587 2021 Final Geotech Report.pdf

OAKRIDGE GEOSCIENCE, INC.

FINAL GEOTECHNICAL REPORT

CALLEGUAS MUNICIPAL WATER DISTRICT’S

LAKE BARD PUMP STATION, CONEJO PUMP

STATION REHABILITATION, AND CREW BUILDING

IMPROVEMENTS

(Project Nos. 587 and 480)

Thousand Oaks, California

Prepared for:

Kennedy/Jenks Consultants, Inc.

February 2021 Project No. 012.009

PO Box 2540, Camarillo, California 93011 www.Oakridgegeo.com

805-603-4900

February 26, 2021 Project No. 022.009

Kennedy/Jenks Consultants, Inc.

2775 North Ventura Road, Suite 100 Oxnard, California 93036

Attention: Mr. Brandon Hale, P.E.

Subject: Final Geotechnical Report, Calleguas Municipal Water District’s Lake Bard Pump Station, Crew Building Improvements, and Conejo Pump Station Rehabilitation (Project Nos. 587 and 480), Thousand Oaks, California

Dear Mr. Hale:

Oakridge Geoscience, Inc. is pleased to present this geotechnical report for three Calleguas Municipal Water District (CMWD) projects: 1) Lake Bard Pump Station, 2) Conejo Pump Station Rehabilitation, and 3) Crew Building Improvements. Based on our discussions, these projects are in various stages of design (conceptual to preliminary) and CMWD requested the geotechnical design services for the three projects be performed together and compiled into a single geotechnical report.

The purpose of the study is to evaluate geotechnical conditions and provide geotechnical design recommendations for the project elements.

Closure

We appreciate the opportunity to provide geotechnical services to Kennedy/Jenks Consultants for Calleguas Municipal Water District’s projects. Please contact us if you have any questions regarding information presented herein.

Sincerely, Lori E. Prentice, CEG President

Rory “Tony” Robinson, PE, GE Principal Geotechnical Engineer

Copies Submitted: 1 electronic copy (pdf) via email

Kennedy/Jenks Consultants, Inc.

i

CONTENTS

Page

ii

CONTENTS (CONTINUED)

Page

REFERENCES

PLATES

PLATE 1 SITE LOCATION MAP

PLATES 2a through 2c EXPLORATION LOCATION MAP

APPENDICES

APPENDIX A FIELD EXPLORATION

APPENDIX B LABORATORY TESTING

APPENDIX C DATA BY OTHERS

1.0 INTRODUCTION

1.1 GENERAL STATEMENT

This geotechnical report summarizes the findings and recommendations of the geotechnical study performed by Oakridge Geoscience, Inc. (OGI) for the Calleguas Municipal Water District’s (CMWD) Lake Bard Pump Station, Conejo Pump Station Rehabilitation, and Crew Building Improvements. The projects are in various stages of design (conceptual to preliminary).

The work for the three projects was performed under a single mobilization of the field exploration equipment and the findings, conclusions, and recommendations are included in this combined report at the request of CMWD. The project locations within the facility are shown on Plate 1.

1.2 PURPOSE AND UNDERSTANDING

The purpose of the study is to evaluate geotechnical conditions at each of the project locations and provide geotechnical design recommendations for the project elements. Our understanding of the projects and the work performed for the study was based on our review of the conceptual to preliminary project design information provided to us by Kennedy Jenks (KJ).

On that basis, the potential exists for the locations and/or design of the various project elements to change from what was evaluated for this study and additional geotechnical information may be required as part of final individual project design(s).

1.3 PROJECT DESCRIPTION

This geotechnical report addresses three projects:

1) Lake Bard Pump Station (LBPS)

2) Conejo Pump Station (CPS) Rehabilitation

3) Crew Building Improvements

The findings are discussed by individual project site in Section 2.0 of this report.

1.4 WORK PERFORMED

The scope of services for this study consists of data review, project-specific field exploration based on the design information available at the time of exploration, laboratory testing, geotechnical engineering evaluation, and preparation of this report for the three projects. Our proposed scope of services was presented in our proposal dated September 28, 2020 and was authorized by receipt of a Subcontract for Professional Services, dated November 2, 2020. Our services for the project consisted of the following work tasks.

1.4.1 Data Review and Project Coordination

We reviewed readily available historical aerial photographs and regional geologic/geotechnical data to characterize the overall site conditions. We also reviewed the existing site-specific geotechnical data provided to us to aid in our understanding of the site conditions. The existing data review included geotechnical reports by Soil Mechanics (1965), Staal, Gardner, and Dunne, Inc. (1992), Converse Consultants, Inc. (1994), and Fugro (2002).

Prior to field exploration, OGI performed a site reconnaissance to locate and mark the exploration locations for utility coordination with Underground Service Alert and CMWD staff.

1.4.2 Field Exploration

Field exploration for the projects was developed based on the locations of conceptual and preliminary project elements provided by KJ and preliminary review of existing geotechnical data provided to us. The field exploration for the conceptual project locations consisted of a combination of hollowstem-auger drill holes and backhoe test pits to evaluate conditions at the four sites as described below. The purpose of the drill holes was to evaluate the subsurface conditions near the proposed facilities in general conformance with 2019 CBC standards. The purpose of the backhoe exploration was to explore the geologic conditions in the slope area in the vicinity of the proposed retaining wall upslope of the Crew Building expansion area. The approximate exploration locations are shown on Plates 2a through 2c.

Our field geologist logged the recovered samples from the drill holes and observed materials exposed in the test pits in general accordance with ASTM D2488 for visual soil classification. The descriptions were revised based on the results of the laboratory testing where appropriate.

Drill Holes. Nine drill holes were advanced to depths of 15 to 30 feet by S/G Drilling, Inc.

on December 3 and 4, 2020 with a CME-85 drill rig equipped with eight-inch-diameter hollowstem augers and a 140-pound automatic trip hammer. Soil samples were recovered at about 2-1/2-foot intervals to about 15 feet and at 5-foot intervals to drilling termination for laboratory testing.

Following completion, the drill holes were backfilled with the excavated cuttings; excess cuttings, if any, were spread in earthen areas onsite. Drill holes advanced in paved areas were patched with cold patch asphalt concrete.

Backhoe Test Pits. Three backhoe test pits were advanced to depths of about 5 to 7-1/2 feet in the slope area in the vicinity of the proposed retaining wall upslope of the Crew Building expansion area by Geske’s Hauling, Inc. with a Kubota KX080 excavator. Our field geologist collected samples from selected locations within the test pits and logged the geologic conditions exposed in the test pits including earth material types and bedrock bedding orientations.

Following completion, the test pits were backfilled with the excavated materials and tamped with the bucket.

1.4.3 Laboratory Testing

Geotechnical laboratory tests were performed on selected earth materials sampled in the drill holes and test pits to characterize the earth materials and estimate relevant engineering design parameters. The testing consists of moisture/density measurements, grainsize, plasticity, Modified Proctor maximum density, strength, consolidation, expansion index, and limited chemical testing (sulfates, sulfides, chlorides, pH, and resistivity). The laboratory test results are summarized in the following sections and are presented on the drill hole and test pit logs (Appendix A) and in Appendix B.

1.4.4 Geotechnical Evaluations and Report

We evaluated the field and laboratory geotechnical data, developed geotechnical engineering recommendations for design and construction of the conceptual to preliminary design projects based on the information provided to us, and prepared this report to summarize our findings, opinions and recommendations for the projects. Our report includes the following:

• Soil and groundwater conditions encountered at the exploration locations;

• Laboratory test results, including moisture content, in-place density, plasticity, grainsize, consolidation potential, strength, expansion index, and corrosivity;

• Potential geohazards including strong ground shaking, liquefaction potential, consolidation, flooding, and slope instability;

• Suitability of onsite soil for use as fill and select fill material;

• Anticipated excavation conditions;

• Grading recommendations, consisting of clearing and grubbing, stockpiling topsoil (if applicable), preparation of areas to receive fill, thickness of lifts;

• Retaining wall and buried wall design including lateral earth pressures and seismic loading for walls greater than six feet in height;

• Foundation design parameters, including bearing pressure, friction, modulus of subgrade reaction and passive pressure for sliding resistance.

• 2019 CBC seismic design parameters for the structures and retaining walls assuming shallow spread footing foundations;

• Foundation design parameters for the floodwall; and

• Differential and total settlement estimates.

2.0 FINDINGS

2.1 GEOLOGIC SETTING AND SITE CONDITIONS

2.1.1 Regional Geology

The Thousand Oaks area is located within the Transverse Ranges geologic/geomorphic province of California. That province is characterized by generally east-west-trending mountain ranges composed of sedimentary and volcanic rocks ranging in age from Cretaceous to Recent.

Major east-trending folds, reverse faults, and left-lateral strike-slip faults reflect regional north-south compression and are characteristic of the Transverse Ranges. Several authors including Dibblee (1993) and Weber (1973) have mapped the Thousand Oaks area.

2.1.2 Local Geology

Published geologic mapping by Dibblee (1993) indicates the Lake Bard Water Filtration Plant site vicinity is underlain by bedrock of the Sespe Formation. Review of existing site-specific geotechnical data, site observations, and the exploration performed for this study indicates the onsite materials consist of artificial fill, alluvial deposits (in valley areas), and Sespe Formation bedrock materials as described in the following sections.

We note the Sespe Formation bedrock materials sampled in the drill holes and observed in the test pits have soil-like properties (the consistency of medium dense to very dense granular materials and medium stiff to hard cohesive materials) and are therefore described using soil description terminology.

2.1.3 Site Conditions

Review of historical aerial photographs indicates that Calleguas Lane and the existing site improvements west of the existing Crew Building and Maintenance Facility area were constructed in a westerly draining canyon area with smaller northerly and southerly draining tributaries along the length of the canyon drainage. The canyon and tributaries are incised into Sespe Formation bedrock slopes. The Crew Building and Maintenance Facility area are located in a saddle area near the head of the westerly-trending Calleguas Lane drainage and a smaller northeasterly trending drainage.

Based on the aerial photograph review, data review, and site observations, the areas of the existing and proposed improvements are underlain by artificial fill associated with previous construction activities, alluvial sediments deposited within the canyon drainages, and bedrock of the Sespe Formation. Additionally, ascending slopes are located proximal to the existing Crew Building, the Lake Bard Pump Station, the Chlorine Building, and the CPS Building sites. Slope stability evaluations of the existing slopes is not part of the work performed for this study.

2.2 CREW BUILDING IMPROVEMENTS

The Crew Building Improvements are located near the existing Crew Building (Plates 1 and 2a). Review of historical aerial photographs indicates the Crew Building Improvements site is located in a saddle area near the head of the westerly-trending Calleguas Lane drainage and a smaller northeasterly trending drainage. Based on the aerial photograph review, the saddle area and a portion of the northeasterly-trending drainage appear to have been filled to create the existing pad area in the mid-1960’s.

Based on conceptual information provided to us by KJ, the Crew Building Improvements will consist of construction of an about 12,000 square-foot building expansion adjacent to the northeastern side of the existing Crew Building (Plate 2a). Also, the western side of the existing Crew Building is one of the location alternatives under consideration for the relocation of the 625 square-foot Networking Center. The new buildings are anticipated to be single-story slab-on-grade structures.

The conceptual plans by KJ indicate the majority of the Crew Building expansion footprint will require excavation into the existing southeasterly facing bedrock slope on the northwestern side of the expansion footprint with cut depths up to about 20 feet. The preliminary plans indicate the bedrock cut will be supported by a retaining wall and we understand that cut depths will be provided along the slope to limit the retaining wall height to five feet or less. Published geologic mapping and field exploration performed for this study indicate the slope is underlain by Sespe Formation bedrock that dips northwest, favorably into the slope (Plate 2a; and Appendix A, TP- 2).

2.2.1 Earth Materials and Engineering Properties

Drill holes DH-1 and DH-2 were advanced to depths of about 20 feet to evaluate the earth materials in the vicinity of the Crew Building expansion and the potential new Networking Center location and to supplement findings for the drill hole advanced by Fugro (DH-4-01, 2002).

Additionally, three backhoe test pits were advanced to depths of about 5 to 7-1/2 feet in the slope area in the vicinity of the proposed retaining wall upslope of the Crew Building expansion to evaluate the earth materials for retaining wall design in that area. The approximate drill hole and test pit exploration locations are depicted on Plate 2a.

2.2.1.1 Crew Building Expansion

The earth materials encountered by drill hole DH-1 advanced in the northeastern area of Crew Building expansion area were interpreted to consist of about 12-1/2 feet of artificial fill overlying very dense clayey sand/sandstone of the Sespe Formation. The material interpreted as fill consisted of clayey sand with gravel and rock fragments, silty sand with gravel and rock fragments, and clay with rock fragments; asphalt concrete pavement and base materials are located at the surface. As described previously, the fill materials are likely related to construction of the large pad area and infilling of the saddle area and a portion of the northerly-trending drainage area to the east of the Crew Building site in the mid-1960’s. Groundwater was not encountered to the maximum depth explored (20 feet).

A summary of the general engineering properties for the materials sampled in drill hole DH-1 and tested for this study consists of:

• Field SPT blowcounts within the interpreted fill materials ranged from 20 blows per foot (bpf) to refusal (greater than 50 bpf); the blowcounts are likely affected by the gravel and rock fragments encountered during sampling. The blowcounts in the Sespe Formation clayey sand/clayey sandstone ranged from 64 bpf to about 100 bpf indicating the sampled bedrock materials are very dense.

• The moisture contents of the tested materials ranged from five to eight percent.

• The results of grainsize evaluations indicate fines contents (percent passing No. 200 sieve) ranging from about 25 to 61 percent for the tested samples indicating the tested materials are clayey sand and clay (Appendix A and B).

• The results of a direct shear test performed on a sample of clayey sand from a depth of 10 feet indicate a peak friction of 36 degrees with a cohesion of 240 pounds per square foot (psf) and a post-peak friction angle of 35 degrees with a cohesion of 0 psf.

• The results of an Expansion Index (EI) test performed on a sample of near surface clayey sand from DH-1 indicate an EI of 61 (medium).

• The results of the soil chemistry test performed on a sample from DH-1 are summarized in Section 3.4 below.

• The results of a Modified Proctor maximum density (ASTM D1557) test performed on near surface soils from DH-1 indicate a maximum density of about 125 pounds per cubic foot (pcf) at an optimum moisture content of 10 percent.

2.2.1.2 Crew Building Retaining Wall

Three backhoe test pits were advanced on the existing Sespe Formation cutslope area north (upslope) of the proposed Crew Building expansion to observe the bedrock materials as part of the retaining wall design (Plate 2a). The test pits encountered silty sand/sandstone, gravelly, cobbley sand/sandstone, and hard clay/claystone that dipped at about 24 degrees northward into the slope (Appendix A).

An Atterberg limits (plasticity) test and an EI test were performed on samples of clay/claystone encountered in TP-2 below about three feet. The plasticity test results indicate the sample is clay with a liquid limit of 45 and a plasticity index of 19, which classifies as a low plasticity clay (CL, Appendix B). The EI test results indicate an EI of 100 (high).

2.2.1.3 Networking Center

The earth materials encountered by drill hole DH-2 (Networking Center) were interpreted to consist of about five feet of artificial fill overlying medium dense to very dense clayey sand/sandstone of the Sespe Formation. The material interpreted as fill consisted of clayey sand with gravel and rock fragments that may be related to construction of the existing Crew Building and/or utilities. Groundwater was not encountered to the maximum depth explored (20 feet).

A summary of the general engineering properties for the materials sampled in the drill holes advanced at this location and tested for this study consists of:

• An attempted SPT sample within the interpreted fill materials reached refusal on a rock at a depth of about three feet. The blowcounts in the Sespe Formation clayey sand/clayey sandstone ranged from 17 bpf to greater than 100 bpf indicating the sampled bedrock materials are medium dense to very dense.

• The moisture contents of the tested materials ranged from five to seven percent.

• The results of grainsize evaluations indicate fines contents (percent passing No. 200 sieve) ranging from about 18 to 29 percent for the tested samples. On the basis of laboratory testing and visual classification, the tested materials are clayey sand.

Previous Data. Fugro (2002) advanced a hollowstem auger drill hole (DH-4-01) to a depth of about eight feet on the northeastern side of the existing Crew Building near the location shown on Plate 2a. Fugro’s drill hole reportedly encountered Sespe Formation silty sandstone bedrock at the ground surface to total depth (eight feet) at that location. Fugro reported SPT blowcounts of about 20 to 44 bpf; no laboratory test data were provided.

2.3 LAKE BARD PUMP STATION SITE

The Lake Bard Pump Station (LBPS) is located near the existing inlet screens southwest of the intersection of Calleguas Lane and Hardy Lane (Plate 1). Based on aerial photograph review, the LBPS area is located near the confluence of the westerly-trending Calleguas Lane drainage and a southerly trending tributary drainage near the toe of an ascending 100-foot-high northeasterly facing bedrock slope (Plate 2b). Published regional geologic mapping indicates the bedrock dips about 42 degrees to the northwest in the LBPS vicinity.

Preliminary project design provided to us by KJ prior to field mobilization in December 2020 indicated the LBPS would consist of construction of an approximately 27- by 30-foot pad near the existing grade and construction of four vertical pump cans, new piping for suction and discharge headers to and from the LBPS, and a new backup flow meter. Excavations for the improvements are anticipated to extend to depths of about 20 feet below the existing and proposed grade. Based on subsequent discussions and recent design concepts, we understand the LBPS design has been revised and may also include relocation of an existing storm drain line to an alignment located between the existing 84-inch internal diameter (ID) waterline south of the proposed LBPS and the toe of the existing 100-foot high bedrock slope. Review of the conceptual realignment plans indicates the potential storm drain pipeline alignment is approximately 170 feet long and will include excavation into the toe of the existing slope to construct the storm drain line at the proposed invert elevations. Review of the conceptual storm drain pipeline alignment, invert elevations, and existing topography indicates excavation depths of about 10+ feet will be required to construct the proposed storm drain pipeline as envisioned. The existing 84-inch diameter water pipeline appears to parallel the existing slope and has an invert depth of about 15 to 20 feet, with about 10 feet of soil cover over the pipe.

2.3.1 Earth Materials and Engineering Properties

Drill hole (DH-3) was advanced near the footprint of the proposed vertical pump area to a depth of about 25 feet to confirm and supplement findings for the drill hole advanced by Fugro (DH-2-01, 2002). The approximate drill hole locations are shown on Plate 2b.

The earth materials encountered by drill hole DH-3 consist of artificial fill materials likely associated with previous onsite grading and construction of the existing improvements, alluvial sediments, and bedrock of the Sespe Formation.

The artificial fill materials sampled in drill hole DH-3 consist of medium dense silty to clayey sand with gravel to a depth of about 7-1/2 feet. From about 7-1/2 feet to 20 feet, the sampled materials consist of dense clayey sand with gravel and hard sandy clay interpreted to be alluvial sediments deposited within the valley area underlain by Sespe Formation bedrock materials. The Sespe Formation materials sampled at 20 and 25 feet consist of very dense clayey sand (soft, moderately weathered clayey sandstone). Firm drilling conditions were noted below about 18 feet and very firm drilling conditions were noted below about 20 feet. Based on the drilling conditions, it is possible the Sespe Formation was encountered at a depth of about 18 feet at the drill hole location. Groundwater was not encountered to the maximum depth explored (25 feet).

A summary of the general engineering properties for the materials sampled in the drill hole advanced at this location and tested for this study consists of:

• Field SPT blowcounts ranged from 22 to 33 bpf in the fill and alluvial materials sampled in the upper 15 feet and the blowcounts in the Sespe Formation clayey sand/clayey sandstone sampled at 20 to 25 feet were greater than 100 bpf indicating the sampled bedrock materials are very dense.

• The dry density of a sample of tested fill material was 121 pcf which is about 95 percent of the relative compaction as compared to the maximum density of 127 pcf based on the results of a Modified Proctor test (ASTM D1557) performed on a near surface sample (0 to five feet) from DH-3 (Appendix B). The dry densities of tested samples of alluvium and Sespe Formation clayey sand were 118 pcf and 112 pcf, respectively.

• The moisture contents of the sampled clayey sand materials ranged from seven to eight percent; the moisture content was 14 percent on a tested sample of sandy clay.

• The results of grainsize evaluations indicate fines contents (percent passing No. 200 sieve) ranging from about 41 to 52 percent for the tested samples indicating the tested materials are clayey sand and sandy clay.

• The results of a direct shear test performed on a sample of clayey sand from a depth of 10 feet indicate a peak friction of 36 degrees with a cohesion of 240 psf and a post-peak friction angle of 35 degrees with a cohesion of 0 psf.

• One consolidation test (ASTM D2435) performed on a sample of clayey sand alluvial material from a depth of 10 feet indicates about three percent consolidation at a loading of 30 kips for the tested sample. The sample expanded about a half percent at a load of 1,000 psf (1 kip) after inundation with water. The results indicate a slightly expansive earth material.

• The results of the soil chemistry test performed on a sample from DH-3 are summarized in Section 3.4 below.

• The results of a compaction test indicate a maximum density of about 127 pcf at an optimum moisture content of 12 percent.

Existing Data. Fugro (2002) advanced hollowstem auger drill hole DH-2-01 to a depth of about 20 feet in the vicinity of the existing treatment plant inlet box (Plate 2b). Fugro’s drill hole also reportedly encountered about 20 feet of artificial fill and alluvial materials overlying claystone bedrock of the Sespe Formation at a depth of 20 feet. Fugro describes the soils at that location as medium dense to dense silty sand to a depth of about 14 feet underlain by hard sandy clay to 20 feet; highly weathered claystone bedrock of the Sespe Formation was encountered at a depth of about 20 feet at that location. No laboratory test data were provided for that drill hole.

2.4 CONEJO PUMP STATION REHABILITATION

The Conejo Pump Station (CPS) Rehabilitation includes numerous elements. The three considered here are the: 1) Chlorine Building Flood Wall, 2) CPS Rehabilitation, and 3) various vault locations.

2.4.1 Chlorine Building Flood Wall

The Chlorine Building Flood Wall (CBFW) will be located on the northern side of Calleguas Lane, southeast of the existing Chlorine Building (Plate 2c). The CBFW will consist of construction of a concrete wall as a flood mitigation measure to protect the Chlorine Building in the event of a breach of Dike 5. Based on conceptual plans by MNS Engineers, Inc. provided to us, the wall is anticipated to be 93 feet long along Calleguas Lane within the alluvial valley south of the building and about 51 feet long in a northeasterly orientation between Calleguas Lane and the ascending southwesterly facing slope southeast of the building. The wall heights vary from about six to eight feet and the wall could experience forces of up to 250 pounds per foot on the upstream face of the wall in the event of a breach.

2.4.1.1 Earth Materials and Engineering Properties

Hollowstem-auger drill holes DH-4 and DH-5 were advanced near the footprint of the proposed CBFW alignment (Plate 2c) to depths of about 15 and 25 feet, respectively.

The earth materials encountered by drill hole DH-4 consist of artificial fill likely associated with existing utilities in the area overlying Sespe Formation bedrock. The fill materials encountered at the drilling location consisted of loose to medium dense sandy silt to silty fine sand with gravel and concrete fragments to a depth of about three feet. The Sespe Formation bedrock sampled in drill hole DH-4 consisted of dense to very dense silty sand/sandstone and clayey sand/sandstone to the total depth of about 15 feet; harder drilling was noted below about eight feet.

The earth materials encountered by drill hole DH-5 consist of artificial fill, alluvial sediments, and Sespe Formation bedrock. The fill materials encountered at the drilling location consisted of asphalt concrete pavement, base materials, and medium dense clayey sand to a depth of about 7-1/2-feet that are likely associated with construction of the adjacent vault and existing improvements. The fill materials are interpreted to be underlain by loose to medium dense clayey sand and clayey sand with gravel alluvial sediments between about 7-1/2 feet and 15 feet deposited within the valley area. The alluvial sediments encountered within the drill hole are underlain by medium dense to very dense clayey sand/sandstone of the Sespe Formation from about 15 feet to drilling termination at 25 feet. Groundwater was not encountered in either drill hole to the maximum depth explored (25 feet).

A summary of the general engineering properties for the materials sampled in the drill holes advanced at this location and tested for this study consists of:

• Field SPT blowcounts ranged from 10 to 18 bpf in the fill and alluvial materials sampled in the upper 12-1/2 feet in DH-5 indicating the materials are loose to medium dense.

The blowcounts for samples of the Sespe Formation sampled in DH-4 and DH-5 ranged from 19 to greater than 100 bpf indicating the sampled materials were medium dense to very dense.

• The dry density of a sample of tested fill material was 114 pcf which is about 90 percent relative compaction as compared to the maximum density of 126 pcf based on the results of a Modified Proctor test (ASTM D1557) performed on a near surface sample (one to six feet) from DH-5. The dry densities of tested samples of alluvium were 111 pcf and 118 pcf and the dry density of a tested sample of Sespe Formation clayey sand was 120 pcf.

• The moisture contents of the sampled materials ranged from four to seven percent for the tested materials from DH-4 and eight to 14 percent for the tested materials from

DH-5.

• The results of grainsize evaluations indicate fines contents (percent passing No. 200 sieve) ranging from about 18 to 30 percent for the tested samples indicating the materials are silty sand and clayey sand.

• The results of a direct shear test performed on a sample of clayey sand alluvium from a depth of 7-1/2 feet indicate peak and post-peak frictions of 31 degrees with cohesions of 360 psf.

• One consolidation test performed on a sample of clayey sand/sandstone bedrock material from a depth of five feet indicates about 3.5 percent consolidation at a loading of 30 kips for the tested sample. The sample expanded less than about 0.25 percent at a load of 1,000 psf (1 kip) after inundation with water. The results indicate a slightly expansive earth material.

• The results of a soil chemistry test performed on a sample from DH-5 are summarized in Section 3.4 below.

• The results of a laboratory maximum density test indicate a maximum density of about 126 pcf at an optimum moisture content of 12 percent.

Existing Data. SM (1965) advanced two 36-inch diameter rotary bucket auger drill holes to depths of about 11 to 15 feet near the footprint of the Chlorine Building (Plate 2c). SM reportedly encountered about 16 to 10 feet of fill and alluvial soils overlying sandstone bedrock at their boring locations, however, no driven samples were collected from the borings to aid in evaluation of the soil properties.

2.4.2 CPS Rehabilitation

The Conejo Pump Station (CPS) Rehabilitation is located on the northern side of Calleguas Lane, west of the existing Chlorine Building (Plate 2c). Based on conceptual design information provided by KJ, the CPS Rehabilitation consists of replacing the existing 140-foot by 40- to 60-foot CPS Building with a new building that will contain mechanical/compressor, electrical, and hydroturbine rooms. The building is anticipated to be a single story slab-on-grade structure near the existing grade with minimal grade changes.

In addition to the new building, the project also includes replacing the existing horizontal split case pumps B, C, D, E, and F with similar equipment that will require modifications of the existing 13-foot-deep vaults. The existing hydroturbine and associated vault will be replaced with modifications and a new hydroturbine will be constructed within the new building.

Review of historical aerial photographs and existing geotechnical data indicates the CPS site is located on the northern side of the main canyon drainage near the confluence of a southwesterly trending tributary drainage at the toe of a steeply inclined of fill slope (SGD, 1992).

2.4.2.1 CPS Building Earth Materials and Engineering Properties

Hollowstem-auger drill holes DH-6 and DH-7 were advanced near the existing CPS Building to depths of about 15 and 30 feet, respectively, to evaluate the soil conditions for the new building (Plate 2c). Drill hole DH-6 was advanced on the northeastern portion of the existing CPS Building near the ascending slope and DH-7 was advanced on the southwestern side of the existing building near the Pump B vault.

The earth materials encountered by drill hole DH-6 consist of artificial fill likely associated with construction of the existing CPS Building overlying Sespe Formation bedrock. The fill materials encountered at the drilling location consisted of asphalt concrete pavement, base materials, and medium dense clayey sand with few fine gravel to a depth of about five feet. The Sespe Formation bedrock sampled in the drill hole consisted of very stiff sandy clay/claystone and very dense clayey sand/sandstone to the total depth of about 15 feet; harder drilling was noted below about 10 feet.

The earth materials encountered in drill hole DH-7 consist of artificial fill, alluvial sediments, and Sespe Formation bedrock. The fill materials encountered at the drilling location consisted of asphalt concrete pavement, base materials, and medium dense and loose clayey sand that extended to about 7-1/2 feet that are likely associated with construction of the adjacent vault and existing improvements. The fill materials are interpreted to be underlain by loose to medium dense clayey sand alluvial sediments deposited within the valley area at depths between about 7-1/2 feet and 20 feet. The alluvial sediments encountered within the drill hole are underlain by very dense clayey sand/sandstone of the Sespe Formation from about 20 feet to drilling termination at 30 feet. Groundwater was not encountered in either drill hole to the maximum depth explored (30 feet).

A summary of the general engineering properties for the materials sampled in the drill holes advanced at this location and tested for this study consists of:

• A field SPT blowcount of 23 bpf was recorded in the fill materials sampled in the upper 2-1/2 feet of DH-6 on the northeastern side of the existing CPS Building, indicating the sampled material is medium dense. The blowcounts for the fill materials sampled on the southwestern side of the building were 10 bpf (medium dense) at about 2-1/2 feet and four bpf (very loose) at a depth of about five feet.

The blowcounts for the alluvial materials ranged from about eight to 20 bpf, indicating the sampled clayey sand sediments are loose to medium dense.

The blowcounts for the sampled Sespe Formation materials ranged from 69 to greater than 100 bpf, indicating the sampled clayey sand/sandstone materials are very dense.

• The dry density of a sample of tested fill material was 108 pcf which is about 85 percent relative compaction as compared to the maximum density of 126 pcf based on the results of a Modified Proctor test (ASTM D1557) performed on the near surface sample (one to six feet) from DH-7. We note that the sample of very loose clayey sand fill materials from DH-7 (blowcount of four) was collected with an SPT sampler, thus, dry density testing was not possible on this sample. However, based on the blowcounts, the very loose fill likely has a low relative compaction. The dry densities of tested samples of alluvium were 114 pcf and 115 pcf and the dry density of a tested sample of Sespe Formation sandy clay was 118 pcf.

• The moisture contents of the sampled materials generally ranged from 10 to 13 percent for the tested materials.

• The results of grainsize evaluations indicate fines contents (percent passing No. 200 sieve) ranging from about 23 to 29 percent for the tested samples indicating the materials are clayey sand and clayey sandstone.

• The results of a direct shear test performed on a sample of clayey sand from a depth of 7-1/2 feet indicate a peak friction of 31 degrees with a cohesion of 650 psf and a post-peak friction of 30 degrees with a cohesion of 470 psf.

• One consolidation test performed on a sample of clayey sand alluvial material from a depth of 7-1/2 feet indicates about 5.5 percent consolidation at a loading of 30 kips for the tested sample. The sample expanded less than about 0.25 percent at a load of 1,000 psf (1 kip) after inundation with water. The results indicate a slightly expansive earth material.

• The results of a soil chemistry test performed on a sample from DH-7 are summarized in Section 3.4 below.

• The results of a compaction test indicate a maximum density of about 126 pcf at an optimum moisture content of 10 percent.

Existing Data. Soil Mechanics (SM, 1965) performed the original geotechnical study for the CPS area in 1965. SM advanced seven 36-inch diameter rotary bucket auger drill holes to depths of about 11 to 20 feet. Few driven samples were collected from the borings to aid in evaluation of the soil properties and the samples that were collected were driven with the Kelly bars on drill rig rather than a 140 pound hammer dropping 30 inches (ASTM standard). SM reportedly encountered about 12 to 17 feet of fill, alluvial sediments, and colluvial topsoil overlying sandstone bedrock at their boring locations. SM indicated the fill materials were related to infilling of the confluence of the two alluvial drainages in the vicinity of the southeastern portion of the CPS Building. SM recommended removal of the fill materials at the site prior to construction of the improvements.

Converse Consultants (CC) performed a study in 1994 to evaluate distress that had occurred to the Pump G concrete vault structure. CC advanced one 18-inch diameter rotary bucket auger drill hole to a depth of about 36 feet and reportedly encountered about 15 feet of clayey sand fill overlying granular material described as silty sand. CC reported the fill had a relative compaction of about 85 percent based on the results of their laboratory testing. Samplers were also driven with the Kelly bars on the drill rig rather than a 140-pound hammer. CC concluded the distress was not related to the low relative compaction of the backfill or to corrosivity of the backfill materials. Rather, the distress was possibly related to “reactive or expansive concrete aggregate”.

Opinions. SM (1965) reportedly encountered about 12 to 17 feet of fill, alluvial sediments, and colluvial topsoil overlying sandstone bedrock at their boring locations. SM indicated the fill materials were related to infilling of the alluvial drainages in the vicinity of the southeastern portion of the CPS Building. SM recommended removal of the fill materials at the site prior to construction of the improvements. However, review of their data, the distress study by CC (1994), and the low blowcounts encountered in the fill materials in DH-7 suggest the fill materials may not have been compacted to a minimum of 90 percent relative compaction during site construction or that the fill materials, alluvial sediments, and topsoil described by SM (1965) may not have been removed as recommended by SM.

2.4.3 Potential Vault Sites

Two about 15-foot-deep vaults may be constructed on the western side of the existing CPS Building; one near the PIT No. 2 vault and one along the 60-inch Tierra Rejada Feeder downstream of PIT No. 2.

2.4.3.1 Earth Materials and Engineering Properties

Drill holes DH-8 and DH-9 were advanced near the conceptual vault locations to depths of about 15 feet to evaluate the soil conditions in the vicinity of the potential vaults. As indicated on Plate 2c, drill hole DH-8 was advanced near PIT No. 2 and DH-9 was advanced near the existing valve vault along the Tierra Rejada feeder.

The earth materials encountered by the drill holes consist of artificial fill overlying Sespe Formation bedrock. The fill materials encountered in DH-8 consisted of asphalt concrete pavement, base materials, and clayey sand to a depth of about three feet. The sampled fill materials encountered in DH-9 consisted of medium dense clayey sand to about 7-1/2 feet that is likely associated with construction of the existing pipeline infrastructure and improvements. The Sespe Formation bedrock sampled in the two locations consisted of medium dense to very dense clayey sand/sandstone with few gravel to the total depth of about 15 feet; harder drilling was noted below about 10 to 11 feet. Groundwater was not encountered in either drill hole to the maximum depth explored (15 feet).

A summary of the general engineering properties for the materials sampled in the drill holes advanced for the potential valve vault locations and tested for this study consists of:

• Field SPT blowcounts of 21 to 24 bpf were recorded in the fill materials, indicating the sampled materials are medium dense. The blowcounts for the sampled Sespe Formation materials ranged from 11 to greater than 100 bpf, indicating the sampled clayey sand/sandstone materials are medium dense to very dense.

• The dry density of a sample of tested fill material was 113 pcf which is about 90 percent relative compaction as compared to the maximum density of 126 pcf based on the results of a compaction test performed on the near surface sample from DH-7 advanced on the northeastern side of the existing CPS Building. The dry densities of samples of tested Sespe Formation materials ranged from 106 to 120 pcf.

• The moisture contents of the sampled fill and bedrock materials generally ranged from five to nine percent for the tested materials.

• The results of grainsize evaluations indicate fines contents (percent passing No. 200 sieve) ranging from about 19 to 36 percent for the tested samples indicating the materials are clayey sand and clayey sandstone.

2.5 GROUNDWATER

Groundwater was not encountered in any of the drill holes advanced for this study to the depths explored or in explorations by SM (1965), CC (1994), SGD (1992), or Fugro (2002).

Groundwater is estimated to be in excess of 50 feet below the ground surface in the project locations based on regional mapping by the California Geologic Survey for the Thousand Oaks area.

2.6 POTENTIAL VARIATION OF SUBSURFACE MATERIALS

There is a potential for variation in the consistency, density, and strength/hardness of the materials from what was encountered in our explorations. The potential exists to encounter perched water, zones of poorly consolidated soils, or other conditions not indicated on the exploration logs. If significant variation in the geologic conditions is observed during construction, we recommend the geotechnical engineer, in conjunction with the project designer, evaluate the impact of those variations on the project design.

3.0 SEISMIC CONSIDERATIONS AND GEOHAZARDS

3.1 FAULTING AND SEISMICITY

3.1.1 Nearby Faults

The project site is located in the seismically active portion of southern California and the project most likely will be subjected to strong earthquake ground motion during its lifetime. We note the M7.1 Northridge earthquake in 1994 and M6.6 San Fernando earthquake in 1971 generated strong ground motion at the site. As summarized in the following table, several active or potentially active faults are known or postulated to exist near the site.

Table 1. Nearby Faults

Fault Approximate

Distance (miles)

Maximum Moment Magnitude

(Mmax) Simi-Santa Rosa Fault 3.9 7.0

Oakridge Fault 8.7 7.5

Santa Susana Fault 8.9 7.0

Fault distances and earthquake magnitudes obtained from the USGS website applications.

3.1.2 Ground Rupture Potential

The site is not located within a State of California Earthquake Fault Zone (formerly Alquist- Priolo…