Exhibit_I_-_GEOTECHNICAL_EVALUATION,_SIDEWALK_EXTENSION_PROJECT_DATED_SEPTEMBER_2,_2021.pdf

Geotechnical Evaluation Sidewalk Extension Project

Crawford Canyon Road and Newport Avenue

North Tustin, California

Orange County Public Works

OC Construction/Materials Lab - Geotechnical

1152 East Fruit Street | Santa Ana, California 92701

September 2, 2021 | Project No. 211686001

Geotechnical | Environmental | Construction Inspection & Testing | Forensic Engineering & Expert Witness

Geophysics | Engineering Geology | Laboratory Testing | Industrial Hygiene | Occupational Safety | Air Quality | GIS

475 Goddard, Suite 200 | Irvine, California 92618 | p. 949.753.7070 | www.ninyoandmoore.com

Geotechnical Evaluation

Sidewalk Extension Project Crawford Canyon Road and Newport Avenue North Tustin, California

Ms. Jennifer Prause

Orange County Public Works

OC Construction/Materials Lab - Geotechnical

1152 East Fruit Street | Santa Ana, California 92701

September 2, 2021 | Project No. 211686001

Morteza Mirshekari, PhD, PE Project Engineer

Ronald Hallum, PG, CEG Principal Geologist

Daniel Chu, PhD, PE, GE Principal Engineer

GM/MRM/RDH/DBC/sc/mlc http://www.ninyoandmoore.com/

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CONTENTS

1 INTRODUCTION 1

2 SCOPE OF SERVICES 1

3 SITE DESCRIPTION 2

4 PROPOSED CONSTRUCTION 2

5 SUBSURFACE EVALUATION AND LABORATORY TESTING 3

6 GEOLOGIC AND SUBSURFACE CONDITIONS 3

6.1 Regional Geology 3

6.2 Site Geology 4

7 GROUNDWATER 4

8 FIELD PERCOLATION TESTING 4

9 FAULTING AND SEISMICITY 5

9.1 Surface Fault Rupture 5

9.2 Seismic Ground Motion 6

9.3 Liquefaction 6

9.4 Landsliding 7

10 CONCLUSIONS 7

11 RECOMMENDATIONS 8

11.1 Earthwork 8

11.1.1 Pre-Construction Conference 9

11.1.2 Clearing and Site Preparation 9

11.1.3 Excavation Characteristics 9

11.1.4 Temporary Excavations 9

11.1.5 Subgrade Preparation 10

11.1.6 Fill Material 10

11.1.7 Fill Placement and Compaction 11

11.2 Seismic Design Considerations 11

11.3 Foundations 12

11.4 Sidewalks 13

11.5 Lateral Earth Pressures for Retaining Walls 13

11.6 Pavement Design 13

11.7 Corrosivity 14

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11.8 Concrete Placement 14

11.9 Drainage 15

12 CONSTRUCTION OBSERVATION 15

13 LIMITATIONS 15

14 REFERENCES 17

TABLES

1 – Percolation Test Results 5

2 – 2019 California Building Code Seismic Design Criteria 12

3 – Preliminary Flexible Pavement Structural Sections 13

FIGURES

1 – Site Location

2 – Boring Locations

3 – Regional Geology

4 – Fault Locations

5 – Seismic Hazard Zones

6 – Lateral Earth Pressures for Temporary Cantilevered Shoring

7 – Lateral Earth Pressures for Yielding Retaining Wall

8 – Retaining Wall Drainage Detail

APPENDICES

A – Boring Logs

B – Laboratory Testing

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1 INTRODUCTION

In accordance with your request and authorization, we have performed a geotechnical evaluation for the proposed Sidewalk Extension Project along Crawford Canyon Road and Newport Avenue in the North Tustin community of Orange County, California (Figure 1). The Orange County Public

Works (OCPW) plans to build a new recreational park at the intersection of Crawford Canyon

Road and Newport Avenue, which will be preceded by extension and improvements of the existing sidewalks and constructing a vehicular entrance to the proposed park. The purpose of our study was to evaluate the soil and geologic conditions at the site and to provide geotechnical recommendations for the design and construction of the proposed sidewalk extension and the associated improvements of the existing infrastructure. This report presents the findings from our background review and subsurface exploration, percolation testing, results of our laboratory testing, conclusions regarding the subsurface conditions at the site, and geotechnical recommendations for design and construction of this project.

2 SCOPE OF SERVICES

Our scope of services included the following:

Project coordination and planning with subcontractors and OCPW representatives.

Review of readily available background materials, including published topographic maps, geologic maps, fault and seismic hazard maps, groundwater data, stereoscopic aerial photographs, and project related plans.

Acquisition of an encroachment permit from the County of Orange for performing our subsurface exploration within the County Right of Way.

Field reconnaissance, performed on April 23, 2021, to observe and document the site conditions, mark the boring locations for underground utility clearance by Underground Service Alert, and meet with County personnel regarding site access and constraints.

Subsurface exploration consisting of the drilling, sampling, and logging of seven hollow-stem auger borings; five borings to depths of approximately 10.3 to 16.5 feet and two borings to depths of approximately 5 feet. The borings were logged in the field by our representative and relatively undisturbed and bulk samples were collected and returned to our laboratory for evaluation and testing. The borings were backfilled with soil cuttings.

Field percolation testing in the two 5-foot-deep borings in general accordance with OCPW Technical Guidance Document guidelines (OCPW, 2011).

Geotechnical laboratory testing of representative soil samples to evaluate in-situ moisture content and dry density, percentage of soil particles finer than the No. 200 sieve, Atterberg limits, direct shear strength, expansion index, R-value, and soil corrosivity characteristics (including pH, resistivity, and water soluble sulfates and chlorides).

Data compilation and engineering analysis of the information obtained from our background review, subsurface exploration, infiltration testing, and laboratory testing.

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Preparation of this geotechnical report presenting our findings, conclusions, and recommendations pertaining to the design and construction of the proposed improvements.

3 SITE DESCRIPTION

The site is located along Crawford Canyon Road and Newport Avenue in the North Tustin community in Orange County, California (Figure 1). The site extends approximately 1,200 feet to the northwest and approximately 700 feet to the southwest from the intersection of Crawford

Canyon Road and Newport Avenue. Based on our review of historic topographic maps and aerial imagery (Historic Aerials, 2021), the site was used for agricultural purposes prior to being developed as a residential area. The site includes relatively flat to gently sloping terrain with site elevations ranging from approximately 405 feet above mean sea level (MSL) at the north end of the site to approximately 380 feet above MSL at the south end of the site (United States Geological

Survey [USGS], 2018).

Crawford Canyon Road is a two-lane road with single traffic lanes in each direction and a striped median. Newport Avenue is a four-lane road with two traffic lanes in each direction and a striped median. Both roads are currently paved with Asphalt Concrete (AC). There is an undeveloped triangular parcel, with sparse woody vegetation, at the intersection of Crawford Canyon Road and

Newport Avenue (southwest of Crawford Canyon Road and northwest of Newport Avenue), which is to be developed as a recreational park. The existing improvements at the site include curbs, paved and unpaved shoulders, utility manholes, storm water drains, a bicycle lane and sidewalk along Newport Avenue, and a drainage swale leading to a drainage culvert along Crawford

Canyon Road.

4 PROPOSED CONSTRUCTION

The County plans to build a new recreational park on the currently undeveloped triangular parcel at the intersection of Crawford Canyon and Newport Avenue. To accommodate for the new park, the County plans to extend and improve sidewalks adjacent to the proposed park and construct a vehicular entrance from Newport Avenue to the park. Detailed project plans were not available at the time of our evaluation; however, based on our review of the Materials Report Request

(OCPW, 2021) and our communications with the County, we understand that the County is evaluating the feasibility of constructing a porous concrete sidewalk along Newport Avenue and adjacent to the proposed park. AC pavement sections are planned for the park entrance from

Newport Avenue. A concrete retaining wall, approximately 4 feet in height, will also be constructed on the southwest side of Crawford Canyon Road. Additional improvements will consist of drainage improvements, inlets, curbs, and gutters. We anticipate that grading for the construction of proposed improvements will consist of minor cuts and fills, up to approximately 5 feet in height.

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5 SUBSURFACE EVALUATION AND LABORATORY TESTING

Our subsurface evaluation was performed on June 21 and 22, 2021, and consisted of the drilling, logging, and sampling of seven small-diameter borings (i.e., B-1 through B-5, P-1, and P-2) and performing percolation testing as further described in Section 8 of this report. The borings were drilled using a truck-mounted drill rig with 8-inch-diameter hollow-stem augers. The exploratory borings (i.e., B-1 through B-5) were drilled to depths ranging from approximately 10.3 to 16.5 feet and the percolation borings (i.e., P-1 and P-2) were drilled to depths of approximately 5 feet. The borings were logged in the field by a representative of Ninyo & Moore and representative bulk and relatively undisturbed soil samples were collected from the borings at selected depths for laboratory testing. The borings were backfilled with soil cuttings. The approximate locations of the borings are shown on Figure 2. Logs of the borings are provided in Appendix A.

Geotechnical laboratory testing was performed on representative samples to evaluate the in-situ moisture content and dry density, percentage of particles finer than the No. 200 sieve, Atterberg limits, direct shear strength, expansion index, R-value, and soil corrosivity characteristics

(including pH, resistivity, and water soluble sulfates and chlorides). The results of the in-situ moisture content and dry density tests are presented on the boring logs in Appendix A. The remaining laboratory testing results are presented in Appendix B.

6 GEOLOGIC AND SUBSURFACE CONDITIONS

6.1 Regional Geology

The subject site is located at the base of the Santa Ana Mountains within the central block of the

Los Angeles Basin in the Peninsular Ranges Geomorphic Province of California (Norris and

Webb, 1990). The Los Angeles Basin has been divided into four structural blocks, which are generally bounded by prominent fault systems: the northwestern, southwestern, central, and northeastern blocks. The site is located in the central block, which is bounded by the Newport-

Inglewood fault to the west, by the Whittier Elsinore fault to the east, by the Malibu Coast-Santa

Monica-Raymond fault to the north, and by the San Joaquin Hills to the south. According to the available geologic maps (Morton and Miller, 2006), the subject site is located near the boundary between young alluvial-fan deposits and Topanga Formation (Figure 3). Young alluvial-fan deposits are generally comprised of unconsolidated to moderately consolidated silt and sand with cobbles and boulders. Topanga Formation is generally characterized by interbedded marine sandstone, siltstone, and shale.

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6.2 Site Geology

Materials encountered during our subsurface exploration consisted of fill underlain by alluvium and the Miocene-age Topanga Formation. Fill was encountered in each of the borings drilled, to depths ranging from approximately 6 to 16.5 feet below ground surface. The fill generally consisted of yellowish brown and grayish brown, moist, loose to very dense, clayey sand with varying amounts of gravel. Alluvium was encountered below the fill in boring B-1 to a depth of approximately 8 feet below ground surface and consisted of yellowish brown, moist, medium dense, clayey sand. Topanga Formation was encountered below the alluvium in boring B-1 to the total depth explored of approximately 10.8 feet and consisted of yellowish brown, moist, moderately indurated, weathered sandstone. More detailed descriptions of the subsurface materials are presented on the boring logs in Appendix A.

7 GROUNDWATER

Groundwater was not encountered in our borings to the total depths explored of up to approximately 16.5 feet. Regional maps indicate that the historic high groundwater within the low-lying areas of the site is approximately 10 feet below ground surface (California Division of Mines and Geology [CDMG], 1997). Groundwater monitoring data from the GeoTracker website

(California State Water Resources Control Board, 2021) indicates that groundwater was encountered approximately 18.4 feet below ground surface at a well located approximately 1 mile northwest of the Crawford Canyon and Newport Avenue intersection. Fluctuations in the level of groundwater will occur due to variations in ground surface topography, subsurface stratification, rainfall, irrigation practices, groundwater pumping, and other factors that were not evident at the time of our field evaluation.

8 FIELD PERCOLATION TESTING

Percolation testing was performed in percolation borings P-1 and P-2 in general accordance with the OCPW Technical Guidance Document guidelines (OCPW, 2011). The objective of percolation testing was to evaluate the infiltration rates and drainage capacity of the on-site soils underlying the proposed improvements. The approximate locations of the percolation borings are shown on

Figure 2.

The percolation borings were drilled to depths of approximately 5 feet. A 2-inch-diameter slotted polyvinyl chloride (PVC) pipe was placed in the boreholes and the annulus between the borehole walls and pipes were backfilled with clean gravel to avoid caving in the test zone. The infiltration zones were pre-soaked with water to a level of at least 5 times the hole’s radius prior to performing percolation testing until all the water percolated through the test hole or for at least 15 hours, per the county’s guidelines.

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The percolation testing was conducted by establishing a head of water in the PVC pipes to a level of at least 5 times the hole’s radius, and measuring the drop in water over a period of 6 hours.

Water was added to the PVC pipes at 30-minute increments to maintain approximately the same head of water during the test. The measured rate of infiltration during the last 30 minutes was used for the calculation of the percolation rates per the OCPW guidelines. The field percolation rates are presented in Table 1. The OCPW guidelines indicate that the measured field percolation rates should be reduced to account for the difference between the full-scale infiltration rates of the proposed facilities and the small-scale percolation testing. As such, the design percolation rate provided in this report incorporates a factor of safety of 2, as recommended by the county’s guidelines (OCPW, 2011).

Per the county’s guidelines, soils with infiltration rates of less than 0.3 inches per hour are not considered suitable for infiltration (OCPW, 2011). Given the design percolation rate of 0.25 inches per hour for this project, the infiltration rate at the site does not meet the minimum requirement of the county, and the site is not suitable for infiltration beneath the proposed developments.

Table 1 – Percolation Test Results

Test Boring Tested Percolation Rate (inch/hour) Adjusted Percolation Rate (inch/hour)

P-1 0.76 0.38

P-2 0.25 0.13

Recommended Design Percolation Rate (inch/hour) 0.25

9 FAULTING AND SEISMICITY

The site is located in a seismically active area, as is the majority of southern California, and the potential for strong ground motion in the project are is considered significant during the design life of the proposed improvements. The approximate locations of major faults in the region and their geographic relationship to the project site are shown on Figure 4. The site is not located within a

State of California Earthquake Fault Zone (formerly known as an Alquist-Priolo Special Studies

Zone) and no active faults are known to cross the subject site (Hart and Bryant, 2018). The active

San Joaquin Hills Fault is located approximately 6.3 miles southwest of the site (USGS, 2008). A brief description of the principal seismic hazards at the site and the potential for their occurrences on site are discussed in the following sections.

9.1 Surface Fault Rupture

Based on our review of the referenced literature and our site reconnaissance, no active faults are known to cross the project site. Therefore, the probability of damage from surface fault rupture is considered to be low. However, lurching or cracking of the ground surface as a result of nearby seismic events is possible.

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9.2 Seismic Ground Motion

Considering the proximity of the site to active faults capable of producing a maximum moment magnitude of 6.0 or more, the project area has a high potential for experiencing strong ground motion. The 2019 California Building Code (CBC) specifies that MCER (risk-targeted maximum considered earthquake) ground motion response accelerations, per American Society of Civil

Engineers (ASCE) 7-16, be used to evaluate seismic loads for design of buildings and other structures. We obtained the site amplification factors and spectral acceleration values for 5 percent damping in accordance with Section 11.4 of ASCE 7-16, using the 2019 Applied

Technology Council (ATC) web-based seismic design tool (ATC, 2020). Based on the information from an available online database (Wills & Clahan, 2006), the average shear wave velocity for the upper 30 meters of soil layers (Vs,30) used in the seismic analysis was 280 meters per second.

Accordingly, the site is classified as Site Class D. The spectral acceleration parameters consistent with the 2019 CBC guidelines are provided in Section 11 of this report. The MCEG (maximum considered earthquake geometric mean) site-modified peak ground acceleration, PGAM, was calculated as 0.584g.

9.3 Liquefaction

Liquefaction is the phenomenon in which loosely deposited granular soils and non-plastic silts located below the water table undergo rapid loss of shear strength when subjected to strong earthquake-induced ground shaking. Ground shaking of sufficient duration results in the loss of grain-to-grain contact due to a rapid rise in pore water pressure, and causes the soil to behave as a fluid for a short period of time. Liquefaction is known generally to occur in saturated or near-saturated cohesionless soils at depths shallower than 50 feet below the ground surface.

Liquefaction is also known to occur in relatively fine-grained soils (i.e., sandy silt and clayey silt) with a plasticity index (PI) of less than 12 and an in-place moisture content more than 85 percent of the liquid limit (LL) and sensitive silts and clays with a PI more than 18. Factors known to influence liquefaction potential include composition and thickness of soil layers, grain size, relative density, groundwater level, degree of saturation, and both intensity and duration of ground shaking.

Review of the State of California Seismic Hazards Zones map (CDMG, 1998) indicates that the site is located in an area mapped as a potential liquefaction hazard zone (Figure 5). While groundwater was not encountered in our borings to the total depths explored of up to 16.5 feet, the historic high groundwater level at the site is approximately 10 feet below ground surface. The materials encountered in our borings below the historic high groundwater level were generally medium dense to very dense clayey sand with the exceptions of loose clayey sand encountered in B-5 from approximately 10 to 16.5 feet below ground surface and sandstone bedrock in B-1 at

Ninyo & Moore | Sidewalk Extension Project, North Tustin, California | 211686001 | September 2, 2021 7 a depth of approximately 8 feet. This shows a higher liquefaction potential in the low-lying areas of the site along the Newport Avenue. However, the proposed improvements do not include structures for human occupancy and liquefaction is not deemed to be a design consideration for the project at this stage. Accordingly, our scope of services did not include a detailed evaluation of the liquefaction hazard at the site.

9.4 Landsliding

Landslides may be induced by strong vibratory motion produced by earthquakes. Research and historical data indicate that seismically induced landslides tend to occur in weak soil and rock on sloping terrain. The process for zoning earthquake-induced landslides incorporates expected future earthquake shaking, existing landslide features, slope gradient, and strength of earth materials on the slope. The project area is not mapped in an area considered susceptible to seismically induced landslides (CDMG, 1998). The subject site is situated on relatively level terrain and slopes with relatively gentle inclinations. We did not observe indications of landslides during our site reconnaissance or background review.

10 CONCLUSIONS

Based on the results of our evaluation, it is our opinion that construction of the proposed sidewalk extension and its associated improvements are feasible from a geotechnical standpoint, provided that the recommendations presented in this report are incorporated into the design and construction of the project. In general, the following conclusions were made:

The site is underlain by fill, alluvium, and the Topanga Formation. Approximately 6 to 16.5 feet of fill was encountered in each of the borings drilled, consisting of moist, loose to very dense, clayey sand with varying amounts of gravel. Alluvium was encountered below the fill in boring B-1 to a depth of approximately 8 feet and consisted of moist, medium dense, clayey sand. Topanga Formation was encountered below the alluvium in boring B-1 to the total depth explored of approximately 10.8 feet and consisted of moist, moderately indurated, weathered sandstone.

Our infiltration testing of the near-surface soils resulted in adjusted infiltration rates ranging from approximately 0.13 to 0.38 inches per hour. The recommended design percolation rate is 0.25 inches per hour. Per the OCPW guidelines (OCPW, 2011), the site is not suitable for infiltration beneath the proposed developments.

Excavations in the fill and alluvial deposits should be feasible with earthmoving equipment in good working condition; however, some oversize materials (cobble) should be anticipated and accounted for by the contractor(s).

The on-site soils should be suitable for re-use as backfill after organic materials (roots) are removed and the soil is moisture-conditioned to near the optimum moisture content. Oversize materials with a diameter of 4 inches or more should be anticipated and should be removed from engineered fill and trench backfill. The contractor should anticipate handling oversize materials during grading and construction.

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Existing utilities and structures are present in the project area that will require protection in-place during construction. The contractor should avoid damaging and/or undermining the utilities and adjacent structures.

Laboratory test results indicate that the on-site surficial soils have a very low to medium potential for expansion.

Groundwater was not encountered in our exploratory borings to the total depths explored of up to approximately 16.5 feet. The historic high depth to groundwater is mapped approximately 10 feet at the site.

The site is mapped in an area susceptible to seismically-induced liquefaction. Given that the proposed improvements do not include structures for human occupancy, our scope of services did not include a detailed evaluation of the liquefaction hazard at the site.

The site is not located within a State of California Earthquake Fault Zone. Therefore, the potential for surface fault rupture within the project limits is considered to be low.

Our limited laboratory corrosivity testing indicates that the on-site materials can be classified as corrosive based on the California Department of Transportation (Caltrans, 2021) corrosion guidelines.

11 RECOMMENDATIONS

The recommendations presented in the following sections provide general geotechnical criteria regarding the design and construction of the proposed improvements. The recommendations are based on the results of our subsurface evaluation, geotechnical analysis, and our project understanding. Detailed construction drawings were not available at the time this report was prepared. We recommend that the final construction drawings be submitted to Ninyo & Moore for review to evaluate conformance to the geotechnical recommendations provided in this report.

Additional or revised recommendations may be appropriate. The proposed work should be performed in conformance with the recommendations presented in this report, project specifications, and appropriate agency standards.

11.1 Earthwork

We anticipate that earthwork at the site will include site clearing, relatively shallow grading, foundation excavations, and subgrade preparation. In areas where the existing pavement sections are to be removed and replaced, the asphalt may be used to generate a crushed miscellaneous base (CMB) material that can be used to construct the new pavement sections.

The CMB generated from recycling or pulverizing the existing asphalt should contain materials less than 2 inches in diameter and meet the requirements of the Standard Specifications for Public

Works (Greenbook). Materials larger than approximately 2 inches should be reduced in size or disposed of offsite. Earthwork operations should be performed in accordance with the recommendations provided in the following sections and appropriate agency standards.

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11.1.1 Pre-Construction Conference

We recommend that a pre-construction conference be held. The owner and/or their representative, the governing agencies’ representatives, the civil engineer, the geotechnical engineer, and the contractor should attend to discuss the work plan, project schedule, and earthwork requirements.

11.1.2 Clearing and Site Preparation

Prior to excavating or other earthwork, the proposed area of improvements should be cleared of surface obstructions, debris, pavement, abandoned utilities, and other deleterious materials. Obstructions that extend below the final grade should be removed and the resulting holes filled with compacted soils. Existing utilities within the project limits should be re-routed or protected from damage by construction activities. Materials generated from the clearing operations should be removed from the project site and disposed of at a legal dumpsite.

11.1.3 Excavation Characteristics

Based on our field exploration, we anticipate that excavations at the site may be accomplished with conventional earthmoving equipment in good working condition. The fill and alluvium generally consisted of moist, loose to very dense, clayey sand with varying amounts of gravel. The formational materials at the site consisted of moist, moderately indurated, weathered sandstone. Cobbles should also be anticipated during construction.

Oversize material is not suitable for backfill and should be broken into smaller pieces or disposed of off-site. Contractors should make their own independent evaluation of the excavatability of the on-site materials prior to submitting their bids.

11.1.4 Temporary Excavations

We recommend that excavations be designed and constructed in accordance with

Occupational Safety and Health Administration (OSHA) regulations. The on-site soils should be considered as OSHA Type C Soil. For trench or other excavations, OSHA requirements regarding personnel safety should be met by using appropriate shoring or by laying back the slopes no steeper than 1½:1 (horizontal to vertical) in the fill and old fan deposits. Although not anticipated, temporary excavations that encounter seepage may need shoring or may be mitigated by placing sandbags or gravel along the base of the seepage zone. Excavations encountering seepage should be evaluated on a case-by-case basis.

Where slopes cannot be laid back, shoring may be appropriate. If shoring systems are used for site excavations, they should be designed for the anticipated soil conditions using the lateral earth pressure values shown on Figure 6 for temporary cantilevered excavations. The

Ninyo & Moore | Sidewalk Extension Project, North Tustin, California | 211686001 | September 2, 2021 10 recommended design pressures are based on the assumption that the shoring system is constructed without raising the ground surface elevation behind the shored sidewalls of the excavation, that there are no surcharge loads, such as soil stockpiles and construction materials, and that no loads act above a 1:1 (horizontal to vertical) plane ascending from the base of the shoring system. For a shoring system subjected to the above-mentioned surcharge loads, the contractor should include the effect of these loads on the lateral earth pressures acting on the shored walls.

We anticipate that settlement of the ground surface will occur behind the shored excavations.

The amount of settlement depends heavily on the type of shoring system, the contractor’s workmanship, and soil conditions. To reduce the potential for distress to adjacent improvements, we recommend that the shoring system be designed to limit the ground settlement behind the shoring system to ½ inch or less. Possible causes of settlement that should be addressed include settlement during installation of the shoring elements, excavation of trenches, construction vibrations, and removal of the support system. We recommend that shoring installation be evaluated carefully by the contractor prior to construction and that ground vibration and settlement monitoring be performed during construction.

11.1.5 Subgrade Preparation

Based on our geotechnical exploration, the materials encountered at the proposed park entrance location (i.e., in B-5) and location of the proposed retaining wall (i.e., in B-1 and B-2) predominantly include loose to dense, clayey sand with trace gravel. In order to provide relatively uniform support for the retaining wall foundations and the new structural pavement sections, the upper 18 inches of the subgrade beneath the proposed retaining wall foundations, pavement sections, concrete curbing, catch basins, and other hardscape improvements should be removed, moisture-conditioned, and re-compacted to a relative compaction of 95 percent or more as evaluated by ASTM International (ASTM) test method

D1557. The compacted subgrade should laterally extend approximately 3 feet and 1.5 feet beyond the outside edges of the retaining wall foundations and the pavement sections, respectively. The exposed bottom of remedial excavations, to a depth of approximately 8 inches, should be scarified, moisture-conditioned, and re-compacted to 95 percent or more relative compaction.

11.1.6 Fill Material

In general, the on-site soils should be suitable for re-use as fill, structural fill, and trench backfill, provided that those are free of trash, debris, roots, vegetation, or other deleterious materials. Fill should generally be free of rocks or lumps of material in excess of 4 inches in

Ninyo & Moore | Sidewalk Extension Project, North Tustin, California | 211686001 | September 2, 2021 11 diameter. Rocks or hard lumps larger than approximately 4 inches in diameter should be broken into smaller pieces or should be removed from the site. On-site soils used as fill will involve moisture-conditioning to achieve appropriate moisture content for compaction.

Fill used as backfill for underground structures should consist of free-draining, granular, non-expansive soil that conforms with the latest edition of “Greenbook” Standard Specifications for Public Works Construction for structure backfill. “Non-expansive” can be defined as soil having an expansion index (EI) of 20 or less in accordance with ASTM International (ASTM) test method D 4829.

Imported materials should consist of clean, non-expansive, granular material, conforming to the latest edition of “Greenbook” Standard Specifications for Public Works Construction for structure backfill in accordance with ASTM D 4829. Soil should also be tested for corrosive properties prior to importing. We recommend that the imported materials comply with the

Caltrans (2018) criteria for non-corrosive soils (i.e., soils having a chloride concentration of

500 ppm or less, a soluble sulfate content of approximately 0.15 percent [1,500 ppm] or less, a pH value of 5.5 or higher, and a resistivity of 1,100 ohm-centimeters [ohm-cm] or more).

Materials for use as fill should be evaluated by the geotechnical consultant prior to importing.

The contractor should be responsible for the uniformity of import material brought to the site.

11.1.7 Fill Placement and Compaction

Fill materials used for trench backfill or other site improvements should be compacted in horizontal lifts to a relative compaction of 90 percent or more as evaluated by ASTM D 1557.

Fill soils should be placed at slightly above the optimum moisture content as evaluated by

ASTM D 1557. The optimum lift thickness of fill will depend on the type of compaction equipment used but generally should not exceed 8 inches in loose thickness. Placement and compaction of the fill soils should be in general accordance with appropriate governing agency grading ordinances and good construction practice.

11.2 Seismic Design Considerations

Design of the proposed improvements should be performed in accordance with the requirements of governing jurisdictions and applicable building codes. Table 2 presents the site-specific spectral response acceleration parameters in accordance with the CBC (2019) guidelines.

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Table 2 – 2019 California Building Code Seismic Design Criteria

Site Coefficients and Spectral Response Acceleration Parameters Values

Site Class D

Site Amplification Factor, Fa 1.0

Site Amplification Factor, Fv 1.811

Mapped Spectral Response Acceleration at 0.2-second Period, Ss 1.372g

Mapped Spectral Response Acceleration at 1.0-second Period, S1 0.489g

Site-Modified Spectral Response Acceleration at 0.2-second Period, SMS 1.372g

Site-Modified Spectral Response Acceleration at 1.0-second Period, SM1 0.886g

Site-Modified Design Spectral Response Acceleration at 0.2-second Period, SDS 0.915g

Site-Modified Design Spectral Response Acceleration at 1.0-second Period, SD1 0.523g

Site-Modified MCEG Peak Ground Acceleration, PGAM 0.584g

11.3 Foundations

The retaining walls and other miscellaneous improvements may be supported on shallow spread footings bearing on compacted fill prepared in accordance with the earthwork recommendations of this report. Footings should extend 24 inches or more below the lowest adjacent finished grade and should have a width of 24 inches or more. Spread footings should be reinforced with a minimum of two No. 4 steel reinforcing bars, one placed near the top and one placed near the bottom of the footings, and further detailed in accordance with the recommendations of the structural engineer.

Footings, as described above and bearing on compacted fill soils with low expansion potential, may be designed using a net allowable bearing capacity of 2,500 psf. The allowable bearing capacity may be increased by 300 psf for every foot of increase in width up to a value of 4,000 psf. The allowable bearing capacity may be increased by one-third when considering loads of short duration such as wind or seismic forces. Total and differential settlements for footings designed and constructed in accordance with the above recommendations are estimated to be less than approximately 1 inch and ½ inch over a horizontal span of 40 feet, respectively.

Footings bearing on compacted fill may be designed using a coefficient of friction of 0.35, where the total frictional resistance equals the coefficient of friction times the dead load. Footings may be designed using a passive resistance of 350 psf per foot of depth for level ground condition up to a value of 3,500 psf. The allowable lateral resistance can be taken as the sum of the frictional resistance and passive resistance provided the passive resistance does not exceed one-half of the total allowable resistance. In the event that the passive resistance is greater than one-half of the total allowable resistance, the passive resistance should be reduced to be the same value as the frictional resistance. The passive resistance may be increased by one-third when considering loads of short duration such as wind or seismic forces.

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11.4 Sidewalks

We recommend that the surficial soils below the exterior flatwork be treated following the recommendations presented in the earthwork section of this report. Exterior slabs-on-grade may be 4 inches thick and reinforced with No. 3 reinforcing bars at a spacing of 18 inches and doweled to curbs. In areas abutting landscape areas, the edge of the slab should be deepened to approximately 8 inches below the adjacent finish subgrade. Expansion joints should be planned for at a spacing of 10 feet or less.

11.5 Lateral Earth Pressures for Retaining Walls

Lateral earth pressures recommended for design of yielding retaining walls are provided on

Figure 7. Passive pressures may be increased by one-third when considering loads of short duration, including wind and seismic loads. Retaining walls should be backfilled with free-draining, granular soil with a low-expansion potential. Measures should be taken to reduce the potential for build-up of moisture behind the retaining walls. Drainage design should include free-draining backfill materials and subsurface drainage provisions as shown on Figure 8.

11.6 Pavement Design

We understand that AC pavement is currently considered for the entrance from Newport Avenue to the proposed park. Based on the direction from OCPW (email correspondence from Mr. Adam

Ramos to Mr. Morteza Mirshekari, dated July 21, 2021), a traffic index (TI) value of 3.5 was used for the design of pavement sections. The R-value of the subgrade soils was evaluated for a representative soil sample obtained from our exploratory boring B-4. Laboratory R-value testing indicates an R-value of 22 for the surficial materials encountered. Based on these assumptions and the guidelines of Caltrans Highway Design Manual (Caltrans, 2019) and Orange County

Highway Design Manual (Orange County Highway Design Manual Committee, 2005), we have developed the following pavement sections for the project (Table 3).

Table 3 – Preliminary Flexible Pavement Structural Sections

Traffic Index R-Value AC over CAB or AC over CMB

(inches) Full Depth AC

(inches)

3.5 22 4 over 6 7

Notes:

AC – Asphalt Concrete CAB – Crushed Aggregate Base CMB – Crushed Miscellaneous Base

Subgrade soils in areas to be paved should be prepared as recommended in the Earthwork section of this report. Crushed aggregate base (CAB) or crushed miscellaneous base (CMB) material should conform to the latest edition of the Standard Specifications for Public Works

Construction “Greenbook,” Section 200. CAB/CMB should be compacted to a relative compaction

Ninyo & Moore | Sidewalk Extension Project, North Tustin, California | 211686001 | September 2, 2021 14 of 95 percent as evaluated by ASTM D 1557, and should be placed at slightly above the optimum moisture content as evaluated by ASTM D 1557. AC should conform to OCPW Standard Plan

1805 (OCPW, 2018), and should be compacted to a relative compaction of 95 percent. Final pavement sections should be selected based on evaluation of the subgrade materials at the time of construction.

11.7 Corrosivity

Laboratory testing was performed on two representative soil samples to evaluate pH, electrical resistivity, water-soluble chloride content, and water-soluble sulfate content. The soil pH and electrical resistivity tests were performed in general accordance with California Test Method (CT)

643. Chloride content test was performed in general accordance with CT 422. Sulfate testing was performed in general accordance with CT 417. The laboratory test results are presented in

Appendix B.

The results of the corrosivity testing indicated a soil pH of ranging from 6.0 to 7.3. The electrical resistivity ranged from 557 to 621 ohm-cm, the chloride content ranging from 90 to 125 ppm, and the sulfate content ranged from 0.004% to 0.030% (i.e., 40 to 300 ppm). Based on the laboratory test results and Caltrans (2021) criteria, the soils at the project site can be classified as corrosive, which is defined as having earth materials with more than 500 ppm chlorides, more than 1,500 ppm sulfates, a pH of 5.5 or less, or an electrical resistivity of 1,500 ohm-cm or less.

11.8 Concrete Placement

Concrete in contact with soil or water that contains high concentrations of water-soluble sulfates can be subject to premature chemical and/or physical deterioration. Based on the CBC criteria, the potential for sulfate attack is negligible for water-soluble sulfate contents in soil ranging from

0.00 to 0.10 percent by weight and moderate for water-soluble sulfate contents ranging from 0.10 to 0.20 percent by weight. The potential for sulfate attack is severe for water-soluble sulfate contents ranging from 0.20 to 2.00 percent by weight and very severe for water-soluble sulfate contents over 2.00 percent by weight. The soil samples tested for this evaluation, using Caltrans

Test Method 417, indicate a water-soluble sulfate content of ranging between 0.004% and 0.030% by weight (i.e., 40 and 300 ppm). Accordingly, the on-site soils are considered to have a negligible potential for sulfate attack. However, due to the potential variability of the soils on site, consideration should be given to using Type II/V cement for the project.

In order to reduce the potential for shrinkage cracks in the concrete during curing, we recommend that the concrete for the proposed structures be placed with a slump of 4 inches based on

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ASTM C 143. The slump should be checked periodically at the site prior to concrete placement.

The structural engineer should be consulted for additional concrete specifications.

11.9 Drainage

Positive surface drainage is imperative for performance of site improvements. Positive drainage incorporates a slope of 2 percent or more over a distance of 5 feet or more away from structures and pavements. Surface water should not be allowed to pond adjacent to structure foundations.

12 CONSTRUCTION OBSERVATION

The recommendations provided in this report are based on our understanding of the proposed project and our evaluation of the data collected based on subsurface conditions disclosed by widely spaced exploratory borings. It is imperative that the geotechnical consultant checks the interpolated subsurface conditions during construction. We recommend that Ninyo & Moore review the project plans and specifications prior to construction. It should be noted that, upon review of these documents, some recommendations presented in this report may be revised or modified.

During construction, we recommend that the duties of the geotechnical consultant include, but not be limited to:

Observing site clearing, grubbing, and removals.

Observing excavation bottoms, and the placement and compaction of fill, including trench backfill.

Evaluating imported materials prior to their use as fill (if used).

Performing field tests to evaluate fill compaction.

Observing foundation excavations for bearing materials and cleaning prior to placement of reinforcing steel or concrete.

Performing material testing services including concrete compressive strength and steel tensile strength tests and inspections.

The recommendations provided in this report assume that Ninyo & Moore will be retained as the geotechnical consultant during the construction phase of this project. If another geotechnical consultant is selected, we request that the selected consultant indicate to the owner and to our firm in writing that our recommendations are understood and that they are in full agreement with our recommendations.

13 LIMITATIONS

The field evaluation, laboratory testing, and geotechnical analysis presented in this geotechnical report have been conducted in general accordance with current practice and the standard of care

Ninyo & Moore | Sidewalk Extension Project, North Tustin, California | 211686001 | September 2, 2021 16 exercised by geotechnical consultants performing similar tasks in the project area. No warranty, expressed or implied, is made regarding the conclusions, recommendations, and opinions presented in this report. There is no evaluation detailed enough to reveal every subsurface condition. Variations may exist and conditions not observed or described in this report may be encountered during construction. Uncertainties relative to subsurface conditions can be reduced through additional subsurface exploration. Additional subsurface evaluation will be performed upon request. Please also note that our evaluation was limited to assessment of the geotechnical aspects of the project, and did not include evaluation of structural issues, environmental concerns, or the presence of hazardous materials.

This document is intended to be used only in its entirety. No portion of the document, by itself, is designed to completely represent any aspect of the project described herein. Ninyo & Moore should be contacted if the reader requires additional information or has questions regarding the content, interpretations presented, or completeness of this document.

This report is intended for design purposes only. It does not provide sufficient data to prepare an accurate bid by contractors. It is suggested that the bidders and their geotechnical consultant perform an independent evaluation of the subsurface conditions in the project areas. The independent evaluations may include, but not be limited to, review of other geotechnical reports prepared for the adjacent areas, site reconnaissance, and additional exploration and laboratory testing.

Our conclusions, recommendations, and opinions are based on an analysis of the observed site conditions. If geotechnical conditions different from those described in this report are encountered, our office should be notified, and additional recommendations, if warranted, will be provided upon request. It should be understood that the conditions of a site could change with time as a result of natural processes or the activities of man at the subject site or nearby sites. In addition, changes to the applicable laws, regulations, codes, and standards of practice may occur due to government action or the broadening of knowledge. The findings of this report may, therefore, be invalidated over time, in part or in whole, by changes over which Ninyo & Moore has no control.

This report is intended exclusively for use by the client. Any use or reuse of the findings, conclusions, and/or recommendations of this report by parties other than the client is undertaken at said parties’ sole risk.

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14 REFERENCES

American Concrete Institute, 2019, Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary (ACI 318R-19).

American Concrete Institute (ACI), 2016, ACI Manual of Concrete Practice.

American Society of Civil Engineers (ASCE), 2016, Minimum Design Loads and Associated Criteria for Building and Other Structures, ASCE Standard 7-16.

ASTM International (ASTM), 2016, Annual Book of ASTM Standards, West Conshohocken, Pennsylvania.

Applied Technology Council (ATC), 2021, Hazards by Location, https://hazards.atcouncil.org/#/.

Building News, 2018, “Greenbook”, Standard Specification for Public Works Construction: BNI Publications.

California Building Standards Commission, 2019, California Building Code (CBC): California Code of Regulations, Title 24, Part 2, Volumes 1 and 2, dated July 1.

California Department of Conservation, California Geological Survey, State of California, 2016, Earthquake Zones of Required Investigation, Orange Quadrangle, 7.5-Minute Series:

Scale 1:24,000.

California Department of Conservation, Division of Mines and Geology, State of California, 1997, Seismic Hazard Zone Report for the Orange 7.5-Minute Quadrangle, Orange County, California: Seismic Hazard Zone Report 011.

California Department of Conservation, Division of Mines and Geology, State of California, 1998, Seismic Hazard Zones Official Map, Orange Quadrangle, 7.5-Minute Series: Scale 1:24,000, Open-File Report 97-19, dated April 15.

California Department of Transportation, 2021, Corrosion Guidelines, Version 3.2, Division of Engineering Services, Materials Engineering and Testing Services, Corrosion Branch, dated May.

California Department of Transportation, 2019, Highway Design Manual Sixth Edition, U.S.

Customary Units.

California State Water Resources Control Board, 2021, GeoTracker Database System, http://geotracker.swrcb.ca.gov/.

County of Orange – OC Public Works/OC Construction, 2021, Materials Report Request, dated February 2.

GoogleEarth, 2021, Website for Viewing Aerial Photographs, http://maps.google.com/.