Parkfield_FS_Geotech_Investigation_and_Geologic_Hazards_Eval.pdf

GEOTECHNICAL INVESTIGATION

AND GEOLOGIC HAZARDS

EVALUATION

PROPOSED PARKFIELD FIRE

STATION

70331 VINEYARD CANYON ROAD

PARKFIELD, CALIFORNIA

PREPARED FOR

DEPARTMENT OF FORESTRY AND FIRE

PROTECTION (CAL-FIRE)

SACRAMENTO, CALIFORNIA

PROJECT NO. S9962-05-23

JULY 27, 2018

Project No. S9962-05-23 July 27, 2018

Mr. Ashok Jain Department of Forestry and Fire Protection (CAL FIRE) Technical Services Section 1300 U Street Sacramento, CA 95818

Subject: GEOTECHNICAL INVESTIGATION AND

GEOLOGIC HAZARDS EVALUATION

PROPOSED PARKFIELD FIRE STATION

70331 VINEYARD CANYON ROAD

PARKFIELD, CALIFORNIA

Dear Mr. Jain:

In accordance with your authorization of Task Order No. 16 of Agreement No. 3178335, we have performed a geotechnical investigation for the proposed Parkfield Fire Station located at 70331 Vineyard Canyon Road in the City of Parkfield, California. The accompanying report presents the findings of our study, and our conclusions and recommendations pertaining to the geotechnical aspects of proposed design and construction. Based on the results of our geotechnical investigation, it is our opinion that the site can be developed as proposed, from a geotechnical standpoint, provided the recommendations of this report are followed and implemented during design and construction.

The site is located in close proximity to the main strand of the San Andreas Fault Zone and adjacent to the boundaries of a state-designated Alquist-Priolo Earthquake Fault Zone. A site-specific fault rupture hazard investigation should be conducted to identify if such hazards exist at the site prior to construction of the proposed project.

If you have any questions regarding this report, or if we may be of further service, please contact the undersigned.

Very truly yours, GEOCON CONSULTANTS, INC.

Rex Panoy Staff Engineer

Jeremy Zorne

GE 2636

Gerald A. Kasman

CEG 2251

(EMAIL) Addressee

TABLE OF CONTENTS

1. PURPOSE AND SCOPE

2. BACKGROUND REVIEW

3. SITE AND PROJECT DESCRIPTION

4. GEOLOGIC SETTING

5. SOIL AND GEOLOGIC CONDITIONS

5.1 Tilled Soil

5.2 Undifferentiated Alluvial and Colluvial Deposits

6. GROUNDWATER

7. GEOLOGIC HAZARDS

7.1 Surface Fault Rupture

7.2 Seismicity

7.3 Ground Motion Hazard Analysis

7.3.1 Probabilistic Seismic Hazard Analysis

7.3.2 Deterministic Seismic Hazard Analysis

7.3.3 Site-Specific Response Spectrum

7.3.4 Mapped Acceleration Parameters

7.3.5 Site-Specific Seismic Design Criteria

7.3.6 Site-Specific Peak Ground Acceleration

7.3.7 Deaggregated Seismic Source Parameters

7.4 Liquefaction Potential

7.5 Seismically-Induced Settlement

7.6 Slope Stability

7.7 Earthquake-Induced Flooding

7.8 Tsunamis, Seiches, and Flooding

7.9 Oil Fields & Methane Potential

7.10 Naturally Occurring Asbestos

7.11 Subsidence

7.12 Radon

7.13 Volcanic Eruption

7.14 Hydro Consolidation

7.15 Expansive Soil

8. CONCLUSIONS AND RECOMMENDATIONS

8.1 General

8.2 Soil and Excavation Characteristics

8.3 Minimum Resistivity, pH, and Water-Soluble Sulfate

8.4 Grading

8.5 Shrinkage

8.6 General Foundation Design

8.7 Conventional Foundation Design – Fire Station and Support Structures

8.8 Conventional Foundation Design – Water Storage Tank

8.9 Mat Foundation Design – Water Storage Tank

8.10 Lateral Design

8.11 Concrete Slabs-on-Grade

8.12 Preliminary Pavement Recommendations

8.13 Retaining Wall Design

8.14 Retaining Wall Drainage

8.15 Temporary Excavations

8.16 Surface Drainage

8.17 Plan Review

TABLE OF CONTENTS (Continued)

LIMITATIONS AND UNIFORMITY OF CONDITIONS

LIST OF REFERENCES

MAPS, TABLES, AND ILLUSTRATIONS

Figure 1, Vicinity Map Figure 2, Site Plan Figure 3, Local Geologic Map Figure 4 Alquist-Priolo Earthquake Fault Zone Map Figure 5, Regional Fault Map Figure 6, Regional Seismicity Map Figures 7 and 9, Ground Motion Hazard Analysis Figures 10 and 11, DE Evaluation of Earthquake-Induced Settlements Figures 12 and 13, MCE Evaluation of Earthquake-Induced Settlements Figures 14 and 15, Empirical Estimation of Seismically Induced Settlement Figures 16 and 17, Retaining Wall Drainage Detail

APPENDIX A

FIELD INVESTIGATION

Figures A1 through A4, Boring Logs

APPENDIX B

LABORATORY TESTING

Figures B1 and B2, Direct Shear Test Results Figures B3 through B6, Consolidation Test Results Figure B7, Atterberg Limit Test Figure B8, Grain Size Analysis Figure B9, Lab Test Results Figure B10, Corrosivity Test Results

APPENDIX C

Preliminary Geological Hazards Letter by The California Geological Survey (CGS)

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GEOTECHNICAL INVESTIGATION AND GEOLOGIC HAZARDS EVALUATION

1. PURPOSE AND SCOPE

This report presents the results of a geotechnical investigation for the proposed Parkfield Fire Station located at 70331 Vineyard Canyon Road in the town of Parkfield, California (see Vicinity Map, Figure

1). The purpose of the investigation was to evaluate subsurface soil and geologic conditions underlying the site and, based on conditions encountered, to provide conclusions and recommendations pertaining to the geotechnical aspects of design and construction.

The scope of this investigation included a site reconnaissance, field exploration, laboratory testing, engineering analysis, and the preparation of this report. The site was explored on May 11, 2018, by excavating four 8-inch diameter borings (B1 through B4) to depths of approximately 50½ and 15½ feet below the existing ground surface using a truck-mounted hollow-stem auger drilling machine.

The approximate locations of the exploratory borings are depicted on the Site Plan (see Figure 2).

A detailed discussion of the field investigation, including boring logs, is presented in Appendix A.

Laboratory tests were performed on selected soil samples obtained during the investigation to determine pertinent physical and chemical soil properties. Appendix B presents a summary of the laboratory test results.

The recommendations presented herein are based on analysis of the data obtained during the investigation and our experience with similar soil and geologic conditions. References reviewed to prepare this report are provided in the List of References section.

If project details vary significantly from those described herein, Geocon should be contacted to determine the necessity for review and possible revision of this report.

2. BACKGROUND REVIEW

As a part of the preparation of this report, we reviewed the prior letter performed by The California

Geological Survey (CGS) provided to us by the Client:

Preliminary Geological Hazards Investigation of the Parkfield Fire Station prepared by the California Geological Survey dated September 14, 2017.

Based on our review the letter, the subject site was explored by CGS on June 20, 2017, to obtain preliminary shallow subsurface information. Three test pits (TP-1 though TP-3) were conducted to a maximum depth of 8 feet below the ground surface. Groundwater was not encountered during the test pit excavations. Additionally, shallow percolation testing was performed at six locations (PT-1 through

PT-6) within the proposed leach field area on June 21, 2017. CGS concluded and recommended the evaluation of surface fault rupture associated faults (mapped and unmapped) that may extend across the site, evaluation of the liquefaction potential of the underlying soil below structures, and potential expansive soils. A copy of the letter is provided herein in Appendix C.

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3. SITE AND PROJECT DESCRIPTION

The subject site is located at 70331 Vineyard Canyon Road in the town of Parkfield, California.

The subject site is a 38-acre parcel of land that is bisected by Vineyard Canyon Road. The majority of the site lies south of Vineyard Canyon road and is relatively flat-lying vacant land used for agriculture.

The area north of the road is gently sloping to the south and currently occupied with a single-family residential structure and appurtenant structures. Vegetation in the area of the site consists of grass, shrubs and localized trees.

Based on the information provided by the Client, it is our understanding that the proposed project will be sited on the south side of the parcel within the relatively flat vacant land. The project will consist of the construction of a fire station building consisting of apparatus and living quarters, a generator and pump building, a well house, a water storage tank (storage capacity of 50,000 gallons), and other support structures. The main building will be occupied more than 2,000 man-hours per year and is considered habitable structure per the California Administrative Code. The preliminary design layout presenting the proposed project, as well as the existing site conditions are depicted on the Site Plan (see

Figure 2).

Based on the preliminary nature of the design at this time, wall and column loads were not available.

It is anticipated that column loads for proposed improvements will be up to 150 kips, and wall loads will be up to 1.5 kips per linear foot, which is typical for this type of structure.

Once the design phase and foundation loading configuration proceeds to a more finalized plan, the recommendations within this report should be reviewed and revised, if necessary. Any changes in the design, location or elevation of any structure or improvement, as outlined in this report, should be reviewed by this office. Geocon should be contacted to determine the necessity for review and possible revision of this report.

4. GEOLOGIC SETTING

The site is situated in an alluvial valley in the unincorporated community of Parkfield. Regionally, the site is located within the Coast Ranges geomorphic province which consists of mountains and valleys located between the Great Valley of California and the Pacific Ocean. The geologic structure of the

Coast Ranges is controlled by faults and folds, with the principal fault being the San Andreas Fault

Zone. The majority of this province is underlain by the Jurassic age Franciscan Formation which is a mélange of folded and faulted blocks of volcanic and sedimentary rocks that were once part of an oceanic trench complex. Younger Tertiary and `subsequently folded to form the Coast Ranges.

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5. SOIL AND GEOLOGIC CONDITIONS

Locally, the site is situated in an alluvial valley formed from sediments derived from the adjacent

Middle Mountain and the Cholame Hills. The site is underlain by interfingered alluvial and colluvial sediments from the Cholame Creek drainage and adjacent slopes to the north of the site. The site is shown with respect to local geologic conditions on Figure 3, Local Geologic Map. Detailed stratigraphic profiles are provided on the boring logs in Appendix A.

5.1 Tilled Soil

The upper surface of the project site is capped by 1 to 2 feet of tilled or plowed soil generally consisting of dark brown silty sand, which can be characterized as slightly moist and firm. Deeper areas of tilled soil or disturbed soil may exist between excavations and in other portions of the site that were not directly explored.

5.2 Undifferentiated Alluvial and Colluvial Deposits

Undifferentiated Holocene age alluvial and colluvial sediments were encountered beneath the tilled soil, consisting of soft to firm clay and silt and medium dense sand and silty sand which gradually coarsen to very dense sand down to a depth of 41 feet. The sand is further underlain by hard clay and silt to the total depth explored of approximately 50½ feet.

6. GROUNDWATER

The site is elevated above the local groundwater producing areas that are generally located along

Cholame Creek, approximately 2,180 feet to the southwest (Monterey County, 2010).

The USGS National Water Information System Website (2018) has cataloged various wells in the vicinity of the subject site. According to the USGS, the closest groundwater well with available data is

USGS Well No. 355405120263301, located approximately 1,000 feet northeast of the project area.

Review of the monitoring data for this well indicates monitoring data is available for the monitoring period between 1979 and 1994. During this time, the depth to groundwater has fluctuated between high and low measurements of 16.18 feet below the existing ground surface (measured on April 19, 1983) to

59.52 feet below the existing ground surface (measured on April 16, 1985), respectively. The most recent groundwater level measurement for Well No. 355405120263301 was measured in April, 1994 and groundwater was at a depth of approximately 34.38 feet below the existing ground surface.

Groundwater data may not be representative of the subject site as geologic conditions may vary from the well location due to the positioning of the site within a valley deposits.

A domestic water well is located in the central portion of the subject site constructed in 1990. Although there are no continuous records of water levels for this well, according to the well construction records, the static water level at the time of construction was 70 feet below the ground surface. According to the property owner (personal communication), the current depth to groundwater in the well is 70 feet below the ground surface.

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Based on these considerations, as well as the referenced CGS letter for the site, the historic high groundwater level of the site is considered to be approximately 16 feet below the ground surface.

Groundwater was not encountered in our field explorations, excavated to a maximum depth of 50½ feet below the existing ground surface. Based on available groundwater level data in the site vicinity and the depth of the proposed construction, groundwater is not anticipated to impact the proposed construction. However, it is not uncommon for groundwater levels to vary seasonally or for groundwater seepage conditions to develop where none previously existed, especially in impermeable fine-grained soils which are heavily irrigated or after seasonal rainfall. Proper surface drainage of irrigation and precipitation will be critical to future performance of the project. Recommendations for drainage are provided in the Surface Drainage section of this report (see Section 8.16).

7. GEOLOGIC HAZARDS

7.1 Surface Fault Rupture

The numerous faults in Southern California include active, potentially active, and inactive faults.

The criteria for these major groups are based on criteria developed by the California Geological Survey

(CGS, formerly known as CDMG) for the Alquist-Priolo Earthquake Fault Zone Program (CGS, 2018a). By definition, an active fault is one that has had surface displacement within Holocene time

(about the last 11,700 years). A potentially active 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.

As shown on Figure 4, Alquist Priolo Earthquake Fault Zone Map, the site is located in close proximity to the main strand of the San Andreas Fault Zone and adjacent to a state-designated Alquist-Priolo

Earthquake Fault Zone (CGS, 2018b; CGS, 2015). According to Manson (1985), the main trace of the

San Andreas Fault Zone is approximately 780 feet to the northeast and the Southwest Fracture Zone is approximately 2,300 feet to the southwest of the site, respectively. The San Andreas fault zone, California's most prominent structural feature, trends in a general northwest direction for almost the entire length of the state. The San Andreas Fault consists of several en echelon or subparallel fault strands, most of the strands exhibit right-lateral strike-slip sense of displacement. Wallace (1968) estimated the recurrence interval for a Magnitude 8.0 earthquake along the total length of the fault to be between 50 and 200 years. More recent data by Sieh (1984) indicates an average earthquake recurrence interval of 140 to 200 years for the San Andreas Fault. Locally, the Parkfield-Cholame Segment of the

San Andreas is thought to have a recurrence interval of approximately 30 years.

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As previously noted, the proposed project site is situated between the main San Andreas Fault and the

Southern Fracture Zone. These two fault zones coalesce approximately 3 miles to the northwest at

Middle Mountain. According to the Fault Evaluation Report Figure 2A (Manson, 1985) an unnamed fault strand may project from the north towards the project site. This unnamed strand is interpreted to have Quaternary displacement; however, the fault could not be identified in aerial photographs south of

Vineyard Canyon Road. Furthermore, a review of historical satellite imagery and as discussed by

Mr. Don Lindsay (CGS, 2017), there appears to be tonal lineament across the northwest-trending drainage that not only parallels the fault but projects towards the project site. Although the lineation could be fault-related, it could potentially also represent the contact between alluvial (stream channel) deposits and the colluvial deposits derived from the adjacent hillside. Additional site-specific studies are warranted to evaluate if these features are fault related and if there is a potential for surface fault rupture at the proposed project site.

Other nearby active faults are the San Juan Fault Zone, the Nunez Fault, Rinconada Fault Zone, the Pond

Fault, and the Pine Rock Fault Zone located approximately 11.4 miles southeast, 21.8 miles north, 23 miles southwest, 65 miles southwest, and 47 miles northwest of the site, respectively (Ziony and Jones, 1989). The site is located in the seismically active Central California region, and could be subjected to moderate to strong ground shaking in the event of an earthquake on one of the many active Southern

California faults. The faults in the vicinity of the site are shown in Figure 5, Regional Fault Map.

7.2 Seismicity

Several moderate earthquakes have occurred along the Parkfield-Cholame segment of the San Andreas fault. Near Parkfield and the Cholame Valley, historic events near the project site in 1922, 1934, 1966, and 2004 have fault displacement up to about 2 inches from right-lateral strike-slip movement (Manson

1985). The seismicity of the region surrounding the site was formulated based on research of an electronic database of earthquake data. The epicenters of recorded earthquakes with magnitudes equal to or greater than 5.0 in the site vicinity are depicted on Figure 6, Regional Seismicity Map. A partial list of moderate to major magnitude earthquakes that have occurred in the Central California area within the last 100 years is included in the following table.

LIST OF HISTORIC EARTHQUAKES

Earthquake (Oldest to Youngest)

Date of Earthquake Magnitude Distance to Epicenter

(Miles)

Direction to

Epicenter

Cholame Valley March 10, 1922 6.5 15 SE SW of Lompoc November 4, 1927 7.3 85 SSW Parkfield, CA June 8, 1934 6.0 10 SE N of San Simeon November 22, 1952 6.0 44 WSW NW of Parkfield June 27, 1966 5.5 4 WNW Coalinga May 2, 1983 6.7 24 NNE Loma Prieta October 18, 1989 7 112 NW Parkfield, CA September 28, 2004 6.0 7 SE

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The site could be subjected to strong ground shaking in the event of an earthquake. However, this hazard is common in Central California and the effects of ground shaking can be mitigated if the proposed structures are designed and constructed in conformance with current building codes and engineering practices.

7.3 Ground Motion Hazard Analysis

Ground motion hazard analyses were performed in accordance with ASCE 7-10 and Section 1613A of the 2016 CBC utilizing the computer program EZFRISK (version 7.65) in conjunction with data from the U.S. Seismic Design Maps web application provided by the USGS.

7.3.1 Probabilistic Seismic Hazard Analysis

The probabilistic Maximum Considered Earthquake (MCER) response spectrum consists of the spectral response accelerations which are expected to achieve a 1 percent probability of collapse within a

50-year period, evaluated at 5 percent damping. The procedure described in ASCE 7-10 Section

21.2.1.1 as Method 1 was used to evaluate the probabilistic response spectrum.

The spectral response accelerations having a 2 percent chance of exceedance in 50 years were evaluated at 5 percent damping. The probabilistic analysis was performed using the ground motion prediction equations (GMPEs) of Abrahamson and Silva (2008) NGA MRC (next generation attenuation, maximum rotated component), Boore and Atkinson (2008) NGA USGS 2008 MRC, Campbell-Bozorgnia (2008) NGA USGS 2008 MRC, and Chiou-Youngs (2007) NGA USGS 2008

MRC. Each GMPE was assigned an equal weight and the maximum rotated component of ground motion derived from the relationships was evaluated. It is our opinion that the use of these four GMPEs is appropriate for the subject site.

The probabilistic analysis was performed by evaluating the ground motions generated by active faults within a 120 mile (200 kilometer) radius of the site. The soil underlying the site was modeled as a Site

Class “D” with a corresponding average shear wave velocity (VS30) of 270 meters per second.

Although there are liquefiable soils underlying the site, we assume that the proposed single-story structure will have a fundamental period of less than 0.5 seconds and therefore will not require a site-response analysis.

The GMPE of Campbell and Borzorgnia requires that the depth to where the shear wave velocity reaches 2.5 kilometers per second (Z2.5) be defined. Additionally, the GMPE of Abrahamson and Silva requires that the depth to where the shear wave velocity reaches 1 kilometer per second (Z1.0) be defined. The values of Z2.5 and Z1.0 were estimated using data from the USGS Bay Area Seismic

Velocity Model. The values of Z2.5 and Z1.0 used in the analysis are 0.694 kilometers and 192 meters, respectively.

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According to ASCE 7-10 Section 21.2.1.1 Method 1, the probabilistic MCER spectral response accelerations may be determined as the product of the spectral response accelerations having a

2 percent chance of exceedance in 50 years and the risk coefficient CR. The value of CR at 0.2 seconds

(CRS) and 1 second (CR1) were determined from ASCE 7-10 Figures 22-17 and 22-18, respectively.

At spectral response accelerations less than or equal to 0.2 seconds, the value of CR was taken as CRS and at spectral response accelerations greater than or equal to 1.0 seconds the value of CR was taken as

CR1. Liner interpolation was used to evaluate the values of CR between 0.2 and 1.0 seconds.

7.3.2 Deterministic Seismic Hazard Analysis

The deterministic analysis was performed using the same GMPEs as the probabilistic analysis, as well as the same active faults within a within a 120 mile (200 kilometer) radius of the site and the same values of Z1.0 and Z2.5. The 84th percentile of the maximum rotated component of ground motion derived from the GMPEs was evaluated.

Based on the results of the analysis, the fault source resulting in the highest spectral accelerations would be a magnitude 8.2 event on the Southern San Andreas fault.

The 84th percentile of the maximum rotated component of ground motion was compared to the

Deterministic Lower Limit MCER response spectrum, and the maximum values taken as the deterministic MCER response spectrum.

7.3.3 Site-Specific Response Spectrum

The lesser of the probabilistic and deterministic MCER response spectrums is the Site-Specific MCER.

Two-thirds of the Site-Specific MCER is the Design Earthquake (DE) Response Spectrum, provided the results are not less than 80 percent of the General Design Response Spectrum determined by ASCE

7-10 Section 11.4.5.

Graphical representations of the analyses are presented on Figures 7 and 8. The Site-Specific Design

Earthquake response spectrum at 5 percent damping is presented on Figure 9 and as Table 1.

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7.3.4 Mapped Acceleration Parameters

The following table summarizes the mapped acceleration parameters obtained from the 2016 California

Building Code (CBC; Based on the 2015 International Building Code [IBC] and ASCE

7-10), Chapter 16A Structural Design, Section 1613A Earthquake Loads. The data was calculated using the computer program U.S. Seismic Design Maps, provided by the USGS. The short spectral response uses a period of 0.2 second.

MAPPED SPECTRAL ACCELERATIONS

Parameter Value 2016 CBC Reference

MCER Ground Motion Spectral Response Acceleration – Class B (short), SS

2.675g Figure 1613A.3.1(1)

MCER Ground Motion Spectral Response Acceleration – Class B (1 sec), S1

1.319g Figure 1613A.3.1(2)

7.3.5 Site-Specific Seismic Design Criteria

Based the site-specific ground motion hazard analysis performed, and in accordance with the ASCE

7-10 Section 21.4, site-specific seismic design parameters shall be derived using the results of the site-specific ground motion hazard analysis.

The parameter SDS shall be obtained from the site-specific spectra at a period of 0.2 second and not less than 90 percent of the peak spectra acceleration at any period larger than 0.2 second. The parameter SD1 shall be taken as the greater of the site-specific spectral acceleration at a period of 1.0 second or twice the spectral acceleration at a period of 2 seconds (whichever is greater). The values of SMS and SM1 shall be taken as 1.5 times the site-specific values of SDS and SD1. The site-specific seismic d esign parameters shall not be less than 80 percent of the general seismic design values determined by

ASCE 7-10 Section 11.4.

The following table presents the site-specific seismic design parameters based on the site-specific ground motion hazard analysis.

SITE-SPECIFIC SEISMIC DESIGN PARAMETERS

Parameter Value

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

2.157g

Site Class Modified MCER Spectral Response Acceleration – (1 sec), SM1

3.144g

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

1.438g

5% Damped Design Spectral Response Acceleration (1 sec), SD1

2.096g

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7.3.6 Site-Specific Peak Ground Acceleration

The site-specific Maximum Considered Earthquake (MCEG) geometric mean peak ground acceleration was evaluated in accordance with ASCE 7-10 Section 21.5.

The probabilistic geometric mean peak ground acceleration was evaluated using the computer program

EZFrisk. The analysis was performed using the GMPE of Abrahamson and Silva (2008) NGA (next generation attenuation), Boore and Atkinson (2008) NGA USGS 2008, Campbell-Bozorgnia (2008)

NGA USGS 2008, and Chiou-Youngs (2007) NGA USGS 2008. Each GMPE was assigned an equal weight. The analysis used the same faults, Site Class, and values of Z2.5 and Z1.0 as described above.

The probabilistic geometric mean peak ground acceleration (probabilistic MCEG) was evaluated at a

2 percent probability of exceedance with a 50 year period.

The deterministic geometric mean peak ground acceleration (deterministic MCEG) was evaluated as the

84th percentile geometric mean peak ground acceleration. The deterministic MCEG shall not be less than 0.5FPGA, where FPGA is determined from ASCE 7-10 Table 11.8-1 with the value of PGA taken as

0.5g.

The site-specific MCEG peak ground acceleration is taken as the lesser of the probabilistic and deterministic MCEG, provided the value is not less than 80 percent of the value of PGAM as determined by ASCE 7-10 Equation 11.8.1.

ASCE 7-10 SITE-SPECIFIC PEAK GROUND ACCELERATION

Parameter Value ASCE 7-10 Reference

Site-Specific MCEG Peak Ground Acceleration, PGAM

0.853g Section 21.5

7.3.7 Deaggregated Seismic Source Parameters

The Maximum Considered Earthquake Ground Motion (MCE) is the level of ground motion that has a

2 percent chance of exceedance in 50 years, with a statistical return period of 2,475 years. According to the 2016 California Building Code and ASCE 7-10, the MCE is to be utilized for the evaluation of liquefaction, lateral spreading, seismic settlements, and it is our understanding that the intent of the

Building code is to maintain “Life Safety” during a MCE event. The Design Earthquake Ground

Motion (DE) is the level of ground motion that has a 10 percent chance of exceedance in 50 years, with a statistical return period of 475 years.

Deaggregation of the MCE peak ground acceleration was performed using the USGS 2008

Probabilistic Seismic Hazard Analysis (PSHA) Interactive Deaggregation online tool. The result of the deaggregation analysis indicates that the predominant earthquake contributing to the MCE peak ground acceleration is characterized as a 6.64 magnitude event occurring at a hypocentral distance of

2.62 kilometers from the site.

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Deaggregation was also performed for the Design Earthquake (DE) peak ground acceleration, and the result of the analysis indicates that the predominant earthquake contributing to the DE peak ground acceleration is characterized as a 6.53 magnitude occurring at a hypocentral distance of 2.94 kilometers from the site.

Conformance to the criteria in the above tables for seismic design does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur if a large earthquake occurs. The primary goal of seismic design is to protect life, not to avoid all damage, since such design may be economically prohibitive.

7.4 Liquefaction Potential

Liquefaction is a phenomenon in which loose, saturated, relatively cohesionless soil deposits lose shear strength during strong ground motions. Primary factors controlling liquefaction include intensity and duration of ground motion, gradation characteristics of the subsurface soils, in-situ stress conditions, and the depth to groundwater. Liquefaction is typified by a loss of shear strength in the liquefied layers due to rapid increases in pore water pressure generated by earthquake accelerations.

According to the Monterey County Safety Element (2010), the site is located within an area identified as having a potential for liquefaction. The current standard of practice, as outlined in the

“Recommended Procedures for Implementation of DMG Special Publication 117, Guidelines for

Analyzing and Mitigating Liquefaction in California” and “Special Publication 117A, Guidelines for

Evaluating and Mitigating Seismic Hazards in California” requires liquefaction analysis to a depth of

50 feet below the lowest portion of the proposed structure. Liquefaction typically occurs in areas where the soils below the water table are composed of poorly consolidated, fine to medium-grained, primarily sandy soil. In addition to the requisite soil conditions, the ground acceleration and duration of the earthquake must also be of a sufficient level to induce liquefaction.

Liquefaction analysis of the soils underlying the site was performed using an updated version of the spreadsheet template LIQ2_30.WQ1 developed by Thomas F. Blake (1996). This program utilizes the

1996 NCEER method of analysis. This semi-empirical method is based on a correlation between values of Standard Penetration Test (SPT) resistance and field performance data.

Screening criteria presented by Bray and Sancio (2006) was used to evaluate the liquefaction susceptibility of the fine-grained soils encountered in the boring. Based on these screening criteria, fine-grained soils with a plasticity index of greater than 18 and a saturated water content of less than

85 percent of the liquid limit, or with a plasticity index of less than 18 but greater than 12 and a saturated water content of less than 80 percent of the liquid limit are considered not susceptible to liquefaction. Atterberg Limits laboratory test results used for the screening criteria are presented as

Figure B7.

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The liquefaction analysis was performed for a Design Earthquake (DE) level by using a historic high groundwater depth of 16 feet below the ground surface, a magnitude 6.53 earthquake, and a peak horizontal acceleration of 0.569g (⅔PGAM). The enclosed liquefaction analysis, included herein for

Boring B1, indicates that the alluvial soils below the historic high groundwater level could be susceptible to approximately 0.7 inch of liquefaction settlement, during a Design Earthquake ground motion (see enclosed calculation sheets, Figures 10 and 11).

It is our understanding that the intent of the Building Code is to maintain “Life Safety” during

Maximum Considered Earthquake (MCE) level events. Therefore, additional analysis was performed to evaluate the potential for liquefaction during a MCE event. The structural engineer should evaluate the proposed structure for the anticipated MCE liquefaction induced settlements and verify that anticipated deformations would not cause the foundation system to lose the ability to support the gravity loads and/or cause collapse of the structure.

The liquefaction analysis was also performed for the MCE level by using a historic high groundwater depth of 16 feet below the ground surface, a magnitude 6.64 earthquake, and a peak horizontal acceleration of 0.853g (PGAM). The enclosed liquefaction analysis, included herein for boring B1, indicates that the alluvial soils below the historic high groundwater level could be susceptible to approximately 1 inch of liquefaction settlement during Maximum Considered Earthquake ground motion (see enclosed calculation sheets, Figures 12 and 13).

7.5 Seismically-Induced Settlement

Dynamic compaction of dry and loose sands may occur during a major earthquake. Typically, settlements occur in thick beds of such soils. The seismically-induced settlement calculations were performed in accordance with the American Society of Civil Engineers, Technical Engineering and

Design Guides as adapted from the US Army Corps of Engineers, No. 9.

The calculations provided herein for Boring B1 indicate that the alluvial soils above the historic high groundwater could be prone to approximately 0.1 inch of settlement as a result of the Design

Earthquake peak ground acceleration (⅔PGAM).

The calculations provided herein for Boring B1 indicate that the alluvial soils above the historic high groundwater level of 16 feet could be prone to approximately 0.2 inch of settlement as a result of the

Maximum Considered Earthquake peak ground acceleration (PGAM).

Calculation of the anticipated seismically-induced settlements is provided as Figures 14 and 15.

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7.6 Slope Stability

The topography at the site is relatively level (<10%) and the topography in the immediate site vicinity slopes gently to the southeast There are no known landslides near the site, nor is the site in the path of any known or potential landslides. Additionally, the site is not located in a county-designated Landslide

Hazard Area (Monterey County, 2010). It is our opinion that the potential for slope stability hazards to adversely affect the proposed development is considered low.

7.7 Earthquake-Induced Flooding

Earthquake-induced flooding is inundation caused by failure of dams or other water-retaining structures due to earthquakes. Based on a review of the Monterey County Safety Element (Monterey

County, 2010), the site is not located within a potential inundation area for an earthquake-induced dam failure. The probability of earthquake-induced flooding is considered very low.

7.8 Tsunamis, Seiches, and Flooding

The site is not located within a coastal area. Therefore, tsunamis, seismic sea waves, are not considered hazards at the site.

Seiches are large waves generated in enclosed bodies of water in response to ground shaking. No major water-retaining structures are located immediately up gradient from the project site. Flooding from a seismically-induced seiche is considered unlikely.

The site is not located within a designated flood zone (FEMA, 2018). It is our opinion that the potential for flooding to adversely affect the site is considered low.

7.9 Oil Fields & Methane Potential

Based on a review of the California Division of Oil, Gas and Geothermal Resources (DOGGR) Well

Finder Website, the site is not located within the limits of an oilfield and oil or gas wells are not located in the immediate site vicinity (DOGGR, 2018). However, due to the voluntary nature of record reporting by the oil well drilling companies, wells may be improperly located or not shown on the location map and undocumented wells could be encountered during construction. Any wells encountered during construction will need to be properly abandoned in accordance with the current requirements of the DOGGR.

Since the site is not located within the boundaries of a known oil field, the potential for the presence of methane or other volatile gases at the site is considered low. However, should it be determined that a methane study is required for the proposed development it is recommended that a qualified methane consultant be retained to perform the study and provide mitigation measures as necessary.

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7.10 Naturally Occurring Asbestos

Naturally-occurring asbestos is a known carcinogen and inhalation of asbestos may result in the development of lung cancer or mesothelioma. Chrysotile and amphibole asbestos (such a tremolite) occur naturally in certain geologic settings in California, most commonly in association with ultramafic rocks and along associated fault lines. The CGS maintains records of known asbestos mines, prospects, reported occurrences and asbestos-bearing ultramafic rocks. According to the CGS, the site is not located near any known sources of naturally-occurring asbestos (CGS, 2011), therefore, the risk of exposure to naturally-occurring asbestos is considered to be low.

7.11 Subsidence

Subsidence occurs when a large portion of land is displaced vertically, usually due to the withdrawal of groundwater, oil, or natural gas. Soils that are particularly subject to subsidence include those with high silt or clay content. The site is not located within an area of known ground subsidence (Monterey

County General Plan, 2010). No large-scale extraction of groundwater, gas, oil, or geothermal energy is occurring or planned at the site or in the general site vicinity. There appears to be little or no potential for ground subsidence due to withdrawal of fluids or gases at the site.

7.12 Radon

Radon is a naturally occurring gas that occurs during the radioactive decay of uranium and thorium within certain shale and igneous rock. The site is located within an area identified as having a low potential for indoor radon. As recommended by the United States Environmental Protection Agency, less than 5 percent of indoor radon measurements within this area do not exceed 4 Picocuries per liter

[pCi/L] (CGS, 2018c). It is our opinion that the potential for indoor radon to adversely affect the site is considered low.

7.13 Volcanic Eruption

Volcanic activity can cause many different hazards can be harmful to life and property. These hazards include lava flows, lahars, ash fall, debris avalanches, and pyroclastic flows, among others. The USGS

Volcano Hazards Program (VHP) monitors and studies active and potentially active volcanoes, assesses their hazards across the entire world. The closest volcanic activity to the site is the Coso volcanic field located approximately 146 miles to the east. The most recent eruption of this field was approximately 40,000 years ago, (USGS 2012). The California Volcanic Observatory division of the

USGS VHP considers the threat potential from the Coso Volcanic Field to be moderate. Based on the distance from the site, we consider the volcanic hazard threat to the site to be very low.

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7.14 Hydro Consolidation

The results of our laboratory testing indicate that the existing upper alluvial soils are subject to hydro consolidation upon saturation (see Figures B3 through B6). Hydro-consolidation is the tendency of a soil structure to collapse upon saturation, resulting in the overall settlement of the affected soils and any overlying soils, foundations, or improvements supported therein. The grading and foundation recommendations presented herein are intended to mitigate the potential for settlement as a result of hydroconsolidation.

7.15 Expansive Soil

The upper 5 feet of existing site soils encountered during this investigation are considered to have a “high” expansive potential (Expansion Index (EI) = 96); and the soils are classified as

“expansive” in accordance with the 2016 California Building Code (CBC) Section 1803.5.3 (see Figure

B9). Recommendations presented herein assume that foundations and slabs will derive support in these materials.

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8. CONCLUSIONS AND RECOMMENDATIONS

8.1 General

8.1.1 The site is located in close proximity to the main strand of the San Andreas Fault Zone and adjacent to the boundaries of a state-designated Alquist-Priolo Earthquake Fault Zone.

A site-specific fault rupture hazard investigation should be conducted to identify if such hazards exist at the site prior to construction of the proposed project. The geotechnical design parameters presented herein should be reviewed and updated, as necessary.

8.1.2 Up to 2 feet of existing tilled or plowed soil was encountered during the site investigation.

The existing tilled soil encountered is believed to be the result of farming activities at the site. Additionally, burrow holes from ground animals were observed throughout the proposed project area and have likely disturbed the upper site soils. Deeper tilled soil and/or disturbed soil may exist in other areas of the site that were not directly explored. It is our opinion that the existing tilled/disturbed soil, in its present condition, is not suitable for direct support of proposed foundations or slabs. Therefore, remedial grading in the form of removal and re-compaction will be required as part of site grading. The site soils are suitable for re-use as engineered fill provided the recommendations in the Grading section of this report are followed (see Section 8.4).

8.1.3 Our liquefaction analyses indicate that the alluvial soils below the historic high groundwater depth of 16 feet could be prone to approximately 0.7 inch of settlement as a result of the

Design Earthquake peak ground acceleration (⅔PGAM). The resulting differential settlement at the ground surface is anticipated to be approximately two-thirds of the total anticipated liquefaction settlement, or less than ½ inch of settlement over a distance of 30 feet.

8.1.4 The liquefaction analyses indicate that the alluvial soils below the historic high groundwater depth of 16 feet could be prone to approximately 1 inch of settlement as a result of the

Maximum Considered Earthquake peak ground acceleration (PGAM). The resulting differential settlement at the ground surface is anticipated to be approximately two-thirds of the total anticipated liquefaction settlement, or less than 0.7 inch of settlement over a distance of 30 feet.

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8.1.5 Based on these considerations, we recommend that the upper 3 feet of soil be excavated and properly compacted within the proposed fire station building, support structures, and water storage tank footprint areas. Deeper excavations should be conducted as needed to remove any unsuitable or soft soils as necessary at the direction of the Geotechnical Engineer

(a representative of Geocon). The excavation should extend laterally a minimum distance of

3 feet beyond the building footprint areas, including building appurtenances. The limits of existing disturbed and/or soft soil removal will be verified by the Geocon representative during site grading activities. Recommendations for earthwork are provided in the Grading section of this report (see Section 8.4).

8.1.6 Subsequent to the recommended remedial grading, the proposed fire station building and support structures (generator/pump building, well house, and storage building) may be supported on a conventional foundation system deriving support in newly placed engineered fill. As a minimum, proposed foundations should be underlain by at least 12 inches of newly placed engineered fill. Recommendations for the design of a conventional foundation system are provided in Section 8.7.

8.1.7 Subsequent to the recommended remedial grading, the proposed water storage tank may be supported on conventional foundation system or a mat foundation system bearing directly on newly placed engineered fill. As a minimum, proposed foundations should be underlain by at least 12 inches of newly placed engineered fill. Recommendations for the design of a conventional and mat foundation systems are provided in Sections 8.8 and 8.9, respectively.

8.1.8 Based on the results of the laboratory testing, the upper alluvial soils encountered are subject to hydroconsolidation upon saturation. The introduction of stormwater into these soils would likely induce settlement of the surrounding soils and would adversely affect the future performance of the site. Based on these considerations, a stormwater infiltration system is not recommended for this project. It is recommended that stormwater be retained, filtered, and discharged in accordance with the requirements of the local governing agency.

8.1.9 The client should be aware that it is essential that proper drainage be maintained in order to reduce settlements of the compressible alluvial soils and any foundations or paving supported therein. These soils are highly sensitive to excessive moisture and in order to prevent settlements, measures should be taken to prevent saturation of the soils.

8.1.10 Once the design and foundation loading configuration proceeds to a more finalized plan, the recommendations within this report should be reviewed and revised, if necessary. If the proposed building loads will exceed those presented herein, the potential for settlement should be reevaluated by this office.

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8.1.11 Any changes in the design, location or elevation of improvements, as outlined in this report, should be reviewed by this office. Geocon should be contacted to determine the necessity for review and possible revision of this report.

8.2 Soil and Excavation Characteristics

8.2.1 The in-situ soils can be excavated with moderate effort using conventional excavation equipment. Some caving should be anticipated in unshored excavations, especially where granular soils are encountered.

8.2.2 It is the responsibility of the contractor to ensure that all excavations and trenches are properly shored and maintained in accordance with applicable OSHA rules and regulations to maintain safety and maintain the stability of adjacent existing improvements.

8.2.3 All 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 1:1 projection down and away from the bottom of an existing foundation or vehicle load. Penetrations below this 1:1 projection will require special excavation measures such as sloping and possibly shoring. Excavation recommendations are provided in the

Temporary Excavations section of this report (see Section 8.15).

8.3 Minimum Resistivity, pH, and Water-Soluble Sulfate

8.3.1 Potential of Hydrogen (pH) and resistivity testing as well as chloride content testing were performed on representative samples of soil to generally evaluate the corrosion potential to surface utilities. The tests were performed in accordance with California Test Method

Nos. 643 and 422 and indicate that the upper site soils are considered “corrosive” with respect to corrosion of buried ferrous metals on site. The results are presented in Appendix B

(Figure B10) and should be considered for design of underground structures.

8.3.2 Laboratory tests were performed on representative samples of the site materials to measure the percentage of water-soluble sulfate content. Results from the laboratory water-soluble sulfate tests are presented in Appendix B (Figure B10) and indicate that the on-site materials possess “negligible” sulfate exposure to concrete structures as defined by 2016 CBC Section

1904 and ACI 318-11 Sections 4.2 and 4.3.

8.3.3 Geocon does not practice corrosion engineering and mitigation. If corrosion sensitive improvements are planned, it is recommended that a corrosion engineer be retained to evaluate corrosion test results and incorporate the necessary precautions to avoid premature corrosion of buried metal pipes and concrete structures in direct contact with the soils.

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8.4 Grading

8.4.1 A preconstruction conference should be held at the site prior to the beginning of grading operations with the owner, contractor, civil engineer and geotechnical engineer in attendance. Special soil handling requirements can be discussed at that time.

8.4.2 Earthwork should be observed, and compacted fill tested by representatives of Geocon.

The existing tilled/disturbed soil and alluvial soil encountered during exploration are suitable for re-use as an engineered fill, provided any encountered oversize material (greater than

6 inches) and any encountered deleterious debris are removed.

8.4.3 Grading should commence with the removal of existing vegetation and existing improvements from the area to be graded. Deleterious debris such as wood and root structures should be exported from the site and should not be mixed with the fill soils.

Asphalt and concrete should not be mixed with the fill soils unless approved in writing by the Geotechnical Engineer. All existing underground improvements planned for removal should be completely excavated and the resulting depressions properly backfilled in accordance with the procedures described herein. Once a clean excavation bottom has been established, it must be observed and approved in writing by the Geotechnical Engineer (a representative of Geocon).

8.4.4 As a minimum, we recommend that the…