Project_Manual_2_of_2_Final.pdf

CALIFORNIA DEPARTMENT OF FORESTRY AND FIRE PROTECTION

REAL ESTATE SERVICES DIVISION

PROJECT MANAGEMENT AND DEVELOPMENT BRANCH

PROJECT MANUAL – Book 2 of 2

APPENDICES

FOR:

MODULAR CLASS ROOM REPLACEMENT

CALIFORNIA DEPARTMENT OF FORESTRY AND

FIRE PROTECTION

IONE TRAINING CENTER

IONE, AMADOR COUNTY, CALIFORNIA

Jenny Li, Project Director West Sacramento, California

Consultants: BKF Engineers

NOVEMBER 19, 2025

000000000010124

APPENDIX A - GEOTECHNICAL

INVESTIGATION AND

GEOLOGIC HAZARDS

EVALUATION

APRIL 2025

PREPARED FOR:

CALIFORNIA DEPARTMENT OF GENERAL SERVICES

707 3RD STREET, 4TH FLOOR

WEST SACRAMENTO, CALIFORNIA 956051

PREPARED BY:

GEOCON CONSULTANTS, INC.

3160 GOLD VALLEY DRIVE, SUITE 800

RANCHO CORDOVA, CALIFORNIA 95742

GEOCON PROJECT NO. S2980-05-02

GEOTECHNICAL INVESTIGATION AND

GEOLOGIC HAZARDS EVALUATION

Modular Classroom Replacement Caifornia Department of Forestry and

Fire Protection (CAL FIRE) Ione Training Center 4501 Highway 104

Ione, Amador County, California

Project No. S2980-05-02 April 16, 2025

VIA ELECTRONIC MAIL

Gisele Geiger | Project Director Department of General Services Real Estate Services Division Project Management and Development Branch 707 3rd Street, 4th Floor, West Sacramento, CA. 95605

Subject: GEOTECHNICAL INVESTIGATION AND GEOLOGIC HAZARDS EVALUATION

MODULAR CLASSROOM AND SANITARY SEWER LINE REPLACEMENT

CALIFORNIA DEPARTMENT OF FORESTRY AND FIRE PROTECTION (CAL FIRE)

IONE TRAINING CENTER

4501 HIGHWAY 104

IONE, AMADOR COUNTY, CALIFORNIA

Ms. Geiger:

In accordance with Agreement No. 29062-A, Task Order No. 2, dated February 12, 2025, we have completed a geotechnical investigation and geologic hazards evaluation for the proposed modular classroom buildings and sanitary sewer line replacement for the CAL FIRE Training Center located in Ione, California.

The purpose of our study was to evaluate the subsurface conditions at the site, provide design-level geotechnical recommendations for the project as presently proposed, and perform a Geologic Hazards Evaluation that meets the current California Geological Survey (CGS) review guidelines. In our opinion, no adverse geological or geotechnical conditions were encountered that would preclude development at the site provided recommendations of this report are incorporated into the design and construction of the project.

The accompanying report presents our findings and conclusions from our study. Please contact us if you have any questions concerning the contents of this report.

Respectfully Submitted, GEOCON CONSULTANTS, INC.

Lauren A. Herbert, EIT, GIT Tom C. DeSimone, PG, CEG Senior Staff Engineer Senior Geologist

Jeremy J. Zorne, PE, GE Senior Engineer/Contract Manager

CAL FIRE Training Center Modular Classroom Replacement Geotechnical Investigation and Geologic Hazards Evaluation

TABLE OF CONTENTS

GEOTECHNICAL INVESTIGATION AND GEOLOGIC HAZARDS EVALUATION PAGE

1.0 INTRODUCTION AND PURPOSE

1.1 Scope of Services

2.0 SITE AND PROJECT DESCRIPTION

2.1 Site Location and Description

2.2 Current Topography

2.3 Project Description

3.0 SOIL AND GEOLOGIC CONDITIONS

3.1 Site and Regional Geology

3.2 Existing Pavement

3.3 Undocumented Fill

3.4 Residual Soil

3.5 Ione Formation (Sandstone and Siltstone)

4.0 GROUNDWATER

5.0 GEOLOGIC HAZARDS

5.1 Mapped Geologic Hazard Zones

5.2 Regional Active Faults / Surface Fault Rupture Hazard

5.3 Seismicity

5.4 Liquefaction / Cyclic Softening and Seismic Settlement

5.5 Lateral Spreading

5.6 Unsaturated Seismic Settlement

5.7 Landslides and Slope Stability

5.8 Tsunamis and Seiches

5.9 Flooding and Dam Failure Inundation

5.10 Expansive Soil

5.11 Soil Corrosion Screening

5.12 Volcanic Activity

5.13 Naturally Occurring Asbestos

5.14 Oil Fields & Methane Zones

5.15 Radon

6.0 CONCLUSIONS AND RECOMMENDATIONS

6.1 General

6.2 Seismic Site Classification / Seismic Design Parameters

6.3 Soil and Excavation Characteristics

6.4 Materials for Fill Seepage, Groundwater, and

6.5 Wet Weather Grading Considerations

6.6 Trench Bottom / Bearing Conditions / Foundation for Sewer Pipeline

6.7 Pipe Loading Design Criteria

6.8 Pipe Bedding and Trench Backfill

6.9 Trench Plugs

6.10 Grading

6.11 Modular Building Pads / Foundations

6.12 Concrete Sidewalks and Flatwork

6.13 Hot Mix Asphalt Pavement

6.14 Rigid Concrete Pavement

6.15 Site Drainage and Moisture Protection

7.0 FURTHER GEOTECHNICAL SERVICES

7.1 Plan and Specification Review

7.2 Testing and Observation Services

8.0 LIMITATIONS AND UNIFORMITY OF CONDITIONS

9.0 LIST OF REFERENCES

FIGURES

Figure 1, Vicinity Map Figure 2, Site Plan Figure 3, Proposed Development Plan Figure 4, Topographic Map Figure 5, Geologic Map Figure 6, Cross-Section A-A’ Figure 7, Cross-Section B-B’ Figure 8, Regional Fault Map Figure 9, Regional Seismicity Map Figure 10, FEMA Flood Hazard Map Figure 11, Dam Inundation Map

PHOTOGRAPHS

Photos 1 through 4

APPENDIX A

FIELD EXPLORATION PROGRAM

Figure A1, Key to Logs Figures A2 through A8, Logs of Exploratory Borings (B1 through B7)

APPENDIX B

LABORATORY TESTING PROGRAM

Table B1, Expansion Index Test Results Table B2, R-Value Test results Figure B1, Summary of Laboratory Results Figure B2, Atterberg Limits Figure B3, Grain Size Distribution Figure B4, Moisture-Density Relationship Figure B5, Unconfined Compressive Strength Results

Geocon Project No. S2980-05-02 - 1 - April 24, 2025

GEOTECHNICAL INVESTIGATION AND GEOLOGIC HAZARDS

EVALUATION

1.0 INTRODUCTION AND PURPOSE

This report presents the results of our geotechnical investigation and geologic hazards evaluation for the proposed modular classroom buildings and sanitary sewer line replacements for the California

Department of Forestry and Fire Protection (CAL FIRE) Ione Training Center located at 4501 California Highway 104 in Ione, California. The approximate site location is depicted on the Vicinity Map, Figure 1.

The purpose of our study was to evaluate the subsurface conditions at the site, provide design-level geotechnical recommendations for the project as presently proposed, and perform a Geologic Hazards

Evaluation that meets the requirements of the Division of the State Architect (DSA) Interpretation of Regulations (IR) A-4.13 that will be subsequently reviewed by the California Geological Survey (CGS).

1.1 Scope of Services

To prepare this report, we performed the following scope of services:

• Reviewed geologic maps and geotechnical reports in our files to aid in evaluating if geologic hazards are present at or near the site.

• Reviewed available design plans and conceptual layouts to select exploration locations.

• Performed a site reconnaissance to review project limits, determine equipment access, and mark out exploratory boring locations for subsequent utility clearance.

• Notified subscribing utility companies via Underground Service Alert (USA) a minimum of 48 hours (as required by law) prior to performing exploratory excavations at the site.

• Retained the services of a California C57-licensed drilling subcontractor to perform exploratory borings.

• Drilled seven exploratory borings (B1 through B7) by using a truck-mounted drilling rig equipped with hollow-stem auger drilling capabilities to depths ranging from approximately 16½ to 26 feet below existing grade.

• Logged the soils encountered in the borings in accordance with the Unified Soil Classification System (USCS).

• Obtained representative disturbed and relatively undisturbed soil samples from the exploratory borings and collected additional representative bulk samples outside of the exploratory borings.

Geocon Project No. S2980-05-02 - 2 - April 24, 2025

• Upon completion, the borings were backfilled with excess soil cuttings.

• Performed laboratory tests to evaluate pertinent geotechnical parameters.

• Prepared this report to summarize our findings, conclusions, and recommendations with respect to design and construction of the project.

Approximate locations of the exploratory borings are shown on the Site Plan, Figure 2, and Proposed

Development Plan, Figure 3. Details of our field exploration program including exploratory boring logs are presented in Appendix A. Details of our laboratory testing program and test results are summarized in Appendix B.

2.0 SITE AND PROJECT DESCRIPTION

2.1 Site Location and Description

The CAL FIRE training center facility is located on California Highway 104 approximately ¾-mile northwest of the intersection with California Highway 124 in Ione, California. The overall facility encompasses approximately 420 acres, the majority of which consists of a single parcel identified as Amador County

Assessor’s Parcel Number 004-290-006-000. The project site is located in the northeast portion of the facility campus and bounded to the north by Preston Reservoir and undeveloped land, beyond which is an industrial development; to the east by the historic Preston Castle and associated development; to the south by California Highway 104, beyond which is a residential subdivision; and, to the west by forestry surrounding Mule Creek, beyond which is the Mule Creek State Prison. The project site is currently developed with several dormitory, classroom, and office buildings (see Photos 1 and 2) and various improvements including a helipad, shade structures, pavement, gravel-paved parking areas, exterior concrete flatwork, and landscaping.

At the time of our field investigation in February of 2025, the portions of the site to be improved with a sanitary sewer line were developed with hot mix asphalt (HMA) pavement. The proposed sites for the new modular classrooms and bathroom were developed with gravel surfacing, concrete pads, and existing modular buildings. Site conditions on the dates of our investigation are shown in Photographs 1 through 4.

Based on our review of our previous report (Geocon, 2013) and historical imagery of the site (Google Earth, 1940 through 2025), we understand that the site was undeveloped prior to 1966, when the original training center was constructed. Original construction occurred in the central portion of campus, consisting of six buildings, several paved driving aisles, and a helipad. We understand that upgrades to the campus have been ongoing since 1984 and have continued through at least 2023. In our study area

Geocon Project No. S2980-05-02 - 3 - April 24, 2025 specifically, the access road appears to have been paved between 1998 and 2002. The site for the modular classroom and bathroom buildings was graded at a similar time and used as a storage and parking area until late 2009, when the existing concrete pads are visible. Existing modular buildings on the eastern portion of the proposed development are also visible after 2009. Existing modular buildings on the northern portion of the proposed development are visible in the 2023 photograph.

2.2 Current Topography

The site is surrounded by gently rolling topography. Based on topographic information provided by CAL FIRE, site elevations range from approximately 305 to 344 feet above mean sea level (MSL). The proposed footprints for the modular building pads are relatively flat from previous grading and range in elevation from approximately 320 to 325 MSL. Topography in the immediate surrounding area based on USGS mapping is shown on the Topographic Map, Figure 4. Site-specific topography is shown on the Site Plan and Proposed Development Plan, Figures 2 and 3.

2.3 Project Description

Based on the 50% Construction Design plans (BKF Engineers, 2023), the project consists of adding two new modular classroom buildings and one modular bathroom building within the northern portion of the site, totaling about 5,500 square feet. Structural plans were not available at the time this report was prepared. However, we understand that the modular buildings are expected to be supported on jack/wood block foundations bearing on compacted aggregate base (AB) material or HMA. The buildings will be constructed at-grade, without basements or other below-grade structures. The project also includes installing approximately 1,275 linear feet of new 12-inch-diameter sanitary sewer line.

The gravity sewer line will be buried approximately 6 to 10 feet below grade along the alignment. The area of the proposed modular buildings will require minor grading to achieve design grades with cuts and fills on the order of one to two feet, along with additional grading for the sewer line. This project will also include the construction of associated underground utility infrastructure, concrete exterior flatwork and asphalt and concrete paved parking areas. New pavement areas are indicated to consist of flexible HMA and/or rigid Portland cement concrete (PCC).

If project details differ from those described herein, we should be contacted to review the applicability of the conclusions and recommendations presented in this report.

Geocon Project No. S2980-05-02 - 4 - April 24, 2025

3.0 SOIL AND GEOLOGIC CONDITIONS

We identified soil and geologic conditions by reviewing referenced geologic literature (Section 9.0), observing exploratory borings, and performing geologic reconnaissance of the site and surrounding area. The soil descriptions provided in this report include the USCS symbol where applicable.

Our boring locations were selected based on the proposed improvements and limitations due to site access and existing utilities/improvements. We encountered relatively continuous soil and bedrock conditions in each of the seven borings throughout the site, as discussed below. The uniform soil and bedrock conditions encountered in our field exploration are considered representative of the subsurface profile at the site, including the proposed modular buildings and pipeline improvements.

3.1 Site and Regional Geology

Based on our review of published geologic maps, the site is located within the foothills of the Sierra Nevada geomorphic province. The Sierra Nevada is broadly characterized as a tilted fault block of massive granites and metamorphic rocks that extends almost 400 miles in length. The site is located within the Sierra Nevada’s western boundary, in which the metamorphic bedrock of the gold-bearing

Mother Lode is often overlain by alluvial sediments of the Great Valley geomorphic province. Published geologic mapping depicts the site vicinity is underlain primarily by the Eocene-age Ione Formation (map symbol Ei), which includes clay, sandstone, and siltstone with abundant quartz (Gutierrez et. al, 2016).

The late Jurassic Gopher Ridge Volcanics and the upper member of the Quaternary-age Modesto

Formation (map symbols Jgo and Qm2, respectively) are also mapped at the site, however we did not observe surficial evidence of these units and they were not encountered in our field exploration.

Subsurface conditions encountered during our field investigation at the site were generally consistent with the mapped geology of the area, indicative of residual soil as a result of the weathering of the Ione Formation overlying less weathered bedrock. A portion of the geologic map covering the site vicinity is presented as Figure 5, Geologic Map. Generalized geologic cross-sections of the site are presented as Figures 6 and 7.

3.2 Existing Pavement

We encountered existing pavement in each of our borings (B1 through B4) in the proposed sanitary sewer line alignment. Approximate pavement structural section material thicknesses are summarized in Table 3.2 below and shown on the boring logs (Appendix A).

Geocon Project No. S2980-05-02 - 5 - April 24, 2025

TABLE 3.2

EXISTING PAVEMENT SECTIONS

Boring Location

HMA1

thickness (inches)

AB2

thickness (inches)

Approximate Fill Thickness (feet)

B1 4 0 2½ B2 4 7 1½ B3 4 8 1 B4 4 11 0

Notes:

1. HMA = hot-mix asphalt AB = aggregate base material

3.3 Undocumented Fill

Borings B1 through B3 encountered approximately 1½ to 2½ feet of undocumented fill beneath existing pavements, generally consisting of medium dense, moist, brown, poorly graded gravel with sand and clay (GP). Additionally, we encountered approximately 4 feet of undocumented fill in Boring B7 beneath surficial gravel pavement, which generally consists of medium dense, reddish brown, clayey gravel with sand (GC). Based on its consistency and appearance, we assume that the fill in this location is native material that was reworked during site grading. In its current state, the existing fill is not suitable for support of new structures or additional fill and will require partial removal and replacement as engineered fill during site grading. Recommendations are provided herein.

3.4 Residual Soil

Beneath the pavement and undocumented fill (where encountered), we encountered residual soil in each of our exploratory borings to depths ranging from 3 to 7 feet below existing site grades.

The residual soil (soil that has been weathered in-place from rock) consisted of medium stiff to hard lean clay (CL), sandy lean clay (CL), and fat clay with sand (CH), with varying amounts of gravel in samples collected.

3.5 Ione Formation (Sandstone and Siltstone)

Beneath the residual soil, we encountered the Eocene-age Ione Formation (map unit Ei) to the maximum depth explored of approximately 26 feet. Where encountered, the Ione Formation exhibited relatively thin vertical bedding and generally consisted of clay, sandstone, and siltstone with varying degrees of weathering and prominent quartz inclusions (see Photos 3 and 4). The weathered sandstone generally excavates as poorly graded gravel with sand with clay (GP), and the weathered siltstone generally excavates as strongly cemented silt (ML). We met drilling refusal in Borings B5 and B6 on Ione

Geocon Project No. S2980-05-02 - 6 - April 24, 2025

Formation at depths of 16 and 26 feet, respectively. This formation is known to contain occasional deposits of smectite clay, which can be highly expansive. This is generally consistent with the results of our laboratory testing (see Section 5.1 and Appendix B).

Subsurface conditions described in the previous paragraphs are generalized. The exploratory boring logs included in Appendix A detail soil type, color, moisture, consistency, and USCS classification of the soils encountered at specific locations and depths.

4.0 GROUNDWATER

Free groundwater was not encountered during our field investigation on February 26, 2025. However, we encountered perched groundwater/seepage within the Ione Formation in Boring B5 at a depth of approximately 20 feet below ground surface (approximate elevation 302 feet above MSL). The water did not appear to appreciably accumulate prior to completion and backfilling of the boring.

We reviewed available depth to groundwater data from an existing monitoring well (AWA Col MW-1A) located approximately one mile south-southwest of the site, published on the California Department of Water Resources (DWR) Water Data Library Station Map (WDL)

(https://wdl.water.ca.gov/waterdatalibrary/Map.aspx). Data available on the website indicates that depth to groundwater at the well was measured at elevations ranging from approximately 257 to 265 feet MSL between December of 2014 and April of 2024, corresponding to a depth of approximately 55 to 63 feet below the proposed modular buildings. The site is within the vicinity of Mule Creek, which passes through the central portion of the site. At the time of our field explorations, this portion of Mule Creek was dry, and we interpret this to be an ephemeral stream lying above the permanent groundwater table. Based on this information and for the purposes of our evaluations, we consider the historic high groundwater depth at the site to be 55 feet.

Although the static groundwater table is likely relatively deep, based on site geology and our field observations, perched groundwater/seepage likely develops at shallow depths near the contacts between fill/residual soil and formational material (bedrock), especially during winter and spring.

Seepage can also occur within formational material based on the degree of weathering, fracturing, and jointing. The occurrence of seepage is dependent on seasonal precipitation, irrigation, and land use, among other factors, and varies as a result. Proper surface and subsurface drainage provisions will be important to future performance of the project. Conclusions, recommendations, and construction considerations with respect to seepage are included in subsequent sections of this report.

Geocon Project No. S2980-05-02 - 7 - April 24, 2025

It should be noted that fluctuations in the level of groundwater may occur due to variations in precipitation, temperature, and other factors. Depth to groundwater can also vary significantly due to localized pumping, irrigation practices, subsurface soil conditions, and seasonal fluctuations. Therefore, it is possible that groundwater may be higher or lower than the levels observed during our investigation.

5.0 GEOLOGIC HAZARDS

5.1 Mapped Geologic Hazard Zones

According to our review of the CGS Information Warehouse website, (https://maps.conservation.ca.gov/cgs/informationwarehouse/regulatorymaps/) as well as other published literature, the site is not located within a mapped geologic hazard zone associated with seismic hazards, landslides, liquefaction, tsunami/seiche, or surface fault rupture.

5.2 Regional Active Faults / Surface Fault Rupture Hazard

The numerous faults in California include Holocene-active, pre-Holocene (Quaternary), and inactive faults (pre-Quaternary). The criteria for these major groups were developed by the California Geological Survey (CGS, formerly known as the California Division of Mines and Geology) for the Alquist-Priolo

Earthquake Fault Zone Program (CGS, 2018). By definition, a Holocene-active fault is one that has had surface displacement within Holocene time (about the last 11,700 years).

A pre-Holocene fault has demonstrated surface displacement during Quaternary time (approximately the last 1.6 million years) but has had no known Holocene movement. Faults that have not moved in the last 1.6 million years are considered inactive.

The site is not within a state-designated Alquist-Priolo Earthquake Fault Zone for surface fault rupture hazards (CGS, 2024). No Holocene-active or pre-Holocene faults with the potential for surface fault rupture are known to pass directly beneath the site. Therefore, the potential for surface rupture due to faulting occurring beneath the site during the design life of the proposed development is considered low.

According to the Fault Activity Map of California by the California Geological Survey (CGS, https://maps.conservation.ca.gov/cgs/fam/), the closest fault with historic displacement is the

Greenville Fault, which ruptured in 1980 about 59 miles southwest of the site. According to the United States Geological Survey’s 2008 National Seismic Hazard Map, (USGS, 2024a, https://earthquake.usgs.gov/cfusion/hazfaults_2008_search/) the closest mapped Holocene-active fault is the Cordelia Fault within the Cordelia Fault system, located about 65 miles northeast of the site. The closest mapped pre-Holocene (Quaternary) fault to the site is the Ione Fault within the Foothills fault system, located approximately 2 miles south of the site. Based on the CGS Fault

Geocon Project No. S2980-05-02 - 8 - April 24, 2025

Activity Map and the USGS National Seismic Hazard Maps website (https://earthquake.usgs.gov/cfusion/hazfaults_2008_search/query_main.cfm), Table 5.2 lists faults and fault systems within 70 miles of the site that are considered capable of producing earthquakes with a moment magnitude (MW) of 6.5 or greater. Additional faults within the vicinity of the site are shown in the Regional Fault Map, Figure 8.

TABLE 5.2

FAULT SYSTEMS WITHIN 70 MILES OF THE SITE

Fault Name Approximate Distance Maximum Earthquake

Magnitude (Mw) Miles Foothills Fault System

Ione Fault

2.0 6.5

Foothills Fault System Waters Peak Fault

6.8 6.5

Foothills Fault System Youngs Creek Fault

6.6 6.5

Foothills Fault System Haupt Creek Fault

10.8 6.5

Foothills Fault System Poorman Gulch Fault

11.5 6.5

Great Valley 7 54.1 6.9 Great Valley 5

Pittsburg Kirby Hills

54.6 6.7

Great Valley 4b Gordon Valley

54.9 6.8

Great Valley 4a Trout Creek

58.5 6.6

West Tahoe 58.5 7.1 Greenville Connected 59.0 7.0

Great Valley 3 Mysterious Ridge

64.0 7.1

Carson Range Kings Canyon fault

64.8 7.2

Carson Range fault 64.8 7.1 Mount Diablo Thrust 65.2 6.7

Green Valley Connected 65.4 6.8 Great Valley 8 65.5 6.8

Hunting Creek-Berryessa 68.4 7.1 Calaveras 69.5 7.0

Geocon Project No. S2980-05-02 - 9 - April 24, 2025

5.3 Seismicity

As with all of California, the site has experienced historic earthquakes from various regional faults, although the local site region has a history of relatively low seismicity in comparison with more active seismic regions such as the San Francisco Bay Area or southern California.

An examination of available historic data from the California Geological Survey’s Historical Earthquake Online Database (CGS, https://maps.conservation.ca.gov/cgs/historicearthquakes/) suggests that the site may have experienced ground shaking equivalent to Modified Mercalli Intensity (MMI) of IV. The most intense earthquake ground shaking likely resulted from an earthquake north of Vacaville on April 19, 1892, with an epicenter located approximately 56 miles west of the site. The earthquake had approximate Richter Scale Magnitudes of 6.6 and was felt as far away as Red Bluff to the north, and Salinas to the south. Additionally, an earthquake occurred on April 30, 1892, with an epicenter about 51 miles southeast of the site. The earthquake had an approximate Richter Scale Magnitude of 5.6 and resulted in ground shaking in the site vicinity equivalent to a Modified Mercalli Intensity (MMI) of II.

Additional earthquakes in the vicinity of the site are shown in the Regional Seismicity Map, Figure 9.

We used the USGS Unified Hazard Tool (USGS, 2024b) to determine the deaggregated seismic source parameters including controlling magnitude and fault distance. The USGS estimated modal magnitude is 5.5 and the estimated Peak Ground Acceleration (PGA) for the Maximum Considered Earthquake (MCE) is 0.20g with a 2,475-year return period.

While listing PGA is useful for comparison of potential effects of fault activity in a region, other considerations are important in seismic design, including frequency and duration of motion and soil conditions underlying the site. The site could be subjected to ground shaking in the event of an earthquake along the faults mentioned above or other area faults.

5.4 Liquefaction / Cyclic Softening and Seismic Settlement

Liquefaction is a phenomenon in which loose, saturated, cohesionless soil deposits located beneath the groundwater table lose strength when subjected to intense and prolonged ground shaking. The seismic excitation increases pore water pressure creating a buoyant effect of the loose soil. When liquefaction occurs, building foundations may sink or tilt and differential ground settlement may occur. Other effects may include sand boils (ground loss) and lateral spreading if the liquefiable soil is located adjacent to a steep free face. The areas that have the greatest potential for liquefaction are those in which the water table is less than 50 feet below ground surface and the soils are predominately clean, poorly graded sand deposits of loose to medium-dense relative density. Similar to liquefaction of granular (sandy) soil, silt and clay may undergo strength loss due to seismic shaking. This phenomenon is termed “cyclic softening.”

Geocon Project No. S2980-05-02 - 10 - April 24, 2025

The site is not located in a currently established State of California Seismic Hazard Zone for liquefaction.

Based on the subsurface conditions encountered at the site, including shallow bedrock and a lack of groundwater in the upper 50 feet, liquefaction is not a hazard for the site. Mitigation and specific design measures with respect to liquefaction are not necessary for the project.

5.5 Lateral Spreading

Because the site topography is generally flat and level from previous grading activities and there is no adjacent free-face or sloping geometry, lateral spreading resulting from liquefaction is not anticipated and is not considered to be a hazard for the site.

5.6 Unsaturated Seismic Settlement

Strong seismic shaking can induce settlement of unsaturated, loose sandy soil. Based on the results of our subsurface investigation, the soil above the historic high groundwater depth includes dense to very dense gravels and hard clay and sandy silt. Therefore, unsaturated seismic settlement is not a significant hazard for the site.

5.7 Landslides and Slope Stability

The site has not been evaluated with respect to seismic landslide hazard by CGS, and no landslide data are available on the California Department of Conservation interactive Landslide Inventory map (https://maps.conservation.ca.gov/cgs/lsi/). The site is relatively flat and level from previous grading activities and there are no significant slopes on or adjacent to the site. Therefore, landslides and slope instability are not hazards for the site.

5.8 Tsunamis and Seiches

The site is located approximately 118 miles from the Pacific Ocean and is not located near any large body of water. Therefore, tsunamis (seismic sea waves) or seiches (wave oscillations in an enclosed or semi-enclosed body of water) are not hazards for the site at this time.

5.9 Flooding and Dam Failure Inundation

Based on the Flood Hazard Zone Layer from the National Flood Hazard Database prepared by the Federal

Emergency Management Agency (FEMA) (https://hazards-fema.maps.arcgis.com/home/index.html), the site is within an “area of minimal flood hazard” (FEMA, 2010). Therefore, flooding is not considered to be a hazard for the site.

Geocon Project No. S2980-05-02 - 11 - April 24, 2025

Based on the California Division of Safety of Dams (DSOD) California Dam Breach Inundation Map Web Publisher (DWR, https://fmds.water.ca.gov/webgis/?appid=dam_prototype_v2), a portion of the site is located within the inundation zone of Preston Reservoir, which has a hazard classification of “high” and is approximately 300 feet east of the site. While the inundation boundary is mapped just south of and outside the proposed modular buildings, the proposed pipeline improvements are within the inundation boundary (see Figure 11). Although the proposed buildings are outside the inundation boundary, these conditions should be reviewed and considered during development of final grading plans.

5.10 Expansive Soil

Laboratory Atterberg Limits and Expansion Index tests on near surface soil samples indicate moderate to high plasticity and corresponding medium to high expansion potential (Appendix B). In addition, the site is underlain by Ione Formation bedrock, which is known to have occurrences of smectite clay, which can latently exhibit high expansion potential despite the apparent granular soil texture. Re-working of these soils during earthwork/grading/compaction and subsequent wetting/drying cycles can increase expansion potential. As such, specific mitigation measures for the project are provided in this report.

5.11 Soil Corrosion Screening

We performed pH, resistivity, chloride, and sulfate tests on one sample to generally evaluate the corrosion potential of the soil with respect to proposed subsurface structures. These tests were performed in accordance with California Test Method (CTM) Nos. 643, 422, and 417. The results are presented in Table 5.11A and should be considered for design of underground structures.

TABLE 5.11A

SOIL CORROSION PARAMETER TEST RESULTS

(CALIFORNIA TEST METHODS 643, 417, AND 422)

Sample No.

Sample Depth

(ft.)

pH

Minimum Resistivity (ohm-cm)

Chloride (ppm)

Sulfate (ppm)

B2-10.5 10.5 7.5 2,140 6.6 77.6 Note: ppm = parts per million; ohm-cm – Ohm centimeters

Soil with a low pH (higher acidity) is considered corrosive as it can react with lime in cement to leach out soluble reaction products and result in a more porous and weaker concrete. Per Caltrans Corrosion Guidelines (Caltrans, 2021), soil with a pH of 5.5 or lower may be corrosive to concrete or steel in contact with the ground.

Geocon Project No. S2980-05-02 - 12 - April 24, 2025

Soil resistivity is the measure of the soil’s ability to transmit electric current. Corrosion of buried ferrous metal is proportional to the resistivity of the soil. A lower resistivity indicates a higher propensity for transmitting electric currents that can cause corrosion of buried ferrous metal items. In general, the higher the resistivity, the lower the rate for corrosion. Per Caltrans Corrosion Guidelines (Caltrans, 2021), resistivity serves as an indicator parameter for the possible presence of soluble salts and it is not included as a parameter to define a corrosive area for structures. A minimum resistivity value for soil less than 1,500 ohm-cm may indicate the presence of high quantities of soluble salts and a higher propensity for corrosion. Based on the laboratory minimum resistivity test results and Caltrans criteria, soil at the location tested does not have a higher propensity for corrosion.

Table 5.11B presents a summary of concrete requirements set forth by the California Building Code (CBC)

Section 1904 and American Concrete Institute (ACI) 318 for possible chloride exposure. Chlorides can break down the protective oxide layer on steel surfaces resulting in corrosion. Sources of chloride include, but are not limited to, deicing chemicals, salt, brackish water, seawater, or spray from these sources.

TABLE 5.11B

REQUIREMENTS FOR CONCRETE EXPOSED TO CHLORIDE-CONTAINING SOLUTIONS

(AFTER ACI 318 TABLES 19.3.1.1 and 19.3.2.1)

Chloride Severity

Exposure Class Condition

Maximum Water to Cement Ratio by Weight

Minimum Compressive Strength (psi)

Not Applicable C0 Concrete dry or protected from moisture N/A 2,500

Moderate C1 Concrete exposed to moisture but not to external sources of chlorides N/A 2,500

Severe C2 Concrete exposed to moisture and an external source of chlorides 0.40 5,000

Note: psi = Pounds per square inch

The appropriate Chloride Severity/Exposure Class should be determined by the project designer based on the specific conditions at the location of the proposed improvements. Further guidance is provided in ACI 318. Per Caltrans Corrosion Guidelines, soil with a chloride concentration of 500 ppm or higher may be corrosive to steel structures or steel reinforcement in concrete. Based on Caltrans criteria, soil at the locations tested is not corrosive with respect to chloride content.

Table 5.11C presents a summary of concrete requirements set forth by CBC Section 1904 and ACI 318 for sulfate exposure. Similar to chlorides, sulfates can break down the protective oxide layer on steel leading to corrosion. Sulfates can also react with lime in cement to soften and crack concrete.

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TABLE 5.11C

REQUIREMENTS FOR CONCRETE EXPOSED TO SULFATE-CONTAINING SOLUTIONS

(AFTER ACI 318 TABLES 19.3.1.1 and 19.3.2.1)

Sulfate Severity

Exposure Class

Water-Soluble Sulfate (SO4) Content

Cement Type

(ASTM

C 150)

Maximum Water to Cement Ratio by Weight1

Minimum Compressive

Strength (psi)

Percent By Mass

Parts Per Million (ppm)

Not Applicable S0 SO4 < 0.10 SO4 < 1,000 No Type

Restriction N/A 2,500

Moderate S1 0.10 < SO4 <

0.20 1,000 < SO4 < 2,000 II 0.50 4,000

Severe S2 0.20 < SO4 < 2.00

2,000 < SO4 <

20,000 V 0.45 4,500

Very Severe S3 SO4 > 2.00 SO4 > 20,000 V+Pozzolan or Slag 0.45 4,500

Notes:

1. Maximum water to cement ratio limits are different for lightweight concrete, see ACI 318 for details.

Based on the laboratory test results, the Sulfate Severity is classified as “Not Applicable”, and the Exposure Class is S0. The concrete mix design(s) should be developed accordingly. The presence of water-soluble sulfates is not a visually discernible characteristic; therefore, other soil samples from the site could yield different concentrations. Additionally, over time landscaping activities (i.e., addition of fertilizers and other soil nutrients) may affect the concentration.

Geocon does not practice in the field of corrosion engineering and the above information is provided as screening criteria only. If corrosion sensitive improvements are planned, we recommend that further evaluations by a corrosion engineer be performed to incorporate the necessary precautions to avoid premature corrosion on buried metal pipes and metal or concrete structures in direct contact with the soils.

5.12 Volcanic Activity

The nearest active volcanic area to the site is the Mono Lake Volcanic Field, located approximately 106 miles southeast of the site (USGS, 2025). Due to the distance between the site and the nearest volcanic field, the potential for direct impacts to the site due to regional volcanic activity is low.

5.13 Naturally Occurring Asbestos

The site is not located within an area mapped as an ultramafic rock unit, former asbestos mine, historic asbestos prospect, or other reported occurrence of asbestos in California. Naturally occurring asbestos (NOA) minerals (i.e. chrysotile, tremolite, actinolite, crocidolite, anthophyllite, and amosite)

Geocon Project No. S2980-05-02 - 14 - April 24, 2025 are more likely to be encountered in areas with ultramafic rocks or sheared metavolcanic rocks due to metamorphic processes. The site is not within an area of known mapped NOA occurrence (Van Gosen and Clinkenbeard, 2011). Based on the site geology, which consists of sedimentary bedrock and residual soil, the likelihood of NOA being present at the site is considered to be low.

5.14 Oil Fields & Methane Zones

Based on a review of the California Geologic Energy Management Division (CalGEM) online mapping system, the Lodi gas field is located approximately 17 miles southwest of the site. No oil or gas wells are mapped in the immediate vicinity of the site (CalGEM, 2025), the closest being a plugged dry gas well located approximately 6 miles south of the site. Due to the voluntary nature of record reporting by the oil and gas well drilling companies, wells may be improperly located or not shown on the location map. Other wells could be encountered during construction. Any wells encountered would need to be properly abandoned in accordance with the current requirements of CalGEM.

5.15 Radon

The United States Environmental Protection Agency’s (USEPA) Map of Radon Zones (USEPA, 2021) depicts the radon potential in each U.S. County. Areas in Zone 1 have the highest radon potential, and those in Zone 3 have the lowest. Amador County is depicted on the map in Zone 2 (i.e., moderate potential). According to the California Department of Conservation study area for indoor radon potential (2024), the site is mapped as having a moderate potential. Moderate potential is further described as a risk of 5 to 19.9% of home indoor radon measurements are likely exceeding the USEPA action limit of 4 picocuries per liter. Therefore, there is moderate potential for radon at the site.

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6.0 CONCLUSIONS AND RECOMMENDATIONS

The following discussion summarizes our findings and presents our conclusions based on the results of our geotechnical investigation including literature review, site observations, subsurface exploration, laboratory testing results, and engineering analysis.

6.1 General

6.1.1 No soil or geologic conditions were encountered during our investigation that would preclude construction of improvements at the site as planned, provided the recommendations contained in this report are incorporated into the design and construction of the project.

6.1.2 Based on our findings, evaluation, and analyses to date, we have identified the following geotechnical constraints for the site:

• Undocumented Fill: Fill material of variable thickness is present in portions of the site.

Since we do not know the placement and compaction history of undocumented fill, if/where present, it is not suitable for support of proposed structures or additional fill.

Therefore, fill material will need to be partially removed and re-compacted within proposed building areas. Specific recommendations are provided in this report.

• Existing Pavement, Structures, and Utilities: The site currently contains existing modular buildings with associated improvements in the northern portion of the site. Existing pavements, foundations, and utilities in conflict with the proposed improvements will need to be completely removed. Existing undocumented fill associated with existing utilities and foundations will need to be removed to expose undisturbed native soil.

Specific recommendations are provided in this report.

• Expansive Soil: Highly expansive soils are present beneath the site. Proper soil moisture conditioning, compaction and surface drainage are recommended to reduce the shrink-swell potential of the site soils and reduce the potential for adverse post-construction impacts on proposed improvements. A layer of low-expansive material will be required beneath interior slabs-on-grade (if any) and exterior flatwork.

6.1.3 Conclusions and recommendations provided in this report are based on our review of referenced literature, analysis of data obtained from our exploratory borings, laboratory testing program, and our understanding of the proposed development at this time. Geocon should be retained to review the project plans as they develop further, provide engineering consultation as needed during final design, and perform geotechnical observation and testing services during construction.

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6.2 Seismic Site Classification / Seismic Design Parameters

6.2.1 Seismic design of the structure should be performed in accordance with the provisions of the

2022 CBC which is based on the American Society of Civil Engineers (ASCE)/Structural Engineering Institute (SEI) publication: ASCE/SEI 7-16, Minimum Design Loads and Associated

Criteria for Buildings and Other Structures (ASCE/SEI, 2017). We used the Structural Engineers Association of California (SEAOC) and Office of Statewide Health Planning and

Development (OSHPD) web application Seismic Design Maps (https://seismicmaps.org/) to evaluate site-specific seismic design parameters in accordance with ASCE 7-16.6.2.2.

6.2.2 For seismic design purposes, sites are classified as Site Class “A” through “F” as follows:

• Site Class A – Hard Rock;

• Site Class B – Rock;

• Site Class C – Very Dense Soil and Soft Rock;

• Site Class D – Stiff Soil;

• Site Class E – Soft Clay Soil; and

• Site Class F – Soils Requiring Site Response Analysis.

6.2.3 We evaluated seismic Site Class in accordance with Chapter 20 of ASCE 7-16. Based on the subsurface conditions at the site and measured penetration resistance in our borings, the average shear wave velocity for the upper 30 meters of soil (Vs30) is estimated to be 783 feet per second. Therefore, the site is classified as Site Class “C” (Very Dense Soil and Soft Rock) per Table 20.3-1 of ASCE 7-16.

6.2.4 For the purposes of evaluating code-based seismic parameters for design, we assumed a seismic Risk Category IV (per the CBC) for the project. Results are summarized in Table 6.2.4.

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TABLE 6.2.4

ASCE 7-16 SEISMIC DESIGN PARAMETERS

SITE CLASS “C” – VERY DENSE SOIL AND SOFT ROCK

Parameter Value ASCE 7-16 Reference MCER Ground Motion Spectral Response

Acceleration – Class B (short), SS 0.383g Figure 22-1

MCER Ground Motion Spectral Response Acceleration – Class B (1 sec), S1 0.200g Figure 22-2

Site Coefficient, FA 1.300 Table 11.4-1 Site Coefficient, FV 1.500 Table 11.4-2

Site Class Modified MCER Spectral Response Acceleration (short), SMS

0.498g Eq. 11.4-1

Site Class Modified MCER Spectral Response Acceleration (1 sec), SM1 0.299g Eq. 11.4-2

5% Damped Design Spectral Response Acceleration (short), SDS

0.332g Eq. 11.4-3

5% Damped Design Spectral Response Acceleration (1 sec), SD1 0.200g Eq. 11.4-4

6.2.5 Table 6.2.5 presents additional seismic design parameters for projects with Seismic Design

Categories of D through F in accordance with ASCE 7-16 for the mapped maximum considered geometric mean (MCEG).

TABLE 6.2.5

ASCE 7-16 SITE ACCELERATION DESIGN PARAMETERS

Parameter Value ASCE 7-16 Reference Mapped MCEG Peak Ground Acceleration, PGA 0.162g Figure 22-7

Site Coefficient, FPGA 1.238 Table 11.8-1 Site Class Modified MCEG Peak Ground

Acceleration, PGAM 0.200g Section 11.8.3 (Eq. 11.8-1)

6.2.6 Conformance to the criteria presented in Tables 6.2.4 and 6.2.5 for seismic design does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur if a maximum level earthquake occurs. The primary goal of seismic design is to protect life and not to avoid structural damage, as such design may be economically prohibitive.

6.3 Soil and Excavation Characteristics

6.3.1 Grading and excavations at the site may be accomplished with standard to moderate effort using heavy-duty grading/excavation equipment.

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6.3.2 Temporary excavations deeper than 4 feet and entered by workers must meet Cal-OSHA requirements, as appropriate. Excavation sloping, benching, the use of trench shields, and the placement of trench spoils should conform to the latest applicable Cal-OSHA standards.

The contractor should have a Cal-OSHA-approved “competent person” onsite during excavation to evaluate trench conditions and to make appropriate recommendations where necessary. It is the contractor’s responsibility to provide sufficient and safe excavation support, as well as to protect nearby utilities, structures, and other improvements that may be damaged by earth movements.

6.3.3 The excavation support recommendations provided by Cal-OSHA are generally geared towards protecting human life and not necessarily towards preventing damage to nearby structures or surface improvements. The contractor should be responsible for using the proper active shoring systems or sloping to prevent damage to any structure or improvements near underground excavations.

6.3.4 Some project excavations will be adjacent to other existing utilities. The condition of existing utility backfill is not known and there is a potential for existing backfill (particularly granular backfill) adjacent to excavations which can cause excavation sidewall instability and sloughing. The contractor should be aware of the potential for sloughing (and possibly caving/undermining of adjacent ground surface or improvements) and have equipment readily available to flatten slopes or install shoring if necessary.

6.3.5 Project excavations must be conducted in such a manner that potential surcharges from existing structures, construction equipment, and vehicle loads are resisted. The surcharge area may be defined by a 1H:1V projection down and away from the surcharging object.

Penetrations below this 1H:1V projection will require special excavation measures or shoring.

6.3.6 Permanent cut and fill slopes should be constructed no steeper than 2H:1V (horizontal to vertical). To mitigate potential erosion, slopes should be vegetated as soon as possible and surface drainage should be directed away from tops of slopes.

6.3.7 If grading occurs during or after the wet season (typically winter and spring), or in periods of precipitation, in-place and excavated soils will likely be wet. Earthwork contractors should be aware of moisture sensitivity of the near-surface clayey soils and potential compaction/workability difficulties.

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6.3.9 Based on laboratory testing, in-situ moisture content of site soils ranges from approximately 12% to 33% and is generally higher than optimum moisture content for this material

(optimum moisture is approximately 7% to 9%). Due to the fine-grained nature of the soils and measured in-situ moisture contents above optimum, additional drying efforts to attain moisture contents suitable for compaction should be anticipated regardless of the time of year. Mitigation alternatives may include aerating/drying the exposed soils (assuming favorable weather conditions), or chemical treatment (e.g., lime treatment). Unstable excavation bottoms may require over-excavating 12 to 18 inches and placing geotextile fabric/geogrid covered with aggregate, for stabilization. We can provide specific recommendations during construction, based on conditions encountered.

6.3.10 Earthwork operations in these conditions will likely be difficult with low productivity. Often, a period of at least one month of warm and dry weather is necessary to allow the site to dry sufficiently so that heavy grading equipment can operate effectively. In addition, soil below existing pavements is often wet, regardless of the time of year. Conversely, during dry summer and fall months, dry clay soils may require additional grading effort (discing, mixing, or other means) to attain proper moisture conditioning.

6.4 Materials for Fill Seepage, Groundwater, and

6.4.1 From a geotechnical perspective, excavated soils generated from cut operations at the site are suitable for use as general fill below the upper 12 inches of subgrade, provided they do not contain deleterious matter, organic material, or rock/cobble/cementations larger than 6 inches in maximum dimension. Onsite soils reused as engineered fill will require proper moisture conditioning and processing. All material used as fill should have an organic content of 3 percent by dry weight or less.

6.4.2 Excavated native and fill soil along the pipeline alignment will also be suitable for reuse as general trench backfill which is defined as the area 12 inches above the top of pipe to the bottom of the pavement section subgrade (where present) provided it does not contain deleterious matter, debris, organic material, rock or cementations larger than 3 inches in maximum dimension.

6.4.3 Based on our laboratory test results, moisture content of excavated soils may be on the order of 10% or more above optimum moisture content. Therefore, considerable drying will likely be necessary to achieve proper compaction when reused as backfill. We recommend performing excavation and backfill operations during the dryer months of the year to aid in soil drying.

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