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GEOTECHNICAL ENGINEERING AND

GEOLOGIC HAZARDS STUDY

Ygnacio Valley High School Chemistry Laboratory Classroom Building

Concord, California

Prepared for:

Mt. Diablo Unified School District 3333 Ronald Way

Concord, California 94519

Prepared by:

GEOSPHERE CONSULTANTS, INC. 2001 Crow Canyon Road, Suite 100

San Ramon, California 94583 Geosphere Project No. 91-02968-A

TABLE OF CONTENTS

1.0 INTRODUCTION ............................................................................................................................................ 1 1.1 Purpose and Scope ........................................................................................................................... 1 1.2 Site Description ................................................................................................................................. 1 1.3 Proposed Development .................................................................................................................... 2 1.4 Validity of Report .............................................................................................................................. 2

2.0 PROCEDURES AND RESULTS ......................................................................................................................... 3 2.1 Literature Review.............................................................................................................................. 3 2.2 Drilling and Sampling ........................................................................................................................ 3 2.3 Laboratory Testing ............................................................................................................................ 4

3.0 FINDINGS ...................................................................................................................................................... 5 3.1 Regional and Local Geologic Conditions ........................................................................................... 5 3.2 Subsurface Soil Conditions ............................................................................................................... 5 3.3 Groundwater .................................................................................................................................... 5 3.4 Expansive Soils .................................................................................................................................. 6 3.5 Corrosion .......................................................................................................................................... 6 3.6 Faults and Seismicity ........................................................................................................................ 7 3.7 Surface Fault Rupture ....................................................................................................................... 9 3.8 Settlement Due to Collapsible Soils ................................................................................................ 10 3.9 Settlement Due to Consolidation ................................................................................................... 10 3.10 Liquefaction Induced Phenomena .................................................................................................. 10 3.11 Dynamic Compaction (Seismically Induced Settlement) ................................................................ 11 3.12 Flooding .......................................................................................................................................... 11 3.13 Soil Erosion ..................................................................................................................................... 12 3.14 Other Geologic Hazards .................................................................................................................. 12

4.0 CONCLUSIONS AND RECOMMENDATIONS ................................................................................................ 13 4.1 General ........................................................................................................................................... 13 4.2 Site Grading and Drainage .............................................................................................................. 14 4.3 Utility Trench Construction ............................................................................................................. 16 4.4 Temporary Excavations .................................................................................................................. 18 4.5 Building Foundations ...................................................................................................................... 19 4.6 Concrete Slabs-on-Grade ................................................................................................................ 19 4.7 Plan Review .................................................................................................................................... 20 4.8 Observation and Testing During Construction ............................................................................... 20

REFERENCES .............................................................................................................................................................. 22 LIMITATIONS AND UNIFORMITY OF CONDITIONS .................................................................................................... 24

TABLE OF CONTENTS (continued) FIGURES

Figure 1 - Site Vicinity Figure 2 - Site Plan Figure 3 - Site Vicinity Geology Map Figure 4 - Schematic Geologic Cross-Section A-A’ Figure 5 - Site Geologic Map Figure 6 - Liquefaction Susceptibility Map Figure 7 - Flood Hazard Map Figure 8 - Regional Geologic Map

APPENDIX A

Boring Logs APPENDIX B LABORATORY TEST RESULTS Atterberg Limits Direct Shear Sieve Analysis Corrosion APPENDIX C

Liquefaction Analysis

GEOTECHNICAL ENGINEERING AND GEOLOGIC HAZARDS STUDY

Project: Ygnacio Valley High School –Chemistry Laboratory Classroom Project Concord, California

Client: Mt. Diablo Unified School District Concord, California

1.0 INTRODUCTION

1.1 Purpose and Scope

The purposes of this study were to evaluate the subsurface conditions at the site of the proposed chemistry lab

structure and prepare geotechnical recommendations for the design and construction. This study provides

recommendations for foundations, site preparation, grading, drainage and guideline specifications for grading. This

study was performed in accordance with the scope of work outlined in our revised proposal dated December 6, 2012.

The scope of this study included the review of pertinent published and unpublished documents related to the site,

the drilling of two subsurface borings, laboratory testing of selected samples retrieved from the borings, engineering

analysis of the accumulated data, and preparation of this report. The conclusions and recommendations presented in

this report are based on the data acquired and analyzed during this study, and on prudent engineering judgment and

experience. This study did not include an assessment of potentially toxic or hazardous materials that may be present

on or beneath the site.

1.2 Site Description

Ygnacio Valley High School is located at 755 Oak Grove Road in Concord, California, as shown on Figure 1. The

proposed site improvement will be located at the west corner of the high school campus at the very western edge of

the main driveway and parking lot to the school. The site is relatively flat, with the general site vicinity topography

sloping gently to the northeast. The campus is bounded on the north and south by developed commercial and retail

properties and to the east and west by residential development. The site is located at approximately 37.934815°

north latitude and 122.027017° west longitude, and approximately 96 feet above mean sea level.

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1.3 Proposed Development

It is our understanding that the proposed site improvement is to consist of the installation of a modular chemistry

laboratory classroom building. Other minor improvements may consist of utility upgrades, exterior concrete

hardscapes, and landscaping. The proposed improvements are shown on the attached Site Plan, Figure 2.

1.4 Validity of Report

This report is valid for three years after publication. If construction begins after this time period, Geosphere should

be contacted to confirm that the site conditions have not changed significantly. If the proposed development differs

considerably from that described above, Geosphere should be notified to determine if additional recommendations

are required. Additionally, if Geosphere is not involved during the geotechnical aspects of construction, this report

may become wholly or in part invalid; Geosphere’s geotechnical personnel should be retained to verify that the

subsurface conditions anticipated when preparing this report are similar to the subsurface conditions revealed during

construction. Geosphere’s involvement should include grading and foundation plan review, grading observation and

testing, foundation excavation observation, and utility trench backfill testing.

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2.0 PROCEDURES AND RESULTS

2.1 Literature Review

Pertinent geologic and geotechnical literature pertaining to the site area were reviewed. These included various

USGS, CGS and other agency publications and maps.

2.2 Drilling and Sampling

A subsurface exploration program was undertaken to evaluate the soil conditions at the site. Two borings were

drilled on January 3, 2013. The locations of the borings in relation to the proposed improvements are shown on the

attached Figure 2. The borings were drilled using a Mobile D-53 drill rig equipped with eight-inch hollow stem augers.

A Geosphere representative visually classified the materials encountered in the borings according to the Unified Soil

Classification System as the borings were advanced. Relatively undisturbed soil samples were recovered at selected

intervals using a three-inch outside diameter Modified California split spoon sampler containing six-inch long brass

liners. A two-inch outside diameter Standard Penetration Test (SPT) sampler was used to obtain SPT blow counts and

obtain disturbed soil samples. The samplers were driven by using a mechanical-trip, 140-pound hammer with an

approximate 30-inch fall utilizing N-rods as necessary. Resistance to penetration was recorded as the number of

hammer blows required to drive the sampler the final foot of an 18-inch drive. All of the blow counts recorded using

Modified California split spoon sampler in the field was converted to equivalent SPT blow counts using appropriate

modification factors suggested by Burmister (1948), i.e. a factor of 0.65 with inner diameter of 2.5 inches. Therefore,

the boring logs reported in this report are all equivalent SPT blow counts. Bulk samples were obtained in the upper

few feet of the borings from the auger cuttings as needed.

The boring logs with descriptions of the various materials encountered in each boring, the penetration resistance

values, and some of the laboratory test results are presented in Appendix A. The ground surface elevations indicated

on the soil boring logs are approximate (rounded to the nearest ½ foot) and were estimated from Google Earth. True

surface elevations at the boring locations could differ. The locations and elevations of the borings should only be

considered accurate to the degree implied by the means and methods used to define them. The approximate

locations of the borings are shown on the Site Plan, Figure 2.

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2.3 Laboratory Testing

Laboratory tests were performed on selected samples to determine some of the physical and engineering properties

of the subsurface soils. The results of the laboratory testing are presented on the boring logs and are included in

Appendix B. The following soil tests were performed for this study:

Dry Density and Moisture Content (ASTM D2216 and ASTM 2937) – In-situ density and moisture tests were

conducted to determine the in-place dry density and moisture content of the subsurface materials. These properties

provide information for evaluating the physical characteristics of the subsurface soils.

Atterberg Limits (ASTM D4318 and CT204) - Liquid Limit, Plastic Limit, and Plasticity Index are useful in the

classification and characterization of the engineering properties of soil, helps evaluate expansive characteristics of

the soil, and aids in determining the soil type according to the USCS.

Direct Shear (modified ASTM D3080) - Direct shear testing is performed on samples to determine the angle of

internal friction and cohesion of soil or rock materials. This data can be utilized in determining allowable bearing

capacity, retaining wall design parameters, and strength characteristics of the materials. Direct shear specimens are

saturated under a 100-psf surcharge for a period of 24 hours prior to testing.

Particle Size Analysis (Wet and Dry Sieve) - Sieve analysis testing is conducted on selected samples to determine the

soil particle size distribution. This information is useful for the evaluation of liquefaction potential and characterizing

the soil type according to USCS.

Soil Corrosivity, Redox (ASTM D1498), pH (ASTM D4972), Resistivity (ASTM G57), Chloride (ASTM D4327), and Sulfate

(ASTM D4327) - Soil corrosivity testing is performed to determine the effects of constituents in the soil on buried

steel and concrete. Water-soluble sulfate testing is required by the UBC, CBC, and IBC.

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3.0 FINDINGS

3.1 Regional and Local Geologic Conditions

The site is located within the central portion of the Coast Ranges Geomorphic Province. The Coast Ranges are

characterized by northwest –southeast trending regional faults and mountain ranges. The site is located east of San

Francisco Bay and northwest of Mt. Diablo, which is the northern peak of the Diablo mountain range. The site is

mapped as being underlain by Pleistocene-aged alluvium. According to the Natural Resources Conservation Service,

Web Soil Survey, the site soil is part of the Zamora Clay Loam and Silty Clay Loam unit, which generally has a low to

moderate expansive potential. Regional geology is shown on Figure 3, Site Vicinity Geology Map.

3.2 Subsurface Soil Conditions

The subsurface soil encountered in the borings consisted predominately of three to four feet of stiff to very stiff

orange-brown lean clay fill with gravel, overlying three feet of stiff to very stiff brown lean clay (possible fill). The

underlying soils were generally silty to sandy clays to the depths explored, with the exception of a four-foot layer of

granular soil (loose to medium dense gravelly sand to sandy gravel) extending between approximately 12 and 16

feet below existing ground surface (bgs). We have included the boring logs performed for this study in Appendix A.

A near surface soil sample had a Plasticity Index of 21, and corresponding Liquid Limit of 47. This soil has a

moderately high plasticity. Direct shear testing of sandy clay samples from two feet in Boring B-1 and from 4 ½ feet in

boring B-2 resulted in an angles of internal friction of 35 and 29, with unit cohesions of 200psf and 280psf,

respectively. Details of materials encountered in the exploratory borings, including laboratory test results, are

included in the boring logs in Appendix A.

3.3 Groundwater

Groundwater was encountered in the two borings drilled for this study at 12 feet below existing ground surface.

Historically, wells in the vicinity show the groundwater level as high as seven feet. Groundwater levels can vary in

response to time of year, variations in seasonal rainfall, well pumping, irrigation, and alterations to site drainage. A

detailed investigation of local groundwater conditions was not performed and is beyond the scope of this study.

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3.4 Expansive Soils

Samples of the clayey soil obtained from the near surface of the site were found to be moderately highly plastic.

These plastic soils will exhibit a moderate to high expansion potential with moisture variation. Recommendations for

the mitigation of the effect of these soils are contained in the earthwork and foundation section of this report.

3.5 Corrosion

Corrosion test results of soil samples obtained from the site were evaluated based on ASTM A888 methods. Table 1,

Soil-Test Evaluation, from the ASTM procedure is presented below. If the summed points are equal to 10, the soil

should be considered corrosive to cast iron pipe. If sulfides are present and low or negative redox potential results

are obtained, three points shall be given for this range.

Table 1: Soil Test Evaluation Criteria (ASTM A888 Methods)

Soil Characteristics Points Soil Characteristics Points Resistivity, ohm-cm, based on single probe or water-saturated soil box.

Redox Potential, mV

<700 10 >+100 0 700-1,000 8 +50 to +100 3.5 1,000-1,200 5 0 to 50 4 1,200-1,500 2 Negative 5 1,500-2,000 1 Sulfides >2,000 0 Positive 3.5 PH Trace 2 0-2 5 Negative 0 2-4 3 Moisture 4-6.5 0 Poor drainage, continuously wet 2 6.5-7.5 0 Fair drainage, generally moist 1 7.5-8.5 0 Good drainage, generally dry 0 >8.5 5

A bulk sample collected from the near surface had a pH of 6.5, a resistivity of 1,378 ohm-cm, negative sulfide, a redox

of 532mV, and 8 ppm chloride. The sum of the points is 1, and the soil is considered not to be corrosive to buried

metal.

These results are preliminary, and provide information on the specific soils sampled and tested. Other soil at the site

may be more or less corrosive. Providing a detailed assessment of the corrosion potential of the site soils is not

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within our scope of work. A more detailed explanation of the test results is included in the ETS lab data sheet located

in Appendix B. Appropriate corrosion specialists should be contacted if a detailed evaluation is required.

Water-soluble sulfate can affect the concrete mix design for concrete in contact with the ground, such as shallow

foundations, piles, piers, and concrete slabs. The UBC, CBC, and IBC provide the following evaluation criteria.

Table 2: Soluble Sulfate Evaluation Criteria

Sulfate Exposure

Water-Soluble Sulfate in Soil, Percentage by

Weight or (mg/kg)

Sulfate in Water, ppm

Cement Type Max. Water Cementitious

Ratio by Weight

Min. Unconfined

Compressive Strength, psi

Negligible 0.00-0.10 (0-1,000)

0-150 NA NA NA

Moderate 0.10-0.20 (1,000-2,000)

150-1,500 II, IP (MS), IS (MS)

0.50 4,000

Severe 0.20-2.00 (2,000-20,000)

1,500-10,000 V 0.45 4,500

Very Severe Over 2.00 (20,000) Over 10,000 V plus pozzolan 0.45 4,500

The test results show that the onsite soil contains approximately 252 ppm of water-soluble sulfate. Hence, the water-

soluble sulfate content in the site soil is considered to have a moderate impact on buried concrete at the site.

However, it should be pointed out that the water-soluble sulfate concentrations can vary due to the addition of

fertilizer, irrigation, and other possible development activities. An appropriate expert should be contacted if a

detailed evaluation is required.

3.6 Faults and Seismicity

Regional transpression has caused uplift and folding of the bedrock units within the Coast Ranges. This structural

deformation occurred during periods of tectonic activity that began in the Pliocene and continues today. This seismic

activity appears to be largely controlled by displacement between the Pacific and North American crustal plates,

separated by the San Andreas Fault zone, and located approximately 30 miles (49 kilometers) southwest of the site.

This plate displacement produced regional strain that is concentrated along major faults of the San Andreas Fault

System including the San Andreas, Rodgers Creek, and Hayward faults in this area.

The site is located in a seismically active region dominated by major faults of the San Andreas Fault System. Major

faults include the San Andreas Fault, located approximately 30 miles (49 km) southwest of the site; Hayward Fault,

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located approximately 12.6 miles (20.2 km) southwest of the site; the Calaveras Fault, located approximately 8.2

miles (13.2 km) southwest of the site; the Concord-Green Valley Fault, located approximately 0.7 miles (1.2 km) east

of the site; the Mt. Diablo Thrust Fault, located approximately 2.1 miles (3.4 km) southeast of the site.

San Andreas Fault

The northwest-trending San Andreas Fault runs along the western coast of California extending approximately 625

miles from the north near Point Arena to the Salton Sea area in Southern California (Jennings, 1994). The fault zone

has been divided into 11 segments. The site is located approximately 30 miles (49 km) to the east of the Peninsula

segment. The slip rate on the nearest segment of the San Andreas Fault is estimated to be about 17 mm/year and has

been assigned a moment magnitude (Mmax) of 6.9 (CGS, 2003). The Working Group on California Earthquake

Probabilities (WG07) has estimated that there is a 21 percent probability of at least one magnitude 6.7 or greater

earthquake before 2036 along the San Andreas Fault (USGS, 2008).

Concord/Green Valley Fault

The north to northwest trending Concord Fault extends from the approximate central, Walnut Creek and Concord

border, northward into the Green Valley Fault. The Green Valley Fault extends northward from Suisun Bay up to just

west of Lake Curry, northeast of Napa. The site is located approximately 0.7 miles (1.2 km) southwest of the Concord

Fault. The slip rate of the Concord Fault is estimated to be about four mm/year and has been assigned a moment

magnitude (Mmax) of 6.6 (CGS, 2002). The Working Group on California Earthquake Probabilities (WG07) has

estimated that there is a four percent probability of at least one magnitude 6.7 or greater earthquake before 2036

along the Concord Fault (USGS, 2008).

Calaveras Fault

The Calaveras Fault trends northwesterly approximately 77 miles (88 km) from near Hollister to the San

Ramon/Dublin area. The Calaveras Fault has been divided into three segments, the Northern, Central, and Southern

segments. The site is located approximately 8.2 miles (13.2 km) from the Northern segment of the Calaveras Fault.

The slip rate on the Northern segment of the Calaveras Fault is estimated to be about six mm/year and has been

assigned a moment magnitude (Mmax) of 6.9 (CGS, 2002). The Working Group on California Earthquake Probabilities

(WG99) has estimated that there is a 7 percent probability of at least one magnitude 6.7 or greater earthquake

before 2036 along the Calaveras Fault (USGS, 2008).

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Mt. Diablo Thrust Fault

The northwest trending Mt. Diablo Fault extends from near the Alamo and Walnut Creek border along Highway 680,

extending southward to Cottonwood Canyon, in northern Dublin. The Mt. Diablo Fault is not currently mapped by

CGS, but fault coordinates have been published. The fault is different from the majority of Bay Area faults in that it is

not a strike-slip fault exhibiting horizontal plate motion, but rather a “blind thrust” fault. A blind thrust fault is a

compressional fault without apparent surface expression. In the case of the Mt. Diablo Fault, the compression is

caused by the differential; horizontal motions of the Concord and Greenville faults which abut Mt. Diablo. The fault

locations for this blind thrust fault are inferred. The 1994 Northridge earthquake is a recent example of faulting on a

blind thrust fault. The site is located approximately 2.1 miles (3.4 km) north of the Mt. Diablo Fault. The slip rate of

the Mt. Diablo Thrust Fault is estimated to be about two mm/year and has been assigned a moment magnitude

(Mmax) of 6.7 (CGS, 2002). The Working Group on California Earthquake Probabilities (WG07) has estimated that

there is a three percent probability of at least one magnitude 6.7 or greater earthquake on the Mt. Diablo thrust fault

before 2036 (USGS, 2008).

Hayward Fault

The Hayward Fault trends northwesterly approximately 55 miles (88 km) from the Milpitas area to San Pablo Bay.

The Hayward Fault has been divided into two segments, the Northern and Southern segments. The site is located

approximately 13 miles (21 km) from the Northern segment of the Hayward Fault, and more distant from the

Southern segment. The slip rate on the Northern segment of the Hayward Fault is estimated to be about nine

mm/year and has been assigned a moment magnitude (Mmax) of 6.9 (CGS, 2002). The Working Group on California

Earthquake Probabilities (WG07) has estimated that there is a 31 percent probability of at least one magnitude 6.7 or

greater earthquake before 2036 along the Hayward Fault (USGS, 2008).

3.7 Surface Fault Rupture

According to DMG Special Publications 42 (Hart, 1994), the site does not lie within an Earthquake Fault Zone, as

defined by the Alquist-Priolo Act of 1972. According to published mapping by DMG, no known fault traces cross the

site, and no evidence of surface ground rupture was noted during our site reconnaissance. Therefore, it is our opinion

that the likelihood of surface fault rupture at the site is low.

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3.8 Settlement Due to Collapsible Soils

Collapsible soils are fine sandy and silty soils that have been laid down by the action of flowing water, usually in

alluvial fan deposits. Terrace deposits and fluvial deposits can also contain collapsible soil deposits. The soil particles

are usually bound together with a mineral precipitate. The loose structure is maintained in the soil until a load is

imposed on the soil and water is introduced. The water breaks down the inter-particle bonds and the newly imposed

loading densifies the soil. Based on the soil classification and visual observation in the field, the site soils are

considered to have a low collapse potential.

3.9 Settlement Due to Consolidation

Consolidation is the densification of soil into a more dense arrangement from additional loading, such as new fills or

foundations. Consolidation of clayey soils is usually a long-term process, whereby the water is squeezed out of the

soil matrix with time. Sandy soils consolidate relatively rapidly with an introduction of a load. Consolidation of soft

and loose soil layers and lenses can cause settlement of the ground surface or buildings. Based on visual observation

in the field and laboratory testing, the soils at this site are generally stiff to very stiff lean clays with a low potential to

consolidate under the anticipated loads and consolidation settlement should be minimal.

3.10 Liquefaction Induced Phenomena

Research and historical data indicate that soil liquefaction generally occurs in saturated, loose granular soil (primarily

fine to medium-grained, clean sand deposits) during or after strong seismic ground shaking and is typified by a loss of

shear strength in the affected soil layer, thereby causing the soil to flow as a liquid. However, because of the higher

inter-granular pressure of the soil at greater depths, the potential for liquefaction is generally limited to the upper 40

feet of the soil. Potential hazards associated with soil liquefaction below or near a structure include loss of

foundation support, lateral spreading, sand boils, and areal and differential settlement.

Lateral spreading is lateral ground movement, with some vertical component, as a result of liquefaction. The soil

literally rides on top of the liquefied layer. Lateral spreading can occur on relatively flat sites with slopes less than two

percent under certain circumstances. Lateral spreading can cause ground cracking and settlement.

The site is mapped by the USGS and William Lettis & Associates as being located within a zone of low liquefaction

potential (see attached Figure 5). Groundwater was encountered at approximately 12 feet below ground surface in a

boring drilled at the site. The site was predominantly underlain with medium stiff to very stiff medium plastic clay

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(CL) with a layer of sandy clay (CL). Boring B-2 encountered a gravelly sand layer from a depth of 12 feet to 16 feet

below ground surface. This soil had a field blow count (modified California Sampler) of 23 which is corrected to an

SPT blow count of 14. We ran Liquefy-Pro software to analyze a potential for the liquefaction settlement. For this

analysis we considered water table as seven feet below ground surface, seismic coefficient of 0.50g (Sds/2.5), and

earthquake magnitude of 7.0. The results of the liquefaction analysis are attached as Appendix C. Based on the

information collected during the field investigation, laboratory test results, types of soils encountered in the borings

within the project site and liquefaction analysis, we determined the maximum settlement of 1 ½ inches with a safety

factor of 1.3 and with a differential settlement of about ¾ inch. This settlement should be taken into account by the

Structural Engineer during the design of the building foundations. We evaluated the potential for bearing capacity

failure in accordance with SCES 1999 and determined that there is sufficient capping in non-liquefiable soils to

preclude bearing capacity failure.

Based on the consistency of the soil, we judge this isolated layer to have a moderately high liquefaction potential. In

the event this layer did liquefy, surface manifestation of liquefaction would not be observed as there are 12 feet of

stiff to very stiff non-liquefiable soil overlying a four-foot layer of potentially liquefiable soil. Due to the soils type and

their stiffness, the potential for liquefaction in this project site is low, except for the isolated layer encountered in

Boring B-2.

3.11 Dynamic Compaction (Seismically Induced Settlement)

Dynamic compaction is a phenomenon where loose, sandy soil located above the water table densifies from

vibratory loading, typically from seismic shaking or vibratory equipment. The site is generally underlain by medium

stiff to very stiff clay above the water table. Thus, the site should not be susceptible to dynamic compaction

phenomena.

3.12 Flooding

The site is not subject to flooding, primarily because of its topographic position. FIRM (2009) has mapped the site

vicinity as Zone X, “areas determined to be outside the 0.2% annual chance floodplain”. Because of the fact that

there are no creeks crossing or in the immediate vicinity of the site, we conclude that the hazard of flooding at the

site is low. Determining the flood potential of the site is beyond the scope of this study or our expertise, and a flood

specialist should be contacted if a more in-depth flooding analysis is desired.

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3.13 Soil Erosion

Present construction techniques and agency requirements have provisions to limit soil erosion and resultant siltation

during construction. These measures will reduce the potential for soil erosion at the site during the various

construction phases. Long-term erosion at the site will be reduced by landscaping and hardscape areas, such as

parking lots and walkways, designed with appropriate surface drainage facilities.

3.14 Other Geologic Hazards

The site is not subject to the potential geologic hazards of landsliding, loss of mineral resources, presence of naturally

occurring asbestos, volcanism, tsunamis, seiches, or loss of unique geologic features, due to the sites location,

subsurface soil conditions, groundwater levels and land use factors.

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4.0 CONCLUSIONS AND RECOMMENDATIONS

The following conclusions and recommendations are based upon the analysis of the information gathered during the

course of this study and our understanding of the proposed improvements.

4.1 General

The site is considered geotechnically suitable for the proposed improvements provided the recommendations of this

report are incorporated into the design and implemented during construction. The predominant geotechnical and

geological issues that will need to be addressed at this site are summarized below.

Liquefaction – The site is mapped as being located within a zone of low liquefaction, with the exception of a localized

four-foot-thick sand lens at a depth of 12 feet in Boring B-2. The Structural Engineer should take the potential 1 ½

inch total settlement and ¾ inch differential settlement into account in the design of the structure.

Corrosive Soil – The site soils are considered to have a relatively low corrosion potential in regard to buried metal and

a moderate corrosion potential relative to concrete.

Expansive Soils – The site is underlain by highly expansive soils and some mitigation will be required during grading,

including placement of a 24-inch section of non-expansive fill.

Existing Fill - During subexcavation of the pad for placement of the 24-inch section of Select Non-expansive Fill, the

exposed existing fill should be evaluated by the Geotechnical Engineer relative to whether more over-excavation of

the fill will be needed. The maximum depth of over-excavation for fill removal is unlikely to be more than three to

four feet from pad grade, if necessary. Excavated fill soil may be placed back as compacted fill below the upper 24-

inch section of Select Fill.

Seismic Considerations – The site is located within a seismically active region. As a minimum, the building design

should consider the effects of seismic activity in accordance with the latest edition of the CBC.

4.1.1 Seismic Considerations

The site is located within a seismically active region and should be designed to account for earthquake ground

motions as described in this report. For seismic analysis of the proposed site in accordance with the seismic

provisions of the CBC 2010, we recommend the following parameters and summary is attached in Appendix C.

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Table 3: Seismic Design Parameters Based on 2010 CBC (2009 IBC)

Item Value Location Site Class D Table 1613.5.2R1 Mapped Spectral Response Accelerations Short Period, Ss 1-second Period, S1

1.885g 0.671 g

USGS R2

Site Coefficient, Fa 1.0 Table 1613.5.3(1)R1 Site Coefficient, Fv 1.5 Table 1613.5.3(2)R1 MCE (SMS) 1.885 g MCE (SM1) 1.007g Design Spectral Response Acceleration Short Period, SDS 1-second Period, SD1

1.256g 0.671g

R1 California Building Standards Commission (CBSC), “California Building Code,” 2010 Edition. R2 U.S. Seismic “Design Maps” Web Application, https://geohazards.usgs.gov/secure/designmaps/us/application.php

4.2 Site Grading and Drainage

The grading section of this report is divided into several sections. The first section provides the compaction criteria

for the project. The remaining sections discuss grading in general for building pads and concrete hardscape areas,

and drainage.

4.2.1 Project Compaction Recommendations

The following table provides the recommended compaction requirements for this project. Not all soils, aggregates

and scenarios listed below may be applicable for this project. Specific grading recommendations will be discussed

individually within applicable sections of this report.

PROJECT COMPACTION REQUIREMENTS

Description Min. Percent Relative Compaction

Min. Percent Above Optimum Moisture Content

Fill Areas, Engineered Fill, Onsite Soil 90 3 Fill Areas, Engineered Fill, Select Fill 90 2 Building Pads, Onsite Soil 90 3 Building Pads, Class 2 AB or Select Fill 90 2 Concrete Flatwork, Subgrade Soil 90 3 Concrete Flatwork, Class 2 AB 90 2

https://geohazards.usgs.gov/secure/designmaps/us/application.php

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PROJECT COMPACTION REQUIREMENTS (cont’d.) Description Min. Percent Relative

Compaction Min. Percent Above

Optimum Moisture Content Underground Utility Backfill, Upper five feet 95 3 Underground Utility Backfill, Deeper than five feet 90 2 Pavement section, Class 2 AB 95 2

4.2.2 Site Preparation and Demolition

Site grading should be performed in accordance with these recommendations. A pre-construction conference should

be held at the jobsite with representatives from the owner, general contractor, grading contractor, and Geosphere

prior to starting the clearing and demolition operations at the site.

Prior to commencement of grading activities, areas to receive fill, structures, or pavements should be cleared of

existing surface vegetation, organic-laden soils, building materials including foundations if present, existing loose soil,

AC and AB pavement section, and debris. Debris resulting from site stripping operations should be removed from the

site, unless otherwise permitted by the Geotechnical Engineer.

Excavations resulting from the removal of abandoned underground utilities, or deleterious materials should be

cleaned down to firm soil, processed as necessary, and backfilled with engineered fill in accordance with the grading

sections of this report. The Geotechnical Engineer’s representative should verify the adequacy of site clearing

operations during construction, prior to placement of engineered fill.

Existing underground utilities proposed to be abandoned, if present, should be properly grouted, closed, or removed

as needed. If the utilities are removed, the excavations should be backfilled with properly compacted fill or other

material approved by the Geotechnical Engineer. The extent of removal/abandonment depends on the diameter of

the pipe, depth of the pipe, and proximity to buildings and pavement.

4.2.3 General Grading

Onsite soil generated from cut areas following clearing and grubbing that is free of excess organic material (three

percent or less by weight) or debris may be suitable for use as structural fill at the site. Imported fill should be non-

expansive, having a Plasticity Index of 12 or less, an R-Value greater than 40, and enough fines so the soil can bind

16

together. Imported soil should be free of organic materials and debris, and should not contain rocks or lumps greater

than three inches in maximum size. The Geotechnical Engineer should approve imported fill prior to delivery onsite.

If grading occurs in the winter rainy season, unstable subgrade conditions may be present. These conditions may

require stabilizing the subgrade with admixtures, such as lime. Isolated areas may be stabilized using one foot of

Class 2 baserock over the geogrid. Additional recommendations can be provided, if required, during construction.

4.2.4 Building Pad Grading

Because the near surface consists of expansive soil, the building pads should be over-excavated at least 24-inches

from finish subgrade. The bottom of the over excavation should then be scarified at least 10-inches, moisture

conditioned and compacted. Engineered Fill can then be placed in eight-inch, uncompacted lifts, moisture

conditioned and compacted. For expansive soil mitigation, the upper 24 inches of the building pad should be

underlain by Select, non-expansive fill. The Select Fill should extend at least five-feet outside the building perimeter.

4.2.5 Grading Flatwork Areas

Flatwork areas can be scarified eight-inches, uniformly moisture conditioned, and compacted. Onsite soil can then be

placed in eight-inch thick loose lifts and compacted to construct the flatwork up to finish subgrade elevation.

4.2.6 Drainage

Final grading should be designed to provide drainage away from the structure. Soil areas within 10 feet of proposed

structures should slope at a minimum of five percent away from the building. Adjacent concrete hardscape should

slope a minimum two percent away from the building. Roof leaders and downspouts should not discharge into

landscape areas adjacent to buildings.

4.3 Utility Trench Construction

4.3.1 Trench Backfilling

Utility trenches may be backfilled with onsite soil above the utility bedding and shading materials. If rocks or concrete

larger than four inches in maximum size are encountered, they should be removed from the fill material prior to

placement in the utility trenches. Backfill more than five feet should have a higher compaction requirement than the

soil in the upper five feet. The subgrade soil in building pads and pavement areas may also have different compaction

requirements (see Section 4.3.1, Project Compaction Requirements).

17

Pea gravel, rod mill, or other similar self-compacting material should not be utilized for trench backfill since this

material will transmit the shallow groundwater to other locations within the site and potentially beneath the

building. Additionally, fines may migrate into the voids in the pea gravel or rod mill, which could cause settlement of

the ground surface above the trench.

4.3.2 Utility Penetrations at Building Perimeter

Flexible connections at building perimeters should be considered for utility lines going through perimeter

foundations. This would provide flexibility during a seismic event. This could be provided by special flexible

connections, pipe sleeving with appropriate waterproofing, or other methods.

Utility trenches should be sealed with concrete, clayey soil, sand-cement slurry, or controlled density fill (CDF) where

the utility enters the building under the perimeter foundation. This would reduce the potential for migration of water

beneath the building through the shading material in the utility trench.

4.3.3 Pipe Bedding and Shading

Pipe bedding material is placed in the utility trench bottom to provide a uniform surface, a cushion, and protection

for the utility pipe. Shading material is placed around the utility pipe after installation and testing to protect the pipe.

Bedding and shading material and placement are typically specified by the pipe manufacturer, agency, or project

designer. Agency and pipe manufacturer recommendations may supersede our suggestions. These suggestions are

intended as guidelines and our opinions based on our experience to provide the most cost-effective method for

protecting the utility pipe and surrounding structures. Other geotechnical engineers, agency personnel, contractors,

and civil engineers may have different opinions regarding this matter.

Bedding and Shading Material - The bedding and shading material should be the same material to simplify

construction. The material should be clean, uniformly graded, fine to medium grained sand. It is suggested that

bedding and shading material contain less than three percent fines with 100 percent passing the No. 8 sieve. Coarse

sand, angular gravel, or baserock should be avoided since this type of shading material may bridge when backfilling

around the pipe, possibly creating voids, and may be too stiff as bedding material. Open graded gravel should be

avoided for shading since this material contains voids, and the surrounding soil could wash into the voids, potentially

causing future ground settlement. However, open graded gravel may be required for bedding material when water is

entering the trench. This would provide a stable working surface and a drainage path to a sump pit in the trench for

water in the trench. The maximum size for bedding material should be limited to about ¾ -inch.

18

Bedding Material Placement - The thickness of the bedding material should be minimized to reduce the amount of

trench excavation, soil export, and imported bedding material. Two to three inches for pipes less than eight-inches in

diameter and about four to six inches for larger pipes are suggested. Bedding for very large diameter pipes are

typically controlled by the pipe manufacturer. Compaction is not required for thin layers of bedding material. The

pipe needs to be able to set into the bedding, and walking on a thin layer of bedding material should sufficiently

compact the sand. Rounded gravel may be unstable during construction, but once the pipe and shading material is in

place, the rounded gravel will be confined and stable.

Shading Material Placement – Jetting is not typically recommended since the type of shading material is unknown

when preparing the geotechnical report and agencies typically do not permit jetting. If the sand contains fines or if

the sand is well graded, jetting will not work. Additionally, if too much water is used during jetting, this could create a

wet and unstable condition. However, clean, uniformly graded and fine to medium sand can be placed by jetting. The

shading material should be able to flow around and under the utility pipe during placement. Some compactive effort

along the sides of the pipe should be made by the contractor to consolidate the shading material around the pipe. A

minimum thickness of about six-inches of shading material should be placed over the pipe to protect the pipe from

compaction of the soil above the shading material. The contractor should provide some compactive effort to densify

the shading material above the pipe. Relative compaction testing is not usually performed on the shading material.

However, the contractor is ultimately responsible for the integrity of the utility pipe.

4.4 Temporary Excavations

The contractor should utilize proper Cal OSHA methods during construction. Excavations in soil more than five feet

deep for utility trenches and the basement should have side slopes constructed at 1H:1V (horizontal to vertical). If

excavations are more than eight feet deep, the Geotechnical Engineer should be advised to review the impacts. The

contractors should make selection of temporary side slopes based upon the materials encountered during the

excavation. Maximum slope ratios provided above are assumed to be uniform from top to toe of the slope. Adequate

provisions should be made to prevent water from ponding on top of the slope and from flowing over the slope face.

Surcharge loads should not be permitted within 10 feet of the top of the slope. Desiccation or excessive moisture in

the excavation could reduce stability and require shoring or laying backside slopes.

19

4.5 Building Foundations

The proposed building can be constructed on shallow foundations founded at least 24 inches below the lowest

adjacent finished grade. The Structural Engineer should determine foundation reinforcement requirements. The

spread footings may be designed using an allowable bearing pressure of 3,000 psf for dead plus live loads at the

recommended minimum depth. A one-third increase in allowable dead plus live load bearing pressure may be used

when considering the effects of temporary wind or seismic forces.

For resistance to lateral loads, an allowable coefficient of friction of 0.30 between the base of the foundation

elements and underlying material is recommended. In addition, an allowable passive resistance equal to an

equivalent fluid weighing 300 pounds per cubic foot (pcf) acting against the foundation may be used to resist lateral

forces. The top foot of passive resistance at foundations should be neglected unless the ground surface around the

footing is covered by concrete or pavement.

Footing excavations should have firm bottoms and be free from excessive slough prior to concrete or reinforcing steel

placement. If construction occurs during the winter months, it is suggested that a thin layer of concrete be placed at

the bottom of the footings at the time of excavation. This will protect the bearing soil and facilitate removal of water

and slough if rainwater fills the excavations.

Where utility trenches are to be located adjacent to foundations, the bottom of the footing should be located below

an imaginary 1:1 (horizontal to vertical) plane projected upward from the nearest bottom edge of the utility trench.

Total and differential settlement should be approximately on the order of one-inch and a half-inch or less,

respectively. Approximately half of the total settlement should occur during construction. A representative of

Geosphere Consultants, Inc., prior to placement of reinforcing steel or concrete, should observe the foundation

excavations to evaluate the exposed soil conditions.

4.6 Concrete Slabs-on-Grade

4.6.1 Interior Floor Slabs

It is recommended that the floor slab be at least five-inches thick. The floor slab should be tied to the perimeter

footings. The floor slab should be placed on a 24-inch thick layer of Select Fill or Class 2 baserock, per Section 4.3 of

this report. Floors with moisture sensitive floor coverings should be underlain by a high quality vapor retarder

meeting ASTM E1745 Class C requirements, such as StegoWrap, Griffolyn Type 65, Moistop Ultra C, or equivalent.

20

The vapor retarder can be placed directly on the prepared subgrade soil. If the floor slab will have very highly

moisture sensitive floor coverings, such as wood floors or special vinyl floors, ASTM Class B requirements should be

met (Griffolyn Type 85, Moistop Ultra B, or equivalent). ASTM E1643 should be utilized as a guideline for the

installation of the vapor retarder. A capillary rock layer or rock cushion is not required beneath the floor slab and a

sand layer is not required over the vapor retarder. If the design engineers require sand on top of the vapor retarder,

the thickness should be minimized to less than one-inch. If construction occurs in the winter months, water may

pond within the sand layer since the vapor retarder may prevent the vertical percolation of rainwater.

4.6.2 Exterior Concrete Flatwork

Exterior concrete flatwork with pedestrian traffic should be at least five-inches thick and should be underlain by at

least four-inches of Class II AB. The flatwork should be reinforced to reduce potential tripping hazards; welded wire

mesh should not be utilized. The flatwork should be doweled into the building foundation adjacent to doorways and

into curbs to prevent possible tripping hazards.

If possible, the building should have a concrete apron around the building to reduce the potential for surface water

percolating down through the soil adjacent to the buildings. Landscaping adjacent to the building should be avoided

if possible. Typically, landscape areas adjacent to buildings are surrounded by concrete flatwork, which prevents

irrigation and rainwater from flowing away from the building. The ponded water trapped by the surrounding flatwork

could percolate down, or possibly laterally through perimeter foundation construction joints or pipe sleeves and

travel beneath the floor slab. Drainage can be provided in these landscape areas, but the top of the drains should be

located below the building pad subgrade elevation.

4.7 Plan Review

It is recommended that Geosphere be provided the opportunity to review the final project plans prior to

construction. The purpose of this review is to assess the general compliance of the plans with the recommendations

provided in this report and the incorporation of these recommendations into the project plans and specifications.

4.8 Observation and Testing During Construction

It is recommended that Geosphere be retained to provide observation and testing services during site preparation,

mass grading, underground utility construction, foundation excavation, and to observe final site drainage. This is to

21

observe compliance with the design concepts, specifications and recommendations, and to allow for possible

changes in the event that subsurface conditions differ from those anticipated prior to the start of construction.

22

REFERENCES

Abrahamson, Norman A., Effects of Rupture Directivity on Probabilistic Seismic Hazard Analysis, Proceedings GICSZ, Palm Springs, California, November 2000. Abrahamson, Norman A., State of the Practice of Seismic Hazard Evaluation, Proceedings of Geotechnical Engineering, 2000, Melbourne, Australia, November 2000. Abrahamson, N., and Shedlock, K., editors, Ground Motion Attenuation Relationships, Seismological Research Letters, v. 68, no. 1, January 1997 special issue, 256 pp. American Society for Testing and Materials, West Conshohocken, Pennsylvania. Association of Bay Area Governments (ABAG), April 2003, “On Shaky Ground”, website: http://www.abag.ca.gov/ Blake, Thomas F., EQSearch version 3.00, EQFault1 version 3.00, FriskSP version 4.00, software and manuals with 2004 CGS fault model updates. California Building Code, 2010, California Code of Regulations, Title 24, Chapter 16. California Geological Survey, Seismic Hazard Mapping Program, 2003 website http://gmw.consrv.ca.gov/shmp California Geological Survey, 1996, Probabilistic seismic hazard assessment for the state of California, DMG Open-File report 96-08 (USGS Open-File Report 96-706), and updated Appendix A, Appendix A – 2002 California Fault Parameters. California Geological Survey, 2008, Guidelines for evaluating and mitigating seismic hazards in California: California Geological Survey Special Publication 117, 60 p. Campbell, Kenneth W., and Bozorgnia, Yousef, Updated Near-Source Ground-Motion (Attenuation) Relations for Horizontal and Vertical Components of Peak Ground AcGeosphereeration and AcGeosphereeration Response Spectra, Bulletin of the Seismological Society of America, Volume 93, No. 1, pp. 314-331, February 2003. Cao, Tianquing, Bryant, William A., Rowshandel, Badie, Branum, Dave, and Wills, Christopher J., The Revised 2002 California Probabilities Seismic Hazard Maps, June 2003. Division of Mines and Geology, 1990. Geologic Map of the San Francisco-San Jose Quadrangle compiled by D. L. Wagner and E. J. Bortugno. Scale 1:250,000. FIRM, Flood Insurance Rate Map, Contra Costa County, California, Panel 292 of 602, Map Number 06013C0292F, June 16, 2009. Association of Bay Area Governments (ABAG), 1995, “Bay Area Dam Failure Maps for Contra Costa County”, http://www.abag.ca.gov/cgi-bin/pickdamx.pl

http://www.abag.ca.gov/

http://gmw.consrv.ca.gov/shmp

23

Hart, E. W., 1983, Summary Report: Fault Evaluation Program, 1981 – 1982, Area-Northern Coast Ranges region, California, California Department of Conservation, Division of Mines and Geology, Open-File Report 83-10. Jennings, C.W., compiler, 1994, Fault activity map of California and adjacent areas with locations and ages of recent volcanic eruptions: California Geological Survey, Geologic Data Map No. 6, scale 1:750,000, with 92-page booklet. Lawson, A. C. (ed.), 1908, The California Earthquake of April 18, 1906, State Earthquake Investigation Commission, reprinted 1969 by the Carnegie Institution of Washington. Malhotra, Praveen K., Earthquake Induced Ground Motions, American Society of Civil Engineers Continuing Education Seminar, 2011. Checklist for the review of engineering geology and seismology reports for California Public Schools, Hospitals, and Essential Services Buildings: California Geological Survey – Note 48, (dated January 1, 2011). California Geological Survey, 2008 “Guidelines for Evaluating and Mitigating Seismic Hazards In California” Special Publication 117. U. S. Geological Survey, Earthquake Hazards Program website eqhazmaps.usgs.gov. U.S. Geological Survey, Geologic Map of Contra Costa County, USGS Scientific Investigation Map American Society for Testing and Materials, West Conshohocken, Pennsylvania.

24

LIMITATIONS AND UNIFORMITY OF CONDITIONS

The recommendations of this report are based upon the soil and conditions encountered in the borings. If variations

or undesirable conditions are encountered during construction, Geosphere should be contacted so that supplemental

recommendations may be provided.

This report is issued with the understanding that it is the responsibility of the owner or his representatives to see that

the information and recommendations contained herein are called to the attention of the other members of the

design team and incorporated into the plans and specifications, and that the necessary steps are taken to see that

the recommendations are implemented during construction.

The findings and recommendations presented in this report are valid as of the present time for the development as

currently proposed. However, changes in the conditions of the property or adjacent properties may occur with the

passage of time, whether by natural processes or the acts of other persons. In addition, changes in applicable or

appropriate standards may occur through legislation or the broadening of knowledge. Accordingly the findings and

recommendations presented in this report may be invalidated, wholly or in part, by changes outside our control.

Therefore, this report is subject to review by Geosphere after a period of three (3) years has elapsed from the date of

issuance of this report. In addition, if the currently proposed design scheme as noted in this report is altered

GEOSPHERE should be provided the opportunity to review the changed design and provide supplemental

recommendations as needed.

Recommendations are presented in this report which specifically request that Geosphere be provided the

opportunity to review the project plans prior to construction and that we be retained to provide observation and

testing services during construction. The validity of the recommendations of this report assumes that GEOSPHERE will

be retained to provide these services.

This report was prepared upon your request for our services, and in accordance with currently accepted geotechnical

engineering practice. No warranty based on the contents of this report is intended, and none shall be inferred from

the statements or opinions expressed herein.

The scope of our services for this report did not include an environmental assessment or investigation for the

presence or absence of wetlands or hazardous or toxic materials in the soil, surface water, groundwater or air, on,

25

below or around this site. Any statements within this report or on the attached figures, logs or records regarding

odors noted or other items or conditions observed are for the information of our client only.

FIGURES

Figure 1 – Site Vicinity Figure 2 – Site Plan

Figure 3 – Site Vicinity Geology Map Figure 4 – Schematic Geologic Cross-Section A-A’

Figure 5 – Site Geologic Map Figure 6 – Liquefaction Susceptibility Map

Figure 7 – Flood Hazard Map Figure 8 - Regional Geologic Map

91-02968-A January 2013

Figure 1

Ygnacio Valley High School - Chemistry Lab755 Oak Grove RoadConcord, California

Site Vicinity Map

N

Site

Ygnacio Valley High School - Chemistry LabConcord, California

Base Map Reference: Google Earth

Figure 2 Site Plan and Site

Geology Map

January 201391-02968-A

N

- Approximate Scale100 ft0

- Geologic Cross Section

- Proposed Building QpaQpa - Alluvium, Pleistocene

- Approximate Boring Location

B-2B-2

B-1B-1

B-2B-2AA

A'A'

QpaQpa

QpaQpa

QpaQpa

QpaQpa


Figure 3Site Vicinity Geologic Map

January 201391-02968-A

Source: United StatesGeologic Survey, GeologicMap of Contra Costa County, USGSScientific Map Investigations2918

Site

QhaQha

QhaQha

QpaQpa

QpaQpa

QhaQha

QhaQha

QhaQha

QpaQpa

QpaQpa

afafQpaQpa

KsKs

af - Artificial Fill Qha - Alluvium, HoloceneK , Cretaceous Qpa - Alluvium, Pleistocene s - Great Valley complex sedimentary rocks

Geologic contacts Geologic faults

45

50

55

60

65

70

75

80

85

90

95

100

0 10 20 30 40 50 60 70 80 90 100 110 120 13045

50

55

60

65

70

75

80

85

90

95

100

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Schematic Geologic Cross-Section A-A'Distance Along Baseline (ft)

Projected

SUBSURFACE DIAGRAM

A

Ele

vatio

n (f

t)

CL - Unified Soil Classification System (USCS)14 - Blows Per Six Inches, Standard Penetration Test(21) - N Value

CLIENT Mt Diablo Unified School District

PROJECT NUMBER 91-02968-A

PROJECT NAME Ygancio Valley High School - Chemistry Lab

PROJECT LOCATION 755 Oak Grove Road, Concord, CA

2001 Crow Canyon Road, Suite 100San Ramon, CA 94583Telephone: 925-314-7100Fax: 925-855-7140

4-5-6(11)

5-8-12(20)

6-8-12(20)

2-1-3(4)

2-2-3(5)

3-5-8(13)

3-5-9(14)

5-8-10(18)

4-5-6(11)

6-12-18(30)

CL

CL

CL

CL

2-4-5(9)

5-8-8(16)

5-7-8(15)

5-6-6(12)

4-8-9(17)

8-10-10(20)

CL

CL

CL

GP

CL

Figure 4

ProjectedProposedBuilding

B-1B-2

Treat B

lvd

Ygnacio Valley Rd

David A

ve

Moh

r Ln

Oak G

rove R

d

Bancro

ft Rd

Walnut Ave

Cow

ell R

d

North Gate Rd

Monum

ent B

lvd

La

s J

un

tas

Way

Wh

it

man R

d

Ygnacio V

alle

y R

d

Ygnacio Valley Rd

Treat B

lvd

Min

ert Rd

Wig

et L

n Arbolado Dr

Citrus A

ve

San

Carlo

s D

r

Ryan R

d

Ch

err

y L

n

Pea

ch P

l

Pe

ar

Dr

Cedro Ln

Arke

ll R

d

Waln

ut

Blv

d

La Casa Via

Nuala S

t

Valley Vista Rd

Dover D

r

Eb

an

o D

r

Nav

aro

nn

e W

ay

Smith

Ln

Sn

yd

er

Ln

San Antonio D

r

Ro

ck O

ak R

d

Cly

de D

r

G

ill P

ort Ln

Shadelands Dr

Sti

mel D

rM

itchell

Dr

K

inross Dr

Santa Paula D

r

Lennon L

n

Quiet Place Dr

Nara

nja

Dr

Deerpark Dr

Geto

un D

r

San M

iguel R

d

Whitm

an Rd

Comistas Dr

Rockne D

r

Win

to

n Dr

Peachwill

ow Ln

La

s L

om

as

Wa

y

L ane Dr

Fyne Dr

Sugarberr

y Ln

Whi tehaven Dr

Kaski Ln

Jo

ne

s R

d

Hu

tch

ins

on

Rd

Marc

ia D

r

Pera

da D

r

Stratto

n Rd

Par

ish D

r

Lyon C

irRam

on

a D

r

Candelero

Dr

Sierra R

d

B

ow

ling Green

Dr

Banbury R

d

Madig

an A

ve

Via

A

ppia Via Verde

Indian Hill Dr

Lynn D

r

Sha

ry Cir

Entrance

Diablo Shadow Dr

Co

gg

ins

Dr

Kirby Ln

Dias Dr

Tra

ud

Dr

Rae A

nne Dr

Ald

erw

oo

d R

d

Dupre Ct

Pers

hin

g D

r

Till

ey C

ir

Walnut Creek

Concord

§¨¦ 680

This map is intended for planning use only and

is not intended to be site-specific. Rather, it

depicts the general hazard level of a

neighborhood and the relative hazard levels

from community to community. Hazard levels

are less likely to be accurate if your

neighborhood is on or near the border between

two zones. This information is not a substitute

for a site-specific investigation by a licensed

professional.

This map is available at

http://quake.abag.ca.gov

Sources:

This map is based on work by William

Lettis & Associates, Inc. and USGS.

USGS Open-File Report 00-444, Knudsen

& others, 2000 and

USGS Open-File Report 2006-1037, Witter

& others, 2006

For more information visit:

http://pubs.usgs.gov/of/2000/of00-444/

http://pubs.usgs.gov/of/2006/1037/

1 inch = 0.41 milesScale:

Liquefaction Susceptibility

Map

Local Roads

Major Roads

Very High

High

Moderate

Low

Very Low

Susceptib ility Level

Figure 5Liquefaction

Susceptibility Map

Site

Ygnacio Valley High School - Chemistry LabConcord, California January 201391-02968-A

Map Prepared by the ABAG Earthquake Program. April 2004.

Reproduced with permission, California Geological

Survey from CD-ROM 2001-04 (2001), Official Map

of Alquist-Priolo Earthquake Fault Zones

This interactive map was created using digital files of AP

EFZ quadrangles and is considered an electronic

facsimile of the Official Alquist-Priolo Earthquake Fault

Zone map. If there is any doubt or conflict with respect

to the location of EFZ boundaries, the original clear-film

overlay compiled by and on file with CGS is the official

version of the map. Fault information in these digital files

is not sufficient to serve as a substitute for the geological

site studies required under Chapter 7.5 of Division 2 of

the California Public Resources Code.

For more information visit:

http://www.consrv.ca.gov/CGS/rghm/ap/

This map is available at:

http://quake.abag.ca.gov/

Alquist-Priolo Earthquake

Fault Zones

Water

Major Roads

Local Roads

Scale:

Earthquake Fault Zones

Greenville

San Andreas-North Golden Gate

San Andreas -- Peninsula

San Andreas -- Santa Cruz

Rodgers Creek

North Hayward

South Hayward

Northern Calaveras

Central Calaveras

Maacama

West Napa

Concord/Green Valley

Northern San Gregorio

Sargent

Solano

County

Alameda

County

Contra Costa

County

Napa

CountySonoma

County

San Mateo

County

Marin

County

San Francisco

Sacramento

County

§¨¦ 580§¨¦ 880

§¨¦ 680

§¨¦ 80

§¨¦ 780

§¨¦ 580

§¨¦ 680

§¨¦ 580

§¨¦ 80

§¨¦ 780

£¤ 101

£¤ 101

1 inch = 6.65 miles

Figure 6Regional Fault

Map

Site

Ygnacio Valley High School - Chemistry LabConcord, California January 201391-02968-A

Treat B

lvd

Main

St

Clayton Rd

Concord Blvd

Ygnacio Valley Rd

Co

ntra

Co

sta

Blv

d

Bai

ley

Rd

Civ

i c D

r

Detro

it Ave

Boyd Rd

Geary Rd

Concord Ave

Wes

t St

David A

ve

Mohr Ln

Oak G

rove R

d

Taylor Blvd

Will

ow P

ass Rd

Viking Dr

Aye

rs R

d

Bancro

ft Rd

Diablo

North Gate

Rd

Cowell Rd

Walnut Ave

Salvio

St

Oak Park Blvd

Bu

en

a V

ista

Ave

Gregory Ln

Meadow

Ln

Ba

be

l Ln

Den

kin

ger

Rd

Dia

mond B

lvd

Chilpancingo Pkwy

Oly

mpic

Blv

d

Bu

skir

k A

ve

Bro

adw

ay

Oa

kla

nd

Blv

d

Mount D

iablo

Scenic B

lvd

Bu

sk

irk

Av

e

Treat B

lvd

Ygnacio Valle

y R

d

Ygnacio Valley Rd

Concord

Walnut Creek

Pleasant Hill

Martinez

Lafayette

AB

242

This map is intended for planning use only,

and is not intended to be site-specific.

Rather, it depicts the general risk within

neighborhoods and the relative risk from

community to community.

This map is available at

http://quake.abag.ca.gov

For more detailed informtion regarding this map,

please visit the USGS website at

http://wrgis.wr.usgs.gov/open-file/of97-745/

Source:

USGS Open File Report 97-745 E, 1997

1 inch = 0.82 milesScale:

Summary Distribution of

Slides and Earth Flows

in the San Francisco

Bay Region

Mostly Landslides

Many Landslides

Flatland

Few Landslides

Very Few Landslides

Figure 7Existing Landslide

Map

Ygnacio Valley High School - Chemistry LabConcord, California 91-02968-A

Site

January 2013

Figure 8Flood Hazard Map

Site

Zone X - Areas determined to be outside the 0.2% annual chance floodplain.


January 201391-02969-A

Site

APPENDIX A

Boring Logs

MC1-1

MC1-2

MC1-3

MC1-4

SPT1-5

SPT1-6

4-5-6(11)

5-8-12(20)

6-8-12(20)

2-1-3(4)

2-2-3(5)

3-5-8(13)

105

115

110

95

20

14

18

31

47 26 21

51

21

(CL) SANDY CLAY/CLAYEY SAND : Orange/Brown, moist,very stiff, medium plasticity, w/ gravels and traces of organics. Fill.

(CL) SANDY CLAY : Gray/Brown, moist, very stiff, mediumplasticity, with some gravels. Possible fill.

(CL) LEAN CLAY : Gray/Brown, moist, very stiff, low plasticity.

(CL) SANDY CLAY : Brown, wet, soft to medium stiff.

NOTES

GROUND ELEVATION 95 ft

LOGGED BY RJW

DRILLING METHOD Hollow Stem Auger 8"

HOLE SIZE 8"

DRILLING CONTRACTOR Exploration Geoservices Inc. GROUND WATER LEVELS:

CHECKED BY GH

DATE STARTED 1/3/13 COMPLETED 1/3/13

AT TIME OF DRILLING 12.00 ft / Elev 83.00 ft

AT END OF DRILLING ---

AFTER DRILLING ---

SA

MP

LE

TY

PE

NU

MB

ER

RE

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%(R

QD

)

BLO

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OU

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S(N

VA

LU

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PO

CK

ET

PE

N.

(tsf)

DR

Y U

NIT

WT

.(p

cf)

MO

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ON

TE

NT

(%

)

LIQ

UID

LIM

IT

PLA

ST

ICLIM

IT

PLA

ST

ICIT

YIN

DE

X

FIN

ES

CO

NT

EN

T(%

)

ATTERBERGLIMITS

(Continued Next Page)

PLA

ST

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YIN

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GR

AP

HIC

LO

G

DE

PT

H(f

t)

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5

10

15

20

25

MATERIAL DESCRIPTION

PAGE 1 OF 2

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SPT1-7

SPT1-8

SPT1-9

SPT1-10

3-5-9(14)

5-8-10(18)

4-5-6(11)

6-12-18(30)

94 21 59

(CL) SANDY CLAY : Brown, wet, soft to medium stiff.(continued)

gravelly sand lense approximately 0.5 feet

becomes very stiff to hard.

Bottom of borehole at 50.0 feet.

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MC2-1

MC2-2

MC2-3

SPT2-4

SPT2-5

2-4-5(9)

5-8-8(16)

5-7-8(15)

5-6-6(12)

4-8-9(17)

106

111

106

19

17

10 4

(CL) LEAN CLAY : Orange/Brown, moist, stiff, low plasticity, w/lots of gravels and traces of organics. Fill.

(CL) SANDY CLAY : Brown, moist, stiff, low plasticity, w/ somegravels and roots. Possible fill.

(CL) LEAN CLAY : Gray/Brown, moist, very stiff, low plasticity.

(GP) FINE GRAVELLY SAND/SANDY FINE GRAVEL : wet,dense.

(CL) LEAN CLAY : Brown, wet, stiff, low plasticity, w/ somefine sand.

NOTES

GROUND ELEVATION 95 ft

LOGGED BY RJW

DRILLING METHOD Hollow Stem Auger 8"

HOLE SIZE 8"

DRILLING CONTRACTOR Exploration Geoservices Inc. GROUND WATER LEVELS:

CHECKED BY GH

DATE STARTED 1/3/13 COMPLETED 1/3/13

AT TIME OF DRILLING 12.00 ft / Elev 83.00 ft

AT END OF DRILLING ---

AFTER DRILLING ---

SA

MP

LE

TY

PE

NU

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ER

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.(p

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ST

ICLIM

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(Continued Next Page)

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PAGE 1 OF 2

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SPT2-6

8-10-10(20)

(CL) LEAN CLAY : Brown, wet, stiff, low plasticity, w/ somefine sand. (continued)

Bottom of borehole at 30.0 feet.

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30


PAGE 2 OF 2

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APPENDIX B

LABORATORY TEST RESULTS Atterberg Limits

Direct Shear Sieve Analysis

Corrosion

APPENDIX C

Liquefaction Analysis

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