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Palo Verde TR 32279 BCPR2023-0011 - Foundation LetterENGINEERS + GEOLOGISTS + ENVIRONMENTAL SCIENTISTS June 7, 2023 J.N. 21-468 WILLIAMS HOMES 24911 Avenue Stanford Santa Clarita, California 91355 Attention: Mr. Zachary Nordby Subject: Updated Geotechnical Design and Construction Recommendations, Palo Verde Project, Tracts 33336 (Lots 1— 23), Cherrywood Place and Rosewood Court, North of Avenue 58 and East of Paseo Del Lago, City of La Quinta, Riverside County, California References: See Attached List Dear Mr. Nordby: At your request, Petra Geosciences, Inc. (Petra) is providing herewith our updated geotechnical design and construction recommendations for the subject 23 residential units within Tracts 33336 (Lots 1 through 23) of the Palo Verde project located in the city of La Quinta, California. The purpose of this report is to present updated geotechnical recommendations for site precise/remedial grading, and for the design and construction of the foundations for the proposed residential structures and other site improvements located within these tracts that are based on the current site conditions and the 2022 CBC requirements. The recommendations provided herein supersedes those provided earlier (please see referenced Petra, 2021 report). This report is based on our review of the preliminary and as -graded geotechnical reports prepared by various consultants, our supplemental sampling and laboratory testing, the requirements of the 2022 California Building Code (2022 CBC), and our engineering judgment and professional opinion. It is our understanding that as -graded reports have been approved by the City of La Quinta. Petra has reviewed the referenced reports and we are in general concurrence with their findings, conclusions and recommendations contained therein, except where to be noted in our subsequent reports and letters. Petra hereby accepts the referenced reports as the basis for our geotechnical services on the site subject to modifications as to be dictated by our findings during our independent investigation, as well as those dictated by the project plans, specifications and applicable codes. Offices Strategically Positioned Throughout Southern California LOS ANGELES COUNTY OFFICE 28358 Constellation Road, Unit 680, Valencia, CA 91355 T:661.255.5790 F:661.255.5242 For more information visit us online at www.i)etra-inc.com WILLIAMS HOMES Palo Verde Project /La Quinta SITE GENERAL OVERVIEW June 7, 2023 J.N. 21-468 Page 2 The study area considered under the purview of this report, which is comprised of one tract, Tract 33336, is located north of Avenue 58 and west of Paseo Del Lago in the city of La Quinta, Riverside County, California. Tract 33336, which is comprised of 23 lots, is bisected by Cherrywood Place in the north -south direction. The project site is relatively flat, and the elevation difference is on the order of 4 to 7 feet, increasing in the northerly direction. Previous Site Investigation and Grading Earth Systems Southwest (ESS) performed the initial geotechnical engineering investigation within Tract 32279 in 2004 (ESS, 2004). While their boring locations and logs and laboratory test results were not available, it appears they drilled 5 exploratory to depths varying from 14 to 51.5 feet below ground surface. In January 2005, ESS published the results of their geotechnical investigation performed within Tract 33336 (ESS, 2005). In the latter investigation, ESS drilled 6 exploratory borings to the same depth ranges and, in both reports, concluded the subject sites are suitable for the proposed development. In February 2006, Stoney -Miller Consultants, Inc. (SMC) provided a Geotechnical Consultant of Record and a review of rough grade letter for Tract 33336 (SMC, 2006a, 2006b). And, in June and August of 2006, they provided a foundation design parameters letter for Tracts 32279 and 33336 and a pavement recommendation letter for Tract 33336 (SMC, 2006c, 2006d). SMC provided observation and testing during rough grading of the subject tracts which reportedly took place between March and April 2006 for Tract 32279 and April and May 2006 for Tract 33336 (SMC, 2006e, 2006f). During the earthwork process, total of 4 to 6 feet of fill was placed within these tracts that include the remedial over -excavation thicknesses. Recent Site Remedial Grading and Building Pad Preparation The building pad surficial soils had become dry, slightly desiccated and eroded since the completion of rough grading; therefore, building pad re -conditioning was required to reprocess all disturbed, desiccated and eroded surficial soils to create suitable pads for the construction of the proposed improvements. Remedial/re-conditioning grading took place on March 20, 2023. Following clearing/grubbing operations, the subject building pad surface soils were scarified to a depth of at least 6 to 8 inches, thoroughly moisture - conditioned to above optimum and then recompacted in -place to a minimum relative compaction of 90 percent based on ASTM D 1557.The limits of pad preparation essentially extended from property line to property line of the pads (the earthwork operation details are described in referenced Petra, 2023 report). I� GEO INRolm SOLID AS A HOCK WILLIAMS HOMES June 7, 2023 Palo Verde Project /La Quinta J.N. 21-468 Page 3 Current Site Condition A representative of Petra visited the sites on June 6, 2023, to observe the existing conditions. No homes or foundations have been constructed on the 23 lots of Tract 33336. The Pads have been recertified for compaction and are ready for foundation construction. The lots were stabilized with a spray -on polymer and show little to no erosion. The walls constructed at the site showed no observable distress. Cherrywood Place in Tract 33336 is not paved, and utilities were not observed. Supplemental Sampling and Laboratory Testing During March 2021 site visit, several bulk soil samples were collected by a representative of Petra from the building pad surfaces to depths on the order of 24± inches below pad grades for confirmation laboratory testing. The laboratory program consisting of testing pad grade soils for expansion index and general corrosion potential (sulfate, chloride, pH, resistivity). Petra's laboratory test results as well as those by others are presented in Plate 1 and reflected in the following sections. Proposed Construction We understand the proposed construction will consist of building two-story, single-family homes with attached garages, as well as various site improvement activities including placement of main and lateral utility lines, block walls, etc. The single-family residences will be of wood -frame construction with first floor slabs constructed on -grade. Concrete driveways and walkways will provide access to the adjacent street and to the front doors. The building pads will be graded to collect any surface water and deliver it to the curb and gutter of the adjacent street CONCLUSIONS AND RECOMMENDATIONS Feasibility Based on the current design, as -graded conditions and our current understanding of the project, the proposed residential construction within the site is feasible from a geotechnical standpoint provided they are performed in accordance with the City of La Quinta requirements and our following recommendations. However, it should be noted that any changes in the precise grading plan should be reviewed by this firm for verification of the following conclusions and recommendations. Geotechnical Recommendations General As stated herein, Tract 33336 has recently been re -conditioned in March 2023 (Petra, 2023). Our recent, June 2023, site visit has shown the building pads are in acceptable condition for construction. However, OPEIRANCES� SOUO AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 4 based on the grading industry standard, the surficial remediation process is essentially required after maximum of 6 months of the last grading. Building Pad Preparation and Precise Grading Should the building pad surficial soils become dry, desiccated and eroded prior to construction, building pad re -conditioning will be required to reprocess all disturbed, desiccated and eroded surficial soils to create suitable pads for the construction of the proposed improvements. That is, following clearing/grubbing operations, the majority of the subject building pad surface soils should be scarified to a depth of at least 6 to 8 inches, thoroughly moisture -conditioned to near two percent above optimum and then recompacted in - place to a minimum relative compaction of 90 percent based on ASTM D 1557. Some deeper scarification/removal and recompaction should also be anticipated based on the field condition at the time of this remedial grading. It is recommended that the deeper erosional gullies (i.e., those deeper than 8 inches), if any, that would not be eliminated during pad restoration should be widened as necessary to provide equipment access, cleared of all loose soil and/or desiccated soil material and debris, and backfilled with properly moisture conditioned onsite soils and compacted to a minimum relative compaction of 90 percent. Following the remedial grading, the site may be brought to proposed finish elevation and proper surface drainage may be established. A representative of the project geotechnical consultant should be present during clearing, remedial grading and fill placement operations. It should be noted that the sequence of precise grading, as recommended above, is left to the grading contractor's discretion, however, our experience indicates that for conditions where site surficial soils exist at a moisture content well below optimum, the grading operation may be performed more efficiently if the soils are thoroughly moisture conditioned utilizing a temporary sprinkler system prior to scarification and recompaction. Exposed bottom surfaces areas to receive compacted fill should be observed and approved by the project geotechnical consultant prior to fill placement. No fill should be placed without prior approval from the geotechnical consultant. The project geotechnical consultant should also be present onsite during re- processing and/or grading operations to document proper placement and adequate compaction of fill, as well as to observe compliance with the other recommendations presented herein. 0 GErG ENC� SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta Importin of f Fill June 7, 2023 J.N. 21-468 Page 5 Depending on the requirements of the forthcoming precise grading plan, some pads may need to receive maximum of 6 inches of fill to achieve to finish pad elevation. If the required fill will be imported from outside of the area, potential import sources should be evaluated prior to importing to the site such that non - expansive soils that are free of deleterious materials will be used. Foundation Design Considerations Faulting Based on our review of the referenced geologic maps and literature, no active faults are known to project through the property. Furthermore, the site does not lie within the boundaries of an "Earthquake Fault Zone" as defined by the State of California in the Alquist-Priolo Earthquake Fault Zoning Act (CGS, 2018). The Alquist-Priolo Earthquake Fault Zoning Act (AP Act) defines an active fault as one that "has had surface displacement within Holocene time (about the last 11,000 years)." The main objective of the AP Act is to prevent the construction of dwellings on top of active faults that could displace the ground surface resulting in loss of life and property. However, it should be noted that according to the USGS Unified Hazard Tool website and/or 2010 CGS Fault Activity Map of California, the San Andreas Fault Zone, located approximately 8.3 miles northeast of the site, would probably generate the most severe site ground motions and, therefore, is the majority contributor to the deterministic minimum component of the ground motion models. [The subject site is located at a distance of less than 9.5 miles (15 km) from the surface projection of this fault system, which is capable of producing a magnitude 7 or larger events with a slip rate along the fault greater than 0.04 inch per year. As such, the site should be considered as a Near -Fault Site in accordance with ASCE 7-16, Section 11.4.1.] Seismic Design Parameters Earthquake loads on earthen structures and buildings are a function of ground acceleration which may be determined from the site -specific ground motion analysis. Alternatively, a design response spectrum can be developed for certain sites based on the code guidelines. To provide the design team with the parameters necessary to construct the design acceleration response spectrum for this project, we used two computer applications. Specifically, the first computer application, which was jointly developed by Structural Engineering Association of California (SEAOC) and California's Office of Statewide Health Planning and Development (OSHPD), the SEAOC/OSHPD Seismic Design Maps Tool website, https:Hseismicmaps.org, is used to calculate the ground motion parameters. The second computer application, the United Stated GEiG ENCi SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 6 Geological Survey (USGS) Unified Hazard Tool website, https://earthquake.usgs.gov/hazards/interactive/, is used to estimate the earthquake magnitude and the distance to surface projection of the fault. To run the above computer applications, site latitude and longitude, seismic risk category and knowledge of site class are required. The site class definition depends on the direct measurement and the ASCE 7-16 recommended procedure for calculating average small -strain shear wave velocity, Vs30, within the upper 30 meters (approximately 100 feet) of site soils. A seismic risk category of II was assigned to the proposed buildings in accordance with 2022 CBC, Table 1604.5. No shear wave velocity measurement was performed at the site, however, the subsurface materials at the site appears to exhibit the characteristics of stiff soils condition for Site Class D designation. Therefore, an average shear wave velocity of 750 feet per second for the upper 100 feet was assigned to the site based on engineering judgment and geophysical experience. As such, in accordance with ASCE 7-16, Table 20.3-1, Site Class D (D- Default as per SEAOC/OSHPD software) has been assigned to the subject site. The following table, Table 1, provides parameters required to construct the seismic response coefficient, C5j curve based on ASCE 7-16, Article 12.8 guidelines. A printout of the computer output is attached in Appendix A. Remainder of Page Intentionally Left Blank— OPE ENC■ A SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta TABLE 1 Seismic Design Parameters June 7, 2023 J.N. 21-468 Page 7 Ground Motion Parameters Specific Reference Parameter Value Unit Site Latitude (North) - 33.6292 ° Site Longitude (West) - -116.2583 ° Site Class Definition Section 1613.2.2 (1), Chapter 20 (2) D-Default (4) - Assumed Seismic Risk Category Table 1604.5 0) II - MW - Earthquake Magnitude USGS Unified Hazard Tool (3) 7.3 (3) - R — Distance to Surface Projection of Fault USGS Unified Hazard Tool (3) 13.40) km Ss - Mapped Spectral Response Acceleration Figure 1613.2.1(1) (1) 1.50 (4) g Short Period 0.2 second SI - Mapped Spectral Response Acceleration Figure 1613.2.1(2) (1) 0.60 (4) g Long Period 1.0 second Fa— Short Period (0.2 second) Site Coefficient Table 1613.2.3(1) (1) 1.2 (4) - F, — Long Period (1.0 second) Site Coefficient Table 1613.2.3(2) (t) Null (4) - SMs — MCER Spectral Response Acceleration Parameter Equation 16-20 (1) 1.800(4) g Adjusted for Site Class Effect 0.2 second SI , - MCER Spectral Response Acceleration Parameter Equation 16-21 0) Null (4) g I Adjusted for Site Class Effect 1.0 second SDs - Design Spectral Response Acceleration at 0.2-s Equation 16-22 (1) 1.200 (4) g F SDI - Design Spectral Response Acceleration at 1-s Equation 16-23 (1) Null (4) g To = 0.2 SDI/ SDs Section 11.4.6 (2) Null s T5= SDI/ SDs Section 11.4.6 (2) Null s TL - Long Period Transition Period Figure 22-14 (2) 8 (4) s PGA - Peak Ground Acceleration at MCEG M Figure 22-9 (2) 0.572 g FPGA - Site Coefficient Adjusted for Site Class Effect (2) Table 11.8-1 (2) 1.2 (4) - PGA,,I —Peak Ground Acceleration (2) Equation 11.8-1 (2) 0.687 (4) g I Adjusted for Site Class Effect Design PGA �z (2/3 PGAM) - Slope Stability M Similar to Eqs. 16-22 & 16-23 (2) 0.458 g F Design PGA z (0.4 SDs) — Short Retaining Walls O Equation 11.4-5 (2) 0.480 g F CRs - Short Period Risk Coefficient Figure 22-18A (2) 0.915 (4) - CRI - Long Period Risk Coefficient Figure 22-19A (2) 0.895 (4) - SDC - Seismic Design Category W Section 1613.2.5 (1) Null (4) - References: (D California Building Code (CBC), 2022, California Code of Regulations, Title 24, Part 2, Volume I and 1I. (2) American Society of Civil Engineers/Structural Engineering Institute (ASCE/SEI), 2016, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Standards 7-16. (3) USGS Unified Hazard Tool - htips://earthquake.usg_s.gov/hazards/interactive/ 0) SEI/OSHPD Seismic Design Map Application — hiips://seismicgiaps.org Related References: Federal Emergency Management Agency (FEMA), 2015, NEHERP (National Earthquake Hazards Reduction Program) Recommended Seismic Provision for New Building and Other Structures FEMA P-1050 . Notes: * PGA Calculated at the NICE return period of 2475 years (2 percent chance of exceedance in 50 years). t PGA Calculated at the Design Level of % of MCE; approximately equivalent to a return period of 475 years (10 percent chance of exceedance in 50 years). PGA Calculated for short, stubby retaining walls with an infinitesimal (zero) fundamental period. § The designation provided herein may be superseded by the structural engineer in accordance with Section 1613.2.5.1, if applicable.. 16 PETRA SOLID AS A HOCK GEOSCIENCES" WILLIAMS HOMES Palo Verde Project /La Quinta Discussion June 7, 2023 J.N. 21-468 Page 8 General Owing to the characteristics of the subsurface soils, as defined by Site Class D-Default designation, and proximity of the site to the sources of major ground shaking, the site is expected to experience strong ground shaking during its anticipated life span. Under these circumstances, where the code -specified design response spectrum may not adequately characterize site response, the 2022 CBC typically requires a site - specific seismic response analysis to be performed. This requirement is signified/identified by the "null" values that are output using SEAOC/OSHPD software in determination of short period, but mostly, in determination of long period seismic parameters, see Table 1. For conditions where a "null" value is reported for the site, a variety of design approaches are permitted by 2022 CBC and ASCE 7-16 in lieu of a site -specific seismic hazard analysis. For any specific site, these alternative design approaches, which include Equivalent Lateral Force (ELF) procedure, Modal Response Spectrum Analysis (MRSA) procedure, Linear Response History Analysis (LRHA) procedure and Simplified Design procedure, among other methods, are expected to provide results that may or may not be more economical than those that are obtained if a site -specific seismic hazards analysis is performed. These design approaches and their limitations should be evaluated by the project structural engineer. Seismic Design Category Please note that the Seismic Design Category, SDC, is also designated as "null" in Table 1. For condition where the mapped spectral response acceleration parameter at 1 — second period, S1, is less than 0.75, the 2022 CBC, Section 1613.2.5.1 allows that seismic design category to be determined from Table 1613.2.5(1) alone provided that all 4 requirements concerning fundamental period of structure, story drift, seismic response coefficient, and relative rigidity of the digpliragnis are met. Our interpretation of ASCE 7-16 is that for conditions where one or more of these 4 conditions are not met, seismic design category should be assigned based on: 1) 2022 CBC, Table 1613.2.5(1), 2) structure's risk category and 3) the value of SDS, at the discretion of the project structural engineer. Equivalent Lateral Force Method Should the Equivalent Lateral Force (ELF) method be used for seismic design of structural elements, the value of Constant Velocity Domain Transition Period, TS, is estimated to be 1.7 seconds and the value of Long Period Transition Period, TL, is provided in Table 1 for construction of Seismic Response Coefficient — Period (Cs -T) curve that is used in the ELF procedure. 10 GEiG ENCi A SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 9 As stated herein, the subject site is considered to be within a Site Class D-Default. A site -specific ground motion hazard analysis is not required for structures on Site Class D-Default with Si > 0.2 provided that the Seismic Response Coefficient, CS, is determined in accordance with ASCE 7-16, Article 12.8 and structural design is performed in accordance with Equivalent Lateral Force (ELF) procedure. Allowable Soil Bearing Capacities Pad Footings An allowable soil bearing capacity of 1,500 pounds per square foot may be utilized for design of isolated 24-inch-square footings founded at a minimum depth of 12 inches below the lowest adjacent final grade for pad footings that are not a part of the slab system and are used for support of such features as roof overhang, second -story decks, patio covers, etc. This value may be increased by 20 percent for each additional foot of depth and by 10 percent for each additional foot of width, to a maximum value of 2,500 pounds per square foot. The recommended allowable bearing value includes both dead and live loads, and may be increased by one-third for short duration wind and seismic forces. Continuous Footings An allowable soil bearing capacity of 1,500 pounds per square foot may be utilized for design of continuous footings founded at a minimum depth of 12 inches below the lowest adjacent final grade. This value may be increased by 20 percent for each additional foot of depth and by 10 percent for each additional foot of width, to a maximum value of 2,500 pounds per square foot. The recommended allowable bearing value includes both dead and live loads, and may be increased by one-third for short duration wind and seismic forces. Footing Settlements Based on the allowable bearing values provided above and settlement potential of existing fill, total settlement of the footings under the anticipated loads is estimated to be less than 1/2 inches. Differential settlement is expected to be less than 1/2 inch over a horizontal span of 40 feet. The majority of the anticipated settlement is likely to take place as footing loads are applied or shortly thereafter. A differential settlement of 2 inches over a horizontal distance of 40 feet should be considered in design under the `seismic `dry sand' settlement. Lateral Resistance A passive earth pressure of 250 pounds per square foot per foot of depth, to a maximum value of 2,500 pounds per square foot, may be used to determine lateral bearing resistance for footings. In addition, 16 GEiG ENCi A SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 10 a coefficient of friction of 0.30 times the dead load forces may be used between concrete and the supporting soils to determine lateral sliding resistance. The above values may be increased by one-third when designing for transient wind or seismic forces. It should be noted that the above values are based on the condition where footings are cast in direct contact with compacted fill or competent native soils. In cases where the footing sides are formed, all backfill placed against the footings upon removal of forms should be compacted to at least 90 percent of the applicable maximum dry density. Guidelines for Footings and Slabs on -Grade Design and Construction Expansive Soil Conditions The results of laboratory testing performed by Petra on representative samples of near -surface soils within the subject tracts indicate that the soils underlying the subject units predominantly exhibit a Very Low expansion potential (Expansion Index less than or equal to 20). Thus, the site soils may generally be classified as "non -expansive" as defined in Section 1803.5.3 of the 2022 CBC. As such, the design of slabs on -grade is considered to be exempt from the procedures outlined in Sections 1803.5.3 and 1808.6.2 of the 2022 CBC and may be performed using any method deemed rational and appropriate by the project structural engineer. Test results performed by Petra and other consultants on the samples obtained from the tracts are summarized on Plate I. The following minimum recommendations are presented herein for conditions where the project design team may require geotechnical engineering guidelines for design and construction of footings and slabs on - grade the project site. The design and construction guidelines that follow are based on the above soil conditions and may be considered for reducing the effects of variability in fabric, composition and, therefore, the detrimental behavior of the site soils such as excessive short- and long-term total and differential settlements. These guidelines have been developed on the basis of the previous experience of this firm on projects with similar soil conditions. Although construction performed in accordance with these guidelines has been found to reduce post -construction movement and/or distress, they generally do not positively eliminate all potential effects of variability in soils characteristics and future settlement. It should also be noted that the suggestions for dimension and reinforcement provided herein are performance -based and intended only as preliminary guidelines to achieve adequate performance under the anticipated soil conditions. However, they should not be construed as replacement for structural engineering analyses, experience and judgment. The project structural engineer, OGEiG ENCi A SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 11 architect and/or civil engineer should make appropriate adjustments to slab and footing dimensions, and reinforcement type, size and spacing to account for internal concrete forces (e.g., thermal, shrinkage and expansion), as well as external forces (e.g., applied loads) as deemed necessary. Consideration should also be given to minimum design criteria as dictated by local building code requirements. Post -Tensioned Slabs on -Grade System (Very Low Expansion) In consideration of the expansion index of less than or equal to 20, as predominantly exhibited by onsite soils, any rational and appropriate procedure may be chosen by the project structural engineer for the design of post -tensioned slabs on -grade. Should the design engineer choose to follow the most current procedure published by the Post -Tensioning Institute (PTI DC10.5-12), the following minimum design criteria are provided Table 2, below. TABLE 2 Post -Tensioned Slab on -Grade Design Parameters for PTI Procedure Soil Information Approximate Depth of Constant Suction, feet 9 Approximate Soil Suction, pF 3.9 Inferred Thornthwaite Index: -20 Average Edge Moisture Variation Distance, em in feet: Center Lift 9.0 Edge Lift 4.7 Anticipated Swell, ym in inches: Center Lift 0.25 Edge Lift 0.45 Modulus of Subgrade Reaction The modulus of subgrade reaction for design of load bearing elements depends on the size of the element and soil -structure interaction. However, as a fist level of approximation, this value may be assumed to be 125 pounds per cubic inch. Minimum Design Recommendations The soil values provided above may be utilized by the project structural engineer to design post -tensioned slabs on -ground in accordance with Section 1808.6.2 of the 2022 CBC and the PTI publication. Thicker floor slabs and larger footing sizes may be required for structural reasons and should govern the design if more restrictive than the minimum recommendations provided below: 1* F ` ERA SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 12 1. Exterior continuous footings for both one-story and two-story structures should be founded at a minimum depth of 12 inches below the lowest adjacent finished ground surface. Interior footings may be founded at a minimum depth of 10 inches below the tops of the adjacent finish floor slabs. 2. In accordance with Table 1809.7 of 2022 CBC for light -frame construction, all continuous footings should have minimum widths of 12 inches for one- and two-story construction. We recommend all continuous footings should be reinforced with a minimum of two No. 4 bars, one top and one bottom. Alternatively, post -tensioned tendons may be utilized in the perimeter continuous footings in lieu of the reinforcement bars. A minimum 12-inch-wide grade beam founded at the same depth as adjacent footings should be provided across the garage entrances or similar openings (such as large doors or bay windows). The grade beam should be reinforced in a similar manner as provided above. 4. Exterior isolated pad footings intended for support of roof overhangs such as second -story decks, patio covers and similar construction should be a minimum of 24 inches square and founded at a minimum depth of 18 inches below the lowest adjacent final grade. The pad footings should be reinforced with No. 4 bars spaced a maximum of 18 inches on centers, both ways, placed near the bottoms of the footings. Exterior isolated pad footings may need to be connected to adjacent pad and/or continuous footings via tie beams at the discretion of the project structural engineer. 5. The thickness of the floor slabs should be determined by the project structural engineer with consideration given to the expansion potential of the onsite soils; however; we recommend that a minimum slab thickness of 4 inches be considered. 6. As an alternative to designing 4-inch-thick post -tensioned slabs with perimeter footings as described in Item 1 and 2 above, the structural engineer may design the foundation system using a thickened slab design. The minimum thickness of this uniformly thick slab should be 8 inches. The engineer in charge of post -tensioned slab design may also opt to use any combination of slab thickness and footing embedment depth as deemed appropriate based on their engineering experience and judgment. Living area concrete floor slabs and areas to receive moisture sensitive floor covering should be underlain with a moisture vapor retarder consisting of a minimum 10-mil-thick polyethylene or polyolefin membrane that meets the minimum requirements of ASTM E96 and ASTM E1745 for vapor retarders (such as Husky Yellow Guard®, Stego(& Wrap, or equivalent). All laps within the membrane should be sealed, and at least 2 inches of clean sand should be placed over the membrane to promote uniform curing of the concrete. To reduce the potential for punctures, the membrane should be placed on a pad surface that has been graded smooth without any sharp protrusions. If a smooth surface cannot be achieved by grading, consideration should be given to lowering the pad finished grade an additional inch and then placing a 1-inch-thick leveling course of sand across the pad surface prior to the placement of the membrane. At the present time, some slab designers, geotechnical professionals and concrete experts view the sand layer below the slab (blotting sand) as a place for entrapment of excess moisture that could adversely impact moisture -sensitive floor coverings. As a preventive measure, the potential for moisture intrusion into the concrete slab could be reduced if the concrete is placed directly on the vapor retarder. However, if this sand layer is omitted, appropriate curing methods must be implemented to ensure that the concrete slab cures uniformly. A qualified materials engineer with experience in slab design and construction 0 GE■�G ENCi� SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 13 should provide recommendations for alternative methods of curing and supervise the construction process to ensure uniform slab curing. Additional steps would also need to be taken to prevent puncturing of the vapor retarder during concrete placement. 8. Garage floor slabs should be designed in a similar manner as living area floor slabs. Consideration should be given to placement of a moisture vapor retarder below the garage slab, similar to that provided in Item 7 above, should the garage slab be overlain with moisture sensitive floor covering. 9. Presaturation of the subgrade below floor slabs will not be required; however, prior to placing concrete, the subgrade below all dwelling and garage floor slab areas should be thoroughly moistened to achieve a moisture content that is at least equal to or slightly greater than optimum moisture content. This moisture content should penetrate to a minimum depth of 12 inches below the bottoms of the slabs. 10. The minimum footing dimensions and reinforcement recommended herein may be modified (increased or decreased subject to the constraints of Chapter 18 of the 2022 CBC) by the structural engineer responsible for foundation design based on his/her calculations, engineering experience and judgment. Foundation Excavation Observations Foundation excavations should be observed by a representative of this firm to document that they have been excavated into competent engineered fill soils prior to the placement of forms, reinforcement or concrete. Following remedial/precise grading, the presence of rock, up to 12 inches diameter, if any, in the compacted fill may require the use of forms when pouring concrete. The excavations should be trimmed neat, level and square. All loose, sloughed or moisture -softened soils and/or any construction debris should be removed prior to placing of concrete. Excavated soils derived from footing and/or utility trenches should not be placed in building slab -on -grade areas or exterior concrete flatwork areas unless the soils are compacted to at least 90 percent of maximum dry density. Soil Corrosivity Screening As a screening level study, limited chemical and electrical tests were performed on samples considered representative of the onsite soils to identify potential corrosive characteristics of these soils. The common indicators associated with soil corrosivity include water-soluble sulfate and chloride levels, pH (a measure of acidity), and minimum electrical resistivity. It should be noted that Petra does not practice corrosion engineering; therefore, the test results, opinion and engineering judgment provided herein should be considered as general guidelines only. Additional analyses would be warranted, especially, for cases where buried metallic building materials (such as copper and cast or ductile iron pipes) in contact with site soils are planned for the project. In many cases, the project geotechnical engineer may not be informed of these choices. Therefore, for conditions where such elements are considered, we recommend that other, relevant GEOr ENA SOLID AS A ROCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 14 project design professionals (e.g., the architect, landscape architect, civil and/or structural engineer) also consider recommending a qualified corrosion engineer to conduct additional sampling and testing of near -surface soils during the final stages of site grading to provide a complete assessment of soil corrosivity. Recommendations to mitigate the detrimental effects of corrosive soils on buried metallic and other building materials that may be exposed to corrosive soils should be provided by the corrosion engineer as deemed appropriate. In general, a soil's water-soluble sulfate levels and pH relate to the potential for concrete degradation; water-soluble chlorides in soils impact ferrous metals embedded or encased in concrete, e.g., reinforcing steel; and electrical resistivity is a measure of a soil's corrosion potential to a variety of buried metals used in the building industry, such as copper tubing and cast or ductile iron pipes. Table 3, below, presents a values of individual test results by Petra and other consultants for the project with an interpretation of current code indicators and guidelines that are commonly used in this industry. The table includes the code - related classifications of the soils as they relate to the various tests, as well as a general recommendation for possible mitigation measures in view of the potential adverse impact on various components of the proposed structures in direct contact with site soils. The guidelines provided herein should be evaluated and confirmed, or modified, in their entirety by the project structural engineer, corrosion engineer and/or the contractor responsible for concrete placement for structural concrete used in exterior and interior footings, interior slabs on -ground, garage slabs, wall foundations and concrete exposed to weather such as driveways, patios, porches, walkways, ramps, steps, curbs, etc. TABLE 3 Soil Corrosivity Screening Results Test Results Classification General Recommendations Soluble Sulfates 0.0189 to 0.0414 Sol Min. fc'= 2,500 psi No water/cement ratio restrictions 11 (Cal 417 ercent p H Slightly to (Cal 643) 7.7 - 8.5 Moderately Type I-P (MS) Modified or Type II Modified cement Alkaline Residence: Increase concrete cover thickness; f,'(2) Soluble Chloride 65 to 3,900 ppm C12 should not be less than 2,500 psi. Consult a corrosion (Cal 422) C24 engineer. Spas/Decking: water/cement ratio 0.40, f,,' _ 5,000 psi Resistivity 405 to 2,800 Corrosive to Protective wrapping/coating of buried pipes; corrosion (Cal 643) ohm -cm Extremely resistant materials; or cathodic protection. Consult a Corrosive corrosion en ineer. Notes: 1. ACI 318-14, Section 19.3 2. ACI 318-14, Section 19.3 3. Pierre R. Roberge, "Handbook of Corrosion Engineering" 4. Exposure classification C2 applies specifically to swimming pools/spas and appurtenant concrete elements I� GEO ENCiSOLID AS A ROCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 15 As depicted in Table 3 and Plate 1, one sample, obtained from Lot 7, Tract 33336, exhibited an excessive level of soluble chloride content. Currently, this is considered a `hot spot' for soluble chloride and may require special recommendations by a corrosion engineer for the entire project. However, considering other test results, this high value may be limited to surficial soils on and within the vicinity of Lot 7. It is highly recommended that at the end of precise grading additional surficial samples be obtained from this area for further verification. If, upon further testing this condition persists, protective measures such as encasing post -tensioned cables in plastic sheathing may become necessary. Further, a corrosion engineer should also examine the results and provide appropriate mitigative recommendations. Post -Grading Considerations Precise Grading and Drainage Surface and subsurface drainage systems consisting of sloping concrete flatwork and graded swales will be constructed on the subject lots to collect and direct all surface water to the curb and gutter of the adjacent streets. In addition, the ground surface around the proposed buildings should be sloped to provide a positive drainage gradient away from the structures. The purpose of the drainage systems is to prevent ponding of surface water within the level areas of the site and against building foundations and associated site improvements. The drainage systems should be properly maintained throughout the life of the proposed development. Section 1804.4 of the 2022 CBC requires that "The ground immediately adjacent to the foundation shall be sloped away from the building at a slope of not less than one unit vertical in 20 units horizontal (S percent slope) for a minimum distance of 10 feet (3048 mm) measured perpendicular to the face of the wall." Further, "Swales used for this purpose shall be sloped a minimum of 2 percent where located within 10 feet (3048 mm) of the building foundation". These provisions fall under the purview of the Design Civil Engineer. However, exceptions to allow modifications to these criteria are provided within the same section of the code as "Where climatic or soil conditions warrant, the slope of the ground away from the buildingfoundations is permitted to be reduced to not less than one unit in 48 units horizontal (2 percent slope)." This exemption provision appears to fall under the purview of the Geotechnical Engineer -of -Record. It is our understanding that the state -of -the -practice for projects in various cities and unincorporated areas of Ventura Counties, as well as throughout Southern California, has been to construct earthen slopes at 2 I* GEOS ENCi� SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 16 percent minimum gradient away from the foundations and at 1 percent minimum for earthen swale gradients. Structures constructed and properly maintained under those criteria have performed satisfactorily. Therefore, considering the semi -arid climate, site soil conditions and an appropriate irrigation regime, Petra considers that the implementation of 2 percent slopes away from the structures and 1 percent swales to be acceptable for the subject lots. It should be emphasized that the homeowners are cautioned that the slopes away from the structures and swales to be properly maintained, not to be obstructed, and that future improvements not to alter established gradients unless replaced with suitable alternative drainage systems. Further, where the flow line of the swale exists within five feet of the structure, adjacent footings shall be deepened appropriately to maintain minimum embedment requirements, measured from the flow line of the swale. Utility Trench Backfill All utility trench backfill should be compacted to a minimum relative compaction of 90 percent. Trench backfill materials should be placed in approximately 8- to 12-inch thick maximum lifts, moisture conditioned as necessary to achieve near optimum moisture conditions, and mechanically compacted in place with a hydra -hammer, pneumatic tamper or similar equipment to achieve a minimum relative compaction of 90 percent. A representative of this firm should probe and test the backfills to document the adequate compaction has been achieved. For shallow trenches where pipe or utilities might be damaged by mechanical compaction equipment, imported sand having a Sand Equivalent (SE) value of 30 or greater may be used for backfill. Sand backfill materials should be watered to achieve optimum (or above) moisture conditions, and then tamped with hand -operated pneumatic tampers to ensure proper consolidation of the backfill. No specific relative compaction will be required; however, observation, probing and, if deemed necessary, testing should be performed by a representative of this firm to verify that the backfill is adequately compacted and will not be subject to excessive settlement. Where an exterior or interior utility trench is proposed in a direction that is parallel to a building footing, the bottom of the trench should not extend below a 1:1 plane projected downward from the bottom edge of the adjacent footing. Where this condition occurs, the adjacent footing should be deepened or the trench backfilled and compacted prior to construction of the footing. Masonry Block Screen Walls Footings for masonry block walls may be designed in accordance with the bearing and lateral resistance values provided previously for building footings. However, as a minimum, the wall footings should be 10 PE ERA SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 17 embedded at a minimum depth of 18 inches below the lowest adjacent final grade. The footings should also be reinforced with a minimum of four No. 4 bars, two near top and two near bottom. In order to minimize the potential for unsightly cracking related to the possible effects of differential settlement and/or expansion, positive separations (construction joints) should also be provided in the block walls at each corner and at horizontal intervals of approximately 20 to 25 feet. The separations should be provided in the blocks and not extend through the footings. The footings should be poured monolithically with continuous reinforcement bars to serve as effective "grade beams" below the walls. Exterior Concrete Flatwork General Near -surface compacted fill soils within the site indicate expansion index ranging from 3 to 20 which is a borderline value between Very Low and Low expansion potential. For this reason, we recommend that additional testing of subgrade soils be performed at the completion of precise grading in order to provide specific recommendations for all exterior concrete flatwork. However, due to typical project scheduling constraints, it may not be feasible to collect additional samples of subgrade soils for testing to verify their expansion potential immediately prior to pouring concrete. For this reason, we recommend that all exterior concrete flatwork such as sidewalks, patio slabs, large decorative slabs, concrete subslabs that will be covered with decorative avers, private and/or public vehicular driveways and/or access roads within and adjacent to the site be designed by the project architect and/or structural engineer with consideration given to mitigating the potential cracking and uplift that can develop in soils exhibiting expansion index values that fall in the upper band of Very Low category. The guidelines that follow should be considered as minimums and are subject to review and revision by the project architect, structural engineer and/or landscape consultant as deemed appropriate. If sufficient time will be allowed in the project schedule for verification sampling and testing prior to the concrete pour, the test results generated may dictate that a somewhat less conservative design could be used. Subgrade Preparation Compaction To reduce the potential for distress to concrete flatwork, the subgrade soils below concrete flatwork areas to a minimum depth of 12 inches (or deeper, as either prescribed elsewhere in this report or determined in the field) should be moisture conditioned to at least equal to, or slightly greater than, the optimum moisture content and then compacted to a minimum relative compaction of 90 percent. Where concrete public roads, concrete segments of roads and/or concrete access driveways are proposed, the upper 6 inches of subgrade soil should be compacted to a minimum 95 percent relative compaction. 10 GEOS ENCi� SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta Pre -Moistening June 7, 2023 J.N. 21-468 Page 18 As a further measure to reduce the potential for concrete flatwork cracking, subgrade soils should be thoroughly moistened prior to placing concrete. The moisture content of the soils should be at least 1.2 times the optimum moisture content and penetrate to a minimum depth of 12 inches into the subgrade. Flooding or ponding of the subgrade is not considered feasible to achieve the above moisture conditions since this method would likely require construction of numerous earth berms to contain the water. Therefore, moisture conditioning should be achieved with sprinklers or a light spray applied to the subgrade over a period of few to several days just prior to pouring concrete. Pre -watering of the soils is intended to promote uniform curing of the concrete, reduce the development of shrinkage cracks and reduce the potential for differential expansion pressure on freshly poured flatwork. A representative of the project geotechnical consultant should observe and verify the density and moisture content of the soils, and the depth of moisture penetration prior to pouring concrete. Thickness and Joint Spacing To reduce the potential of unsightly cracking, concrete walkways, patio -type slabs, large decorative slabs and concrete subslabs to be covered with decorative pavers should be at least 4 inches thick and provided with construction joints or expansion joints every 6 feet or less. Private driveways that will be designed for the use of passenger cars for access to private garages should also be at least 4 inches thick and provided with construction joints or expansion joints every 10 feet or less. Concrete pavement that will be designed based on an unlimited number of applications of an 18-kip single -axle load in public access areas, segments of road that will be paved with concrete (such as bus stops and cross -walks) or access roads and driveways, which serve multiple residential units or garages, that will be subject to heavy truck loadings should have a minimum thickness of 5 inches and be provided with control joints spaced at maximum 10-foot intervals. A modulus of subgrade reaction of 125 pounds per cubic foot may be used for design of the public and access roads. Reinforcement All concrete flatwork having their largest plan -view panel dimensions exceeding 10 feet should be reinforced with a minimum of No. 3 bars spaced 18 inches for 4-inch-thick slabs and No. 4 bars spaced 24 inches for 5-inch-thick slabs on centers, both ways. Alternatively, the slab reinforcement may consist of welded wire mesh of the sheet type (not rolled) with 6x6/W 1.4xW 1.4 designations for 4-inch-thick slabs and 6x6/W2.9xW2.9 designations for 5-inch-thick slabs in accordance with the Wire Reinforcement Institute (WRI). The reinforcement should be properly positioned near the middle of the slabs. All foot and equipment traffic on the reinforcement should be avoided or reduced to a minimum. I� GEO INRolm SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 19 The reinforcement recommendations provided herein are intended as a guideline to achieve adequate performance for anticipated soil conditions. As such, this guideline may not satisfy certain acceptable approaches, e.g. the area of reinforcement to be equal to or greater that 0.2 percent of the area of concrete. The project architect, civil and/or structural engineer should make appropriate adjustments in reinforcement type, size and spacing to account for concrete internal (e.g., shrinkage and thermal) and external (e.g., applied loads) forces as deemed necessary. Edge Beams (Optional) Where the outer edges of concrete flatwork are to be bordered by landscaping, it is recommended that consideration be given to the use of edge beams (thickened edges) to prevent excessive infiltration and accumulation of water under the slabs. Edge beams, if used, should be 6 to 8 inches wide, extend 8 inches below the tops of the finish slab surfaces. Edge beams are not mandatory; however, their inclusion in flatwork construction adjacent to landscaped areas is intended to reduce the potential for vertical and horizontal movement and subsequent cracking of the flatwork related to uplift forces that can develop in expansive soils. Drainage Drainage from patios and other flatwork areas should be directed to local area drains and/or graded earth swales designed to carry runoff water to the adjacent streets or other approved drainage structures. The concrete flatwork should be sloped at a minimum gradient of one percent, or as prescribed by project civil engineer or local codes, away from building foundations, retaining walls, masonry garden walls and slope areas. Tree Wells Tree wells are not recommended in concrete flatwork areas since they introduce excessive water into the subgrade soils and allow root invasion, both of which can cause heaving and cracking of the flatwork. Pavement Design A sample of site soils was taken by SMC for R-Value testing. The sample exhibited and R-Value of 70. Based on this result, and a Traffic Index (TI) of 5.0, SMC recommended (SMC, 2006d) a structural pavement section consisting of 3 inches of hot mix asphalt concrete (AC) over 4.5 inches of crushed aggregate base (AB). GEiG ENCi SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 Page 20 We agree with their assessment and recommend the same pavement section for the unpaved interior street within the project. Subuade Preparation Subgrade soils immediately below the aggregate base should be compacted to a minimum of 90 percent relative compaction based on ASTM D 1557 to a depth of 12 inches or more. Final subgrade compaction should be performed prior to placing the base material and after utility -trench backfills have been compacted and tested. Subgrade shall be firm and unyielding, as exhibited by proof -rolling, prior to placement of base. Should conditions be encountered where significantly higher moisture contents are present within the subgrade soil, additional overexcavation may be required to achieve a firm, unyielding excavation bottom. A jurisdictional relative compaction standard in excess of the aforementioned minimum may exist and should be complied with, as applicable. Crushed Ammegate Base and Asphaltic Concrete Crushed Aggregate Base (CAB) should conform to Section 200-2.2 of the Standard Specifications for Public Works Construction (Greenbook). It should be noted that the base thickness is predicated on the use of Crushed Aggregate Base material. For conditions where either Crushed Miscellaneous Base or Processed Miscellaneous Base Materials are used, a 10 percent increase in base section thickness should be incorporated in the design and construction of the structural pavement section. The base materials should be brought to a uniform moisture content near optimum and then compacted to at least 95 percent of ASTM D 1557. Optional Considerations Typical project sequencing often involves construction of a pavement section consisting of the design aggregate base course that is initially capped with an asphalt layer that is thinner than the final design asphalt thickness. This practice provides for a temporary pavement surface during the construction period when streets are commonly subjected to heavy construction traffic. In light of the inherent weakness of this temporary structural pavement section and the damage that can occur to the pavement as a result of repeated heavy construction loads, it is our professional opinion that the streets may be paved with the full recommended structural section provided herein prior to the construction phase of the project. If needed after construction, the pavement surface should be brushed off (micro cold planed), all divots and depressions patched with a tack coat and hot mix asphalt and sealed with a Type II slurry seal. I SOLID AS A HOCK 16 GEOSCIENCES" WILLIAMS HOMES June 7, 2023 Palo Verde Project /La Quinta J.N. 21-468 Page 21 Plan Reviews, Future Improvements and/or Grading Petra should review any subsequent plans when they become available and issue an addendum letter to this report. If additional site improvements are considered in the future, our firm should be notified so that we may provide design recommendations to mitigate movement, settlement and/or tilting of the structures. Potential problems can develop when drainage on the pads and slopes is altered in any way such as placement of fill and construction of new walkways, patios, landscape walls, swimming pools, spas and/or planters. Therefore, it is recommended that we be engaged to review the final design drawings, specifications and grading plan prior to any new construction. If we are not provided the opportunity to review these documents with respect to the geotechnical aspects of new construction and grading, it should not be assumed that the recommendations provided herein are wholly or impart applicable to the proposed improvements. Post Grading Observations and Testing Petra should be notified at the appropriate times in order that we may provide the following observation and testing services during the various phases of construction and precise grading. 1. Building Construction • Observe all footing trenches when first excavated to verify adequate depth and competent bearing conditions. • Re -observe all footing trenches, if necessary, if trenches are found to be excavated to inadequate depth and/or found to contain significant slough, saturated or compressible materials. 2. Concrete Flatwork Construction • Observe and test subgrade soils below all concrete flatwork areas to verify adequate compaction, moisture content and moisture penetration prior to pouring concrete. 3. Utility Trench Backfill • Observe and test placement of all utility trench backfill mains and laterals to verify adequate compaction. 4. Precise Grading • Observe and test placement of any fill to be placed on the subject lots to verify adequate compaction. ItGEOS ENCi� SOLID AS A HOCK WILLIAMS HOMES June 7, 2023 Palo Verde Project /La Quinta J.N. 21-468 Page 22 5. Masonry Screen Walls • Observe all screen wall footing trenches when first excavated to verify adequate depth and competent bearing conditions. REPORT LIMITATIONS This report is based on the proposed residential tract and the geotechnical observations made during our literature review of the prior consultant's as -graded (SMC, 2006e and 2006f) reports and our limited soil laboratory testing within the site. No representatives of Petra were present during the previous grading activities that have been completed to -date at this site. This report has been prepared consistent with that level of care being provided by other professionals providing similar services at the same locale and in the same time period. The contents of this report are professional opinions and as such, are not to be considered a guaranty or warranty. Based on our findings, the conclusions and recommendations presented herein and within the referenced reports by our firm were prepared in conformance with generally accepted professional engineering practices. We appreciate this opportunity to be of service. If you have questions, please contact this office. Respectfully submitted, PETRA GEOSCIENCES, INC. Q�OFESS/pNq • / ����¢tCJAFj�.O �F,L �No. GE002024 E 1 Siamak Jafroudi, PhD �, 0 Gam` Senior Principal Engineer 0 CHN� o �� GE 2024oF CAL�F� SJ/ly Attachments: References Plate I — Chemical, Electrical and Expansion Index Test Data Appendix A — Seismic Design Analyses W:\2020-2025\2021\400\21468\Reports\21-468 250 Updated Foundation Design and Constratiion Recommendations -Tract 33336.docx OPEIR GEOA SOLID AS A HOCK WILLIAMS HOMES Palo Verde Project /La Quinta REFERENCES June 7, 2023 J.N. 21-468 Page 23 Earth Systems Southwest, 2004, Geotechnical Engineering Report, Proposed Residential Development, Tract Number 32279, Avenue 58, West of Madison Street La Quinta, California, dated April 21. 2005, Geotechnical Engineering Report, Proposed Residential Development, 8.11-Acre Portion of APN 762-240-01 80-600, Avenue 58, La Quinta, California, dated January 25. Petra Geosciences, Inc., 2021, Geotechnical Design and Construction Recommendations, Palo Verde Project, Tracts 33336 (Lots 1 — 23) and 32279 (Lots 2, 9 — 12, 16 — 22, 29 and 30), Cherrywood Place and Rosewood Court, North of Avenue 58 and East of Paseo Del Lago, City of La Quinta, Riverside County, California, J.N. 21-468 dated December 17. 2023, Geotechnical Report of Building Pad Preparation and Precise Grading, Palo Verde Project, Tract 33336, Lots 1 through 23, Cherrywood Place, North of Avenue 58 and East of Paseo Del Lago, City of La Quinta, Riverside County, California, J.N. 21-468 dated March 27. Schiff Associates, 2006, Laboratory Tests on Soil Samples, STD.PAC., La Quinta, dated April 18. Stoney -Miller Consultants, Inc., 2006a, Geotechnical Consultant of Record, Tract 33336, La Quinta, California, dated February 6. 2006b, Geotechnical Review of Rough Grading Plans, Tract 33336, La Quinta, California, dated February 28. 2006c, Review of Foundation Design Parameters, Tracts 32279 and 33336, La Quinta, California, dated June 13. 2006d, Pavement Recommendations, Tract 33336, Mirage II of La Quinta, California, dated August 8. 2006e, Earthwork Observation and Testing Report Rough Grading, Lots 1 through 30, Tract 32279, La Quinta, California, dated August 24. 2006f, Earthwork Observation and Testing Report Rough Grading, Lots 1 through 23, Tract 33336, La Quinta, California, dated August 24. OPETFA SOLID AS A ROCK GEOSCIENCES- WILLIAMS HOMES Palo Verde Project /La Quinta June 7, 2023 J.N. 21-468 PLATE I CHEMICAL, ELECTRICAL AND EXPANSION INDEX TEST DATA LABORATORY DATA SUMMARY Consultant Sample ID Sample Location Expansion Index Sulfate Content (%) Chloride Content I (PPM) pH Minimum Resistivity (ohm -cm) Petra Tract 33336 Lot 2 0 - - - - Lot 7 1 0.0189 3,900 8.5 810 Lot 17 0 - - - - Lot 23 0 - - - - SMC Tract 33336 Boring B-5, 1 - 4' - 445 ppm 726 7.8 405 #1 - - 243 ppm 90 7.7 2,200 Schiff #2 - - 158 ppm 65 7.9 2,800 #3 - - 246 ppm 105 7.8 1,900 *PETRA SOLID AS A HOCK GEOSCIENCES- APPENDIX A SEISMIC DESIGN ANALYSES PETRASOLID AS A HOCK GEOSCIENCES- 6/7/23, 1:56 PM U.S. Seismic Design Maps OSH PD Palo Verde Williams Homes 21-468 Latitude, Longitude: 33.6292,-116.2583 Joseph H Hofrnan Law Offices �o m n r o m ., m 77 o W old Rnch T^ o a o m _ M Z 3 W '' Stone Creek Ranch 19 Goode Avenue 58 Date Design Code Reference Document Risk Category Site Class Augustin Wall Art Stone Creek Rancho Homeowners - __ Avenue 58 Map data C2023 6/7/2023. 1:56:27 PM ASCE7-16 11 D - Default (See Section 11.4.3) Type Value Description Ss 1.5 MCER ground motion. (for 0.2 second period) S1 0.6 MCER ground motion. (for 1.0s period) SMS 1.8 Site -modified spectral acceleration value SM1 null -See Section 11.4.8 Site -modified spectral acceleration value SIDS 1.2 Numeric seismic design value at 0.2 second SA Sol null -See Section 11.4.8 Numeric seismic design value at 1.0 second SA Type Value Description SDC null -See Section 11.4.8 Seismic design category Fe 1.2 Site amplification factor at 0.2 second Fv null -See Section 11.4.8 Site amplification factor at 1.0 second PGA 0.572 MCEo peak ground acceleration FPGA 1.2 Site amplification factor at PGA PGAM 0.687 Site modified peak ground acceleration TL 8 Long -period transition period in seconds SsRT 1.629 Probabilistic risk -targeted ground motion. (0.2 second) SsUH 1.78 Factored uniform -hazard (2% probability of exceedance in 50 years) spectral acceleration SsD 1.5 Factored deterministic acceleration value. (0.2 second) S1RT 0.621 Probabilistic risk -targeted ground motion. (1.0 second) S1UH 0.694 Factored uniform -hazard (2% probability of exceedance in 50 years) spectral acceleration. SID 0.6 Factored deterministic acceleration value. (1.0 second) PGAd 0.572 Factored deterministic acceleration value. (Peak Ground Acceleration) PGAUH 0.703 Uniform -hazard (2% probability of exceedance in 50 years) Peak Ground Acceleration CRS 0.915 Mapped value of the risk coefficient at short periods https://www.seismicmaps.org 1/3 6/7/23, 1:56 PM Type Value CR1 0.895 CV 1.4 U.S. Seismic Design Maps Description Mapped value of the risk coefficient at a period of 1 s Vertical coefficient https://www.seismicmaps.org 2/3 6/7/23, 1:56 PM U.S. Seismic Design Maps DISCLAIMER While the information presented on this website is believed to be correct, SEAOC /OSHPD and its sponsors and contributors assume no responsibility or liability for its accuracy. The material presented in this web application should not be used or relied upon for any specific application without competent examination and verification of its accuracy, suitability and applicability by engineers or other licensed professionals. SEAOC / OSHPD do not intend that the use of this information replace the sound judgment of such competent professionals, having experience and knowledge in the field of practice, nor to substitute for the standard of care required of such professionals in interpreting and applying the results of the seismic data provided by this website. Users of the information from this website assume all liability arising from such use. Use of the output of this website does not imply approval by the governing building code bodies responsible for building code approval and interpretation for the building site described by latitude/longitude location in the search results of this website. https://www.seismicmaps.org 3/3