Appendix_C_-_Geotechnical_Evaluation.pdf

Geotechnical Evaluation Moss Avenue Pump Station Control Room

City of Santa Monica Water Resources

Santa Monica, California

Woodard & Curran

9665 Chesapeake Drive, Suite 320 | Monterey Park, California 91754

June 23, 2025 | Project No. 213043001

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

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

NINYO & MOORE, A SOCOTEC COMPANY

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

Geotechnical Evaluation Moss Avenue Pump Station Control Room

City of Santa Monica Water Resources

Santa Monica, California

Mr. David Moering

Woodard & Curran

9665 Chesapeake Drive, Suite 320 | Monterey Park, California 91754

June 23, 2025 | Project No. 213043001

Michelle Manzano Senior Staff Geologist

Michael L. Putt, PG, CEG Principal Geologist

Soumitra Guha, PhD, PE, GE Principal Engineer

MXM/MLP/SG/mlc http://www.ninyoandmoore.com/

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CONTENTS

1 INTRODUCTION 1

2 SCOPE OF SERVICES 1

3 SITE DESCRIPTION AND PROPOSED CONSTRUCTION 1

4 SUBSURFACE EVALUATION AND LABORATORY TESTING 2

5 GEOLOGY AND SUBSURFACE CONDITIONS 3

5.1 Regional Geology 3

5.2 Subsurface Conditions 3

5.3 Groundwater 3

6 FLOOD HAZARDS 4

7 FAULTING AND SEISMICITY 4

7.1 Surface Fault Rupture 4

7.2 Ground Motion 4

7.3 Liquefaction Potential 5

7.4 Tsunamis 5

8 CONCLUSIONS 5

9 RECOMMENDATIONS 7

9.1 Earthwork 7

9.1.1 Pre-Construction Conference 7

9.1.2 Site Clearing and Preparation 7

9.1.3 Excavation Characteristics 8

9.1.4 Subgrade Preparation for At-Grade Structures 8

9.1.5 Temporary Excavations 8

9.1.6 Shoring 9

9.1.7 Fill Material 10

9.1.8 Fill Placement and Compaction 10

9.2 Underground Utilities 10

9.2.1 Pipe Bedding 10

9.2.2 Modulus of Soil Reaction 11

9.3 Seismic Design Considerations 11

9.4 Foundations 11

9.4.1 Mat Foundations 12

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9.5 Corrosivity 12

9.6 Concrete Placement 13

9.7 Drainage 13

10 CONSTRUCTION OBSERVATION 13

11 LIMITATIONS 14

12 REFERENCES 16

TABLE

1 – 2022 California Building Code Seismic Design Criteria 11

FIGURES

1 – Site Location

2 – Site Plan and Boring Location

3 – Regional Geology

4 – Fault Locations

5 – Seismic Hazard Zones

6 – Lateral Earth Pressures for Braced Excavation

7 – Lateral Earth Pressures for Temporary Cantilevered Shoring

APPENDICES

A – Boring Log

B – Laboratory Testing

Moss Avenue Pump Station Control Room, Santa Monica, California | 213043001 | June 23, 2025 1

1 INTRODUCTION

In accordance with your request and authorization, we have performed a geotechnical evaluation for the Moss Avenue Pump Station (MAPS) Control Room project located in Santa Monica, California (Figure 1). The purpose of our study was to evaluate the soil and geologic conditions at the site and provide geotechnical recommendations for the design and construction of the proposed improvements. This report presents the findings from our background review and subsurface exploration, 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, planning, and scheduling of the subsurface exploration.

• Review of readily available background materials including construction drawings for the existing pump station, published geologic maps, fault and seismic hazards maps, groundwater data, published literature, and aerial photographs.

• A site reconnaissance to observe the general site conditions, mark the proposed boring location, and coordination with Underground Service Alert for utility clearance. In addition, a geophysical survey was performed to clear the boring location of identifiable underground utilities.

• Subsurface exploration consisting of the drilling of one hand-auger boring to a depth of approximately 10 feet. The boring was 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 boring was backfilled with soil cuttings.

• Laboratory testing on selected soil samples including evaluation of in-situ moisture content and dry density, percent of soil particles finer than the No. 200 sieve, Proctor density, direct shear strength, and soil corrosivity.

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

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

3 SITE DESCRIPTION AND PROPOSED CONSTRUCTION

The MAPS is located northeast of the intersection of Moss Avenue and Appian Way. The site is bounded to the north and northeast by a slope that ascends to Moomat Ahiko Way, to the east by an apartment building, to the south by Appian Way, and to the west by the Santa Monica Urban

Runoff Recycling Facility.

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The area of the pump station site where the control room will be located is relatively flat at an elevation of approximately 28 feet above the mean sea level (Montgomery Watson, 2001). Based on our review of the construction drawings for the existing pump station, the pump station includes an underground electrical and generator room overlying a wet well and dry well (Montgomery

Watson, 2001). The bottom of the wet well extends to an elevation of approximately 14 feet below the mean sea level, approximately 42 feet deep. The site is generally paved with concrete and has a landscape area on the northwest side of the pump station structure. A toe-of-slope concrete retaining wall is located along the north/northeast side of the pump station structure. Other improvements at the site include existing pipelines, utilities, and other electrical equipment.

Based on our review of the Rehabilitation Project plans (Woodard & Curran, 2025), we understand that a new control room building will be constructed in the landscape area adjacent to the northwest side of the pump station structure. The control room will be a 20-foot-long by 8-foot-wide single-story container building that will be constructed at grade and will be supported by a

22-foot-long by 10-foot-wide, 12-inch-thick concrete mat. Earthwork for the project is anticipated to include remedial grading to prepare the site for the new structure and utility trenching on the order of 5 feet deep.

4 SUBSURFACE EVALUATION AND LABORATORY TESTING

Our subsurface exploration consisted of the drilling, logging, and sampling of one small-diameter soil boring on April 28, 2025. Initial attempts of the hand auger boring within the proposed control room building footprint encountered drilling refusal at shallow depths due to the presence of construction debris. The boring was relocated a total of nine times until boring B-1 reached the planned depth of approximately 10 feet. The boring was logged in the field by a representative of

Ninyo & Moore. Representative bulk and relatively undisturbed soil samples were collected from the boring at selected depths for laboratory testing and transported to our laboratory. The approximate location of the boring is presented on Figure 2. The boring log is presented in

Appendix A.

Laboratory testing was performed on representative soil samples collected from the boring. The laboratory testing included evaluation of in-situ moisture content and dry density, percent of soil particles finer than the No. 200 sieve, Proctor density, direct shear strength, and soil corrosivity

(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 log in Appendix A. The remaining laboratory testing results are presented in Appendix B.

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5 GEOLOGY AND SUBSURFACE CONDITIONS

5.1 Regional Geology

The project site is located within the Los Angeles Basin of the Peninsular Ranges Geomorphic

Province (Norris and Webb, 1990). The basin has been divided into four blocks, the northeastern, northwestern, southwestern, and central blocks that are separated by prominent fault systems.

The project site is located within the southwestern block, the majority of which is beneath the

Pacific Ocean. The exposed part of the southwestern block mostly consists of a low plain that is approximately 28 miles long and extends from Santa Monica at the northwest to Long Beach at the southeast and is bounded by the Newport-Inglewood fault zone to the east.

Regional geologic maps indicate that the site is underlain by Quaternary-age old alluvial fan deposits consisting of slightly to moderately consolidated silt, sand, and gravel deposits

(Campbell, et al., 2014). Artificial fill and beach deposits are mapped to the west and southwest of the pump station. A geologic map of the site vicinity is presented on Figure 3.

5.2 Subsurface Conditions

Materials encountered during our subsurface exploration consisted of artificial fill underlain by old alluvial fan deposits to the explored depth of up to approximately 10 feet. The artificial fill was encountered up to a depth of approximately 8 feet below the ground surface and consisted of moist, medium dense to dense silty sand with gravel and silt with sand. As indicated above, several hand auger borings encountered refusal on construction debris within the fill. Deeper fill associated with the backfill of the pump station structure that extended to an elevation of approximately 14 feet below the mean sea level is anticipated at the site (Montgomery Watson, 2001). The old alluvial fan deposits consisted of moist, very dense, clayey sand with gravel.

Refusal was encountered on cobbles or possible boulders at approximately 10 feet. More detailed descriptions of the earth materials encountered during our subsurface exploration are presented on the boring log in Appendix A.

5.3 Groundwater

Groundwater was not encountered during drilling to the explored depth of approximately 10 feet.

Regional maps indicate that the historic high groundwater at the site is between approximately 10 and 20 feet below the ground surface (California Department of Conservation, Division of Mines and Geology [CDMG], 1998). Based on the California State Water Resources Control Board

GeoTracker (2025) website, groundwater has been encountered at depths of between 37 and 57 feet at a site located 0.3 miles northeast of the project site. Fluctuations in groundwater levels will occur due to variations in precipitation, ground surface topography, subsurface stratification, Moss Avenue Pump Station Control Room, Santa Monica, California | 213043001 | June 23, 2025 4 irrigation, groundwater pumping, and other factors that may not have been evident at the time of our field evaluation.

6 FLOOD HAZARDS

Based on our review of flood insurance rate maps (Federal Emergency Management Agency

[FEMA], 2021), the project area is designated as Zone X, an “area of minimal flood hazard.”

7 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 area is considered to be 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 sites are shown on Figure 4. The site is not located within a State of California Earthquake Fault Zone (CDMG, 1999; California Geological Survey

[CGS], 2018).

The principal seismic hazards evaluated at the subject site are surface fault rupture, ground motion, liquefaction, and landslides. Brief descriptions of these seismic hazards are provided in the following sections.

7.1 Surface Fault Rupture

Surface fault rupture is the offset or rupturing of the ground surface by relative displacement across a fault during an earthquake. Based on our review of referenced geologic and fault hazard data, the project site is not transected by known active faults. Therefore, the potential for surface rupture is relatively low. However, lurching or cracking of the ground surface as a result of nearby seismic events is possible.

7.2 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 2022 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. Based on our review of CGS’s shear wave velocity map, the average shear wave velocity in the upper 100 feet (i.e., 30 meters) of the subsurface profile (VS30) is approximately 1,270 feet per second (387 meters per second) at the site. In accordance with Chapter 20 of the American Society of Civil Engineers (ASCE) Publication

7-16 (2016) for the Minimum Design Loads and Associated Criteria for Building and Other

Structures, the site classification is Site Class C.

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In accordance with ASCE 7-16, the mapped MCER ground motion response accelerations were determined using the 2025 Structural Engineers Association of California (SEAC) seismic design maps (web-based tool). 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. Spectral response acceleration parameters, consistent with the 2022

CBC, are provided in Section 9.3 for the evaluation of seismic loads on buildings and other structures.

7.3 Liquefaction Potential

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 7. 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.

The State of California Seismic Hazards Zones map (CDMG, 1999) indicates that the site is not located in an area mapped as being potentially susceptible to liquefaction (Figure 5). The pump station site is underlain by old alluvial fan deposits which are relatively dense and generally not susceptible to liquefaction.

7.4 Tsunamis

Tsunamis are waves generated in large bodies of water by fault displacement or major ground movement. Based on our review, the project site is not located within a mapped tsunami hazard area (CGS, 2025).

8 CONCLUSIONS

Based on the results of our evaluation, it is our opinion that construction of the proposed control room building for the MAPS is feasible from a geotechnical perspective provided that the recommendations presented in this report are incorporated into the design and construction of the project. The primary geotechnical consideration for the project is the proximity of the proposed control room building to the existing pump station retaining walls. Based on the preliminary site

Moss Avenue Pump Station Control Room, Santa Monica, California | 213043001 | June 23, 2025 6 plans, we understand that the proposed control room building will be located approximately 15 to

20 feet away from the existing below-grade pump station. The below-grade pump station extends to a depth of approximately 42 feet below the ground surface. The impact of surcharge loading from the proposed control building on the existing below-grade pump station should be considered. For preliminary planning purposes, a lateral surcharge pressure of 0.5q on the existing pump station may be used, where q is the uniform surface load of the proposed control building. We anticipate that the pump station wall will be able to accommodate the additional surcharge pressure from the new control room building supported on a mat foundation. However, the project structural engineer should evaluate this condition. If the structural engineer finds that the pump station structure cannot accommodate the additional surcharge, recommendations for deep foundations can be provided to transfer the load from the control room building to depths at which additional surcharge would not be a concern for the pump station wall.

In general, the following additional conclusions were made:

• The site consists of artificial fill overlying old alluvial fan deposits. The fill material generally consisted of moist, medium dense to dense silty sand with gravel and silt with sand.

Construction debris was encountered within the fill that resulted in drilling refusal with the hand auger. The alluvium consisted of moist, very dense clayey sand with gravel. Refusal was encountered on cobbles or possible boulders at approximately 10 feet.

• Artificial fill was encountered up to a depth of approximately 8 feet below the ground surface;

however, deeper fill may be present within the footprint of the previous MAPS site. Fill depth within the previous MAPS site is expected to be more than 40 feet deep.

• Based on preliminary site plans, we understand that the proposed control building will be located approximately 15 to 20 feet away from the existing below-grade pump station. The below-grade pump station extends to a depth of approximately 42 feet below the ground surface. The impact of surcharge loading from the proposed control building on the existing below-grade pump station should be considered.

• Excavations in the fill soils should be feasible with earthmoving equipment in good working condition. However, construction debris is present within the fill and should be anticipated by the contractor.

• The on-site soils should be suitable for re-use from a geotechnical perspective as general fill and backfill once moisture-conditioned to near the optimum moisture content. Oversized materials with a diameter of 4 inches or more should be removed from engineered fill and trench backfill.

• The on-site soils should be considered as Type C soils in accordance with the Occupational Safety and Health Administration (OSHA) regulations. The contractor’s competent person should make their own evaluation of the soil types encountered during construction.

• Groundwater was not encountered during our subsurface exploration to the explored depth of approximately 10 feet. Historical high groundwater at the site is between 10 and 20 feet below the ground surface. Groundwater has been reportedly encountered at depths of between 37 and 57 feet at a site located 0.3 miles northeast of the project site (GeoTracker, 2025). Groundwater is not anticipated to be a design consideration for the project.

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• The site is not located in a mapped Seismic Hazard Zone considered susceptible to seismically-induced liquefaction (CDMG, 1999).

• The site is not located within a State of California Earthquake Fault Zone with the potential for surface fault rupture. The probability of surface fault rupture at the site is considered to be low.

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

9 RECOMMENDATIONS

The recommendations presented in the following sections provide geotechnical criteria regarding the design and construction of the proposed control room building and associated site improvements. The recommendations are based on the results of our subsurface evaluation, geotechnical analysis, and our project understanding. 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.

9.1 Earthwork

Based on our understanding of the project, earthwork at the site is anticipated to consist of site clearing, remedial grading for foundation support, and trenching and backfilling associated with underground utility installation. Earthwork operations at the site should be performed in accordance with the recommendations provided in the following sections of this report and applicable governing agencies.

9.1.1 Pre-Construction Conference

We recommend that construction plans be submitted to Ninyo & Moore for review to evaluate conformance to the geotechnical recommendations provided in this report. We further 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.

9.1.2 Site Clearing and Preparation

Prior to performing excavations or other earthwork, the area should be cleared of existing structures, piping under and above the ground, abandoned utilities, rubble and debris, surface obstructions, and other deleterious materials. Existing utilities within the project limits

Moss Avenue Pump Station Control Room, Santa Monica, California | 213043001 | June 23, 2025 8 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.

9.1.3 Excavation Characteristics

Based on our exploratory borings, we anticipate that excavations within the fill at the site may be accomplished with grading equipment in good operating condition. We do not anticipate that excavations will extend to depths where the old alluvial fan deposits would be encountered. The fill material generally consisted of moist, medium dense to dense silty sand with gravel and silt with sand. Construction debris was encountered within the fill. Oversized materials (i.e., materials 4 or more inches in diameter) are not considered suitable for use as backfill and should be disposed of off-site. The contractor should plan on processing (i.e., drying and/or wetting) the excavated materials to bring those near the laboratory optimum moisture content prior to use as fill. Contractors should make their own independent evaluation of the excavatability of site soils prior to submitting their bids, including allowances for processing the soils and removal of oversized materials/construction debris.

9.1.4 Subgrade Preparation for At-Grade Structures

In order to provide suitable support and reduce the potential settlements of the proposed control room building, we recommend that the mat foundation be supported on 2 feet of newly compacted fill. The recompaction work should consist of 1) removing existing fill material to a depth of 2 feet below the bottom of the proposed 12-inch-thick concrete mat, 2) scarifying, moisture-conditioning, and compacting the exposed subgrade soils, and 3) placing the fill and compacting it to a relative compaction of 90 percent or more at or near the laboratory optimum moisture content as evaluated by the ASTM International (ASTM) test method D

1557.

9.1.5 Temporary Excavations

We recommend that trenches and excavations be designed and constructed in accordance with the OSHA regulations. These regulations provide trench sloping and shoring design parameters for excavations of up to 20 feet deep based on the soil types encountered.

Excavations should be designed by the contractor’s engineer based on site-specific geotechnical analyses. For planning purposes, we recommend that on-site soils be considered as OSHA soil type C. The contractor’s competent person should make their own evaluation of the soil types encountered during construction and adjust project requirements per OSHA accordingly.

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Temporary excavations should be constructed in accordance with the OSHA recommendations. 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 1.5:1 (horizontal to vertical). 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. On-site safety of personnel is the responsibility of the contractor.

Care should be taken by the contractor to avoid undermining adjacent existing foundations and improvements. New excavations should not extend within the “zone of influence” of existing foundations, which is defined as a 1:1 (horizontal to vertical) plane projecting out from the bottom outside edge of the foundations. In the event that excavations will extend within the “zone of influence” of existing foundations, our office should be notified for review and development of appropriate recommendations such as temporary underpinning of impacted foundations and/or temporary shoring.

9.1.6 Shoring

Where slopes cannot be laid back, shoring may be appropriate. Shoring system design should consider the excavation characteristics of the on-site soil, temporary excavation stability, and the impact of construction on existing structures.

If shoring systems are used for site excavations, they should be designed for the anticipated soil conditions using the lateral earth pressures values presented on Figures 6 and 7 for braced and cantilevered shoring, respectively. The recommended design lateral earth pressures do not include the loads imposed on the shoring system from raising the ground surface elevation behind the shoring, soil stockpiles, construction materials, construction equipment, and other loads acting above a 1:1 (horizontal to vertical) plane extending up and back from the base of the shoring. For shoring subjected to the above-mentioned surcharge loads, the contractor should include the effects of these loads on lateral earth pressures against the shoring system.

The contractor should retain a licensed, qualified, and experienced engineer to design the shoring system. The shoring parameters presented in this report are minimum requirements, and the contractor should evaluate the adequacy of these parameters and make the appropriate modifications for their design.

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9.1.7 Fill Material

In general, the on-site soils should be suitable for general fill and trench backfill material provided those are free of rocks or lumps of material in excess of 4 inches in diameter. On-site materials used as general fill and/or trench backfill will involve moisture-conditioning to achieve appropriate moisture content for compaction.

Imported materials, if needed, should consist of clean, non-expansive granular materials that conform to the “Greenbook” Standard Specifications for Public Works Construction (Public

Works Standard, Inc., 2024) for structure backfill. The imported materials should also meet the Caltrans (2021) criteria for non-corrosive soils (i.e., soils having a chloride concentration of 500 parts per million [ppm] or less, a soluble sulfate content of approximately 1,500 ppm or less, a pH value of 5.5 or higher, and a minimum resistivity of 1,500 ohm-centimeters [ohm-cm] or higher). Materials for use as fill should be evaluated by the geotechnical consultant prior to importing. The contractor should be responsible for the uniformity of imported materials brought to the site.

9.1.8 Fill Placement and Compaction

Fill and trench backfill should be compacted in uniform horizontal lifts to a relative compaction of 90 percent or more as evaluated by ASTM D 1557. Fill soils should be moisture-conditioned to near the optimum moisture content. 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. Special care should be taken to avoid pipe damage when compacting trench backfill above the pipes. Placement and compaction of fill soils should be in general accordance with the appropriate governing agencies and good construction practices.

9.2 Underground Utilities

Utility trenches should not be excavated parallel to structure footings. If needed, trenches can be excavated adjacent to a continuous footing, provided that the bottom of the trench is located above a 1:1 (horizontal to vertical) plane projected downward from a point 6 inches above the bottom of the adjacent footing. Utility lines that cross beneath footings should be encased in concrete below the footing.

9.2.1 Pipe Bedding

We recommend that pipelines be supported on 6 inches or more of granular bedding material such as sand with a sand equivalent (SE) value of 30 or more. Bedding material should be placed and compacted around the pipe, and 12 inches or more above the top of the pipe in accordance with the Greenbook (Public Works Standard, Inc., 2024). We do not recommend the use of crushed rock for bedding material. It has been our experience that the voids within

Moss Avenue Pump Station Control Room, Santa Monica, California | 213043001 | June 23, 2025 11 a crushed rock material are sufficiently large enough to allow fines to migrate into the voids, thereby creating the potential for sinkholes and depressions to develop at the ground surface.

Special care should be taken not to allow voids beneath and around the pipe. Bedding material and compaction requirements should be in accordance with the recommendations of this report, the project specifications, and applicable requirements of the appropriate agencies. Compaction of the bedding material and backfill should proceed along both sides of the pipe concurrently and be compacted to a relative compaction of 90 percent or more as evaluated by ASTM D 1557.

9.2.2 Modulus of Soil Reaction

The modulus of soil reaction is used to characterize the stiffness of soil backfill placed on the sides of buried flexible pipelines for the purpose of evaluating lateral deflection caused by the weight of the backfill above the pipe. We recommend that a modulus of soil reaction of

1,000 pounds per square inch be used for design, provided that relatively granular bedding material is placed adjacent to the pipe, as recommended in this report.

9.3 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 2022 CBC guidelines.

Table 1 – 2022 California Building Code Seismic Design Criteria

Spectral Response Acceleration Parameters Value

Site Class C

Mapped MCER Spectral Response Acceleration at Short Periods, Ss 1.924g

Mapped MCER Spectral Response Acceleration at 1.0-Second Period, S1 0.687g

MCER Spectral Response Acceleration at Short Periods, Adjusted for Site Class, SMS 2.309g

MCER Spectral Response Acceleration at 1.0-Second Period, Adjusted for Site Class, SM1 0.961g

Design Spectral Response Acceleration at Short Periods, SDS 1.539g

Design Spectral Response Acceleration at 1.0-Second Period, SD1 0.641g

Maximum Considered Earthquake Geometric Mean (MCEG) Peak Ground Acceleration, PGAM

0.988g

9.4 Foundations

The control room building may be supported on a shallow mat foundation as proposed.

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.

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9.4.1 Mat Foundations

The mat foundations should be supported on compacted fill soils as recommended in this report and extend 6 inches or more below the lowest adjacent finished grade. The mat foundation may be designed using a net allowable bearing capacity of 2,000 pounds per square foot (psf). The allowable bearing capacity may be increased by one-third when considering loads of short duration such as wind or seismic forces. The total and differential settlements corresponding to this allowable bearing load are estimated to be less than approximately 1 inch and 0.5 inch over a horizontal span of 40 feet, respectively. A mat foundation 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. The mat foundation 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 that the passive resistance does not exceed one-half of the total allowable resistance. The passive resistance may be increased by one-third when considering loads of short duration such as wind or seismic forces.

Mat foundations typically experience some deflection due to loads placed on the mat and the reaction of the soils underlying the mat. The appropriate contact pressure(s) beneath the bases of mat foundations will vary with their size, shape, and other factors. A design modulus of subgrade reaction (Kv) of 150 pounds per cubic inch (pci) may be used for the subgrade soils in evaluating such deflections. This value is based on a unit square foot area and should be adjusted for the planned mat size. The coefficient of subgrade reaction, Kb, for a mat of a specific width may be evaluated using the following equation:

Kb = Kv[(b+1)/2b]2

Where, b is the width of the mat in feet.

9.5 Corrosivity

Laboratory testing was performed on a representative soil sample 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 (CT) method

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 7.7. The electrical resistivity was 4,894 ohm-cm; the chloride content was 35 ppm; the sulfate content was 0.003 percent (i.e., 30 ppm).

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Based on the laboratory test results and Caltrans (2021) criteria, the soils at the project site can be classified as non-corrosive which is defined as having earth materials with less than 500 ppm chlorides, less than 0.15 percent sulfates (i.e., 1,500 ppm), a pH of 5.5 or higher, or an electrical resistivity greater than 1,500 ohm-cm.

9.6 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 sample tested for this evaluation, using CT 417, indicates a water-soluble sulfate content of 0.003 percent by weight (i.e., 30 ppm). Accordingly, the on-site soils are considered to have a negligible potential for sulfate attack. However, due to the potential variability of site soils, consideration should be given to using Type II/V cement for the project.

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

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

We further recommend that concrete cover over reinforcing steel for foundations be provided in accordance with CBC (2022). The structural engineer should be consulted for additional concrete specifications.

9.7 Drainage

Positive surface drainage is imperative for performance of site improvements. Positive drainage should be provided and maintained to transport surface water away from foundations and other site improvements. Positive drainage incorporates a slope of 2 percent or more over a distance of 5 feet or more away from structures, pavements, and top of slopes. Surface water should not be allowed to flow over slope faces or pond adjacent to footings.

10 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 observed during limited subsurface exploration performed at the site. It is imperative that the geotechnical consultant checks the subsurface conditions during construction. We recommend that Ninyo &

Moss Avenue Pump Station Control Room, Santa Monica, California | 213043001 | June 23, 2025 14

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 clearing, grubbing, and removals.

• Observing remedial grading excavations, placement, and compaction of fill, including trench backfill.

• Evaluating on-site soil for suitability as use as engineered fill/structural backfill prior to placement.

• 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 are based on the assumption that Ninyo & Moore will provide geotechnical observation and testing services during construction. In the event that the services of Ninyo & Moore are not utilized during construction, we request that the selected consultant provide the owner with a letter (with a copy to Ninyo & Moore) indicating that they fully understand Ninyo & Moore’s recommendations, and that they are in full agreement with the design parameters and recommendations contained in this report.

11 LIMITATIONS

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

Moss Avenue Pump Station Control Room, Santa Monica, California | 213043001 | June 23, 2025 15

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.

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.

Moss Avenue Pump Station Control Room, Santa Monica, California | 213043001 | June 23, 2025 16

12 REFERENCES

American Concrete Institute, 2025, Building Code Requirements for Structural Concrete and Commentary (ACI 318-25).

American Society of Civil Engineers, 2016, Minimum Design Loads for Building and Other Structures, Standard ASCE/SEI 7-16.

ASTM International, 2025, Annual Book of ASTM Standards, West Conshohocken, Pennsylvania.

California Building Standards Commission, 2022, California Building Code (CBC): California Code of Regulations, Title 24, Part 2, Volumes 1 and 2, based on the 2021 international Building Code.

California Department of Conservation, Division of Mines and Geology, 1998, Seismic Hazard Zone Report for the Beverly Hills 7.5-Minute Quadrangle, Los Angeles County, California:

Seismic Hazard Zone Report 023.

California Department of Conservation, Division of Mines and Geology, 1999, Seismic Hazard Zones, Beverly Hills Quadrangle, 7.5-Minute Series: Scale 1:24,000, dated March 25.

California Department of Transportation, 2020, Highway Design Manual, Seventh Edition, dated July 1.

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

California Department of Water Resources, 2025, Water Data Library Website, https://wdl.water.ca.gov/waterdatalibrary/Map.aspx/.

California Geological Survey, 2008, Guidelines for Evaluating and Mitigating Seismic Hazards in California, Special Publication 117A, dated September 11.

California Geological Survey, 2015, CGS Map Sheet 48: Shear-wave Velocity in Upper 30m of Surficial Geology (Vs30); https://maps.conservation.ca.gov/cgs/DataViewer/, dated May 24.

California Geological Survey, 2018, Earthquake Fault Zones, A Guide for Government Agencies, Property Owners/Developers, and Geoscience Practitioners for Assessing Fault Rupture Hazards in California: Special Publication 42.

California Geological Survey, 2025, Tsunami Hazard Area Map, https://www.conservation.ca.gov/cgs/tsunami/maps.

California State Water Resources Control Board, 2025, GeoTracker Website, http://geotracker.waterboards.ca.gov.

Campbell, R.H., Willis, C.J., Irvine, P.J., and Swanson, B.J., 2014, Preliminary Geologic Map of the Los Angeles 30’ x 60’ Quadrangle, California, Version 2.1. United States Geologic Survey.

Federal Emergency Management Agency, 2021, Flood Insurance Rate Map, Los Angeles County, California, Map Number 06037C1588G, effective date April 21.

Google Earth, 2025, http://earth.google.com.

Historic Aerials, 2025, Website for Viewing Aerial Photographs, www.historicaerials.com.

Moss Avenue Pump Station Control Room, Santa Monica, California | 213043001 | June 23, 2025 17

Montgomery Watson, 2001, City of Santa Monica Environmental and Public Works Management Department, Volume 2 – Drawings for the Construction of Moss Avenue Pump Station Phase 2, April 8, 1999, Record Drawings dated July 30.

Ninyo and Moore, 2025, Revised Proposal for Geotechnical Consulting Services, Moss Avenue Pump Station Improvements, City of Santa Monica Water Resources, Santa Monica, California, dated March 14.

Norris, R.M. and Webb, R.W., 1990, Geology of California, Second Edition: John Wiley & Sons.

Public Works Standard, Inc., 2024, The “Greenbook”: Standard Specifications for Public Works Construction, BNI Building News, Vista, California.

Structural Engineers Association of California (SEAC), 2025, Seismic Design Maps, https://www.seismicmaps.org/.

United States Geological Survey, 2008, National Seismic Hazard Maps, http://geohazards.usgs.gov/cfusion/hazfaults_search/hf_search_main.cfm.

United States Geological Survey, 2024, Quaternary Fault and Fold Database of the United States, https://www.usgs.gov/natural-hazards/earthquakehazards/hazards.

United States Geological Survey, 2025, Beverly Hills Quadrangle, Beverly Hills, California, 7.5 Minute Series: Scale 1:24,000.

Woodard & Curran, 2025, Moss Avenue Pump Station, Rehabilitation Project, Control Room Plan, Elevations, and Notes, Sheet S-104, dated May 29.

Moss Avenue Pump Station Control Room, Santa Monica, California | 213043001 | June 23, 2025

Appendix A

Photographic Documentation

FIGURES

405 210

MAP INDEX

Los Angeles County

SITE

4,0002,0000

FEET

P

1.

ap rx

/2

3/

D R

A F

T E

D B

Y : J

D L

FIGURE 1

NOTE: DIRECTIONS, DIMENSIONS AND LOCATIONS ARE APPROXIMATE. | SOURCE: USGS, 2025

SITE LOCATION

213043001 | 6/25

MOSS AVENUE PUMP STATION CONTROL ROOM

SANTA MONICA, CALIFORNIA

M O

SS A

VE

A P

P I A

N W

A Y

M O O M AT A H I K O WAY

B-1

TD=10.0

P

1.

ap rx

/2

3/

A F

T E

D B

Y : J

D L

SITE PLAN AND BORING LOCATION

FIGURE 2

0 25 50

FEET

BORING

TD=TOTAL DEPTH IN FEET

B-1

TD=10.0

LEGEND

SITE BOUNDARY

NOTE: DIRECTIONS, DIMENSIONS AND LOCATIONS ARE APPROXIMATE. | SOURCE: GOOGLE, 2025

213043001 | 6/25

LEGEND

4,0002,0000

FEET

EOLIAN DEPOSITS

ARTIFICIAL FILL

Qof2

BEACH DEPOSITS FAULT; DASHED WHERE INFERRED,

DOTTED WHERE CONCEALED

Qom?

Qya2

YOUNG ALLUVIUM

Qe?

Qya2

Qb af

SITE

P

1.

ap rx

/2

3/

A F

T E

D B

Y : J

D L

FIGURE 3

NOTE: DIRECTIONS, DIMENSIONS AND LOCATIONS ARE APPROXIMATE. | REFERENCE: (CAMPBELL, ET AL., 2014).

REGIONAL GEOLOGY

213043001 | 6/25

INCLINED BEDDING21

GEOLOGIC CONTACT

OLD ALLUVIAL FAN DEPOSITS,

UNIT 2

OLD SHALLOW MARINE DEPOSITS

ON WAVE CUT SURFACES

Qof2

Qom?

C

ABR

ILLO

FAU

LT

COMPTON

THRUST FAULT

S A

N P

E D

R O

B A

S

IN

FA

U

LT

Z

O N

E

DUME FAUL ZONE

LO

S

A

LA

M

ITO

S

FA

U

LT

WALNUT C

REEK FAULT

LOWER ELYSIAN PARK THRUSTPUENTE HILLS BLIND

THRUST SYSTEM

FAULT

PUENTE HILLS BLIND

THRUST SYSTEM

UPPER ELYSIAN PARK

CHATSW

ORTH

SOLEDAD FAULT

HOLLYWOOD FAULT

RAYMOND FAULT

SIERRA MADRE FAULT ZONE

DEL VALLE FAULT

SAN ANDREAS FAULT ZONE

EAGLE ROCK

FAULT

MALIBU COAST FAULT

SAN GABRIEL FAULT ZONE

O V

E R

LA

N

D A

V E

N U

E

FA

U

LT

OAK RIDGE FAULT

SAN

TA F

ELIC

IA

FAU

LT

C H

A R

N O

C K

F A

U

LT

PELONA FAULT

HOLSER FAULT

VERDUGO FAULT

NORTHRIDGE HILLS FAULT

PALO

S VERDES FAULT ZO

NE

SANTA MONICA FAULT

NORTHRIDGE BLIND THRUST

C O

M P

TO

N

TH

R

U S

T FA

U

LT

SIERRA MADRE FAULT ZONE

SAN GABRIEL

FAULT ZONE

BONEY MOUNTAIN FAULT

SIMI-SANTA ROSA FAULT ZONE

CLEARWATER FAULT ZONE

SYCAMORE C

ANYON F

AULT

SAN CAYETANO FAULT

FAULT

Ventura County

Los Angeles County

Orange County

Long Beach

Los Angeles

Santa Monica

Glendale

Palmdale

Simi Valley

Beverly Hills

Torrance

MILES

LEGEND

STATE/COUNTY BOUNDARY

QUATERNARY

(POTENTIALLY ACTIVE)

LATE QUATERNARY

(POTENTIALLY ACTIVE)

HOLOCENE ACTIVE

HISTORICALLY ACTIVE

SOURCES: QUATERNARY FAULTS DATABASE - U.S. GEOLOGICAL SURVEY AND

CALIFORNIA GEOLOGICAL SURVEY, QUATERNARY FAULT AND FOLD DATABASE

FOR THE UNITED STATES, ACCESSED NOVEMBER 4, 2024, AT:

https://www.usgs.gov/programs/earthquake-hazards/faults

CALIFORNIA

Pacif ic Ocean

CALIFORNIA FAULT ACTIVITY

SITE

P

1.

ap rx

/2

3/

A F

T E

D B

Y : J

D L

FAULT LOCATIONS

FIGURE 4

NOTE: DIRECTIONS, DIMENSIONS AND LOCATIONS ARE APPROXIMATE.

213043001 | 6/25

LIQUEFACTION ZONES

4,0002,0000

FEET

Areas where historical occurrence of liquefaction, or local geological, geotechnical and ground water conditions indicate a potential for permanent ground displacements such that mitigation as defined in Public Resources Code Section 2693(c) would be required.

LEGEND

P

1.

ap rx

/2

3/

A F

T E

D B

Y : J

D L

FIGURE 5

NOTE: DIRECTIONS, DIMENSIONS AND LOCATIONS ARE APPROXIMATE. | SOURCE: CDMG, 1999

SEISMIC HAZARD ZONES

SITE

213043001 | 6/25

EARTHQUAKE FAULT ZONES

Zone boundaries are delineated by straight-line segments; the boundaries define the zone encompassing active faults that constitute a potential hazard to structures from surface faulting or fault creep such that avoidance as described in Public Resources Code Section 2621.5(a) would be required.

FIGURE 6

SANTA MONICA, CALIFORNIA

213043001 I 6/25

LATERAL EARTH PRESSURES FOR

BRACED…