Attachment_G_Geotech_Report_for_Lystek_2024-12-11.pdf

Geotechnical Evaluation Valley Sanitary District Proposed Lystek System Storage Tank and Building 45500 Van Buren Street, Indio, Riverside County, California

Prepared for:

Lystek International 11014 Chadbourne Road Fairfield, California 94534-9700

Prepared by:

Verdantas 41945 Boardwalk, Suite V, Palm Desert, CA 92211 760.776.4192

Verdantas Project No: 042.24343

November 2024 Revised December 2024

41945 Boardwalk, Suite V Palm Desert, CA 92211

760.776.4192

Verdantas.com

November 12, 2024 Revised December 11, 2024

Proposal No. 042.24343 Tristan Pyke, P. Eng Project Engineer Lystek International 11014 Chadbourne Road Fairfield, California 94534-9700 519.998.7385 tpyke@lystek.com

Subject: Geotechnical Exploration Proposed Lystek System Storage Tank and Building Valley Sanitary District 45500 Van Buren Street, Indio, Riverside County, California

In accordance with your request, we are pleased to present herewith our geotechnical report for the proposed Storage Tank and Building associated with Valley Sanitary District project, within the existing Valley Sanitary District complex located at 45500 Van Buren Street, Indio, CA. Based on the results of our geotechnical exploration, the proposed improvement is considered feasible from a geotechnical perspective. The site is generally underlain by sandy and silty alluvial soils.

The opportunity to be of service is sincerely appreciated. If you should have any questions, please do not hesitate to call our office.

Sincerely, Verdantas Inc.

Bashir S. Saiid, PE Associate Engineer 1 951.252.8927 bsaiid@verdantas.com

Brent Adam, CEG Senior Project Geologist 1 951.252.8923 badam@verdantas.com

Distribution: (1) addressee (PDF copy via email) https://www.verdantas.com/

Geotechnical Exploration 042.24343 Proposed Lystek System Storage Tank and Building, Indio, CA November 12, 2024, revised 12/11/24

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Table of Contents

1. INTRODUCTION

1.1 Site Location and Description

1.2 Project Description

1.3 Purpose and Scope of Evaluation

1.4 Field Exploration

1.5 Laboratory Testing

1.6 Previous Reports

2. SUMMARY OF GEOTECHNICAL FINDINGS

2.1 Subsurface Conditions

2.1.1 Surficial Soils

2.1.2 Alluvium

2.2 Surface and Groundwater

2.3 Faulting and Seismic Design Parameters

2.4 Secondary Seismic Hazards

2.4.1 Liquefaction Potential

2.4.2 Landslide and Rockfall

2.4.3 Flooding

2.4.4 Seiches and Tsunamis

3. CONCLUSIONS AND RECOMMENDATIONS

3.1 General

3.2 Earthwork Considerations

3.2.1 Excavation Characteristics

3.2.2 Subgrade Preparation/Remedial Grading

3.2.3 Structural Fills

3.2.4 Subgrade Preparation – Pipelines

3.2.5 Trench Backfill

3.2.6 General Backfill

3.2.7 Import Soils

3.2.8 Shrinkage and Subsidence

3.3 Foundation Design / Earth Pressures

3.3.1 Bearing Capacity

3.3.2 Soils Parameters for Pipeline Design

3.3.3 External Loads on Pipe by Soil

3.3.4 Static Lateral Earth Pressures for Retaining Walls:

3.3.5 Retaining Wall Surcharges:

3.3.6 Incremental Seismic Loads - Retaining Structures

3.3.7 Settlement Estimates

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3.4 Dewatering

3.5 Corrosivity Testing

3.6 Preliminary Pavement Design

4. CONSTRUCTION CONSIDERATIONS

4.1 Temporary Cut Slopes

4.2 Temporary Shoring

4.3 Additional Geotechnical Services

5. LIMITATIONS

6. REFERENCES

Tables Table 1. 2022 CBC Site Categorization and Seismic Coefficients Table 2. Soil Parameters for Pipe Design Table 3. Retaining Wall Design Earth Pressures (Static, Drained) Table 4. Sulfate Concentration and Sulfate Exposure Table 5. Relationship between Soil Resistivity and Soil Corrosivity Table 6. Corrosion Sample Results Table 7. Asphalt Pavement Sections Table 8. Static Lateral Earth Pressures

Figures Figure 1 – Site Location Map Figure 2 – Regional Geology Map Figure 3 – Liquefaction Map Figure 4 – Boring Location Map

Appendices

Appendix A – Field Exploration / Logs of Exploratory Borings Appendix B – Results of Geotechnical Laboratory Testing Appendix C – Site-Specific Ground Motion and Settlement Analyses Appendix D – General Earthwork and Grading Specifications Appendix E – GBA Important Information About This Geotechnical Report

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1. INTRODUCTION

1.1 Site Location and Description

As shown on Figure 1, Site Location Map, this Valley Sanitary District (VSD) plant is bounded by the Whitewater River Storm Channel to the northeast, Cabazon Indian Reservation land to the east, Cabazon Road to the south, and Van Buren Street to the west. The proposed storage tank and building are located within eastern end of the plant, which is currently occupied by a sludge drying bed, a concrete-lined embankment, and a paved road. A chlorine contact tank is north of the proposed tank location and a belt press building is west of the proposed building location. Site access is through a locked gate off Van Buren Street, through the driveway to the facility.

1.2 Project Description

Based on information provided, we understand that new building and an above ground storage tank (unknown volume) is planned at the east end of the VSD plant, just east of the press belt building (see Figure 4, Boring Location Map). A portion of the above ground storage tank footprint is proposed over a portion of the sludge drying bed area. We anticipate construction will include the installation of connection piping, along with site minor grading. It is our understanding that the anticipated hydrostatic pressure of the proposed improvements is expected to be less-than (≤) 2,500 pounds-per-square-foot.

1.3 Purpose and Scope of Evaluation

The purpose of our evaluation is to (1) evaluate geotechnical engineering characteristics of the earth materials at the proposed site, and (2) provide geotechnical recommendations for design and construction of the proposed tank/building. The scope of our evaluation included the following tasks:

Background Review: We reviewed readily available, relevant, geotechnical/ geologic reports previously prepared for this site, and maps pertinent to the site.

Geotechnical Borings: Drilled, logged, and sampled two (2) hollow-stem auger borings within an accessible area of the site to a maximum depth of 51.5 feet using a track-mounted drill rig equipped with an 8-inch hollow stem auger. The borings were backfilled with the excavated soils and asphalt patch where needed.

Geotechnical Laboratory Testing: Driven “California” ring-lined samples and bulk soil samples were collected from our borings and transported to our in-house geotechnical laboratory for testing. Tests included in-situ moisture/density, sieve analysis, expansion potential, maximum dry density/ optimum moisture content, and one corrosivity test (pH and resistivity, chloride and soluble sulfate content).

Engineering Analysis: Data obtained from our background review, previous field explorations, and geotechnical laboratory testing program was evaluated to develop geotechnical conclusions and recommendations for the proposed tank.

Report Preparation: Results have been summarized in this report, presenting our findings, conclusions, and geotechnical recommendations.

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1.4 Field Exploration

Our field exploration consisted of the excavation of two (2) geotechnical borings (B-1 and B-2) in accessible areas within project site. Prior to drilling, we located and marked boring locations for coordination with DigAlert (811) and Lystek personnel. Our field exploration was performed on October 22, 2024. Approximate locations of the borings are depicted on the Boring Location Plan (Figure 4). The exploratory borings were excavated utilizing a track-mounted drill rig and 8-inch hollow-stem flight auger. During the drilling operation, bulk and relatively undisturbed samples were obtained from the borings for laboratory testing and evaluation. Sampling of the borings was conducted by an engineer from our office. The collected samples were transported to our laboratory for testing. Borings were backfilled with native soils and patched with cold patch asphalt where boring went through existing asphalt. The logs of borings are presented in Appendix A of this report.

1.5 Laboratory Testing

Laboratory tests were performed on representative samples to provide a basis for development of geotechnical design parameters. Selected samples were tested to determine the following parameters: in-situ moisture/density, sieve analysis, sand equivalent, maximum dry density/ optimum moisture content, consolidation, swell/collapse, R-value, and one corrosivity test (pH and resistivity, chloride and soluble sulfate content). The results of our laboratory testing are presented in Appendix B.

1.6 Previous Reports

On March 4, 2005, Leighton (Leighton Consulting, 2005) prepared a Geotechnical Exploration for VSD as part of their Phase I Site Upgrades, which included advancing five hollow stem auger borings to a maximum depth of 76.5 feet bgs. Subsequently, on October 16, 2020, (Leighton Consulting, 2020) prepared an Update Geotechnical Exploration for VSD which included advancing five additional hollow stem auger borings to a maximum depth of 51.5 feet bgs. Native site soils consisted predominantly of lacustrine deposits of silt and silty sand that was primarily medium dense, often finely laminated, with layers of low to high plasticity clay. During our previous investigation, fines content in our previous borings ranged from 47% to 81%. Atterberg Limits showed consistent low-plasticity clays (CLs). Prior collapse tests showed ¼-percent collapse or less (considered negligible).

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2. SUMMARY OF GEOTECHNICAL FINDINGS

A summary of our findings from research of pertinent literature, site-specific field exploration, geotechnical laboratory testing and engineering analysis, is discussed in this section.

2.1 Subsurface Conditions

Based on observations made during our field exploration and published geologic maps, the tank facility is primarily underlain by dense alluvial deposits with small amounts of surficial soil and artificial fill anticipated in some areas of the site. Detailed descriptions of the earth materials encountered in our exploratory borings are provided in Appendix A.

2.1.1 Surficial Soils

Although not differentiated in our borings, artificial fill and surficial soils are expected on-site within existing utility trenches and pads of existing equipment and areas of previous grading/disturbance. The artificial fill and surficial soils are assumed to be generated from onsite sources and generally consist of silty sand (SM) and sandy silt (ML). This fill and surficial soil is not expected to exceed 8 feet in depth on-site.

2.1.2 Alluvium

The recent alluvium was found in all our borings and extend to the explored depth of 51.5 feet. The alluvium, as encountered, generally consisted of silty sand (SM), clay (CL) with varying amounts of sand and silt, and sandy silt (ML). The soil density varies greatly depending on depth and soil type. Based on the results of our laboratory testing on representative samples, the alluvial soils are expected to generally possess a low to medium expansion potential (EI<91) and slight collapse potential (< 2 percent in the upper 10 feet). A more detailed description of each unit is provided on the logs of borings in Appendix A.

2.2 Surface and Groundwater

Groundwater was encountered in B-1 at a depth of 41.17 feet bgs. Based on available data, the groundwater in the area has a historic high of -46.3 feet msl, which correlates to 13 feet below the current site elevation, according to California Water Data Library, State Well 337210N1162143W001, located approximately 1.1 miles west northwest of the subject site (recorded on March 2, 1994). As discussed during our previous report (Leighton, 2020), groundwater as shallow as 18½-feet deep in a boring drilled on January 10, 1997, for the headworks located in the northwestern portion of the plant, as reported by Southland Geotechnical (1997).

2.3 Faulting and Seismic Design Parameters

The subject site, like the rest of Southern California, is located within a seismically active region as a result of being located near the active margin between the North American and Pacific tectonic plates. The principal source of seismic activity on this site is movement along the northwest-trending regional fault systems such as the Coachella Valley segment of the San

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Andreas. Based on our review of published geologic maps (CGS, 2018), the subject site is not located within a County Fault Zone or Alquist-Priolo Earthquake Fault Zone.

Based on our explorations and review, the site will be underlain by dense alluvium. As such, the site is classified as a Class D site, and the site-specific seismic coefficients following the ASCE 7-16 procedures are as listed in the following table:

Table 1. 2022 CBC Site Categorization and Seismic Coefficients CBC Categorization/Coefficient Value

Site Longitude (decimal degrees) -116.1957 Site Latitude (decimal degrees) 33.7160

Site Class Definition D

Mapped Spectral Response Acceleration at 0.2s Period, Ss 2.27g Mapped Spectral Response Acceleration at 1s Period, S1 0.97g

Adjusted Spectral Response Acceleration at 0.2s Period, SMS 2.35g Adjusted Spectral Response Acceleration at 1s Period, SM1 3.32g Design Spectral Response Acceleration at 0.2s Period, SDS 1.57g Design Spectral Response Acceleration at 1s Period, SD1 2.21g g = Gravity acceleration

2.4 Secondary Seismic Hazards

Secondary seismic hazards for this site are discussed below.

2.4.1 Liquefaction Potential

Liquefaction is loss of soil shear strength due to a build-up of pore water pressure during severe and sustained ground shaking. Soils most susceptible to liquefaction are clean, loose, saturated fine-grained sands. Due to the presence of shallow groundwater and the presence of medium dense alluvium, the potential for liquefaction is considered a geotechnical concern. Additionally, the site is mapped by the County in an area of high susceptibility to liquefaction (Figure 3).

Assuming that loose, near-surface soils will be removed and recompacted in accordance with the recommendations of Section 3.0 of this report in the areas of development, the potential for dynamic settlement (dry settlement) due to the design earthquake event to affect structures at this site is estimated to be approximately 2 inches. Due to relatively homogenous subsurface conditions, this settlement is expected to be global and uniform across the site. As such, following completion of the recommended remedial grading, we estimate differential settlement not to exceed ½ inch in a 30 feet horizontal distance.

2.4.2 Landslide and Rockfall

Ground shaking during earthquakes can result in landsliding on natural slopes. No evidence of existing landslides was observed during our field mapping or during the previous field investigations of the subject site. Given the flat nature of the site, rockfall hazards are considered negligible.

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2.4.3 Flooding

The site is located within an “Area with Minimal Flood Hazard (Zone X)” on the official FEMA Flood Hazard Areas Map (FEMA Map Sheet 06065C2254H) dated March 6, 2018. Flood hazard evaluation should be performed by the civil engineer.

2.4.4 Seiches and Tsunamis

Due to the inland location and distance from major bodies of water, the site is not at significant risk from seiches or tsunamis.

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3. CONCLUSIONS AND RECOMMENDATIONS

3.1 General

Construction of the proposed tank and building appear feasible from a geotechnical perspective provided that the following recommendations are incorporated into the design and construction phases of development. Due to the nature of the artificial fill and sandy alluvium, the soils encountered may be considered CalOSHA Type C soils, and sloped excavations will be required to protect workers, if shoring and/or shields are not used.

3.2 Earthwork Considerations

Earthwork associated with the proposed tank should be performed in accordance with applicable VSD Specifications, “Standard Specifications for Public Works Construction” (Greenbook, latest edition) and the recommendations included in the text of this report.

3.2.1 Excavation Characteristics

Based on the results of our exploratory borings, the onsite soils should generally be relatively easy to moderately difficult to excavate (potential cobbles) with conventional earthmoving excavation equipment. Excavation should be performed in accordance with the project plans, specifications, and all applicable OSHA requirements. The contractor should be responsible for providing the "competent person" required by OSHA standards. Contractors should be advised that sandy soils (such as the existing, onsite soils) could make excavations particularly unsafe, and hence necessary safety precautions should be taken at all times.

3.2.2 Subgrade Preparation/Remedial Grading

The subgrade preparation for the proposed improvements should be as follows:

Proposed Tank– The upper 6 feet (minimum) of existing soils, or 5 feet below bottom of ring foundations (whichever is deeper) should be removed and recompacted prior to foundation construction or placement of new fill. If soft or rutting subgrades are encountered, the bottom of the excavation should then be covered with an 18-inch thick ¾-inch crushed rock layer, wrapped-in/surrounded-with (top and bottom) Mirafi® 140N non-woven filter fabric. This remedial grading should be performed a minimum of 6 feet beyond the limits of improvements/foundations.

Building- The upper 5 feet (minimum) of existing soils, or 3 feet below bottom foundations (whichever is deeper) should be removed and recompacted prior to foundation construction or placement of new fill. If soft or rutting subgrades are encountered, the bottom of the excavation should then be covered with an 18-inch thick ¾-inch crushed rock layer, wrapped-in/surrounded-with (top and bottom) Mirafi® 140N non-woven filter fabric. This remedial grading should be performed a minimum of 5 feet beyond the limits of improvements/foundations.

Pavement / Flatwork – Similarly, for any site pavement or hardscape, the upper 2 feet of soils should be removed or scarified and recompacted. Localized over-excavation may be needed depending on the actual conditions encountered during construction.

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The recommended OX should not undermine or encroach to within the zone of influence of existing building foundations or any other settlement sensitive structures. The zone of influence is defined as an imaginary 1:1 line sloping down and away from the bottom edge of existing foundations. Special excavation procedures may be required along the side of existing building (i.e. ABC slot cutting or shoring) if effective OX cannot be achieved. This condition will need to be further evaluated based on prevailing subsurface conditions during construction.

The removal limit should be established by a 1:1 projection from the edge of fill soils downward and outward to competent material identified by Verdantas. Removals will also include benching into competent material as the fills rise. Areas adjacent to existing structures, including existing tank or roadways, may require special monitoring. Temporary slopes in these areas should be no steeper than 1:1 (horizontal:vertical). Friable materials, if encountered, may require additional layback.

After completion of the recommended removal of unsuitable soils and prior to fill placement or foundation construction, the exposed bottom/surface should be scarified to a minimum depth of 8-inches and recompacted to unyielding condition or minimum 90 percent relative compaction per ASTM D1557. Subsequently, all structural fill should be compacted minimum of 90 percent relative compaction.

3.2.3 Structural Fills

The onsite soils are generally suitable for re-use as compacted fill, provided they are free of debris and organic matter. No rock in excess of 12 inches in maximum dimension should be placed in any fill within 10 feet of finish grade without review by Verdantas and approval by the local regulatory agency. Utility area fill zones (pads and street overexcavation areas) should be relatively free of rocks greater than 8 inches.

Areas to receive structural fill and/or other surface improvements should be scarified to a minimum depth of 8 inches, moisture conditioned to at least optimum moisture content and compacted. Fill soils should be placed at a minimum of 90 percent relative compaction (based on ASTM D1557) and at near or above optimum moisture content.

Placement and compaction of fill should be performed in accordance with local grading ordinances under the observation and testing of Verdantas. The optimum lift thickness to produce a uniformly compacted fill will depend on the type and size of compaction equipment used. In general, fill should be placed in uniform lifts not exceeding 8 inches in thickness.

Fill slope keyways will be necessary at the toe of all fill slopes and at fill-over-cut contacts. Keyway schematics, including dimensions and subdrain recommendations, are provided in Appendix D of this report. All keyways should be excavated into dense bedrock or dense alluvium as determined by Verdantas. The cut portions of all slope and keyway excavations should be geologically mapped and approved by a geologist prior to fill placement.

Fills placed on slopes steeper than 5:1 (horizontal:vertical) should be benched into dense soils (see Appendix D for benching detail). Benching should be of sufficient depth to remove all loose material. A minimum bench height of 2 feet into approved material should be maintained at all times.

Fill slopes should be overbuilt a minimum of 2 feet and trimmed back to the compacted core. In areas where overbuilding is not practical, slope faces may be compacted by rolling with weighted sheepsfoot compaction rollers as the fill slope height increases in maximum 5-foot increments.

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3.2.4 Subgrade Preparation – Pipelines

Prior to pipe installation, the subgrade should be firm, uniform, and free of standing water, loose materials and then properly compacted to provide uniform seating and support to the entire section of the pipe placed on bedding material. Oversize particles larger than 3-inches in largest dimension should be removed from the trench subgrade and replaced with compacted uniform bedding materials. If groundwater is encountered or the subgrade become disturbed due to localized seepage or surface water, the contractor should excavate the disturbed or saturated soils to a maximum depth of 2 feet and replace with suitable materials to provide a stable bottom.

Crushed rock (½-inch maximum size) may be used if found necessary to stabilize bottom of trench/pit prior to placing bedding materials.

3.2.5 Trench Backfill

Prior to backfilling, pipes should be bedded in and covered with a uniform, granular material that has a Sand Equivalent (SE) of 30 or greater, and a gradation meeting requirements of the pipe manufacturer. Pipe bedding should be water-densified in-place. Some on-site soils are expected to be too silty to be considered for bedding material and should be verified prior to use. A minimum cover of 12 inches of bedding material should be provided above the top of the pipe. As an alternative, crushed rock per VSD Standards can be used as pipe bedding.

3.2.6 General Backfill

Native soils are considered unsuitable in the upper 2 feet in all structural areas including building pads and pavement. These materials may be used over the pipe bedding zone to a depth of 2 feet below finish subgrade. These materials should be placed in thin lifts (not exceeding 8 inches);

moisture conditioned, as necessary, and mechanically compacted to a minimum of 90 percent relative compaction per ASTM D 1557 or as required per VSD standard specifications. The actual lift thickness should depend on the compaction equipment used. For hand-directed mechanical equipment such as vibratory plates or tampers, the maximum lift thickness should not exceed 4 inches. The contractor should not use jetting to compact trench backfill unless approved by VSD and the jetting procedures and soils requirements comply with Section 306-1.3 of the “Green Book”.

3.2.7 Import Soils

Import soils and/or borrow sites, if needed, should be evaluated by Verdantas prior to import.

Import soils should be uncontaminated, granular in nature, free of organic material (loss on ignition less-than 2 percent), have very low expansion potential (or EI<21) and have a low corrosion impact to the proposed improvements.

3.2.8 Shrinkage and Subsidence

Change in volume of excavated and recompacted soil varies according to initial density, which is a function of soil type and location. This volume change is represented as a percentage increase (bulking) or decrease (shrinkage) in volume of fill after removal and recompaction. Subsidence occurs as natural ground is moisture-conditioned and densified to receive fill. Field and laboratory data used in our calculations included laboratory-measured maximum dry densities for soil types encountered at this site relative to measured, in-place densities of soils sampled. We estimate that shrinkage due to recompaction of onsite soils will vary from one location to another and with

Verdantas.com 9 depth. We suggest an estimated shrinkage ranging from 5 to 15 percent be considered for the upper 5 feet below ground surface.

3.3 Foundation Design / Earth Pressures

3.3.1 Bearing Capacity

A net allowable bearing capacity of 2,000 psf, or a modulus of subgrade reaction of 200 pci may be used for design of footings of appurtenant structures founded into a minimum of 12-inches of compacted fill. A minimum base width of 18 inches for continuous footings and a minimum bearing area of 3 square feet (1.75 ft by 1.75 ft) for pad foundations should be used. Additionally, an increase of one-third may be applied when considering short-term live loads (e.g. seismic and wind). No minimum embedment is required for shallow mat/slab foundations. A minimum of 12-inch embedment should be considered for all isolated shallow spread and continuous footings.

If applicable, lateral loads on thrust blocks and other appurtenant structures may be resisted by passive soil pressure and friction, in combination. An allowable passive pressure based on an equivalent fluid pressure of 350 pounds-per-cubic-foot (pcf), not to exceed 3,500 pounds per square foot (psf) can be used if the pipe is embedded in the alluvium or compacted fill (minimum 2 feet embedment). This equivalent fluid pressure may be doubled for isolated thrust blocks. We have not applied a factor-of-safety to these values. A soil-pipeline surface friction of 0.20 for PVC pipes. A maximum allowable frictional resistance of 0.40 may be used for estimating lateral loads caused by friction between the footings/concrete and the supporting subgrade. Additionally, an increase of one-third may be applied when considering short-term live loads (e.g. seismic and wind).

A modulus of soil reaction (E’) of 1,200 psi can be used to estimate the stiffness of the soil bedding backfill at the sides and below buried flexible pipelines for the purpose of evaluating deflection caused by weight of the backfill over the pipe. This value assumes that the proposed pipelines in embedded at 5 feet below exiting grades and a granular bedding material with an average relative compaction of 90 percent or more (per ASTM D1557) is placed.

3.3.2 Soils Parameters for Pipeline Design

Structural design of pipes requires proper evaluation of possible loads acting on the pipe, including dead and live or transient loads. Stresses and strains induced in a buried pipe depend on many factors, including the type of pipe, depth and width of trench, bedding and embedment conditions, soil density, angle of internal friction, coefficient of passive earth pressure, and coefficient of friction at the interface between the backfill and in-situ soils. We recommend the following soil parameters for the proposed pipe design:

Table 2. Soil Parameters for Pipe Design

Soil Parameters Recommended Values

Average compacted fill moist unit weight, (pcf) 120 Angle of internal friction of soils (degrees) 31 Soil cohesion, c (psf) 100 Sliding friction between pipe and native soils 0.20 Coefficient of friction between backfill and native soils 0.40

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3.3.3 External Loads on Pipe by Soil

Structural design of pipes requires proper evaluation of possible loads acting on the pipe, including dead and live or transient loads. Stresses and strains induced. The magnitude of the load supported depends on the amount of backfill, type of soil, and pipe stiffness. For flexible pipes, the approximate dead load per unit length can be calculated from the following formula:

Where, W External soil load on pipe: (pounds per foot of pipe) C Unit less load coefficient (C = 1.4 for 5 feet deep trench, and 1.8 for 10 feet deep trench, assuming a trench width of 3 feet just above the pipe) γ Total unit weight of soil above pipe (pounds-per-cubic-foot) B Width of the trench (width just above top of the pipe, in feet) D Pipe diameter (feet)

In addition to the load from backfill (above equation), loads due to embankments (if applicable) and other loads (live loads) should be considered.

3.3.4 Static Lateral Earth Pressures for Retaining Walls:

Retaining wall earth pressures are a function of the amount of wall yielding horizontally under load. If the wall can yield enough to mobilize full shear strength of backfill soils, then the wall can be designed for "active" pressure. If the wall cannot yield under the applied load, the shear strength of the soil cannot be mobilized and the earth pressure will be higher. Such walls should be designed for "at rest" conditions. If a structure moves toward the soils, the resulting resistance developed by the soil is the "passive" resistance. We recommend that retaining walls be backfilled with site soils or imported non-expansive soils (EI≤21). For drained retaining walls with level backfill, the following parameters may be used for retaining wall design:

Table 3. Retaining Wall Design Earth Pressures (Static, Drained)

Loading Conditions

Equivalent Fluid Density (pcf) Level Backfill 2:1 Backfill

Active 35 50 At-Rest 55 80 Passive* 300* 150 (2:1, sloping down)

* This assumes level condition in front of the wall will remain for the duration of the project, not to exceed 3,000 psf at depth. If sloping down (2:1) grades exist in front of walls, then they should be designed using passive values reduced to ½ of level backfill passive resistance values.

Cantilever walls that are designed to yield at least 0.001H, where H is equal to the wall height, may be designed using the active condition. Rigid walls and walls braced at the top should be designed using the at-rest condition, which is expected to be the case for vaults. Passive pressure is used to compute soil resistance to lateral structural movement.

Total depth of retained earth for design of walls and for uplift resistance should be measured as the vertical height of the stem below the ground surface at the wall face for stem design or measured at the heel of the footing for overturning and sliding. A total unit weight of 120 pounds-

Verdantas.com 11 per-cubic-foot (pcf) may be assumed to calculate weight of compacted fill soil over wall footings, if properly compacted and drained.

3.3.5 Retaining Wall Surcharges:

In addition to the above lateral forces due to retained earth, surcharge due to above grade loads on the wall backfill, such as traffic, should be considered in design of retaining walls. Vertical surcharge loads behind a retaining wall on or in backfill within a 1:1 (horizontal:vertical) plane projection up and out from the retaining wall toe, should be considered as lateral and vertical surcharge. Unrestrained (cantilever) retaining walls should be designed to resist one-third of these surcharge loads applied as a uniform horizontal pressure on the wall. Braced walls should also be designed to resist an additional uniform horizontal-pressure equivalent to one-half of uniform vertical surcharge-loads.

In areas where autos and pickup trucks will drive, we suggest assuming a uniform vertical surcharge of 300 psf, which would result in active and at-rest horizontal surcharges of 100 psf and 150 psf, respectively. This should be doubled in areas of heavy construction traffic (such as concrete trucks, heavy equipment delivery-trucks, etc.). If crane outrigger loads or other point load sources are applied as wall surcharge, this will require additional analyses based on load source and location relative to the wall.

3.3.6 Incremental Seismic Loads - Retaining Structures

Seismic incremental loads need not be added to retaining walls on the order of (≤) 6-feet deep or less, with level backfill. An incremental seismic earth pressures of 16H pounds-per-cubic-foot (pcf), where H is the retaining wall stem height in feet, may be applied for design in addition to static earth and surcharge pressures presented above. This is based on traditional Mononobe- Okabe (1929) equations. Traditionally, this incremental seismic earth pressure has been applied as an inverted triangle (inverted equivalent fluid pressure), with largest dynamic earth pressure occurring at the top of the wall (upper ground surface). Resultant seismic earth pressure force has traditionally been applied at approximately 0.6H from the bottom of the wall, where H is the wall (stem) height (e.g. Seed and Whitman, 1970). However, recent studies (Sitar, et. al., 2013, UC. Berkeley) suggest a uniform pressure distribution is likely closer to actual lateral seismic loads, so a uniform pressure of 12H applied as a uniform/rectangular pressure distribution can also be considered (based on current research and observations).

3.3.7 Settlement Estimates

For settlement estimates, we assumed that column loads will be no more than 75 kips, with bearing wall loads not exceeding 10 kips per foot of wall. If greater column or wall loads are required, we should reevaluate our foundation recommendation and re-calculate settlement estimates. Settlement of newly placed properly compacted fill materials is expected to predominantly occur during and within 60 days following fill placement. However, some settlement of the remaining loose native sands will occur slowly as these soils are wetted by excess irrigation water percolation. Storage tank and buildings located on compacted fill soils (as recommended in Section 3.2.2) should be designed in anticipation of ½ inch of total settlement and ¼ inch of differential settlement within a 40-foot horizontal run. The majority of this settlement is anticipated to occur during construction as the load is applied. These short-term settlements and angular distortions are from imposed building loads and do not include dynamic settlements. Dynamic liquefaction induced settlement on the order of 2-inches is estimated for this site, resulting from a local large magnitude earthquake on the San Andreas Fault. This total settlement, however, will

Verdantas.com 12 not be manifest as differential settlement, which is expected to be ½ inch in a 30 feet horizontal distance.

3.4 Dewatering

Based on the results of our exploration, groundwater was encountered at a depth of approximately 42 feet 2 inches within the borings performed. If encountered during excavations, groundwater control, such as dewatering, will be required to limit instability of the excavation bottom, side and face, and aid foundation construction and soil backfill. Groundwater due to perched saturated conditions can be dewatered utilizing sump-pumps. Dewatering or any other suitable method for stabilizing excavation bottom may be selected by the contractor based on actual groundwater conditions encountered and based on the contractor’s chosen means-and-methods of construction. The selected method by the contractor should be able to effectively mitigate for bottom heave or stabilize subgrade soils during construction/ backfilling.

3.5 Corrosivity Testing

Sulfate ions in the soil can lower soil resistivity and can be highly aggressive to portland cement concrete by combining chemically with certain constituents of the concrete, principally tricalcium aluminate. This reaction is accompanied by expansion and eventual disruption of the concrete matrix. Potentially high sulfate content could also cause corrosion of the reinforcing steel in concrete.

Table below summarizes current standards for concrete exposed to sulfate-containing solutions.

Table 4. Sulfate Concentration and Sulfate Exposure

Sulfate In Water (parts-per-million)

Water-Soluble Sulfate (SO4) in soil (percentage by weight) Sulfate Exposure

0-150 0.00 - 0.10 Negligible 150-1,500 0.10 - 0.20 Moderate (Seawater)

1,500-10,000 0.20 - 2.00 Severe >10,000 Over 2.00 Very Severe

The sulfate content was determined in the laboratory for representative onsite soil sample. The results indicate that the water-soluble sulfate range is less than 0.1 percent by weight for this site, which is considered negligible as per Table above. Based on the test results, Type II cement or equivalent may be used.

Many factors can affect corrosion potential of soil including soil moisture content, resistivity, permeability and pH, as well as chloride and sulfate concentration. In general, soil resistivity, which is a measure of how easily electrical current flows through soils, is the most influential factor. Based on the findings of studies presented in ASTM STP 1013 titled “Effects of Soil Characteristics on Corrosion” (February, 1989), the approximate relationship between soil resistivity and soil corrosiveness was developed as shown in Table below.

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Table 5. Relationship between Soil Resistivity and Soil Corrosivity

Soil Resistivity (ohm-cm)

Classification of Soil Corrosiveness

0 to 900 Very Severely Corrosive 900 to 2,300 Severely Corrosive

2,300 to 5,000 Moderately Corrosive 5,000 to 10,000 Mildly Corrosive

10,000 to >100,000 Very Mildly Corrosive

Acidity is an important factor of soil corrosivity. The lower the pH (the more acidic the environment), the higher the soil corrosivity will be with respect to buried metallic structures and utilities. As soil pH increases above 7 (the neutral value), the soil is increasingly more alkaline and less corrosive to buried steel structures, due to protective surface films, which form on steel in high pH environments. The pH of representative soils sample from the site is 8.67 which is generally considered less corrosive. Chloride and sulfate ion concentrations, and pH appear to play secondary roles in affecting corrosion potential. High chloride levels tend to reduce soil resistivity and break down otherwise protective surface deposits, which can result in corrosion of buried steel or reinforced concrete structures.

Based on laboratory testing results of soil resistivity, the onsite soil is considered Severly Corrosive. Ferrous pipe can be protected by polyethylene bags, tape or coatings, di-electric fittings, concrete encasement or other means to separate the pipe from wet onsite soils. Further testing of import and possibly site soil corrosivity could be performed and specific recommendations for corrosion protection may need to be provided by a qualified corrosion engineer.

Table 6. Corrosion Sample Results

Boring Sample Depth (ft)

Sulfate Content (ppm)

Chloride Content (ppm) pH

Minimum Resistivity (ohm-cm)

B-1 0-5 450 120 8.67 2,000 B-2 5-10 600 N/A N/A N/A

3.6 Preliminary Pavement Design

Our preliminary pavement design is based on an assumed R-value of 30 or greater and Caltrans Highway Design Manual. For planning and estimating purposes, the pavement sections are calculated based on Traffic Indexes (TI) as indicated in Table below:

Table 7. Asphalt Pavement Sections

General Traffic Condition

Design Traffic

Index (TI)

Asphalt Concrete (inches)

Aggregate Base*

(inches) Automobile

Parking Lanes

4.5 3.0 4.5

5.0 3.0 5.5

Truck Access & Driveways

6.0 3.5 7.5

6.5 4.0 8.5

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Appropriate Traffic Index (TI) should be selected or verified by the project civil engineer or traffic engineering consultant and appropriate R-value of the subgrade soils will need to be verified after completion of rough grading to finalize the pavement design. Pavement design and construction should also conform to applicable District and industry standards. The Caltrans pavement section design calculations were based on a pavement life of approximately 20 years with a normal amount of flexible pavement maintenance.

Where applicable, we recommend that a minimum of 6 inches of PCC pavement be used, in high impact load areas or if to be subjected to truck traffic. The PCC pavement may be placed directly on a compacted subgrade with an R-Value of 30 or higher. The PCC pavement should be adequately reinforced to prevent shrinkage cracking and have a minimum of 28-day flexural strength of 550 psi (or compressive strength of 3,250 psi). Other requirements of Caltrans Standard Specifications regarding mixing and placing of concrete should be followed.

The upper 12 inches of the subgrade soils should be scarified, moisture-conditioned to near optimum moisture content, compacted to at least 95 percent relative compaction (ASTM D1557) and kept in this condition until the pavement section is constructed. Minimum relative compaction requirements for aggregate base should be 95 percent of the maximum laboratory density as determined by ASTM D1557. If applicable, aggregate base should conform to the “Standard Specifications for Public Works Construction” (Green book) current edition or Caltrans Class 2 aggregate base.

If pavement areas are adjacent to heavily watered landscape areas, some deterioration of the subgrade load bearing capacity may result. Moisture control measures such as deepened curbs or other moisture barrier materials may be used to prevent the subgrade soils from becoming saturated. The use of concrete cutoff or edge barriers should be considered when pavement is planned adjacent to either open (unfinished) or irrigated landscaped areas.

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4. CONSTRUCTION CONSIDERATIONS

4.1 Temporary Cut Slopes

The contractor is responsible for all temporary slopes and trenches excavated at the site and the design of any required temporary shoring. Shoring, bracing and benching should be performed by the contractor in accordance with the current edition of the California Construction Safety Orders, see:

http://www.dir.ca.gov/title8/sb4a6.html

During construction, exposed earth material conditions should be regularly evaluated to verify that conditions are as anticipated. The contractor is responsible for providing the "competent person" required by OSHA standards to evaluate soil conditions. Close coordination between the competent person and geotechnical consultant should be maintained to facilitate construction while providing safe excavations. Existing surficial and alluvial soils encountered are classified as OSHA soil Type C. Therefore, unshored temporary cut slopes should be no steeper than 1:1 (horizontal:vertical), for a height no-greater-than 20 feet (California Construction Safety Orders, Appendix B to Section 1541.1, Table B-1). These recommended temporary cut slopes assume a level ground surface for a distance equal to one-and-a-half (x1.5) the depth of excavation. For steeper temporary slopes, deeper excavations, and/or where slopes terrain exists within close proximity to excavation (<1.5xdepth), appropriate shoring methods or flatter slopes may be required to protect the workers in the excavation and adjacent improvements. Such methods should be implemented by the contractor and approved by the geotechnical consultant.

4.2 Temporary Shoring

If the sloped open cut excavation is not feasible based on requirements above and due to existing structures, excavations for the proposed pipeline should be supported by a temporary shoring system such as cross-braced hydraulic shoring, conventional shields, sheet piles, soldier piles and wood lagging. The choice should be left to the contractor’s judgment since economic considerations and/or the individual contractor’s construction experience may determine which method is more economical and/or appropriate. The contractor and shoring designer should also perform additional geotechnical studies as necessary to refine the means-and-methods of shoring construction.

The support of all adjacent area (existing structures, etc.) during excavation and construction (including pavements) without distress is the contractor's responsibility. In addition, it should be the contractor’s responsibility to undertake a pre-construction survey with benchmarks and photographs of the adjacent properties. Shoring systems should be designed by a California licensed civil or structural engineer. As preliminary design guidelines, we present the following geotechnical parameters for shoring design. The following lateral earth pressures are recommended for temporary shoring supporting encountered alignment soils with level ground behind the shoring. Passive pressure also may be used to compute lateral soil resistance, if necessary, for sheet piles. Earth pressures provided are ultimate values and a safety factor should be applied as appropriate.

http://www.dir.ca.gov/title8/sb4a6.html

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Table 8. Static Lateral Earth Pressures

Conditions1 Static Equivalent Fluid Weight (pcf) Active (cantilever) 35 At-Rest (braced) 55

Passive2 300

1. For temporary excavations only, with level backfill, not including surcharges

2. Passive equivalent fluid pressure may be doubled for isolated soldier piles spaced at least 2½ diameters on-center. Passive resistance should not exceed 3,000 pounds-per-square-foot (psf)

Determination of appropriate design conditions (active or at-rest) depends on shoring flexibility.

If a rotation of more than 0.001 radian (0.06 degrees) is allowed, active pressure conditions apply;

otherwise, at-rest condition governs.

Surcharge loads (dead or live) should be added to the indicated lateral earth pressures and should be applied uniformly, if such loads are within a horizontal distance that is less-than the exposed shoring height. The corresponding lateral earth pressure will approximately be 33-percent of the vertical surcharge for active conditions, and 50-percent for at-rest conditions. Surcharge pressures from concentrated loads should be evaluated after geometric constraints and loading conditions are determined on individual basis.

4.3 Additional Geotechnical Services

Verdantas should review site, grading and foundation plans, when available, and comment further on geotechnical aspects of the project. Geotechnical conclusions and preliminary recommendations should be reviewed and verified by Verdantas during construction and revised accordingly if geotechnical conditions encountered vary from our findings and interpretations.

Geotechnical observation and testing during construction should be provided as follows:

• During overexcavation of unsuitable soil,

• During compaction of all fill materials,

• After excavation of all footings and prior to placement of concrete,

• During utility trench backfilling and compaction,

• During pavement construction and when unusual conditions are encountered.

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5. LIMITATIONS

This report was necessarily based in part upon data obtained from a limited number of observances, site visits, soil samples, tests, analyses, histories of occurrences, spaced subsurface explorations and limited information on historical events and observations. Such information is necessarily incomplete. The nature of many sites is such that differing characteristics can be experienced within small distances and under various climatic conditions.

Changes in subsurface conditions can and do occur over time. This exploration was performed with the understanding that the project as described in Section 1.2 of this report.

This report was prepared for Lystek International based on Lystek International needs, directions, and requirements at the time of our investigation. This report is not authorized for use by, and is not to be relied upon by any party except Lystek International, and its successors and assigns as owner of the property, with whom Verdantas Inc. has contracted for the work. Use of or reliance on this report by any other party is at that party's risk. Unauthorized use of or reliance on this report constitutes an agreement to defend and indemnify Verdantas Inc. from and against any liability which may arise as a result of such use or reliance, regardless of any fault, negligence, or strict liability of Verdantas Inc. The client is referred to Appendix E regarding important information on geotechnical engineering studies/reports and their applicability and limitations.

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6. REFERENCES

ASCE 7, 2016, Minimum Design Loads for Buildings and Other Structures by Structural

Engineering institute.

California Building Code (CBC), 2022, “California Code of Regulations,” Title 24, Part 2, Vol. 2.

California Geologic Survey (CGS), 2008 Geologic Map of California, of the Palm Desert & Coachella 15 Minute Quadrangles, Riverside County, California.

California Geologic Survey (CGS), 2018, Earthquake Fault Zones, A guide for Government Agencies, Property Owners / Developers, And Geoscience Practitioners for Assessing Fault Rupture Hazards in California, Department of Conservation, Division of Mines and Geology, Special Publication 42. Revised

California Department of Water Resources (CDWR) 2024, Water Date Library (WDL), home page.

http://well.water.ca.gov/.

Leighton Consulting, Inc., 2005, Phase 1 Geotechnical Investigation, Valley Sanitary District Proposed Plant Expansion, 45500 Van Buren Street, Indio, California, Lee & Ro Project No. 429, LCI Project No. 600797-001, dated April 25, 2005.

Leighton Consulting, Inc., 2020, Updated Geotechnical Exploration, Valley Sanitary District, Wastewater Treatment Plant Proposed Expansion, 45500 Van Buren Street, Indio, Riverside County, California, LCI Project No. 12926.001, dated November 20, 2020.

Lystek International Limited, Valley Sanitary District, Lystek System Site Plan,…