encountered within the project sites are generally considered suitable for re-use as compacted fill. Excavated soils should be processed, including removal of roots and debris, removal of oversized particles, mixing, and moisture conditioning, before placing as compacted fill. On-sites soils used as fill should meet the following criteria.

No particles larger than 8 inches in largest dimension.

Rocks larger than 4 inches should not be placed within the upper 12 inches of subgrade soils.

Free of all significant organic matter, debris, or other deleterious material.

Expansion index of 50 or less.

Sand Equivalent greater than 15 (greater than 30 for pipe bedding).

Contain less than 30 percent by weight retained in 3/4-inch sieve.

Contain less than 40 percent fines (passing #200 sieve).

Based on field investigation and laboratory testing results, on-site soils may be suitable as fill materials provided that appropriate corrosion mitigation and moisture conditioning will be applied.

Imported materials, if required, should meet the above criteria prior to being used as compacted fill. Any imported fills should be tested and approved by a geotechnical representative at least 72 hours prior to delivery to the site.

9.6 Compacted Fill Placement

All surfaces to receive structural fills should be scarified to a depth of 12 inches. The soil should be moisture conditioned to within ±3 percent of optimum moisture content for coarse soils and 0 to 2 percent above optimum moisture content for fine soils. The scarified soils should be recompacted to at least 90 percent of the laboratory maximum dry density.

Fill soils should be thoroughly mixed, and moisture conditioned to within ±3 percent of optimum moisture content for coarse soils and 0 to 2 percent above optimum moisture content for fine soils. Fill soils should be evenly spread in horizontal lifts not exceeding 8 inches in uncompacted thickness.

Fill soils should be thoroughly mixed, and moisture conditioned to at least 0 to 2 percent above optimum moisture content. Fill soils should be evenly spread in horizontal lifts not exceeding 8 inches in uncompacted thickness.

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All fill placed at the site should be compacted to at least 90 percent of the laboratory maximum dry density as determined by ASTM Standard D1557 test method unless a higher compaction is specified herein. The upper 12 inches of subgrade soils underneath pavements intended to support vehicle loads should be scarified, moisture conditioned and compacted to at least 95 percent of the laboratory maximum dry density.

Fill materials should not be placed, spread or compacted during unfavorable weather conditions. When site grading is interrupted by heavy rain, filling operations should not resume until the geotechnical consultant approves the moisture and density conditions of the previously placed fill.

Observations and field tests should be performed by the project soils consultant to confirm that the required degree of compaction has been obtained. Where compaction is less than specified, additional compactive effort should be made with adjustment of the moisture content as necessary, until the specified compaction is obtained.

Additional expansion index and corrosion testing should be completed after all fill has been placed and compacted at the site in order to confirm the soil properties and revise the foundation design parameters if necessary.

9.7 Shrinkage and Subsidence

The volume of excavated and recompacted soils will decrease as a result of grading. The shrinkage would depend on, among other factors, the depth of cut and/or fill, and the grading method and equipment utilized. Based on our exploration as well as previous experience in other projects in close vicinity of this site, for the preliminary estimation, shrinkage factors for various units of earth material at the site may be taken as presented below.

The shrinkage factor (defined as a percentage of soil volume reduction when moisture conditioned and compacted to the average of 92 percent relative compaction) for the upper 10 feet, an average value of 5 percent may be used for preliminary earthwork planning.

Subsidence (defined as the settlement of native materials from the equipment load applied during grading and proposed fill loads) would depend on the construction methods including type of equipment utilized. Ground subsidence is estimated to be approximately 0.10 foot to 0.15 foot.

Although these values are only approximate, they represent our best estimates of the factors to be used to calculate lost volume that may occur during grading. If more accurate shrinkage and subsidence factors are needed, it is recommended that field-testing using the actual equipment and grading techniques be conducted.

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9.8 Site Drainage

Adequate positive drainage should be provided away from the structures and excavation areas to prevent ponding and to reduce percolation of water into the foundation soils. A desirable drainage gradient is 1 percent for paved areas and 2 percent for landscaped areas. Surface drainage should be directed to suitable non-erosive devices.

9.9 Utility Trench Backfill

The following sections present earthwork recommendations for utility trench backfill, including trench zone backfill.

Open cuts adjacent to existing roadways or structures are not recommended within a 1:1 (horizontal: vertical) plane extending down and away from the roadway or structure perimeter (if any).

Soils from the trench excavation should not be stockpiled more than 6 feet in height or within a horizontal distance from the trench edge equal to the depth of the trench.