APPENDIX_A_-_GEOTECHNICAL_REPORT_Pacific_Crest.pdf

G E O T E C H N I C A L | E N V I R O N M E N T A L | C H E M I C A L | M A T E R I A L T E S T I N G | S P E C I A L I N S P E C T I O N S

444 AIRPORT BLVD. , SUITE 106 | WATSONVILLE, CA 95076 | PHONE 831-722-9446 | WWW.4PACIFIC-CREST.COM

Project No. 1922.1-SZ81-C41 September 10, 202 4

Mr. Rodney Cahill, Principal

MME

224 Walnut Avenue, Suite B Santa Cruz, CA 95060

Subject: Geotechnical Plan Review Phase I 100% Design Plans Lee Road Trail Project Watsonville, California

Reference: Pacific Crest Engineering, Inc., Geotechnical Investigation – Design Phase Lee Road Trail Project No. 1922.1-SZ81-C41 dated September 4, 2020

Dear Mr. Cahill, As requested, Pacific Crest Engineering Inc. has performed a geotechnical review of the following plan sheets from the tentative map set:

Sheet Number Prepared By Latest

Revision Date C0.0, 0.1, 0.2, 0.3, 1.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 4.1 MME July 17, 2024

Our review was limited only to the geotechnical aspects of the referenced plan set. Based on our review, and in consideration of the comments herein, it is our professional opinion that the aforementioned plan sheets are in general conformance with our geotechnical recommendations as referenced above.

Our review of these plans assume that Pacific Crest Engineering Inc. will be notified at least four (4) working days prior to any site clearing and grading operations on the property. During this period a pre-construction site conference must be held, with at least the owner, the grading contractor, and one of our engineers present. At this meeting, the project specifications and the testing and inspection responsibilities will be outlined and discussed.

Our review of these plans also assume that Pacific Crest Engineering will be retained to perform geotechnical observation and testing services during construction in order to provide, upon completion, written documentation that the earthwork improvements have been constructed in general conformance with the project plans, specifications, and the geotechnical report. It is the responsibility of the owner, or their representative, to ensure that the information and recommendations provided by Pacific Crest Engineering, Inc. are called to the attention of the Contractor and subcontractors and that the necessary steps are taken to ensure that such recommendations are carried out in the field.

Page 2Lee Road Trail Project – Phase I September 10, 2024 Project Number 1922.1-SZ81-C41

Any work related to grading or foundation excavation that is performed without the full knowledge and direct observation of Pacific Crest Engineering Inc., the Geotechnical Engineer of Record, will render our recommendations invalid. Please refer to the referenced geotechnical report for additional information.

Sincerely, PACIFIC CREST ENGINEERING INC.

Elizabeth M. Mitchell, GE Associate Geotechnical Engineer GE 2718, Expires 12/31/24

Copies: 1 to Client (e-copy)

G E O T E C H N I C A L | E N V I R O N M E N T A L | C H E M I C A L | M A T E R I A L T E S T I N G | S P E C I A L I N S P E C T IO N S

444 AIRPORT BLVD. , SUITE 106 | WATSONVILLE, CA 95076 | PHONE 831-722-9446 | WWW.4PACIFIC-CREST.COM

December 10, 2024 Project No. 1922.1-SZ81-C41

Mr. Rodney Cahill, Principal

MME

224 Walnut Avenue, Suite B Santa Cruz, CA 95060

Subject: Seismic Update Letter Phase I Lee Road Trail Project Watsonville, California

Reference: Pacific Crest Engineering, Inc., Geotechnical Investigation – Design Phase Lee Road Trail Project No. 1922.1-SZ81-C41 dated September 4, 2020

Dear Mr. Cahill, As requested, Pacific Crest Engineering has prepared this letter updating the seismic parameters provided in our previous report so that they are in conformance with the current 2022 CBC. The following parameters supersede the seismic parameters provided in Reference #1 above. All other recommendations provided in that report still apply.

The table below provides 2022 CBC seismic parameters for Site Class D conditions. Site Class D conditions are considered applicable for the Phase 1 trail segment including Harkins Slough Road and Lee Road to Struve Slough, and excluding Struve Slough.

Selection of seismic design parameters should be determined by the project structural designer. The site coefficients and seismic ground motion values shown in the table below were developed based on CBC 2022 incorporating the ASCE 7-16 standard, and the project site location.

Table No. 2C Revised 2022 CBC Seismic Design Parameters 1

Phase I Trail Segment Lee Road From Harkins Slough Road South to Struve Slough (Excluding Struve Slough)

Seismic Design Parameter ASCE 7-16 Value

Site Class D

Spectral Acceleration for Short Periods Ss = 2.308 g Spectral Acceleration for 1-second Period S1 = 0.872 g Short Period Site Coefficient, Fa Fa = 1.0 1-Second Period Site Coefficient, Fv Note 2 MCE Spectral Response Acceleration for Short Period, SMS SMS = 2.308 g MCE Spectral Response Acceleration for 1-Second Period, SM1 Note 2 Design Spectral Response Acceleration for Short Period, SDS SDS = 1.539 g Design Spectral Response Acceleration for 1-Second Period, SD1 Note 2

Lee Road Trail Project – Phase I Page 2 December 10, 2024 Project Number 1922.1-SZ81-C41

Note 1: Design values have been obtained by using the ASCE Hazard Tool at https://asce7hazardtool.online

Note 2: Per Section 11.4.8 of ASCE 7-16, a ground motion hazard analysis is required for Site Class D sites with S1 greater than or equal to 0.2. Exception 2 of Section 11.4.8 of ASCE 7-16 allows the site coefficient Fv and spectral acceleration parameters SM1 and SD1 to be determined from Section 11.4 provided that the seismic response coefficient Cs is determined from Section 12.8 as detailed in Section 11.4.8. Initiating Exception 2 for structural design will result in a 1-second period site coefficient of F1 = 2.0 and corresponding MCE and Design Spectral Response Acceleration values of SM1 = 1.744 and SD1 = 1.163, respectively. This should be verified by the Structural Engineer. Pacific Crest Engineering, Inc. should be contacted for site specific GMHA parameters if the Exception is not employed or applicable for structural design.

We appreciate the opportunity to be of service, if you have any questions regarding this information, please contact me.

Sincerely, PACIFIC CREST ENGINEERING INC.

Elizabeth M. Mitchell, GE Associate Geotechnical Engineer GE 2718, Expires 12/31/24

Copies: 1 to Client (e-copy) https://asce7hazardtool.online/

GEOTECHNICAL

INVESTIGATION

LEE ROAD TRAIL

WATSONVILLE, CALIFORNIA

FOR

MME

SANTA CRUZ, CALIFORNIA

CONSULTING GEOTECHNICAL ENGINEERS

1922-SZ81-C41

REVISED SEPTEMBER 2020

www.4pacific-crest.com

G E O T E C H N I C A L | E N V I R O N M E N T A L | C H E M I C A L | M A T E R I A L T E S T I N G | S P E C I A L I N S P E C T I O N S

444 AIRPORT BLVD., SUITE 106 | WATSONVILLE, CA 95076 | PHONE 831-722-9446 | WWW.4PACIFIC-CREST.COM

(Revised) September 4, 2020 Project No. 1922-SZ81-C41

Mr. Dale Hendsbee, Principal

MME

224 Walnut Avenue, Suite B Santa Cruz, CA 95060

Subject: Geotechnical Investigation – Design Phase Lee Road Trail Watsonville, California

Dear Mr. Hendsbee, In accordance with your authorization, we have completed our geotechnical investigation for the proposed Lee Road Trail located on Lee Road in Watsonville, California. This revision to our December 20, 2019 report has been prepared to present additional retaining wall and grading recommendations, as well as updated seismic design values as prescribed by the 2019 California Building Code. This revised report replaces our December 20, 2019 report in its entirety.

The water surface elevation in Struve Slough remained well above Lee Road during the entire course of our investigation so we were unable to perform subsurface exploration in this area using conventional drilling equipment. We recommend further CPT testing at proposed pile locations within the slough in order to fully develop geotechnical design recommendations for design of the proposed pedestrian bridge. Since it now appears likely that Lee Road remains submerged year round, overwater equipment will be required to complete this testing.

The accompanying report presents our conclusions and recommendations as well as the results of the geotechnical investigation on which they are based. The conclusions and recommendations presented in this report are contingent upon our review of the plans during the design phase of the project, and our observation and testing during the construction phase of the project.

We appreciate the opportunity to be of service. If you have any questions concerning the information presented in this report, please call our office.

Very truly yours, PACIFIC CREST ENGINEERING INC.

Elizabeth M. Mitchell, GE President/Principal Geotechnical Engineer GE 2718, Expires 12/31/20

Copies: 2 to Client

Lee Road Trail Project No. 1922 SZ81-C41 September 4, 2020

444 AIRPORT BLVD., SUITE 106 | WATSONVILLE, CA 95076 | PHONE 831-722-9446 | WWW.4PACIFIC-CREST.COM

TABLE OF CONTENTS

I. INTRODUCTION

PURPOSE AND SCOPE

PROJECT LOCATION

PROPOSED IMPROVEMENTS

II. INVESTIGATION METHODS

FIELD INVESTIGATION

LABORATORY TESTING

III. FINDINGS AND ANALYSIS

GEOLOGIC SETTING

SURFACE CONDITIONS

SUBSURFACE CONDITIONS

FAULTING AND SEISMICITY

GEOTECHNICAL HAZARDS

DISCUSSION AND CONCLUSIONS

IV. RECOMMENDATIONS

EARTHWORK

FOUNDATIONS

PAVEMENT DESIGN

EROSION CONTROL

PLAN REVIEW

V. LIMITATIONS AND UNIFORMITY OF CONDITIONS

VI. IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL REPORT

APPENDIX A

REGIONAL SITE MAP

SITE MAP SHOWING TEST BORINGS

KEY TO SOIL CLASSIFICATION

LOG OF TEST BORINGS & CPT

ATTERBERG LIMITS RESULTS

DIRECT SHEAR TEST RESULTS

ORGANIC CONTENT TEST RESULTS

TYPICAL KEYWAY/BENCH DETAIL

SURCHARGE PRESSURE DIAGRAM

TYPICAL RETAINING WALL DETAIL

APPENDIX B

QUANTITATIVE LIQUEFACTION ANALYSIS

Lee Road Trail Project No. 1922-SZ81-C41

GEOTECHNICAL INVESTIGATION REPORT

Lee Road Trail, Watsonville, California

I. INTRODUCTION

PURPOSE AND SCOPE

This report describes the geotechnical investigation and presents our conclusions and recommendations for the proposed Lee Road Trail located on Lee Road, in Watsonville, California. For purposes of this report “site” refers to the 1.2-mile-long area of the proposed Trail alignment extending along Lee Road between the railroad crossing north of Beach Street to Harkins Slough Road.

Our scope of services for this project has consisted of:

1. Site reconnaissance to observe the existing conditions.

2. Review of the following published maps:

• Geologic Map of Santa Cruz County, California, Brabb, 1997.

• Preliminary Map of Landslide Deposits in Santa Cruz County, California, Cooper-

Clark and Associates, 1975.

• Map Showing Geology and Liquefaction Potential of Quaternary Deposits in Santa

Cruz County, California, Dupré, 1975.

• Map Showing Faults and Their Potential Hazards in Santa Cruz County, California, Hall, Sarna-Wojcicki, Dupré, 1974.

• U.S. Geological Survey (and the California Geologic Survey), 2018, Quaternary fault and fold database for the United States, accessed July 2018, from USGS web site:

http//earthquake.usgs.gov/hazards/qfaults/.

3. The drilling and logging of 6 test borings and one Cone Penetrometer Test (CPT) sounding.

4. Laboratory analysis of retrieved soil samples.

5. Engineering analysis of the field and laboratory test results.

6. Preparation of this report documenting our investigation and presenting geotechnical recommendations for the design and construction of the project.

PROJECT LOCATION

The proposed trail segment will connect to the proposed Lee Road Rail Trail at the south end, extending north along Lee Road to Harkins Slough Road. Please refer to the Regional Site Map, Figure No. 1, in Appendix A for the general vicinity of the project site, which is approximately located by the following coordinates:

Latitude = 36.903963 degrees Longitude = -121.783762 degrees

PROPOSED IMPROVEMENTS

Based on our review of preliminary plans and discussions with MME, it is our understanding that the proposed trail segment will connect to the Lee Road Rail Trail at the south end, extending north along Lee Road to Harkins Slough Road. The proposed Trail includes approximately 1.2 miles of a multi-use asphalt, pervious concrete and/or decomposed granite pathway and will include a pedestrian bridge spanning Struve Slough.

Along the northern segment, the proposed trail is bounded by farms to the west and an ecological preserve to the east. Struve Slough and industrial sites flank the southern portion of the segment.

It is our understanding that the trail section will be eight to twelve feet in width and flanked on both sides by 2-foot wide gravel shoulders. Grading is expected to include minor cuts and fills along with retaining walls ranging from about 3 to 8 feet in height.

II. INVESTIGATION METHODS

FIELD INVESTIGATION

Soil Borings

Six, 6-inch diameter test borings were drilled at the site on April 8 and May 2, 2019. The approximate location of the test borings is shown on Figure No. 2, in Appendix A. The drilling method used was hydraulically operated continuous flight augers on a truck mounted drill rig. A geologist from Pacific Crest Engineering Inc. was present during the drilling operations to log the soil encountered and to choose sampler type and locations.

Relatively undisturbed soil samples were obtained at various depths by driving a split spoon sampler 18 inches into the ground. This was achieved by dropping a 140 pound hammer a vertical height of 30 inches. The hammer was actuated with a wire winch. The number of blows required to drive the sampler each 6-inch increment and the total number of blows required to drive the last 12 inches was recorded by the field engineer. The outside diameter of the samplers used was 3-inch or 2-inch and is designated on the Boring Logs as “L” or “T”, respectively.

The field blow counts in 6-inch increments are reported on the Boring Logs adjacent to each sample as well as the Standard Penetration Test data (SPT). All STP data has been normalized to a 2-inch O.D.

sampler and is reported on the Boring Logs as SPT "N" values. The normalization method used was derived from the second edition of the Foundation Engineering Handbook (H.Y. Fang, 1991). The method utilizes a Sampler Hammer Ratio which is dependent on the weight of the hammer, height of hammer drop, outside diameter of sampler, and inside diameter of sample.

The soils encountered in the borings were continuously logged in the field and visually described in accordance with the Unified Soil Classification System (ASTM D2488) as described in the Boring Log Explanation, Figures No. 3 and 4, in Appendix A. The soil classification was verified upon completion of laboratory testing in accordance with ASTM D2487.

Cone Penetrometer Testing

One (1) cone penetrometer test (CPT) sounding was advanced at the southern edge of Struve Slough on November 12, 2019. A staff geologist from Pacific Crest Engineering Inc. was present to supervise the field operations. The sounding was performed in accordance with the ASTM D5778 test method.

The location of the CPT sounding is shown on Figure No. 2 of Appendix A.

The CPT sounding was advanced using a 15 cm2 piezocone penetrometer with a friction sleeve. A saturated piezo element is placed between the cone and the friction sleeve to obtain dynamic pore pressure parameters. Continuous measurements were made of the tip resistance, the friction sleeve resistance, and the dynamic pore pressure as the cone was pushed into the ground. Real time data along with correlations between these measurements and soil properties were observed as the probe was advanced so that our engineer and/or geologist could determine the depth of soundings required.

In this case the sounding was advanced to refusal at a depth of 75.95 feet below the road surface.

Appendix A contains the site plan showing the locations of the test borings, boring logs and an explanation of the soil classification system used. Stratification lines on the boring logs are approximate as the actual transition between soil types may be gradual. The CPT plots with interpreted soil types is included behind the boring logs in Appendix A.

LABORATORY TESTING

The laboratory testing program was developed to aid in evaluating the engineering properties of the materials encountered at the site. Laboratory tests performed include:

Moisture Density relationships in accordance with ASTM D2937.

Field penetrometer testing to approximate unconfined compressive strength.

Gradation testing in accordance with ASTM D1140.

Atterberg Limits testing in accordance with ASTM D4318.

Unconfined Compression testing in accordance with ASTM D2166.

Direct Shear testing in accordance with ASTM D3080.

Organic Content Test in accordance with ASTM D2974 Method C.

The results of the laboratory testing are presented on the boring logs opposite the sample tested and/or presented graphically in Appendix A.

III. FINDINGS AND ANALYSIS

GEOLOGIC SETTING

The Lee Road Trail alignment transects two distinctive geologic units. The portion of Trail north of Struve Slough is mapped on the USGS Geologic Map of Santa Cruz County (Brabb 1997) as Terrace

Deposits (Qt). The remaining portion of the trail segment (including Struve Slough and Lee Road to the south) is mapped as being underlain by Basin Deposits (Qb).

The Terrace Deposits are described as weakly consolidated to semi-consolidated heterogeneous deposits of moderately to poorly-sorted silt, silty clay, sand and gravel. Basin Deposits typically consist of unconsolidated, plastic clay and silty clay that is rich in organic materials, and can locally contain thin interbedded layers of silt and silty sand. The Basin Deposits were deposited in a variety of environments including estuaries, lagoons, marsh filled sloughs, flood basins and lakes, and are mapped as having a very high potential for liquefaction (Dupre’, 1975; Dupre’ and Tinsley, 1980). The soils encountered during our field investigation are consistent with these descriptions.

SURFACE CONDITIONS

The subject portion of the proposed Lee Road Trail is located on both sides of Struve Slough and is flanked by industrial buildings on the southern portion and agricultural areas and ecological reserve areas on the northern portion. Lee Road traverses the entire area, and is inundated by water within the slough for the majority of the year. The portion of roadway at the south side of Struve Slough is overgrown with brush. Beyond the slough margins the proposed Trail alignment is relatively flat with gently sloping hills on the trail portion north of Struve Slough.

SUBSURFACE CONDITIONS

Our subsurface exploration included six (6) small diameter borings; two of which were drilled as close to the slough edge as was practically possible. Four borings were advanced at accessible intervals along the proposed trail alignment. The borings extended 11½ to 51½ feet below existing grade.

The following briefly describes the general subsurface soil conditions encountered within the test borings. The Logs of Test Borings in Appendix A provide, in more descriptive terms, the soil profiles and classifications, laboratory test results and groundwater conditions encountered at each boring location.

Basin Deposits – CPT-1, Boring B-1, B-2 and B-3

Boring B-1, B-2 and CPT-1 were advanced near the south side of Struve Slough. Consistent with what we infer to be Basin Deposit materials, both borings and the CPT sounding encountered predominately intermediate to high plasticity clay and silt soils with interbedded silty and clayey sands. Intermediate to high plasticity characteristics are indicative of expansive soils. The consistency of the fine-grained materials in the borings were generally stiff to very stiff, although a soft layer of sandy elastic silt was noted between about 3 to 5 feet in B-1. The density of the sand layers were described as medium.

CPT-1, which was located right at the water’s edge (approximately Station 8+45) at the south side of the slough, noted up to 30 feet of soft to very soft clay, silt, and organic materials.

Boring B-3 was drilled along the northern margin of the slough, as close to the water as we could access with our drilling equipment. In this boring we also encountered what we infer to be Basin Deposit materials comprised of about three feet of stiff sandy lean clay overlying soft, highly organic peat at a depth of approximately 5 to 20 feet below the ground surface. The peat soils are underlain by approximately 20 feet of stiff clay with varying sand content. At a depth of about 40 feet we encountered poorly graded, medium dense to very dense sand that continued to the maximum explored depth of 51½ feet.

Based on the materials encountered as well as a review of soil borings at the Highway One Bridge site, it should be expected that the thickness of the soft clay and/or peat soils will vary across the slough.

This should be verified by CPT testing at proposed pile locations within the slough crossing, but for preliminary planning purposes we have estimated the thickness of soft clay/organic soils could be in excess of 50 feet.

All three borings encountered predominately coarse-grained man-made fill soils with varying gravel content within the upper 2½ feet. The density of these materials were described as loose to medium dense. Those borings advanced within the road pavement encountered 3 to 10 inches of asphalt underlain by varying thickness of aggregate base or fill subgrade.

Terrace Deposits – Borings B-4, B-5 and B-6

Borings B-4, B-5 and b-6 were drilled along the northern segment of the proposed trail alignment.

Consistent with what we infer to be Terrace Deposit materials, the boring profiles were comprised of predominately sandy soils with interbeds of sandy clay to the depths explored. The sand materials were generally medium dense to dense. The fine-grained clay soils were typically very stiff and possessed intermediate to high plasticity characteristics. Intermediate to high plasticity characteristics are indicative of expansive soils.

Groundwater Conditions

Groundwater was encountered within B-1 at an approximate depth of 15 feet. Surface water was observed approximately 1 foot below the road surface at B-3. The phreatic surface within CPT-1 was noted to be about 9 feet below the road surface. No ground water was encountered within the other four borings. It should be noted that the groundwater level was not allowed to stabilize for more than a few hours; therefore, the actual groundwater level may be higher or lower than initially encountered.

The groundwater conditions described in this report reflect the conditions encountered during our drilling investigation in April and May of 2019 at the specific locations drilled. It must be anticipated that the perched and regional groundwater tables may vary with location and could fluctuate with variations in rainfall, runoff, irrigation and other changes to the conditions existing at the time our measurements were made. It should be anticipated that the groundwater table may rise significantly in the winter of non-drought years, and is likely to be influenced by water levels in the slough.

FAULTING AND SEISMICITY

Faulting

Mapped faults which have the potential to generate earthquakes that could significantly affect the subject site are listed in Table No. 1. The fault distances are approximate distances based the U.S.

Geological Survey and California Geological Survey, Quaternary fault and fold database, accessed in July of 2018 from the USGS website (http//earthquake.usgs.gov/hazards/qfaults/) and overlaid onto Google Earth.

Table No. 1 - Distance to Significant Faults

Fault Name Distance (miles) Direction

Zayante-Vergeles 3 Northeast San Andreas 6½ Northeast

Sargent 9 Northeast Berrocal 10 Northeast

Monterey Bay-Tularcitos 12 Southeast

Seismic Shaking and CBC Design Parameters

Due to the proximity of the site to active and potentially active faults, it is reasonable to assume the site will experience high intensity ground shaking during the lifetime of the project. Structures founded on thick soft soil deposits are more likely to experience more destructive shaking, with higher amplitude and lower frequency, than structures founded on bedrock. Generally, shaking will be more intense closer to earthquake epicenters. Thick soft soil deposits large distances from earthquake epicenters, however, may result in seismic accelerations significantly greater than expected in bedrock.

The Basin Deposit materials underlying the proposed bridge site are liquefiable, resulting in a Site Class F designation. In accordance with Chapter 11 of ASCE 7-16, site-specific ground motion response procedures are required for Site Class F soils for structures with a fundamental period of vibration greater than 0.5 seconds. It is our understanding that the fundamental period of vibration for the proposed pedestrian bridge is expected to exceed 0.5 seconds. Therefore a site-specific ground motion response analysis will be required to determine spectral acceleration values for the bridge structure and are specifically excluded from this report. This work is expected to be performed as part of the 90% design phase and the resulting seismic design values for the bridge structure will be presented in a future addendum report.

The tables below provide 2019 CBC seismic parameters for both Site Class E and Site Class D conditions. Site Class E conditions should be considered for the southern portion of the trail segment (excluding Struve Slough). Site Class D conditions are considered applicable for the northern trail segment including Harkins Slough Road and Lee Road to Struve Slough (also excluding Struve Slough).

Selection of seismic design parameters should be determined by the project Structural Engineer. The site coefficients and seismic ground motion values shown in the table below were developed based on CBC 2019 incorporating the ASCE 7-16 standard, and the project site location.

Table No. 2A – Struve Slough (Pedestrian Bridge Site) 2019 CBC Seismic Design Parameters

Seismic Design Parameter ASCE 7-16 Value Site Class F

Site Specific Ground Motion Response Analysis Required Not Applicable

Table 2B - Southern Trail Segment (Excluding Struve Slough) 2019 CBC Seismic Design Parameters Note 1

Seismic Design Parameter ASCE 7-16 Value Site Class E Note 2

Spectral Acceleration for Short Periods Ss = 2.308g Spectral Acceleration for 1-second Period S1 = 0.872g Short Period Site Coefficient, Fa Note 3 1-Second Period Site Coefficient, Fv Note 4 MCE Spectral Response Acceleration for Short Period, SMS Note 3 MCE Spectral Response Acceleration for 1-Second Period, SM1 Note 4 Design Spectral Response Acceleration for Short Period, SDS Note 3 Design Spectral Response Acceleration for 1-Second Period, SD1 Note 4

Note 1: Design values have been obtained by using the ASCE Hazard Tool at https://asce7hazardtool.online

Note 2: The site would normally be assigned Site Class F because the Basin Deposit soils are potentially liquefiable, resulting in a Site Class F designation. Section 20.3.1 of ASCE 7-16 allows the following exception for structures overlying Site Class F soil: “For structures having fundamental periods of vibration equal to or less than 0.5 seconds, site response analysis is not required to determine spectral accelerations for liquefiable soils. Rather, a site class is permitted to be determined in accordance with Section 20.3 and the corresponding values of Fa and Fv determined from Section 11.4 of ASCE 7-16. The seismic design parameters for Site Class E may be assumed only for structures with a fundamental period of vibration equal to or less than 0.5 seconds. This must be verified by the project Structural Engineer. Structures on Site Class F soils with a fundamental period of vibration greater than 0.5 seconds, including the proposed pedestrian bridge, will require supplemental design criteria and a site-response analysis as discussed above.

Note 3: Per Section 11.4.8 of ASCE 7-16, a ground motion hazard analysis (GMHA) is required for Site Class E sites with SS greater than or equal to 1.0. Section 11.4.8 of ASCE 7-16 provides an Exception to the GMHA requirement for certain structures. For Site Class E sites, Exception 1 of Section 11.4.8 allows the short period site coefficient Fa to be determined from Table 11.4.1 for Site Class C. Initiating Exception 1 for structural design would result a short period site coefficient of Fa =1.2 and corresponding MCE and Design Spectral Response Acceleration values of SMS=

2.770 and SDS = 1.864, respectively. These values cannot be used for seismically isolated structures or structures with damping systems, and assume that Exception 1 of Section 11.4.8 is therefore applicable. This should be verified by the Structural Engineer. Pacific Crest Engineering, Inc. should be contacted for site specific GMHA parameters if the Exception is not employed or applicable for structural design.

Note 4: Per Section 11.4.8 of ASCE 7-16, a ground motion hazard analysis is required for Site Class E sites with S1 greater than or equal to 0.2. Exception 3 of Section 11.4.8 of ASCE 7-16 allows the site coefficient Fv and spectral acceleration parameters SM1 and SD1 to be determined from Section 11.4 provided that: (1) this is not a seismically isolated structure or a structure with damping systems, (2) Fv can be obtained from Table 1613.2.3(2) of the 2019

CBC, and (3) Exception 3 of Section 11.4.8 is applicable (i.e., the fundamental period of the structure T is less than or equal to Ts (as defined in Section 11.4.6.4 of ASCE 7-16) and equivalent static force procedure is used for design. Initiating Exception 3 for structural design will result in a 1-second period site coefficient of F1 = 2.0 and corresponding MCE and Design Spectral Response Acceleration values of SM1 = 1.744 and SD1 = 1.163, respectively.

This should be verified by the Structural Engineer. Pacific Crest Engineering, Inc. should be contacted for site specific GMHA parameters if the Exception is not employed or applicable for structural design.

Table No. 2C – Lee Road From Harkins Slough Road South to Struve Slough (Excluding Struve

Slough) 2019 CBC Seismic Design Parameters Note 1

Seismic Design Parameter ASCE 7-16 Value Site Class D

Spectral Acceleration for Short Periods Ss = 2.308 g Spectral Acceleration for 1-second Period S1 = 0.872 g Short Period Site Coefficient, Fa Fa = 1.0 1-Second Period Site Coefficient, Fv Note 2 MCE Spectral Response Acceleration for Short Period, SMS SMS = 2.308 g MCE Spectral Response Acceleration for 1-Second Period, SM1 Note 2 Design Spectral Response Acceleration for Short Period, SDS SDS = 1.539 g Design Spectral Response Acceleration for 1-Second Period, SD1 Note 2

Note 1: Design values have been obtained by using the ASCE Hazard Tool at https://asce7hazardtool.online

Note 2: Per Section 11.4.8 of ASCE 7-16, a ground motion hazard analysis is required for Site Class D sites with S1 greater than or equal to 0.2. Exception 2 of Section 11.4.8 of ASCE 7-16 allows the site coefficient Fv and spectral acceleration parameters SM1 and SD1 to be determined from Section 11.4 provided that the seismic response coefficient Cs is determined from Section 12.8 as detailed in Section 11.4.8. Initiating Exception 2 for structural design will result in a 1-second period site coefficient of F1 = 2.0 and corresponding MCE and Design Spectral Response Acceleration values of SM1 = 1.744 and SD1 = 1.163, respectively. This should be verified by the Structural Engineer. Pacific Crest Engineering, Inc. should be contacted for site specific GMHA parameters if the Exception is not employed or applicable for structural design.

The recommendations of this report are intended to reduce the potential for structural damage to an acceptable risk level, however strong seismic shaking could result in architectural damage and the need for post-earthquake repairs. It should be assumed that exterior improvements such as pavements, slabs or sidewalks may need to be repaired or replaced following strong seismic shaking.

GEOTECHNICAL HAZARDS

Based on the results of our investigation, geotechnical hazards associated with the project site include seismic shaking (discussed above), ground surface fault rupture, liquefaction, lateral spreading, landsliding and expansive soils. A discussion of these hazards is presented below.

Ground Surface Fault Rupture

A specific investigation for the presence of active faults at the project site was beyond our scope of services and was not performed. Based upon our review of the Santa Cruz County GIS Hazard Maps, the project site is not mapped within a fault hazard zone.

Ground surface fault rupture typically occurs along the surficial traces of active faults during significant seismic events. Since the nearest known active, or potentially active fault trace is mapped approximately 3 miles from the site, it is our opinion that the potential for ground surface fault rupture to occur at the site should be considered low.

Liquefaction and Lateral Spreading

Liquefaction tends to occur in loose, saturated and fine grained cohesionless sands, coarse silts or clays with a low plasticity. In order for liquefaction to occur there must be the proper soil type, soil saturation, and cyclic accelerations of sufficient magnitude to progressively increase the water pressures within the soil mass. Non-cohesive soil shear strength is developed by the point to point contact of the soil grains. As the water pressures increase in the void spaces surrounding the soil grains the soil particles become supported more by the water than the point to point contact. When the water pressures increase sufficiently, the soil grains begin to lose contact with each other resulting in the loss of shear strength and continuous deformation of the soil where the soil appears to liquefy.

Our review of the Santa Cruz County GIS Hazard Maps indicates the Basin Deposits (which includes the proposed bridge site and Trail segment to the south) are mapped with a “very high” susceptibility for liquefaction. The Highway 1 Struve Slough Bridge, located approximately 1000 feet north of the proposed Lee Road Trail, collapsed during the 1989 Loma Prieta earthquake due to massive lateral displacement of soft foundation soils within the slough.

Substantial advances in liquefaction engineering have occurred over the past 15 years. Liquefaction science has expanded to examine strength loss of low plasticity silts and clays during cyclic earthquake shaking. Bray and Sancio (2006) suggested that fine grained soils meeting the following criteria should also be considered liquefiable:

Silts and clayey silts with low plasticity (PI < 12) and a high-water content to liquid limit ratio (Wc/LL > 0.85).

Clayey silts and silty clays of moderate plasticity (12 < PI < 18) and a moderate water content to liquid limit ratio of (Wc/LL > 0.80).

Sensitive soils with plasticity indices in excess of 18 may also be liquefiable. Engineering judgment should be used in these cases.

As part of our preliminary liquefaction analysis, we screened our laboratory data for liquefaction susceptibility of fine grained materials as defined above. The following table presents the results of this initial screening process.

Table No. 3 – Liquefaction Screening – Fine Grained Soils

Soil Type Avg. Moisture Content, Wc

Liquid Limit, LL

Plasticity Index, PI Wc/LL Susceptible to

Liquefaction

Sandy Elastic Silt 17.4 60 29 0.8 No

Sandy Lean Clay 10.8 23 16 1.2 Yes

Sandy Fat Clay 31.6 -- -- -- No

Sandy Lean Clay 22.9 46 28 1.2 No

Silt 33.0 38 12 0.9 Yes

Sandy Silt 30.5 37 12 0.8 Yes

Fat Clay 33.8 53 30 0.7 No

Using the data presented above and subsurface data from Borings B-1, B-3 and CPT-1 we performed quantitative analysis of liquefaction potential along the proposed bridge route crossing Struve Slough.

Our analysis utilized the software program CLIQ 2.2.0.28 and LiqSVs 1.2.1.6 by Geologismiki, which is based upon the most recent recommendations of the NCEER Workshop and SP117 implementation.

Please refer to Appendix B for the results and related graphics summarizing our analysis.

Based on an estimated mean peak ground acceleration (PGAM) of 0.63g resulting from a 7.9 magnitude

(M) earthquake, our preliminary estimates indicate seismically induced settlement on the order of 4 to 6 inches within the bridge crossing. This analysis is based on subsurface data obtained from the edges of the slough. It is likely that the composition of Basin Deposit materials could vary significantly between the edges and center of the slough. Supplemental CPT soundings are recommended at the proposed pile locations within the slough in order to more fully characterize the liquefaction potential across the bridge site.

Liquefaction induced lateral spreading occurs when a liquefied soil mass fails toward an open slope face, or fails on an inclined topographic slope. Our analysis indicates that the site has a high potential for liquefaction, consequently the potential for lateral spreading is also considered high. It is currently estimated that lateral displacements on the order of 30 inches could occur within sloping areas area of the trail segment underlain by Basin Deposits.

Landsliding

The proposed trail alignment will be situated within areas of relatively level to gently sloping topography and there are no mapped landslide hazards within the proposed trail route. Provided our recommendations are closely followed during the design and construction of the project, it our opinion that deep seated landsliding is a hazard with negligible potential for affecting the proposed project.

We caution however, that those portions of the pathway within sloping areas can become undermined if surface runoff is not adequately controlled.

Expansive Soils

The proposed trail route is underlain by varying layers of moderate to highly expansive clay. Expansive soils tend to heave during the rainy season and contract during the summer and this shrink/swell action extends down to the depth of seasonal moisture change. When this cyclical volume change occurs on sloping ground it results in “soil creep” due to the downward vector of the shrink/swell action. Seasonal moisture fluctuation and subsequent expansion and contraction of these types of soils typically occurs more near the ground surface where the seasonal moisture fluctuation is the greatest and decreases with depth below ground surface.

DISCUSSION AND CONCLUSIONS

GENERAL

1. The water surface elevation in Struve Slough was several feet above Lee Road during the entire course of our investigation so we were unable to perform subsurface exploration in this area using conventional drilling equipment. We recommend further CPT testing at proposed pile locations within the slough in order to more fully develop geotechnical design recommendations for the proposed pedestrian bridge. Since it now appears likely that Lee Road remains submerged year round, overwater equipment will be required to complete this testing.

2. The results of our investigation indicate that the proposed development is feasible from a geotechnical engineering standpoint, provided our recommendations are included in the design and construction of the project.

3. Grading and foundation plans should be reviewed by Pacific Crest Engineering Inc. during their preparation and prior to contract bidding.

4. Pacific Crest Engineering Inc. should be notified at least four (4) working days prior to any site clearing and grading operations on the property in order to observe the stripping and disposal of unsuitable materials, and to coordinate this work with the grading contractor. During this period, a pre-construction conference should be held on the site, with at least the client or their representative, the grading contractor, a County representative and one of our engineers present. At this meeting, the project specifications and the testing and inspection responsibilities will be outlined and discussed.

5. Field observation and testing must be provided by a representative of Pacific Crest Engineering Inc., to enable them to form an opinion as to the degree of conformance of the exposed site conditions to those foreseen in this report, the adequacy of the site preparation, the acceptability of fill materials, and the extent to which the earthwork construction and the degree of compaction comply with the specification requirements. Any work related to grading or foundation excavation that is performed without the full knowledge and direct observation of Pacific Crest Engineering Inc., the Geotechnical Engineer of Record, will render the recommendations of this report invalid, unless the Client hires a new Geotechnical Engineer who agrees to take over complete responsibility for this report’s findings, conclusions and recommendations. The new Geotechnical Engineer must agree to prepare a Transfer of Responsibility letter. This may require additional test borings and laboratory analysis if the new

Geotechnical Engineer does not completely agree with our prior findings, conclusions and recommendations.

PRIMARY GEOTECHNICAL CONSIDERATIONS

6. Based upon the results of our investigation, it is our opinion that the primary geotechnical issues associated with the design and construction of the proposed project are the following:

a. Liquefaction/Seismically Induced Settlement: The Basin Deposit materials underlying Struve

Slough and trail segments to the south are mapped as very highly liquefiable. In our opinion the primary geotechnical hazard affecting this portion of the project area is the potential for liquefaction and lateral spreading of the subsurface soils during a strong seismic event. Those portions of the Trail traversing the Basin Deposits may be subject to settlement during strong seismic shaking, requiring repair or replacement of portions of the Trail. Preliminary estimates indicate total ground surface settlements on the order of 4 to 6 inches within the proposed bridge crossing, and 2 to 4 inches for trail segments south of the slough. Differential settlement should be assumed to be highly differential, with a magnitude of ⅔ to ¾ of total settlement values. Bridge structures should be supported by pile foundations.

As discussed previously, it is likely that the composition of Basin Deposit materials could vary significantly between the edges and center of the slough. Supplemental CPT soundings are recommended at the proposed pile locations within the slough in order to more fully characterize the subsurface conditions and liquefaction potential across the bridge site.

b. Strong Seismic Shaking: The project site is located within a seismically active area and strong seismic shaking is expected to occur within the design lifetime of the project. Improvements should be designed and constructed in accordance with the most current CBC and the recommendations of this report to minimize reaction to seismic shaking. Structures built in accordance with the latest edition of the California Building Code have an increased potential for experiencing relatively minor damage which should be repairable, however strong seismic shaking could result in architectural damage and the need for post-earthquake repairs.

c. Divergent Bearing Conditions and Differential Settlement: The bridge site is underlain by soft and compressible Basin Deposit materials of varying thickness. The upper soils within the Trail route varied from firm to stiff clays and loose to medium dense sand. Man-made fill was encountered in all but one boring. These divergent bearing conditions can result in differential settlement, which could adversely affect proposed structures planned for the alignment and lead to undesirable effects on pavement or pathway surfaces. Subgrade and baserock sections should be adequately compacted in accordance with the recommendations of this report. A pile foundation is recommended for the bridge structure. All other structural foundations, if applicable, should be underlain by a uniform zone of compacted engineered fill.

d. Expansive Soils: The native clay soils underlying the proposed improvements are moderately to highly expansive. Seasonal shrinking and swelling of these soils could result in heave or settlement and damage to improvements. To reduce this potential we recommend that pavements and structural foundations bear upon non-expansive engineered fill. Refer to the Subgrade Preparation section of this report for details.

e. The Presence of Mature Trees: Large trees are located in the proposed trail area near Boring

B-2, and large tree roots and organically laden soils were encountered at depths of 1½ to 4½ feet within the test borings. Consequently, we anticipate that a significant number of large roots, root balls and/or organically laden soil will be encountered during the excavation process for this section of the proposed trail. These materials should be completely removed from the excavated area and should not be used as engineered fill.

IV. RECOMMENDATIONS

EARTHWORK

Clearing and Stripping

1. The initial preparation of the site may consist of demolition of portions of any existing structures and their foundations, and removal of designated trees and debris. All foundation elements from existing structures must be completely removed from improvement areas. Tree removal should include the entire stump and root ball. Septic tanks and leaching lines, if found, must be completely removed.

The extent of this soil removal will be designated by a representative of Pacific Crest Engineering Inc.

in the field. This material must be removed from the site.

2. Any voids created by the removal of old structures and their foundations, tree and root balls, septic tanks, and leach lines must be backfilled with properly compacted engineered fill which meets the requirements of this report.

3. Any wells encountered shall be capped in accordance with the requirements and approval of the County Health Department. The strength of the cap shall be equal to the adjacent soil and shall not be located within 5 feet of a structural footing.

4. Surface vegetation, tree roots and organically contaminated topsoil should then be removed (“stripped”) from the area to be graded. In addition, any remaining debris or large rocks must also be removed (this includes asphalt or rocks greater than 2 inches in greatest dimension). This material may be stockpiled for future landscaping.

5. It is anticipated that the depth of stripping may be 2 to 4 inches. Final required depth of stripping must be based upon visual observations by a representative of Pacific Crest Engineering Inc., in the field. The required depth of stripping will vary based upon the type and density of vegetation across the project site and with the time of year.

Subgrade Preparation

6. Approximately 2 to 3 feet of non-engineered fill was encountered in most of our borings. We anticipate there will be other areas of man-made fill on the site that were not detected during our field investigation. Areas of man-made fill encountered on the project site, where such soils underlie structural foundations, vehicular pavement sections or retaining wall footings, will need to be completely excavated to undisturbed native material. Where man-made fill is encountered within other (non-structural) trail sections, complete removal may not be necessary if the fill can be bridged and/or stabilized with fabric. Any excavation process should be observed and the extent designated by a representative of Pacific Crest Engineering Inc., in the field.

7. Any voids or excavations created by fill removal must be backfilled with properly compacted non-expansive native soils that are free of organic and other deleterious materials, or with approved imported fill.

8. Following clearing and stripping and any required subgrade preparation as described above, the exposed soils in pavement and/or pathway areas should be removed to a minimum depth of 8 inches below finished subgrade or as designated by a representative of Pacific Crest Engineering Inc. Areas to support concrete pavements, structural foundations and retaining walls should be subexcavated a minimum of 12 inches below finished subgrade or bottom of footing, whichever is greater. The base of the excavation must be observed and approved by a representative of Pacific Crest Engineering prior to backfilling. The approved base of the excavation should be scarified to a minimum depth of 6 inches, moisture conditioned and compacted. Approved excavated soil may then be replaced in maximum 8 inch lifts (before compaction). This should result in a minimum of 12 inches of compacted subgrade below pavement/pathway areas, and 18 inches of engineered fill below concrete slabs (including pervious concrete), structural foundations or retaining wall footings.

9. Recompacted sections should extend 2 feet horizontally beyond the pavement perimeter, and 3 feet beyond concrete slabs and retaining wall foundations.

10. Wet and/or soft soils will likely be encountered at bottom of excavation within varying segments of the Trail. If wet or unstable subgrades are encountered they may need to further subexcavated and replaced with stabilization fabric, crushed rock or other materials to create a stable working surface.

The depth of over-excavations and stabilization methods to be used should be determined in the field at the time of construction. All subexcavations should be observed by a representative of Pacific Crest Engineering Inc. and modified as necessary to establish a stable subgrade.

Material for Engineered Fill

11. Native soils to be used as engineered fill should be limited to the predominately granular materials i.e., silty to clayey sand and sandy silt, encountered along Lee Road north of Struve Slough (B4 and B6).

Expansive clay soils that underlie most of the remaining portions of Trail segment should not be used as engineered fill without additional processing (lime treatment, blending, etc.)

12. Non-expansive native or imported soil proposed for use as engineered fill should meet the…