Attachment B - Geotechnical Evaluation PQ Outdoor Classroom Copy.pdf

Geotechnical Evaluation Los Penasquitos Bridge and Amphitheater

Los Penasquitos Canyon County Preserve San Diego County, California

MW Peltz & Associates 143 South Cedros Avenue, Suite B104 | Solana Beach, California 92075

June 17, 2022 | Project No. 109427001

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

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

Christina Tretinjak, PG, CEG Senior Project Geologist

Jeffrey T. Kent, PE, GE Principal Engineer

Geotechnical Evaluation Los Penasquitos Bridge and Amphitheater Los Penasquitos Canyon County Preserve San Diego County, California

Mr. Mike Peltz MW Peltz & Associates 143 South Cedros Avenue, Suite B104 | Solana Beach, California 92075

June 17, 2022 | Project No. 109427001

5710 Ruffin Road | San Diego, California 92123 | p. 858.576.1000 | www.ninyoandmoore.com

CTF/CAT/JTK/mp http://www.ninyoandmoore.com/

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 i

CONTENTS

1 INTRODUCTION 1

2 SCOPE OF SERVICES 1

3 SITE AND PROJECT DESCRIPTION 1

4 SUBSURFACE EXPLORATION 2

5 LABORATORY TESTING 2

6 GEOLOGY AND SUBSURFACE CONDITIONS 2

Regional Geologic Setting 3

Site Geology 3

6.2.1 Fill 3

6.2.2 Alluvium 4

6.2.3 Delmar Formation 4

6.2.4 Friars Formation 4

6.2.5 Metavolcanic Rock 4

Groundwater 4

Faulting and Seismicity 4

Ground Motion 5

Ground Rupture 6

Liquefaction and Seismically Induced Settlement 6

Landsliding 6

Flood Hazards 6

7 CONCLUSIONS 7

8 RECOMMENDATIONS 8

Earthwork 8

8.1.1 Pre-Construction Conference 8

8.1.2 Site Preparation 8

8.1.3 Excavation Characteristics 8

8.1.4 Temporary Excavations 9

8.1.5 Remedial Grading – Amphitheater 9

8.1.6 Remedial Grading – Site Retaining Walls 10

8.1.7 Remedial Grading – Exterior Pedestrian Concrete Flatwork 10

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8.1.8 Remedial Grading – ADA Parking Stall 11

8.1.9 Materials for Fill 11

8.1.10 Compacted Fill 12

8.1.11 Slopes 13

8.1.12 Utility Pipe Zone Backfill 13

8.1.13 Utility Trench Zone Backfill 14

8.1.14 Drainage 14

Seismic Design Considerations 15

Foundations 15

8.3.1 Amphitheater 15

8.3.2 Pedestrian Bridge 16

Site Retaining Walls 17

Preliminary Flexible Pavement Design 17

Rigid Concrete Pavements 18

Exterior Pedestrian Concrete Flatwork 18

Corrosion 18

Concrete 19

9 PLAN REVIEW AND CONSTRUCTION OBSERVATION 19

10 LIMITATIONS 20

11 REFERENCES 21

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TABLES

1 – 2019 California Building Code Seismic Design Criteria 15

2 – Recommended Preliminary Flexible Pavement Section 17

FIGURES

1 – Site Location 2 – Boring Locations 3 – Fault Locations 4 – Geology 5 – Lateral Earth Pressures for Yielding Retaining Walls 6 – Retaining Wall Drainage Detail

APPENDICES

A – Boring Logs B – Laboratory Testing

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 1

1 INTRODUCTION

In accordance with your request and authorization, we have prepared this geotechnical evaluation report for the proposed improvements to the Los Penasquitos Canyon County Preserve in

San Diego County, California (Figure 1). Presented in this report are the results of our background review, field exploration, and geotechnical laboratory testing along with our conclusions regarding the geotechnical conditions at the site and our recommendations for the design and earthwork construction aspects of this project.

2 SCOPE OF SERVICES

Ninyo & Moore’s scope of services for this project included the following tasks:

• Reviewing readily available pertinent information including published in-house geotechnical literature, topographic maps, geologic maps, and fault maps, and historic aerial photographs.

• Performing a field reconnaissance to observe site conditions and to mark the locations of our exploratory borings.

• Coordinating with Underground Service Alert (USA) for utility clearance at our boring locations.

• Performing a subsurface exploration consisting of the excavating, logging, and sampling of three exploratory borings. In-place and bulk samples of the materials encountered were collected at selected intervals from the borings and transported to our in-house geotechnical laboratory for testing.

• Performing geotechnical laboratory testing on representative samples to evaluate soil parameters for design and classification purposes.

• Performing engineering analyses of the site geotechnical conditions based on data obtained from our background review, field exploration, and laboratory testing.

• Preparing this geotechnical evaluation report describing the findings and conclusions of our study and providing recommendations for design and construction of the proposed improvements.

3 SITE AND PROJECT DESCRIPTION

The site of the proposed project is located at the Los Penasquitos Canyon County Preserve in

San Diego County, California (Figure 1). The Los Penasquitos Canyon is an east-west trending canyon located to the north of the community of Mira Mesa and to the west of Black Mountain

Road. The project site is located near the Rancho Penasquitos Adobe. The area generally consists of the historic ranch house, gardens, and various hiking trails. Onsite elevations range from approximately 230 to 240 feet above mean sea level (MSL).

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 2

Based on our correspondence with you, we understand that the proposed improvements to the site include a new amphitheater with an Americans with Disabilities Act (ADA) parking stall and a pedestrian bridge. The preliminary concept for the amphitheater structure is an on-grade structure that is approximately 40 feet long by 30 feet wide, with two to three terraces to support approximately 50 people. The pedestrian bridge is to serve as a creek crossing to provide access to area trails for hikers. We understand that the pedestrian bridge is not intended to be designed for seismic considerations such as liquefaction and that the bridge is considered replaceable if damaged during a seismic event.

4 SUBSURFACE EXPLORATION

Our subsurface exploration was conducted on May 17, 2022, and included the drilling, logging, and sampling of three exploratory borings (B-1 through B-3). Prior to commencing the subsurface exploration, USA was notified for marking of the existing site utilities. The purpose of the borings was to evaluate subsurface conditions and to collect soil samples for laboratory testing.

The borings were excavated to depths ranging from approximately 2 feet to 16.3 feet using a limited access drill rig and manual methods. Ninyo & Moore personnel logged the borings in general accordance with the Unified Soil Classification System (USCS) and ASTM International

(ASTM) Test Method D 2488 by observing cuttings and drive samples. Representative bulk and in-place soil samples were obtained from the borings. The samples were then transported to our in-house geotechnical laboratory for testing. The approximate locations of the exploratory borings are shown on Figure 2. Logs of the borings are included in Appendix A.

5 LABORATORY TESTING

Geotechnical laboratory testing was performed on representative soil samples collected from our subsurface exploration. Testing included an evaluation of gradation (sieve) analysis, consolidation potential, expansion index, and soil corrosivity. Descriptions of the geotechnical laboratory test methods and the results of the geotechnical laboratory tests performed are presented in Appendix B.

6 GEOLOGY AND SUBSURFACE CONDITIONS

Our findings regarding regional and site geology and groundwater conditions are provided in the following sections.

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Regional Geologic Setting The project is situated in the coastal foothill section of the Peninsular Ranges Geomorphic

Province. This geomorphic province encompasses an area that extends approximately 900 miles from the Transverse Ranges and the Los Angeles Basin south to the southern tip of Baja California

(Norris and Webb, 1990; Harden, 2004). The province varies in width from approximately 30 to

100 miles. In general, the province consists of rugged mountains underlain by Jurassic metavolcanic and metasedimentary rocks, and Cretaceous igneous rocks of the southern

California batholith. The portion of the province in San Diego County that includes the project area consists generally of Cretaceous age sedimentary and volcanic rock.

The Peninsular Ranges Province is traversed by a group of sub-parallel faults and fault zones trending approximately northwest. Several of these faults, shown on Figure 3, are considered active faults (Jennings, 2010). The Elsinore, San Jacinto, and San Andreas are active fault systems located northeast of the project area and the Rose Canyon, Coronado Bank, San Diego

Trough, and San Clemente faults are active fault located west of the project area. The Rose

Canyon Fault is the nearest active fault and has been mapped approximately 8.6 miles west of the site. Major tectonic activity associated with these and other faults within this regional tectonic framework consists primarily of right-lateral, strike-slip movement. Further discussion of faulting relative to the site is provided in the Faulting and Seismicity section of this report.

Site Geology The geology of the site vicinity is shown on Figure 4. Geologic units encountered during our site reconnaissance and subsurface exploration included fill, alluvium, materials of the Friars Formation, and metavolcanic rock. Generalized descriptions of the earth units encountered during our field reconnaissance and subsurface exploration and mapped in the vicinity of the site are provided in the subsequent sections (Kennedy and Tan, 2008). Additional descriptions of the subsurface units are provided on the boring logs in Appendix A.

6.2.1 Fill

Fill materials were encountered in our borings B-1 and B-2 from the ground surface to depths of approximately ½ feet. As encountered, the fill generally consisted of light brown, moist, medium dense, silty sand and silty gravel. Numerous cobbles were observed at the surface in the vicinity of the bridge crossing.

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6.2.2 Alluvium

Alluvium was encountered in each of our borings underlying the fill or from the ground surface to depths of approximately 15 feet. As encountered, the alluvium generally consisted of various shades of brown and gray, moist to wet, soft to hard, sandy lean clay and loose to dense, clayey sand, well graded sand, poorly graded sand, poorly graded sand with silt, and well graded gravel. Cobbles were encountered within the alluvium.

6.2.3 Delmar Formation

Although not encountered during our subsurface exploration, materials of the Tertiary-age

Delmar Formation are mapped at the site. The Delmar Formation generally consists of olive sandy claystone interbedded with gray sandstone.

6.2.4 Friars Formation

Materials of the Tertiary-age Friars Formation were encountered in our boring B-2 underlying the alluvium and extending to the total depths explored. As encountered, the materials of the Friars

Formation generally consisted of yellow, wet, strongly cemented sandstone.

6.2.5 Metavolcanic Rock

Mesozoic-age metavolcanic rock was encountered in our boring B-1 underlying the alluvium and extending to the total depths explored. As encountered the metavolcanic rock generally consisted of grayish brown to olive gray, moist, weathered, coarse-grained metavolcanic rock. Unweathered corestones were observed on the surface at the site.

Groundwater Groundwater was encountered during our evaluation in our borings B-2 and B-3 located within the stream crossing at depths of 1 to 4 feet. Surface water was also present at the stream crossing at the time of our evaluation. Fluctuations in groundwater typically occur due to variations in precipitation, ground surface topography, subsurface stratification, irrigation, groundwater pumping, flooding, and other factors.

Faulting and Seismicity The numerous faults in southern California include active, potentially active, and inactive faults.

As defined by the California Geological Survey, active faults are faults that have ruptured within

Holocene time, or within approximately the last 11,000 years. Potentially active faults are those

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 5 that show evidence of movement during Quaternary time (approximately the last 1.6 million years), but for which evidence of Holocene movement has not been established. Inactive faults have not ruptured in the last approximately 1.6 million years. The approximate locations of major active and potentially active faults in the vicinity of the site and their geographic relationship to the site are shown on Figure 3. Additionally, the site is not located within a State of California

Earthquake Fault Zone (formerly known as Alquist-Priolo Special Studies Zone) (Hart and

Bryant, 2007).

The site is located in a seismically active area, as is the majority of southern California, and the potential for strong ground motion is considered significant during the design life of the proposed structures. Based on our review of the referenced geologic maps, as well as on our site reconnaissance, no faults are mapped as underlying the project site. The nearest known active fault is the Rose Canyon Fault, located approximately 8.6 miles west of the site.

In general, hazards associated with seismic activity include strong ground motion, ground rupture, and liquefaction. These hazards, along with landsliding, are discussed in the following sections.

Ground Motion The 2019 California Building Code (CBC) specifies that the Risk-Targeted, Maximum Considered

Earthquake (MCER) ground motion response accelerations be used to evaluate seismic loads for design of buildings and other structures. The MCER ground motion response accelerations are based on the spectral response accelerations for 5 percent damping in the direction of maximum horizontal response and incorporate a target risk for structural collapse equivalent to 1 percent in 50 years with deterministic limits for near-source effects. The horizontal peak ground acceleration (PGA) that corresponds to the MCER for the segments was calculated as 0.41g using a web-based seismic design tool (SEAOC/OSHPD, 2022).

The 2019 CBC specifies that the potential for liquefaction and soil strength loss be evaluated, where applicable, for the Maximum Considered Earthquake Geometric Mean (MCEG) peak ground acceleration with adjustment for site class effects in accordance with the American Society of Civil Engineers (ASCE) 7-16 Standard. The MCEG peak ground acceleration is based on the geometric mean peak ground acceleration with a 2 percent probability of exceedance in 50 years.

The MCEG peak ground acceleration with adjustment for site class effects (PGAM) was calculated as 0.46g using a web-based seismic design tool that yielded a mapped MCEG peak ground acceleration of 0.37g for the site and a site coefficient (FPGA) of 1.2 for the default Site Class D.

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Ground Rupture Based on our review of the referenced literature and our site reconnaissance, no active faults are known to cross the project vicinity. Therefore, the potential for ground rupture due to faulting at the site is considered low. However, lurching or cracking of the ground surface as a result of nearby seismic events is possible.

Liquefaction and Seismically Induced Settlement Liquefaction is the phenomenon in which loosely deposited granular soils with silt and clay contents of less than approximately 35 percent 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 60 feet below the ground surface. 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. Due to the dense nature of the underlying metavolcanic rock and formational materials at the site, along with the cobbly and clayey nature of the alluvium encountered, liquefaction is not a design consideration.

Landsliding Based on our review of referenced geologic maps, literature and topographic maps, and subsurface exploration, landslides or indications of deep-seated landsliding were not noted underlying the project site. In our opinion, the potential for significant large-scale slope instability at the site is not a design consideration.

Flood Hazards Based on review of Federal Emergency Management Agency (FEMA) Flood Insurance

Rate Maps (FIRM), the site is located within the regulatory floodway of the Los

Penasquitos Creek and the surrounding areas are mapped within Special Flood Hazard

Areas. Flooding is anticipated to impact the site and should be considered in the design of the proposed improvements.

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 7

7 CONCLUSIONS

Based on our review of the referenced background data, subsurface exploration, and geotechnical laboratory testing, it is our opinion that construction of the proposed improvements is feasible from a geotechnical standpoint. In general, the following conclusions were made:

• Based on the results of our field and laboratory evaluations, the subsurface soils at the site consist of fill, alluvium, materials of the Friars Formation, and metavolcanic rock.

• Outcroppings of rock are exposed at the surface of the site. Excavations extending into formational materials or metavolcanic rock will encounter very difficult excavation conditions due to the presence of bedrock materials, boulders, and/or corestones. The contractor should be prepared for the use of heavy ripping, rock breaking, rock coring, and/or blasting techniques to perform onsite excavations.

• Groundwater should be expected at or near the ground surface in the area of the stream crossing. Excavations that extend near or below the groundwater table will encounter caving and sloughing soil conditions and the contractor should be prepared to address these conditions.

• The site is located within the regulatory floodway of the Los Penasquitos Creek and the surrounding areas are mapped within Special Flood Hazard Areas. Flooding is anticipated to impact the site and should be considered in the design of the proposed improvements.

• No faults are mapped at the site. The closest known active fault, the Rose Canyon Fault, has been mapped approximately 8.6 miles west of the site.

• Based on our field evaluation and a review of referenced maps, landslides are not present on the project site.

• Onsite excavations will generate oversized materials. Oversized materials should be screened, rock-picked, crushed, removed, or otherwise processed from the excavated materials prior to reuse as compacted fill.

• Based on the results of our laboratory testing, the clayey portions of the alluvium possess a medium potential for expansion. Accordingly, these expansive soils are not suitable for reuse as compacted fill beneath certain portions of the proposed amphitheater, for retaining wall backfill, or as subgrade soil beneath exterior concrete flatwork. Remedial grading recommendations for these areas are presented herein.

• Based on a comparison with the California Department of Transportation corrosion criteria (Caltrans, 2021), the onsite soils would be classified as corrosive due to their electrical resistivity, sulfate content, and chloride content.

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 8

8 RECOMMENDATIONS

The following recommendations are provided for the design and construction of the proposed project.

These recommendations are based on our evaluation of the site geotechnical conditions and our assumptions regarding the planned development. The proposed site improvements should be constructed in accordance with the requirements of the applicable governing agencies.

Earthwork In general, earthwork should be performed in accordance with the recommendations presented in this report. The geotechnical consultant should be contacted for questions regarding the recommendations or guidelines presented herein.

8.1.1 Pre-Construction Conference

We recommend that a pre-construction meeting be held prior to commencement of grading.

The owner or his representative, the agency representatives, the civil engineer, Ninyo & Moore, and the contractor should attend to discuss the plans, the project, and the proposed construction schedule.

8.1.2 Site Preparation

Site preparation should begin with the removal of existing improvements, vegetation, utility lines, asphalt, concrete, and other deleterious debris from areas to be graded. Tree stumps and roots should be removed to such a depth that organic material is generally not present.

Clearing and grubbing should extend to the outside of the proposed excavation and fill areas.

The debris and unsuitable material generated during clearing and grubbing should be removed from areas to be graded and disposed of at a legal dumpsite away from the project area, unless noted otherwise in the following sections.

8.1.3 Excavation Characteristics

During our subsurface evaluation, we observed outcroppings of rocks at the surface and encountered metavolcanic rock. Onsite excavations will encounter very difficult excavation conditions due to the presence of bedrock materials, boulders, and/or corestones. The contractor should be prepared for the use of heavy ripping, rock breaking, rock coring, and/or blasting techniques to perform onsite excavations. Furthermore, excavations that extend near or below the groundwater table will encounter caving and sloughing soil conditions.

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 9

Additionally, onsite excavations will generate oversize materials that should be screened, rock-picked, crushed, removed, or otherwise processed from the excavated materials prior to reuse as compacted fill.

8.1.4 Temporary Excavations

For temporary excavations, we recommend that the following Occupational Safety and

Health Administration (OSHA) soil classifications be used:

Fill, Alluvium Type C

Friars Formation, Metavolcanic Rock Type B

Upon making the excavations, the soil classifications and excavation performance should be evaluated in the field in accordance with the OSHA regulations. Temporary excavations should be constructed in accordance with OSHA recommendations. For trench or other excavations, OSHA requirements regarding personnel safety should be met using appropriate shoring (including trench boxes) or by laying back the slopes to a slope ratio no steeper than 1½:1 (horizontal to vertical) in fill and alluvium and 1:1 in Friars Formation or metavolcanic rock. Temporary excavations that encounter seepage may require shoring or may be stabilized by placing sandbags or gravel along the base of the seepage zone. Excavations encountering seepage should be evaluated on a case-by-case basis. Onsite safety of personnel is the responsibility of the contractor.

8.1.5 Remedial Grading – Amphitheater

The proposed amphitheater is anticipated to be constructed as an on-grade structure cut into sloping ground and may be approximately two to three terraces high. The proposed structure location is underlain by materials which possess a medium potential for expansion and are not considered suitable for reuse as subgrade soil beneath the structure. We recommend that the proposed amphitheater be supported by foundations bearing on compacted aggregate base, and that remedial grading be performed to provide suitable foundation and slab support.

As a means to provide suitable foundation and/or slab support, we recommend the existing alluvium within the amphitheater building pad be removed by overexcavating down to a depth of 18 inches below the subgrade elevation. The overexcavation should extend to the horizontal limits of the structural footprint (including foundations for attached overhangs, canopies, elevators, and other building appurtenances) plus a horizontal distance of 2 feet.

The lateral extents of the overexcavation may be modified in the field based on site

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 10 constraints such as existing buildings and property lines. The extent and depths of removals and overexcavations should be evaluated by Ninyo & Moore’s representative in the field to observe that the existing fills have been removed.

Subsequent to removal, the resulting surface should be scarified to a depth of approximately

8 inches, moisture conditioned, and recompacted to a relative compaction of 90 percent as evaluated by the ASTM D 1557 prior to placing new fill. Once the resulting removal surface has been recompacted, the overexcavation should be backfilled with 18 inches or more of aggregate base materials compacted to a relative compaction of 90 percent relative density as evaluated by the current version of ASTM D 1557. Aggregate base materials should consist of either

Caltrans Class 2 aggregate base, Greenbook crushed aggregate base, Greenbook crushed miscellaneous base, or Greenbook processed miscellaneous base materials.

8.1.6 Remedial Grading – Site Retaining Walls

If site retaining walls are proposed, we recommend that the onsite subgrade soils be overexcavated to a depth of 1 foot below the bottom of the wall foundations. This overexcavation should extend a lateral distance of 1 foot beyond the horizontal limits of the foundation. The lateral extents of the overexcavation may be modified in the field based on site constraints. The extent and depths of removals and overexcavations should be evaluated by Ninyo & Moore’s representative in the field based on the materials exposed.

Subsequent to performance of the overexcavation removal, the resulting surface should be scarified to a depth of approximately 8 inches, moisture conditioned, and recompacted to a relative compaction of 90 percent as evaluated by the ASTM D 1557 prior to placing new fill.

Once the resulting removal surface has been recompacted, the overexcavation should then be backfilled with onsite or import soils that possess a very low to low potential for expansion that are compacted to a relative compaction of 90 percent as evaluated by the ASTM D 1557.

8.1.7 Remedial Grading – Exterior Pedestrian Concrete Flatwork Where exterior pedestrian concrete flatwork is proposed, we recommend that the onsite subgrade soils be overexcavated to a depth of 1 foot below the planned subgrade elevation. The overexcavation should extend outward horizontally 2 feet from the exterior limits of the hardscaping, where feasible. The extent and depth of removals should be evaluated by

Ninyo & Moore’s representative in the field based on the material exposed.

The resulting surface should be scarified 8 inches, moisture conditioned, and recompacted to a relative compaction of 90 percent as evaluated by ASTM D 1557. The removals should then be

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 11 backfilled with onsite or import soils that possess a low to very low potential for expansion (i.e., an

EI less than 50). These compacted fill materials should be placed at a relative compaction of

90 percent as evaluated by ASTM D 1557.

8.1.8 Remedial Grading – ADA Parking Stall

For the ADA parking stall, we recommend that the onsite subgrade soils be overexcavated to a depth of 1 foot below the planned subgrade elevation. The overexcavation should extend outward horizontally 2 feet from the exterior limits of the parking stall, where feasible. The extent and depth of removals should be evaluated by Ninyo & Moore’s representative in the field based on the material exposed.

The resulting surface should be scarified 8 inches, moisture conditioned, and recompacted to a relative compaction of 90 percent as evaluated by ASTM D 1557. The removals should then be backfilled with compacted fill soils placed at a relative compaction of 95 percent as evaluated by

ASTM D 1557.

8.1.9 Materials for Fill

Materials for fill may be processed from onsite excavations or may consist of import materials.

Onsite soils with an organic content of less than approximately 3 percent by volume (or

1 percent by weight) are suitable for reuse as general fill material. Fill soils should be free of trash, debris, roots, vegetation, organics, or other deleterious materials. Due to the shallow groundwater moisture conditioning of onsite materials, including drying and/or aerating, should be anticipated. Fill and utility trench backfill materials should not contain rocks or lumps over

3 inches, and not more than 30 percent larger than ¾ inch. Larger chunks, if generated during excavation, may be broken into acceptably sized pieces or disposed of offsite.

As noted earlier, expansion index testing presented in Appendix B indicates that some of the onsite near-surface soils possess a medium potential for expansion. Soils that possess a medium potential for expansion (i.e., an expansion index of 50 or more) are not suitable for reuse within the upper portion of the subgrade soils beneath the proposed amphitheater subgrade, retaining wall backfill, or as the upper 1 foot of subgrade soils beneath pedestrian concrete flatwork.

Imported fill material should generally be granular soils with a very low to low expansion potential

(i.e., an expansion index of 50 or less). Import fill material should also be non-corrosive in accordance with the California Department of Transportation corrosion criteria (Caltrans, 2021).

Non-corrosive soils are defined as soil with an electrical resistivity more than 1,500 ohm-cm, a chloride content less than 500 ppm, a sulfate content less than 0.1 percent (1,000 ppm), and a pH greater

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 12 than 5.5. Materials for use as fill should be evaluated by Ninyo & Moore’s representative prior to filling or importing. To reduce the potential of importing contaminated materials to the site, prior to delivery, soil materials obtained from off-site sources should be sampled and tested in accordance with standard practice (DTSC, 2001). Soils that exhibit a known risk to human health, the environment, or both, should not be imported to the site.

8.1.10 Compacted Fill

Prior to placement of compacted fill, the contractor should request an evaluation of the exposed ground surface by Ninyo & Moore. Unless otherwise recommended, the exposed ground surface should then be scarified to a depth of approximately 8 inches and watered or dried, as needed, to achieve moisture contents generally at or slightly above the optimum moisture content. The scarified materials should then be compacted to a relative compaction of

90 percent as evaluated in accordance with the ASTM D 1557. The evaluation of compaction by the geotechnical consultant should not be considered to preclude any requirements for observation or approval by governing agencies. It is the contractor's responsibility to notify this office and the appropriate governing agency when project areas are ready for observation, and to provide reasonable time for that review.

Fill materials should be moisture conditioned to generally at or slightly above the laboratory optimum moisture content prior to placement. The optimum moisture content will vary with material type and other factors. Moisture conditioning of fill soils should be generally consistent within the soil mass.

Prior to placement of additional compacted fill material following a delay in the grading operations, the exposed surface of previously compacted fill should be prepared to receive fill.

Preparation may include scarification, moisture conditioning, and recompaction.

Compacted fill should be placed in horizontal lifts of approximately 8 inches in loose thickness.

Prior to compaction, each lift should be watered or dried as needed to achieve a moisture content generally at or slightly above the laboratory optimum, mixed, and then compacted by mechanical methods to a relative compaction of 90 percent as evaluated by ASTM D 1557.

The upper 12 inches of the subgrade materials beneath vehicular pavements should be compacted to a relative compaction of 95 percent relative density as evaluated by ASTM

D 1557. Successive lifts should be treated in a like manner until the desired finished grades are achieved.

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8.1.11 Slopes

We anticipate that new cut and fill slopes may be constructed for the project. Unless otherwise recommended by our offices and approved by the regulating agencies, permanent cut and fill slopes should not be steeper than 2:1 (horizontal to vertical). Buildings, structures, and improvements should be set back from the top of slopes in accordance with the 2019 CBC.

We recommend buildings and structures be set back 20 feet or more from the top of slopes.

Compaction of the face of fill slopes should be performed by backrolling at intervals of 4 feet or less in vertical slope height, or as dictated by the capability of the available equipment, whichever is less. Fill slopes should be overbuilt and cut back to finish grades. The placement, moisture conditioning, and compaction of fill slope materials should be done in accordance with the recommendations presented herein.

Site runoff should not be permitted to flow over the tops of slopes. Positive drainage should be established away from the top of slopes. This may be accomplished by utilizing brow ditches placed at the top of slopes to divert surface runoff away from the slope face where drainage devices are not otherwise available.

The onsite soils may be susceptible to erosion. The project plans and specifications should contain design features and construction requirements to mitigate erosion of soils or contain a maintenance program to redress erosion features as they develop on a periodic basis.

8.1.12 Utility Pipe Zone Backfill

The pipe zone backfill should be placed on top of the pipe bedding material and extend to

1 foot or more above the top of the pipe in accordance with the recent edition of the Standard

Specifications for Public Works Construction (“Greenbook”). Pipe zone backfill should have a Sand Equivalent (SE) of 30 or more, and be placed around the sides and top of the pipe.

Silts and clays should not be used as pipe zone backfill. Special care should be taken not to allow voids beneath and around the pipe. Compaction of the pipe zone backfill should proceed up both sides of the pipe.

It has been our experience that the voids within a crushed rock material are sufficiently large to allow fines to migrate into the voids, thereby creating the potential for sinkholes and depressions to develop at the ground surface. If open-graded gravel is utilized as pipe zone backfill, this material should be separated from the adjacent trench sidewalls and overlying trench backfill with a geosynthetic filter fabric.

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 14

8.1.13 Utility Trench Zone Backfill

Utility trench zone backfill should be free of organic material, clay lumps, debris, and meet the following recommendations. Trench backfill should not contain rocks or lumps over approximately 3 inches in diameter and not more than approximately 30 percent larger than ¾ inch. Backfill materials should be moisture-conditioned to generally at or slightly above the laboratory optimum. Trench backfill should be compacted to a relative compaction of 90 percent as evaluated by ASTM D 1557 except for the upper 12 inches of the backfill beneath pavement areas which should be compacted to a relative compaction of 95 percent as evaluated by ASTM D 1557. Wet soils should be allowed to dry to moisture contents near the optimum prior to their placement as backfill. Lift thickness for backfill will depend on the type of compaction equipment utilized, but fill should generally be placed in lifts not exceeding 8 inches in loose thickness. Special care should be exercised to avoid damaging the pipe during compaction of the backfill.

8.1.14 Drainage

Pad and slope drainage should be directed such that runoff water is diverted away from slopes and structures to suitable discharge areas by nonerodable devices (e.g., gutters, downspouts, concrete swales, etc.). Positive drainage adjacent to structures should be established and maintained. Positive drainage may be accomplished by providing drainage away from the foundations of the structure at a gradient of 2 percent or steeper for a distance of 5 feet or more outside building perimeters, and further maintained by a graded swale leading to an appropriate outlet, in accordance with the recommendations of the project civil engineer and/or landscape architect.

Surface drainage on the site should be provided so that water is not permitted to pond. A gradient of 2 percent or steeper should be maintained over the pad area and drainage patterns should be established to divert and remove water from the site to appropriate outlets.

Care should be taken by the contractor during final grading to preserve any berms, drainage terraces, interceptor swales or other drainage devices of a permanent nature on or adjacent to the property. Drainage patterns established at the time of final grading should be maintained for the life of the project. The property owner and the maintenance personnel should be made aware that altering drainage patterns might be detrimental to foundation performance.

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 15

Seismic Design Considerations Design of the proposed improvements should be performed in accordance with the requirements of governing jurisdictions and applicable building codes. Table 1 presents the seismic design parameters for the site in accordance with the CBC (2019) guidelines and adjusted MCER spectral response acceleration parameters (SEAOC/OSHPD, 2022).

Table 1 – 2019 California Building Code Seismic Design Criteria Seismic Design Factors Value

Seismic Design Category --

Site Class D (Default)

Site Coefficient, Fa 1.2

Site Coefficient, Fv --

Mapped Spectral Acceleration at 0.2-second Period, Ss 0.860g

Mapped Spectral Acceleration at 1.0-second Period, S1 0.314g

Spectral Acceleration at 0.2-second Period Adjusted for Site Class, SMS 1.032g

Spectral Acceleration at 1.0-second Period Adjusted for Site Class, SM1 --

Design Spectral Response Acceleration at 0.2-second Period, SDS 0.688g

Design Spectral Response Acceleration at 1.0-second Period, SD1 --

Site Modified Maximum Considered Earthquake Geometric Mean (MCEG) Peak Ground Acceleration (PGAM) 0.457g

Foundations Provided the remedial grading measures have been implemented, the proposed structures may be founded on shallow foundations. Recommendations for the shallow foundations are presented in following sections. Foundations should be designed in accordance with structural considerations and the following recommendations. In addition, requirements of the appropriate governing jurisdictions and applicable building codes should be considered in the design of the structures.

8.3.1 Amphitheater

The amphitheater is anticipated to be constructed as an on-grade structure with tiered slab configurations cut into sloping ground and may be approximately two to three terraces high.

Shallow, spread or continuous footings supported wholly on compacted aggregate base may be designed using an allowable bearing capacity of 2,500 pounds per square foot (psf) for non-submerged conditions and 1,500 psf for submerged conditions. These allowable bearing capacities may be increased by one-third when considering loads of short duration such as wind or seismic forces. We recommend that shallow foundations for the new amphitheater be founded 18 inches or more below the lowest adjacent grade. Continuous footings should

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 16 have a width of at least 18 inches and spread footings should be at least 24 inches in width.

The footings should be reinforced in accordance with the recommendations of the project structural engineer.

8.3.1.1 Lateral Resistance

For resistance of footings to lateral loads, we recommend an allowable passive pressure of 300 psf per foot of depth be used with a value of up to 3,000 psf for non-submerged conditions and 140 psf per foot up to a value of 1,400 psf for submerged conditions. This value assumes that the ground is horizontal for a distance of 10 feet, or three times the height generating the passive pressure, whichever is more. We recommend that the upper 1 foot of soil not protected by pavement or a concrete slab be neglected when calculating passive resistance. For frictional resistance to lateral loads, we recommend a coefficient of friction of 0.35 be used between soil and concrete. The passive resistance values may be increased by one-third when considering loads of short duration such as wind or seismic forces.

8.3.2 Pedestrian Bridge

Shallow, spread or continuous footings supported wholly on alluvium and/or creek bed materials may be designed using an allowable bearing capacity of 1,500 psf for submerged conditions in the creek. These allowable bearing capacities may be increased by one-third when considering loads of short duration such as wind or seismic forces. We recommend that shallow foundations for the new pedestrian bridge be founded 12 inches or more below the lowest adjacent grade and should be at least 12 inches in width. The footings should be reinforced in accordance with the recommendations of the project structural engineer.

8.3.2.1 Lateral Resistance

For resistance of footings to lateral loads, we recommend an allowable passive pressure of 140 psf per foot of depth be used with a value of up to 1,400 psf for the submerged conditions at the creek. This value assumes that the ground is horizontal for a distance of

10 feet, or three times the height generating the passive pressure, whichever is more. We recommend that the upper 1 foot of soil not protected by pavement or a concrete slab be neglected when calculating passive resistance. For frictional resistance to lateral loads, we recommend a coefficient of friction of 0.4 be used between soil and concrete. The passive resistance values may be increased by one-third when considering loads of short duration such as wind or seismic forces.

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 17

Site Retaining Walls If proposed, site retaining walls that are under 6 feet in height and are not a part of or are not connected to buildings may be supported on continuous footings bearing on compacted fill. The continuous footing should have a width of 18 inches or more and be embedded a depth of

18 inches or more. An allowable bearing capacity of 2,000 psf for non-submerged conditions and

1,500 psf for submerged conditions may be used for the design of site retaining wall foundations.

The allowable bearing capacity may be increased by one-third when considering loads of short duration, such as wind or seismic forces.

For the design of a site yielding retaining wall that is not restrained against movement by rigid corners or structural connections, lateral pressures are presented on Figure 5. These pressures assume select backfill materials are used and free draining conditions. Granular backfill materials should not contain rocks or lumps over 3 inches, and not more than 30 percent larger than ¾ inch, and possess a very low to low potential for expansion (i.e. an expansion index [EI] less than 50).

Measures should be taken to reduce the potential for build-up of moisture behind the retaining walls.

A drain should be provided behind the retaining wall as shown on Figure 6. The drain should be connected to an appropriate outlet.

Preliminary Flexible Pavement Design We understand that preliminary concrete pavements may be used for the ADA parking stalls. We have assumed an R-value of 15, along with an estimated design Traffic Index (TI) of 5 as the basis of our preliminary flexible pavement design. This assumed TI should be evaluated by the Civil Engineer based on anticipated traffic loading at the site. Actual pavement recommendations should be based on R-value tests performed on bulk samples of the soils that are exposed at the finished subgrade elevations across the site at the completion of the grading operations. The preliminary recommended flexible pavement section is presented in Table 2.

Table 2 – Recommended Preliminary Flexible Pavement Section

Traffic Index (Pavement Usage)

Design R-Value

Asphalt Concrete Thickness (inches)

Aggregate Base Thickness (inches)

(Parking Stalls) 15 3 8

As indicated, these values assume a TI of 5.0 for parking stalls. If traffic loads are different from those assumed, the pavement design should be re-evaluated. In addition, we recommend that the upper 12 inches of the subgrade and aggregate base materials be compacted to a relative compaction of 95 percent relative density as evaluated by the current version of ASTM D 1557. The

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 18 subgrade soils and aggregate base materials should be moisture conditioned to generally at or slightly above the laboratory optimum moisture content, and compacted to a relative compaction of 95 percent as evaluated by ASTM D 1557.

Rigid Concrete Pavements We understand that rigid concrete pavements may be used for the ADA parking stalls. We recommend that these ADA parking stalls be 6 inches in thickness and should be reinforced with No. 3 reinforcing bars placed at 18 inches on-center both ways. The concrete for the ADA parking stall should be underlain by 4 inches of aggregate base materials and be compacted to a relative compaction of

95 percent relative density as evaluated by the current version of ASTM D 1557. The subgrade soils should also be moisture conditioned to generally at or slightly above the laboratory optimum moisture content, and compacted to a relative compaction of 95 percent as evaluated by ASTM D 1557. To reduce the potential manifestation of cracks to rigid concrete pavements due to movement of the underlying soil, we recommend that such pavement be installed with crack-control joints at appropriate spacing as designed by the structural engineer. Positive drainage should be established and maintained adjacent to the pavement.

Exterior Pedestrian Concrete Flatwork We recommend that exterior concrete flatwork underlain by 1 foot or more of compacted fill materials of generally very low to low expansion potential (i.e., an EI of 50 or less) be 4 inches in thickness and should be reinforced with No. 3 reinforcing bars placed at 24 inches on-center both ways. A vapor retarder is not needed for exterior flatwork. To reduce the potential manifestation of cracks to exterior concrete flatwork due to movement of the underlying soil, we recommend that such flatwork be installed with crack-control joints at appropriate spacing as designed by the civil engineer. Before placement of concrete, remedial grading should be performed as recommended previously. Positive drainage should be established and maintained adjacent to flatwork.

Corrosion Laboratory testing was performed on a select representative sample of the onsite earth materials to evaluate pH and electrical resistivity, as well as chloride and sulfate contents. The pH and electrical resistivity tests were performed in accordance with California Test (CT) 643 and the sulfate and chloride content tests were performed in accordance with CT 417 and CT 422, respectively. These laboratory test results are presented in Appendix B.

Ninyo & Moore | Los Penasquitos Canyon County Preserve, San Diego County, California | 109427001 | June 17, 2022 19

The results of the corrosivity testing indicated an electrical resistivity of 350 ohm-cm, a soil pH value of 8.7, a chloride content of 920 parts per million (ppm), and a sulfate content of

0.186 percent (i.e., 1,860 ppm). Based on a comparison with the California Department of

Transportation corrosion criteria (Caltrans, 2021), the onsite soils would be classified as corrosive.

Corrosive soils are defined as soil with an electrical resistivity of 1,500 ohm-cm or less, a chloride content of 500 ppm or greater, a sulfate content of 0.1 percent (1,000 ppm) or greater, and/or a pH equal to or less than 5.5.

Concrete Concrete in contact with soil or water that contains high concentrations of water-soluble sulfates that can be subject to premature chemical and/or physical deterioration.