A11. 1-J17_Geotechnical Report.pdf

Geotechnical Engineering ● Engineering Geology

Engineering Geology and Geotechnical Engineering Design Report

USFS San Francisquito Fire Station and Barracks

Santa Clarita, California

Prepared for: United States Army Corps of Engineers Los Angeles District – Geotechnical Branch, RM 13091

915 Wilshire Boulevard Los Angeles, California 90017

Prepared by: Tetra Tech

21700 Copley Drive, Suite 200 Diamond Bar, California 91765

April 19, 2019

Project No. TET 18-155E

21700 Copley Drive, Suite 200 * Diamond Bar, CA 91765 * Tel: 909-860-7777 * Fax: 909-860-8017

Project No. TET 18-155E April 19, 2019

United States Army Corps of Engineers Los Angeles District – Geotechnical Branch, RM 13091 915 Wilshire Boulevard Los Angeles, California 90017

Attention: Mr. Juan Urena

Subject: ENGINEERING GEOLOGY

AND GEOTECHNICAL ENGINEERING DESIGN REPORT

USFS SAN FRANCISQUITO FIRE STATION AND BARRACKS

Santa Clarita, California

Dear Mr. Urena:

Tetra Tech Inc. (Tetra Tech) is pleased to submit the results of our engineering geology and geotechnical engineering design recommendations to the United States Army Corps of Engineers (USACE) for the proposed United States Fire Service (USFS) San Francisquito Fire Station and Barracks in the Angeles National Forest located northeast of the City of Santa Clarita, California. The purpose of our investigation was to evaluate the surface and subsurface conditions, to assess key geotechnical constraints and geologic hazards, and to provide recommendations for the design and construction of the proposed fire station facility. Two potential development sites, North Site and South Site, were included in the evaluation. This report includes a brief description of the proposed development, discussions regarding field and laboratory investigative efforts, subsurface conditions, geology and engineering seismology, and geotechnical conclusions and recommendations for design and construction of the proposed development. The appendices to the report include logs from the test pits and bucket auger borings, stereonet plots, results of laboratory tests, seismic demand, percolation test results, shear strength graphical representations, and results of slope stability and permanent seismically-induced deformation analyses.

We appreciate the opportunity to provide our professional services on this project. If you have any questions regarding this report or if we can be of further service, please do not hesitate to contact the undersigned.

Respectfully submitted, Tetra Tech

David Luka, C.E.G Senior Engineering Geologist

Fernando Cuenca, Ph.D., G.E.

Senior Engineer

Douglas Bell, G.E.

Principal Engineer

Distribution: Addressee (3 hardcopies + pdf by email juan.m.urena@usace.army.mil)

3-31-21

United States Army Corps of Engineers USFS San Francisquito Fire Station and Barracks Project No. TET 18-155E Santa Clarita, California April 19, 2019 i

TABLE OF CONTENTS

Page

1. INTRODUCTION

2. SCOPE OF SERVICES

3. PROPOSED DEVELOPMENT AND SITE DESCRIPTION

4. SITE BACKGROUND REVIEW

5. FIELD EXPLORATION AND LABORATORY TESTING

5.1. FIELD EXPLORATION (SURFACE MAPPING, SUBSURFACE EXPLORATION)

5.1.1. Surface Mapping

5.1.2. Subsurface Exploration (Test Pits, Geotechnical and Percolation Borings)

5.1.3. Fault Trenching

5.2. LABORATORY TESTING

6. SUBSURFACE CONDITIONS

6.1. REGIONAL GEOLOGY

6.2. SITE GEOLOGY AND EARTH MATERIALS

6.2.1. Fill (af)

6.2.2. Landslide Debris (Qls)

6.2.3. Alluvium (Qal)

6.2.4. Older Alluvium/Colluvium (Qoa)

6.2.5. San Francisquito Formation – Sandstone Member (Tsfs)

6.2.6. San Francisquito Formation – Shale Member (Tsfa)

6.3. GEOLOGIC STRUCTURE

6.4. GROUNDWATER

7. ENGINEERING SEISMOLOGY AND GEOLOGIC HAZARDS

7.1. GENERAL SEISMIC SETTING

7.2. SEISMIC HAZARDS RELATED TO FAULTING

7.2.1. Seismic Hazard Zones

7.2.2. Surface Fault Rupture and Local Faulting

7.2.3. Potentially Active Fault (Clearwater Fault)

7.2.4. On-Site Faulting

7.2.5. Fault Fling

7.3. SEISMIC DEMAND AND OTHER SEISMIC HAZARDS

7.3.1. Liquefaction Potential and Dynamic Settlement

7.3.2. Lateral Spreading

7.3.3. Tsunami, Seiche and Inundation

7.4. LANDSLIDES

7.5. MUDFLOWS

7.6. EXPANSIVE SOILS

7.7. COLLAPSIBLE/COMPRESSIBLE SOILS

8. PERCOLATION TESTING

9. SLOPE STABILITY EVALUATION

9.1. MATERIAL SHEAR STRENGTH

ii

9.2. GROUNDWATER IMPACTS

9.3. STATIC SLOPE STABILITY AND PERMANENT SEISMIC DEFORMATION ANALYSES

10. DESIGN RECOMMENDATIONS

10.1. GENERAL

10.2. CLEARING AND GRUBBING

10.3. EXCAVATABILITY AND RIPPABILITY

10.4. SITE PREPARATION – PAD GRADING

10.4.1. Overexcavation

10.4.2. Fill Placement

10.4.3. Construction Observation

10.5. SLOPES

10.5.1. Fill Slopes

10.5.2. Slope Subdrains

10.5.3. Fill Placement

10.5.4. Slope Surface Protection

10.5.5. Slope Setback Zones

10.6. FAULT SETBACK ZONES

10.7. FOOTING FOUNDATIONS

10.7.1. Footing Adjacent to Trenches

10.7.2. Foundation Construction Observations

10.8. SEISMIC DESIGN PARAMETERS

10.9. CONCRETE SLABS

10.9.1. Floor Slabs

10.9.2. Exterior Slabs

10.10. PAVEMENT SECTIONS

10.10.1. Subgrade Preparation

10.10.2. Asphalt Concrete Pavement Design

10.10.3. Portland Cement Concrete Pavement Design

10.10.4. Construction Observations

10.11. SOIL CORROSION

10.12. DRAINAGE CONTROL

10.13. ON-SITE WASTEWATER TREATMENT SYSTEMS

10.14. SUMMARY OF GEOTECHNICAL ISSUES AFFECTING THE SELECTION OF PROJECT SITE 49

11. GENERAL SITE GRADING RECOMMENDATIONS

12. DESIGN REVIEW AND CONSTRUCTION MONITORING

12.1. PLANS AND SPECIFICATIONS

12.2. CONSTRUCTION MONITORING

13. LIMITATIONS

14. SELECTED REFERENCES

iii

Figures Figure 1 – Site Location Map Figure 2 – Regional Geologic Map Figure 3 – Regional Fault and Seismicity Map Figure 4 – Fill Slope Grading Recommendations

Plates

Plate 1 – Project Geologic Map Plate 2 – Fault Trench Logs FT-1a-c, FT-2, FT-3 Plate 3a – Geologic Cross-Sections A-A’ and B-B’ Plate 3b – Geologic Cross-Sections C-C’ and D-D’ Plate 3c – Geologic Cross-Section E-E’ Plate 4 – Recommended Building Setbacks

Appendices

Appendix A – Logs of Test Pits and Exploratory Borings, and Stereonet Plots Appendix B – Results of Laboratory Testing Appendix C – Seismic Demand Appendix D – Logs of Percolation Testing Appendix E – Shear Strength Graphical Representations Appendix F – Slope Stability Analyses Appendix G – Permanent Seismic Deformation Analyses

1. INTRODUCTION

This report presents the results of Tetra Tech Inc.’s (Tetra Tech) geotechnical evaluation for the proposed United States Fire Service (USFS) San Francisquito Fire Station and Barracks in the Angeles National Forest located northeast of the City of Santa Clarita, California. The work was performed for the United States Army Corps of Engineers (USACE), Los Angeles District – Geotechnical Branch under contract W912PL-17-D0004 – Work Order W912PL18F0094.

Currently, 2 potential sites are being considered for the fire station, North Site and South Site, and an evaluation of both sites is included in this report (Figure 1).

The purpose of our investigation was to evaluate the subsurface conditions, to assess key geotechnical constraints and geologic hazards at the 2 alternative sites, and to provide geotechnical recommendations for the design and construction of the proposed fire station, barracks and associated improvements. This report summarizes the data collected and presents our findings, conclusions, and geotechnical design recommendations. Several geotechnical/geologic factors impact differently both sites, including recommended building setbacks from slopes and faults, and the suitability for Onsite Wastewater Treatment System (OWTS). These factors should be considered by the Design Engineer in assessing the 2 alternative sites.

As directed by the USACE, the recommendations provided in this report are based on the requirements and guidelines outlined in the California Building Code (2016 CBC) and the International Building Code (2015 IBC). Seismic evaluation of slopes at the project sites has been performed in general accordance with industry accepted standards based on California Department of Conservation, Division of Mines and Geology, Special Publication 117A (2008) and Southern California Earthquake Center (SCEC, 2002).

2. SCOPE OF SERVICES

Tetra Tech’s scope of services under Work Order W912PL180094 consisted of the following tasks:

• Review of available background data, including Client-provided geotechnical data from nearby projects, and available geotechnical literature, geologic maps, and seismic hazard documents relevant to the subject site.

• Preparation of a work plan describing the proposed field work and laboratory testing.

• A site reconnaissance to observe the site surface conditions and to select and stake boring, test pit, and fault trench locations.

• Notification of Underground Service Alert (USA) prior to subsurface exploration for the clearance of buried on-site utilities.

• A subsurface field exploration program consisting of:

♦ 21 test pits excavated to depths varying from about 2 to 14 feet.

♦ 6 bucket auger borings drilled to depths varying from about 46 to 61 feet.

♦ 5 additional bucket auger borings excavated to depths varying from about 35 to 50 feet to perform on-site percolation tests.

♦ Excavation of 3 fault trenches totaling approximately 500 lineal feet at the South Site.

• Laboratory testing of selected samples collected from the test pits and borings performed to evaluate geotechnical engineering properties of the on-site soils and bedrock.

• Engineering evaluation of the geological and geotechnical data collected to develop geotechnical recommendations for the design and construction of the proposed development, including the following items:

♦ An evaluation of general subsurface conditions and description of types, distribution, and engineering characteristics of subsurface materials.

♦ An evaluation of general groundwater conditions and the potential impact on the design and construction of the proposed development.

♦ Preparation of a site geologic map and geologic cross-sections representative of key site conditions.

♦ An evaluation of geologic hazards at the site, including the potential for surface fault rupture and recommended fault setback.

♦ An evaluation of the liquefaction potential and dynamic settlement of the on-site materials.

♦ Performance of static and seismic slope stability analyses for the existing slopes and proposed fill slopes and evaluation of minimum building setbacks from the top of slopes.

♦ Evaluation of the suitability of on-site soils and bedrock for the support of structures.

♦ Recommendations for site preparation and grading.

♦ Recommendations for design of foundation systems including allowable bearing capacity, lateral resistance, and settlement estimates.

♦ Recommendations for design of slab-on-grade at the site.

♦ Evaluation of the percolation properties of the on-site material to assist in the design of on-site wastewater treatment systems (OWTS) in accordance with Los Angeles County Department of Public Health (LACDPH) guidelines.

♦ Recommendations for asphalt and Portland cement concrete pavement sections.

♦ Determination of seismic design parameters in accordance with the 2016 California

Building Code.

♦ An evaluation of the corrosion potential of the on-site materials to buried concrete and ferrous metals.

• Preparation of this report, including the provision of reference maps and illustrations, a summary of the collected data, and conclusions and geotechnical recommendations for the design and construction of the proposed development.

3. PROPOSED DEVELOPMENT AND SITE DESCRIPTION

Two potential building sites are currently being evaluated for the proposed USFS San Francisquito Fire Station and Barracks. The 2 sites, designated as North Site and South Site, are located within the Angeles National Forest roughly 8 miles north of the City of Santa Clarita, California. Both sites are located in hillside terrain and are accessed through San Francisquito Canyon Road and along Runner Road (Figure 1).

The North Site is located on a partially graded two-tiered pad bordered to the west, south, and southeast by moderately to steeply descending slopes up to a maximum height of approximately 235 feet. The site is bordered on the north by Runner Road with slightly higher terrain to the north of Runner Road. Currently the western portion of the North Site is roughly 20 feet higher than the eastern portion. The current surface drainage within the upper pad of North Site generally trends towards the western slope, while surface drainage within the lower pad trends toward the southern slope.

The South Site is located on a partially graded hilltop pad bordered to the north, west, and south by moderately to steeply descending slopes up to a maximum height of approximately 170 feet.

Runner Road is located on the east side of the pad at the toe of an ascending slope. An electric power plant (Power Plant No. 1), belonging to the City of Los Angeles Department of Water and Power (LADWP), is located near the base of the northwest facing slope descending from the South Site. Surface drainage on the South Site is easterly across the pad towards Runner Road.

Runner Road provides the most direct route from San Francisquito Canyon Road to both the North and South Sites. The road length between the 2 sites is approximately 800 feet. The existing paved road width varies from about 10 to 20 feet with some additional unpaved shoulder.

Descending slopes up to approximately 100 feet in height are located adjacent to the west side of the road. Ascending slopes on the order of 10 to 30 feet in height border the easterly side of the road.

Based on the conceptual architectural plans it is understood that the proposed fire station facility will include a 2-bay engine garage with adjoining office, storage rooms and work spaces. The selected site will also have a separate barracks building which will include food preparation, dining, and sleeping facilities. Both structures are expected to be single story, with high ceiling clearance in the garage area and will be connected to an OWTS. Parking areas and access roads will also be improved and/or constructed.

4. SITE BACKGROUND REVIEW

4.1. Available Reports

Inquiries with the Los Angeles County Department of Public Works, Geotechnical and Materials Engineering Division did not provide any site-specific geotechnical studies. Furthermore, a review of available web-based search sites did not provide any site-specific geotechnical reports.

Available regional and site-specific in-house and web-based geologic data reviewed for this study included published geologic maps, academic studies, and fault evaluation reports. A listing of reviewed data is presented following the text in Section 14 (Selected References). From the available geologic information, the two alternative building sites, and the existing Runner Road alignment are underlain by early Cenozoic (about 60 million years old) sedimentary rocks consisting principally of sandstone and argillaceous rocks (shale). Thin deposits of native alluvium and colluvium mantle the local ridgelines. Previous grading performed at both candidate sites has locally stripped these native soils resulting in bedrock exposures at or near the existing grades. Additionally, fill placement associated with previous grading has resulted in the distribution of thin to relatively substantial fill depths at both sites.

4.2. Salient Site History

Tetra Tech conducted a review of readily available commercial historic vertical aerial photographs covering the period from 1928 through 2017 to establish a site development and grading history as well as to look for evidence of past slope instability. A site history summary based on the reviewed available aerial photography and site data follows:

• 1911-1917 – Construction of the LADWP Power Plant No. 1 and associated structures, i.e., pipelines, tailrace (LADWP, 2017).

• 1928 – Oldest vertical aerial photograph reviewed shows the LADWP Power Plant No. 1

(power plant) building, associated structures and access road from the south in their current locations. Pipelines associated with the Los Angeles Aqueduct are shown on the ascending ridge spur north of the current alignment of San Francisquito Canyon Road. Disturbed ground between the power plant and the future San Francisquito Canyon Road alignment is evident and consistent with the below ground section of the pipelines. Runner Road is located along its current alignment from San Francisquito Canyon several hundred feet down canyon of the power plant up to the future San Francisquito Canyon Road alignment.

Upwards of 30 structures, likely small residential houses, are located in the area of the North Site and positioned on either side of Runner Road. Evidence of grading on the North Site suggests that building pads were created to support the development. An excerpt of the 1928 aerial photograph is shown in Photograph No. 1.

Photograph No. 1: 1928 aerial photograph excerpt showing the candidate sites, power plant, pipeline alignment, structures, and Runner Road.

• 1952 – Additional grading at the North Site since 1928 evident: expanded building pads and the installation of power line towers to the east. Vegetation (trees) at the North Site appear to be well established (Photograph No. 2).

Photograph No. 2: 1952 aerial photograph excerpt showing the candidate sites. Additional grading areas evident at the North Site and to the east for the installation of electrical towers.

North Site

South Site

• 1974 – San Francisquito Canyon Road established from south of the power plant up to the LADWP housing at Runner Road. Significant road cuts required along the upgradient (west) side of San Francisquito Canyon Road to establish the road width.

• 1989 - San Francisquito Canyon Road established at the current alignment to a point a few miles north and west of the candidate sites (Photograph No. 3).

Photograph No. 3: 1989 infrared aerial photograph excerpt showing the candidate sites. Areas of concentrated and actively growing vegetation are designated in red. Areas of water-stressed or sparse vegetation appear as lighter red. Additional grading areas evident along San Francisquito Canyon Road to the north of the North Site.

• 2005 – Previous grading, based on available aerial photographs, is evident along the west-and north-facing descending slope east of the power plant. Based on the aerial photographs it appears that the majority of excavated materials were exported from the site. However, a significant fill slope was created along the southeast boundary of the South Site (Photograph No. 4).

Photograph No. 4: November 2, 2005 Google Earth image showing the South Site. The yellow-highlighted region is the approximate limits of fill. The red dashed region delineates an area of disturbed ground, possibly a post-grading slope failure.

• 2005 to 2018 – No substantial site changes are evident from a review of aerial photographs.

Photograph No. 5 dates from May 24, 2013 and shows an enlargement of the area of disturbed ground shown in Photograph No. 5.

Photograph No. 5: May 24, 2013 Google Earth image showing the South Site and the LADWP remedial grading area. The red dashed region indicates larger area of disturbed ground.

5. FIELD EXPLORATION AND LABORATORY TESTING

5.1. Field Exploration (Surface Mapping, Subsurface Exploration)

Field evaluation performed for the project included surface geologic mapping and subsurface exploration during October and November 2018. Surface mapping was completed during the initial phase of work for the purpose of documenting geologic conditions and for confirmation of planned subsurface exploration locations.

5.1.1. Surface Mapping

Surface geologic mapping was recorded on a topographic plan provided by the USACE at a scale of 1 inch to 50 feet. Geologic features were recorded on the plan using conventional location methods, i.e., tape, compass, and hand level in relation to topographic and cultural features.

Additionally, commercial grade GPS units were also used for the purpose of locating geologic features. Mapped features were checked against available published geologic maps and aerial photographs. Mapped surface conditions are presented on Plate 1.

5.1.2. Subsurface Exploration (Test Pits, Geotechnical and Percolation Borings)

Based on the results of the surface mapping, subsurface exploration locations were field-located using surface mapping methods. Proposed subsurface exploration locations were field-marked using paint and survey lath. Underground Service Alert was notified of the exploratory locations at least 48 hours prior to drilling for the purpose of buried utility clearance.

The initial subsurface exploration included the excavation of 24 backhoe test pits to a maximum depth of 14 feet. Test pits were completed at both sites, and within the roadway between the 2 sites, and were performed to evaluate the depth and distribution of fill, native soils and bedrock materials. All test pits were observed by a Tetra Tech engineering geologist, who logged the exposed test pit walls and obtained bulk soil and rock samples. During the test pit logging, the description of the material type, color, moisture, grain size, density/consistency, and other pertinent geologic characteristics were recorded. Where excavations complied with OSHA guidelines and were deemed safe for entry, a geologist entered the excavation for direct examination and documentation of the earth materials. Following excavation and subsurface documentation, the test pits were backfilled with the excavated spoils. Periodic compaction of the backfill materials was performed using the backhoe bucket and tires and the completed surface was wheel rolled to a firm condition. Excess soil cuttings not returned to the test pits were spread on-site. It should be understood that the backfill was placed without formal compaction and that some settlement of the backfill may occur with the need for future maintenance. Logs of test pits TP-01 through TP-23 are presented in Appendix A, and the mapped locations are presented on Plate 1.

In mid- to late-October, 11 bucket auger borings were drilled, 6 at the North Site and 5 at the South Site, to a maximum depth of 61 feet. Borings were advanced with a truck-mounted drill rig using a telescoping Kelly bar, a 24-inch diameter bucket, and hydraulic down-crowds for enhanced penetration capacity. The borings included percolation borings (P-1 through P-5) and geotechnical borings (BA-1 through BA-6). All the bucket auger borings were logged and observed by a Tetra Tech engineering geologist, who logged the drill cuttings and collected soil and bedrock samples.

Samples were recovered from each boring by driving a California-type ring sampler using the drill rig Kelly bar as a driving weight. In general, drive samples were taken at 2.5- to 5-foot depth intervals. Where highly resistant bedrock materials were encountered, drive samples were not taken in that horizon. For each sample, blowcounts and Kelly bar drop weights were recorded for each 6-inch penetration interval of the 12-inch drive. In addition to the drive samples, bulk samples of selected subsurface materials were collected in plastic bags. Following drilling completion, a Tetra Tech geologist evaluated the safety of each boring for entry by surface observation with a flashlight and also with a portable gas meter that was lowered to the total depth of the boring.

Once boring conditions were deemed safe for entry, the Tetra Tech engineering geologist entered the boring to log the exposed geology in detail. During the downhole logging, the descriptions of the material type, color, moisture, grain size, density/consistency, and other pertinent geologic characteristics were recorded. The logs of the bucket auger borings are presented in Appendix A.

Both the percolation and geotechnical borings were downhole logged.

Bucket auger borings were backfilled following drilling or percolation testing with the drill cuttings. To facilitate compaction, a water truck was used to introduce water into the borings along with the cuttings. A plate was attached to the drill rig Kelly bar to tamp the soil cuttings. In borings BA-1 and P-1, where groundwater had accumulated to a depth of about 25 feet below the top of the boring, soil cuttings were introduced into the borings to a point above the seepage depth prior to using the Kelly bar to tamp the backfill. Excess soil cuttings not returned to the borings were spread on-site. It should be understood that the backfill was informally placed and compacted and that some settlement of the backfill may occur with the need for future maintenance.

5.1.3. Fault Trenching

Fault trenching on the South Site was performed in November 2018 using a track-mounted excavator. Approximately 500 feet of trench was excavated along a generally north-south trend across the west and central part of the pad. Fault trench depths varied from 2 feet to approximately 10 feet. Where trench depths exceeded 5 feet the trench top was benched to provide for an overall trench wall gradient of approximately 1(H):1(V). The majority of trench segments were positioned as close to perpendicular to the strike of bedding as practicable. Where a structural gap occurred near the northerly end of segment FT-1c, additional trench segments FT-2 and FT-3 were excavated to the north. Additional surface mapping was performed south of fault trench segment FT-3 to eliminate a structural gap in the mapping coverage. Trench locations were established using a commercial grade GPS and checked with reference to on-site cultural features using a tape, compass and hand level.

The fault trench segments were cleaned of loose material, and a horizontal string line was set along the west-north wall to establish vertical control. A trench wall profile was plotted on a plan at a scale of 1 inch to 2 feet. Geologic data were recorded on the plan by a Tetra Tech engineering geologist. The trench segments were peer reviewed in the field by an additional Tetra Tech engineering geologist and by a soil dating expert.

Fault trench segment locations are shown on Plate 1 and the geologic log of the trench exposures is shown on Plate 2.

Following trench logging, the trench segments were backfilled with the excavated cuttings. A steel sheepsfoot wheel attached to the excavator arm was used to compact the cuttings in lifts. To facilitate compaction, a water truck was used to introduce water into the trench along with the cuttings. Resistant bedrock blocks upwards of 3 feet or more in size and not readily degradable were not returned to the trench. These blocks are stockpiled near the easterly limit of the pad. It should be understood that the backfill was informally placed and compacted and that some settlement of the backfill may occur with the need for future maintenance.

5.2. Laboratory Testing

Laboratory tests were performed on selected samples recovered from the borings and test pits to aid in the classification of soils and to evaluate pertinent engineering properties of the on-site soils and bedrock. The following laboratory tests were performed:

• In-situ Moisture Content and Dry Density − ASTM D2216, D2937;

• Grain Size Distribution − ASTM D6913, D7928;

• Atterberg Limits − ASTM D4318;

• Maximum Dry Density and Optimum Moisture Content − ASTMD1557;

• Direct Shear (Consolidated - drained) − ASTM D3080;

• Unconfined Compression – ASTM D2166;

• Triaxial (Consolidated, Undrained) – ASTM D2850;

• Expansion Index – ASTM D4829;

• R-value Test – CTM301

• Corrosivity series:

♦ pH, Resistivity – ASTM G51, G187, ♦ Sulfates – ASTM D516, ♦ Chlorides – ASTM D512B.

Testing was performed in general accordance with the referenced ASTM and CTM Standards.

Results of laboratory tests are presented in Appendix B. For ease of referral to the soil profile, selected laboratory results, including moisture and density determinations, have been included on the boring logs included in Appendix A.

6. SUBSURFACE CONDITIONS

6.1. Regional Geology

The sites are located in the central portion of the Transverse Ranges Physiographic Province. The province is characterized by generally east-west trending mountain ranges and intervening alluvium filled valleys extending approximately 250 miles from the Pacific Ocean on the west to the Mojave Desert on the east (Norris and Webb, 1990). Major regional faults within the province, such as the Big Pine, Santa Ynez, Mission Ridge-Arroyo Parida, San Cayetano, San Gabriel, Oak Ridge, Santa Susana, and Sierra Madre faults, are also predominantly oriented east-west. The San Andreas fault located about 5.4 miles northeast of the site forms the northern boundary of the Transverse Ranges in the area.

Based on geologic mapping by Dibblee (1997a), used herein as the base map for Figure 2, the site is underlain by marine sedimentary bedrock units consisting of sandstone and shale of the San Francisquito Formation; biostratigraphically dated as late Paleocene in age (60 million years old) (Prothero and Vacca, 2001; Kooser, 1982). The bedrock units have been regionally tilted and folded resulting in moderately to very steeply dipping beds to the southeast.

Adjacent geologic units in fault contact with the San Francisquito Formation include Mesozoic and older crystalline basement rocks to the north of the candidate sites, i.e., north of the Clearwater fault, and Mesozoic and older Pelona Schist, approximately 1.6 miles to the south of the South Site at the San Francisquito fault.

6.2. Site Geology and Earth Materials

Based on the results of our field exploration, the North Site is predominantly underlain by the shale member of the San Francisquito Formation. Surficial soils deposits consisting of undocumented fill and undifferentiated older alluvium/colluvium mantle the shale over the majority of the site.

The South Site is predominantly underlain by the sandstone member of the San Francisquito Formation. Surficial soils deposits consisting of undocumented fill and undifferentiated older alluvium/colluvium mantle the sandstone over the southern and eastern part of the site.

Interpretation of the collected geologic data is shown on Plate 1 and presented in the test pit and boring logs in Appendix A and was used to develop models of the subsurface geologic conditions underlying the subject sites. These interpreted geologic models are presented as Plates 3a through 3c – Geologic Cross-Sections A-A’ through E-E’.

Generalized descriptions of the encountered units from youngest to oldest are provided in the sections below. More detailed descriptions of the soil/bedrock conditions encountered during the field exploration are presented on the test pit and boring logs in Appendix A.

6.2.1. Fill (af)

Undocumented fill was encountered at both candidate sites at the exposed grades and in the subsurface test pits, fault trench, and borings.

• North Site – Fill soils in excess of 13 feet in depth were observed along the west side of the upper pad at the southeast limit of the lower pad. Where encountered in the test pits the materials consisted of silty and clayey sand with locally abundant gravel clasts and a trace of boulders. The materials were medium dense to dense and dry to slightly damp.

• Runner Road – Test pit exposures noted thin fills consisting of silty sand with locally abundant gravel- to boulder-size sandstone clasts. The materials were medium dense to dense and dry to slightly damp.

• South Site – Fill soils up to approximately 19 feet in depth were observed along the southeastern half of the pad and to shallower depths in the upper elevated part of the pad in the vicinity of fault trench segment FT-2. Subsurface exposures observed in several of the test pits and in borings BA-5 and BA-6 consisted of silty sand with locally abundant gravel-to boulder-size igneous and sandstone clasts. A trace of scattered construction debris was also noted. Photograph No. 6 illustrates the observed fill materials in boring BA-6 at a depth of about 3 to 5 feet.

Photograph No. 6: Downhole observation of fill materials in boring BA-6. Photograph view is looking east. The base of the surface protective casing is at the top of the photograph. The matrix consists of a yellow brown clayey-silty sand. The red cross arrows are superimposed on large cobble-size sandstone clasts; some of which are clast-supported.

6.2.2. Landslide Debris (Qls)

Landslide debris was field-observed at the westerly descending cut slope adjacent to the west side of the South Site pad. The exposed materials consisted of intensely fractured shale and lesser amounts of similarly fractured sandstone. The materials were locally noted to be loose. Very steep and unstable surface conditions did not allow for detailed surface mapping of the landslide.

6.2.3. Alluvium (Qal)

Recent alluvium was not encountered in any of the subsurface explorations or mapped within the candidate sites. Interpreted recent alluvium is located in the canyon near the south end of Section E-E’ (Plate 3c).

6.2.4. Older Alluvium/Colluvium (Qoa)

Quaternary-aged undifferentiated older alluvium/colluvium was observed during surface mapping and encountered in subsurface exploration locations across the majority of the North Site and locally at the South Site. The soils were observed either beneath the undocumented fill soils or exposed at the existing grades. Explored thicknesses up to about 8 feet were encountered overlying the bedrock. The soils generally consisted of brown (7.5 YR) silty and clayey sand, and sandy clay with varying gravel content. The soils were observed to be somewhat variable in density and consistency, loose to medium dense and/or stiff, and dry to slightly damp. In test pits TP-1 and TP-3, the gravel component was near 50 percent with a clast supported framework and visible voids between clasts. Clay films and abundant strongly reactive carbonate surfaces were noted.

6.2.5. San Francisquito Formation – Sandstone Member (Tsfs)

Sedimentary bedrock of the San Francisquito Formation, Sandstone Member (Tsfs) underlies the majority of the South Site. The unit consists of deep marine, arkosic fine to medium grained sandstone with thin interbeds of shale. A few thin gravel conglomerate beds were field mapped near the north boundary of the pad. Bedding is generally poorly expressed except where thin to thick beds of shale area present. The materials are slightly to intensely fractured. In general, surface exposures are weathered and moderately soft to hard, i.e., can be broken with light hammer blows to broken only with repeated hammer blows. With depth the sandstone was observed to be less weathered and fractured and typically hard, i.e., scratched with a pick or broken with heavy hammer blows. In most instances, drilling in the less weathered sandstone required use of the core bucket and hydraulic down-crowds. The stratigraphy is described in more detail on the subsurface exploration logs included in Appendix A.

6.2.6. San Francisquito Formation – Shale Member (Tsfa)

Sedimentary bedrock of the San Francisquito Formation, Shale Member (Tsfa) underlies the North Site as well as the canyon areas between the candidate sites and the westerly facing cut slope at the west side of the South Site. The unit consists of deep marine, argillaceous clay shale and siltstone with thin sandstone interbeds. Bedding is well developed as expressed in outcroppings

(and in the subsurface explorations for this study). The materials are typically intensely to very intensely fractured. In general surface exposures are weathered and very soft to moderately soft, i.e., can be completely broken with hand pressure to broken with light hammer blows. With depth the shale was observed to be less weathered and fractured and typically moderately soft to moderately hard, i.e., broken with moderate hammer blows. In most instances, drilling in the less weathered shale did not require the use of the core bucket. At the west- and east-facing cut slope adjacent to the South Site the materials exposed at the surface grades excavated by LADWP in 2005 were observed to be completely weathered in the outer few to several inches. In general, the shale fabric was noted to be completely disintegrated into sizes on the order of coarse sand to fine gravel. The weathering zone was observed to attenuate rapidly within the upper foot. The stratigraphy is described in more detail on the subsurface exploration logs included in Appendix A.

6.3. Geologic Structure

The geologic structure is generally uniform across both candidate sites and characterized by a steeply south to southeast dipping homocline. Bedding in both of the mapped members of the San Francisquito Formation, as observed in the test pits, borings, fault trench segments, and mapping of outcrops, strikes generally northeast and dips 45 to 90 degrees towards the southeast. Downdip inclinations are steeper than the existing natural slopes.

Joint patterns within the bedrock units were measured at both candidate sites in the subsurface exploration locations and during surface mapping. The general pattern shows a predominately northwest-southeast striking with steep dips to the southwest and northeast, generally co- to sub-planar with the regional bedding. A second prominent joint pattern was documented at both candidate sites and is characterized as northwest-southeast striking with steep to vertical dips.

Shallow dipping joint sets, i.e., less than 25° were also measured, however, the density of joints was widely scattered. Joints were observed to be generally tight or healed with fracture infilling consisting of clay, carbonates or crushed sandstone. Infilling thicknesses were generally less than 1/8-inch in width with some being upwards of 1/2-inch in width.

Observed shear and fault features were documented at both candidate sites. Shears were documented within the fault trench segments (Plate 2). Shears were measured to be generally co-planar with bedding and lacked expression of striations or other directional indicators of last deformation imprinting. Based upon the relative hardness of the majority of shear surfaces and slight waviness of the surfaces, the shears are interpreted to be bedding plane deformations associated with previous tilting and fold deformation.

Faults features were noted in the fault trench segments excavated at the South Site, and during downhole logging of boring P-3 (North Site) and boring BA-6 (South Site). Fault features measured were northeast striking and southeast dipping, i.e., generally co-planar with bedding north to northwest striking and steeply southwest-northeast dipping to vertical, and east-west striking and near vertical.

Faulting was also observed and documented in some of the fault trench segments and surface exposures. Documenting criteria included measurable offset of beds, indeterminate offset of beds from one side of the trench to the other, evidence of sheared and deformed bedding or joints, and striations. Discussion of local on-site faulting is presented in Section 7.

Stereonet plots of structure planes and poles to planes for bedding, joints/fractures, and shear/fault surfaces are in included in Appendix A following the exploration logs.

6.4. Groundwater

At the time of our subsurface exploration, groundwater was encountered in 2 of the geotechnical borings and in 1 percolation test boring drilled on the North Site. Groundwater seepage was noted during drilling or downhole logging in borings BA-1 and P-1 at a depth of about 25 feet. Standing groundwater levels in both of these borings were measured at that depth less than 24 hours following drilling. In boring BA-3, seepage was observed during drilling and downhole logging at a depth of 49 feet and standing water was measured at 50 feet following drilling.

The above described groundwater seepage noted during the subsurface exploration program appears to be related to a local upgradient source, possibly the existing on-site residential structures. There are seven residential buildings located northerly of borings BA-1 and P-1. The homes date to the mid-20th century. Based on their assumed age they may have compromised pressurized water supply lines and on-site water system disposal units. At the time of our field exploration in October 2018 the only evidence of surface moisture at the North Site was from a leaking fire hydrant riser pipe located approximately 165 feet west-southwest of boring BA-1. No evidence of seepage was observed during excavation of test pits in the vicinity or down gradient of the hydrant, i.e., test Pits TP-3, TP-22, TP-23, or in boring BA-2 located almost directly down dip from the hydrant.

Planned OWTS at the North Site will need to consider setbacks from the borings that encountered groundwater seepage. A recommended area of OWTS exclusion based upon the recently drilled borings is shown on Inset 1.

No evidence of seepage was observed during or following drilling for any of the borings advanced on the South Site (BA-4 through BA-6, P-4 and P-5).

A seismic hazard report for the Green Valley 7.5-Minute Quadrangle has not been published by the State of California. No records documenting local groundwater conditions are on file with the State of California GeoTracker web site (https://geotracker.waterboards.ca.gov).

Fluctuations of the groundwater level, localized zones of perched water, and increased soil moisture content should be anticipated during and following the rainy season. Irrigation of landscaped areas on or adjacent to the site can also cause a fluctuation of local groundwater levels.

Evaluation of such factors is beyond the scope of our services.

https://geotracker.waterboards.ca.gov/

Inset 1: Excerpt of Plate 1 showing recommended OWTS exclusion area (red shaded region) based on the borings that encountered groundwater seepage during drilling. Additional exploration and percolation testing are recommended prior to construction to confirm the design locations for conformance with LACDPH OWTS guidelines (LACDPH, 2016, 2018).

7. ENGINEERING SEISMOLOGY AND GEOLOGIC HAZARDS

7.1. General Seismic Setting

The Southern California region is known to be seismically active. Earthquakes occurring within approximately 60 miles of a site are generally capable of generating ground shaking of engineering significance at the site. The project area is located in the general proximity of several active and potentially active faults, as shown on Figure 3 – Regional Faults and Seismicity Map. Active faults defined as those that have experienced surface displacement within the Holocene period (approximately the last 11,000 years) are summarized in order of increasing distance from the project site in Table 1.

Table 1 Significant Known Active Regional Faults

Fault Name Approximate

Fault Distance to Site1 (miles)

Maximum Moment Magnitude2

(Mmax) San Andreas 5.4 7.8

San Gabriel (Palomas) 10.7 7.2

Sierra Madre 17.8 7.2

Oak Ridge 20.1 7.5

San Cayetano 20.2 7.3

Garlock 22.8 7.6

Verdugo 23.0 6.9

Santa Ynez 24.2 7.5

Hollywood 33.6 6.4

Raymond 34.8 6.5

Newport-Inglewood 35.3 7.1

Santa Monica 36.1 6.6

Charnock 38.2 6.5

Malibu Coast 39.5 6.7

Palos Verdes 44.3 7.3

Anacapa-Dume 46.0 7.5

Whittier 46.4 6.8

Notes: 1 per Jennings, 2010 2 per Cao, et al., 2003

Though no currently considered active, the Clearwater fault zone, estimated Mw 6.7 (32 km in length, USGS, 2017), is the closest mapped fault to the site. The main strand of the fault is located less than 0.1 miles to the north of the North Site near San Francisquito Canyon Road. Several short arcuate fault segments closely aligned to the main trace are mapped in the area to the east and west of the site. The Clearwater fault is classified by the USGS as having last moved in the Late Pleistocene. A review of aerial photographs indicates a well-defined lineament extending east-west along the trace of the fault in the vicinity of the site.

Significant earthquake epicenters recorded by the USGS since about 1900 are shown on Figure 3.

Significant seismic activity and associated earthquake events have been recorded surrounding the project site. However, only relatively few earthquake epicenters have been recorded in the immediate area of the subject site. Notable historic earthquakes in Southern California of significance to the project are listed in Table 2. The most significant historic earthquakes near the project site include the 1971 San Fernando earthquake and the 1994 Northridge earthquake.

Table 2 Historic Earthquakes in Southern California

Earthquake Name Year Fault and Fault Type Earthquake

Magnitude*

Epicenter

Latitude Longitude Epicenter

Distance (miles) and Bearing

Northridge 1994 Northridge Thrust (blind thrust) 6.7 Mw 34.21°N 118.54°W 26/191°

Sierra Madre 1991 Clamshell-Sawpit Canyon fault (reverse) 5.8 ML 34.20°N 118.14°W 32/147°

Upland 1990 San Jose fault?

(left-lateral strike-slip) 4.6ML 34.13°N 117.70°W 54/127°

Upland 1988 San Jose fault?

(left-lateral strike-slip) 5.2ML 34.13°N 117.71°W 53/147°

Pasadena 1988 Raymond fault (left lateral strike-slip) 5.0 Mw 34.14°N 118.13°W 36/150°

Whittier Narrows 1987 Puente Hills fault (blind thrust) 5.9 ML 34.06°N 118.08°W 42/150°

San Fernando 1971 San Fernando fault (thrust) 6.5-6.7 Mw 34.42°N 118.37°W 13/158°

Torrance-Gardena 1941 Palos Verdes fault (right-reverse) 4.8 ML 33.82°N 118.22°W 55/166°

Long Beach 1933 Newport-Inglewood fault (right-lateral strike-slip) 6.4 Mw 33.63°N 118.00°W 71/159°

*Mw refers to Moment Magnitude scale and ML refers to Local Magnitude scale

Table 2 (continued) Historic Earthquakes in Southern California

Earthquake Name Year Fault and Fault Type Earthquake

Magnitude*

Epicenter

Latitude Longitude Epicenter

Distance (miles) and Bearing

San Jacinto 1923 San Jacinto fault (right-lateral strike-slip) 6.3 ML 34.00°N 117.24°W 80/121°

San Jacinto 1918 San Jacinto fault (right-lateral strike-slip) 6.7 Mw 33.65°N 117.43°W 87/138°

Elsinore 1910 Elsinore fault (right-lateral strike-slip) 6 ML 33.75°N 117.45°W 82/136°

Fort Tejon 1857 South Central Segment of San Andreas fault (right-lateral strike-slip)

7.9 Mw 35.43°N 120.19°W 114/300°

*Mw refers to Moment Magnitude scale and ML refers to Local Magnitude scale

7.2. Seismic Hazards related to Faulting

Issues with regard to earthquake faulting and the potential impact on the proposed project are discussed in the following sections.

7.2.1. Seismic Hazard Zones

Maps of seismic hazard zones are issued by the California Geological Survey (CGS, formerly California Department of Conservation, Division of Mines and Geology (CDMG)) in accordance with the Seismic Hazards Mapping Act enacted in April 1997. The intent of the act is to provide for a statewide seismic hazard mapping and a technical advisory program to assist cities and counties in developing compliance requirements to protect the public health and safety from the effects of strong ground shaking, liquefaction, landslides, or other ground failure and other seismic hazards caused by earthquakes.

The Green Valley Quadrangle is not currently zoned by the State of California for liquefaction hazards or areas susceptible to seismically induced landslides. However, landslide features within the vicinity of the South Site were observed during the field investigation and they are discussed in the Site Geology Section of this report. Stability evaluation of the slopes for both candidate sites is presented in Section 9 of this report.

7.2.2. Surface Fault Rupture and Local Faulting

Official Maps of Earthquake Fault Zones were reviewed to evaluate the location of the project site relative to active fault zones. Earthquake Fault Zones (known as Special Studies Zones prior to 1994) have been established in accordance with the Alquist-Priolo Special Studies Zones Act enacted in 1972. The Act directs the State Geologist to delineate the regulatory zones that encompass surface traces of active faults that have a potential for future surface fault rupture. The purpose of the Alquist-Priolo Act is to regulate development near active faults in order to mitigate the hazard of surface fault rupture.

Neither candidate site is not located within a currently established Earthquake Fault Zone for fault surface rupture hazard. The surface traces of known active faults are not currently known to pass directly through or project towards either site. However, fault trenching performed by Tetra Tech did encounter evidence of faulting related to the Clearwater fault that is interpreted as likely late- Quaternary in age (indicating a potentially active fault) within the South Site. Details of this mapping and recommended setbacks are discussed in Section 7.2.4.

7.2.3. Potentially Active Fault (Clearwater Fault)

The closest mapped fault to the site is the Clearwater fault, located just to the north of San Francisquito Canyon Road, i.e., approximately 350 feet north of the North Site. The Clearwater fault is oriented generally east-west in the area and is identified as a single to locally multi-stranded north-dipping fault juxtaposing granitic basement complex rocks in the hills to the north of the road and sedimentary rocks (San Fransiquito Formation) to the south of the road (Figure 2).

Several short arcuate fault segments closely aligned to the main trace are mapped in the vicinity to the east and west of the site. The USGS (2017) fault database indicates the last evidence of movement on the fault as late Quaternary (<130 ka). The CDMG published Fault Evaluation Reports (FER) for the Clearwater fault and the San Andreas fault in the 1970s as part of an evaluation of the faults for ground rupture hazard zoning (California Division of Mines and Geology, 1977a, 1977b, 1977c, 1978). The Southern California Earthquake Center (SCEC) database for the Clearwater fault reports a fault length of 32 km, reverse motion with steeply north-dipping to vertical fault plane, and a most recent ground rupture of late Quaternary.

In-place native soils observed in test pits on the North Site suggest that the older alluvium mapped by Dibblee is pre-Holocene in age. As previously described in Section 6.2.4, 7.5 YR colors were noted as well as the presence of clay films and abundant strongly reactive carbonate surfaces.

Dibblee notes two areas of older alluvium covering the…