Geotechnical_Report_and_CGS_Acceptance_Rincon_FFS.pdf

OFFICE OF THE STATE FIRE MARSHAL

APPROVED FIRE AND PANIC ONLY

07/20/22

Approval of this plan does not authorize or approve any omission or deviation from applicable regulations. Final approval is subject to field inspection. One set of approved plans shall be available on the project site at all times.

20-2611

Gavin Newsom, Governor

David Shabazian, Director

State of California Natural Resources Agency | Department of Conservation

Office of the State Geologist, 801 K Street, MS 12-30, Sacramento, CA 95814 conservation.ca.gov | T: (916) 445-1825 | F: (916) 445-5718

Gregory Vincent May 26, 2020 Senior Civil Engineer CAL FIRE Technical Services PO Box 944246 Sacramento, CA 94244

Subject: Engineering Geology and Seismology Review for Rincon Fire Station New Fire Station 16971 Highway 76, Pauma Valley, CA CGS Application No. 04-CGS4354

Dear Gregory Vincent:

In accordance with your request and transmittal of documents received on March 12, 2020, the California Geological Survey (CGS) has reviewed the engineering geology and seismology aspects of the consulting report prepared for the subject project at Rincon Fire Station in Pauma Valley. It is our understanding that this project involves construction of a new fire station, generator, storage, and wash buildings; fuel vault cover; and dry stack rock retaining walls. This review was performed in accordance with Title 24, California Code of Regulations, 2019 California Building Code (CBC) and followed CGS Note 48 guidelines. We reviewed the following report:

Preliminary Geotechnical Investigation, Rincon Forest Fire Station (FFS), San Diego County, California: prepared by CGS (Forest & Watershed Geology Program), 6105 Airport Road, Redding, CA 96002; report dated February 19, 2020, 28 pages, 8 tables, 9 figures, 3 appendices.

Based on our review, the consultants provide a thorough and well-documented assessment of engineering geology and seismology issues with respect to the proposed improvements. The principal concern identified by the consultants are the potential for very strong ground shaking.

The consultants recommend site-specific design spectral acceleration parameters of SDS = 1.0250g and SD1 = 0.9406, which are considered reasonable. Their evaluation indicates fault deformation, liquefaction, dynamic settlement, and deep-seated slope instability are not design concerns for the project.

Engineering Geology and Seismology Review May 26, 2020 Rincon Fire Station New Fire Station

In conclusion, the engineering geology and seismology issues at this site are adequately assessed in the referenced reports, and no further information is requested. If you have any further questions about this review letter, please contact the primary reviewer at ante.mlinarevic@conservation.ca.gov.

Respectfully submitted, Ante Mlinarevic Engineering Geologist

PG 8352, CEG 2552

Concur:

Jennifer Thornburg Senior Engineering Geologist

PG 5476, CEG 2240

Enclosures:

Note 48 Checklist Review Comments

Keyed to: Note 48 - Checklist for the Review of Engineering Geology and Seismology Reports for California Public Schools, Hospitals, and Essential Services Buildings

Copies to:

Donald Lindsay, Certified Engineering Geologist and Registered Geotechnical Engineer

California Geological Survey, Forest & Watershed Geology Program 6105 Airport Road, Redding, CA 96002

Gregory Vincent, Senior Civil Engineer

California Department of Forestry and Fire Protection (CAL FIRE), Technical Services PO Box 944246, Sacramento, CA 94244

Geoffrey Chan, Senior Structural Engineer Division of State Architect, 10920 Via Frontera, Suite 300, San Diego, CA 92127

CGS Application No. 04-CGS4354

Note 48 Checklist Review Comments

In the numbered paragraphs below, this review is keyed to the paragraph numbers of California Geological Survey Note 48 (November, 2019 edition), Checklist for the Review of Engineering Geology and Seismology Reports for California Public Schools, Hospitals, and Essential Services Buildings.

Project Location

1. Site Location Map, Street Address, County Name: Adequately addressed.

2. Plot Plan with Exploration Data with Building Footprint: Adequately addressed.

3. Site Coordinates: Adequately addressed. Latitude and Longitude provided in report:

33.288103°N, 116.961797°W

Engineering Geology/Site Characterization

4. Regional Geology and Regional Fault Maps: Adequately addressed.

5. Geologic Map of Site: Adequately addressed. The consultants present a figure depicting potential areas of undocumented fill.

6. Geologic Hazard Zones: Adequately addressed. The consultants report the site is not located within a currently designated San Diego County Special Study Fault Zone or Alquist-Priolo Earthquake Fault Zone. They also report San Diego County identifies the subject site as an area of potential liquefaction, but that it is not located in an area of potential for landslides. The data presented appears to be reasonable. CGS notes the site has not yet been evaluated by the State Seismic Hazard Zone mapping program.

7. Subsurface Geology: Adequately addressed. The consultants report the site is underlain by disturbed soils consisting of sands with gravels, cobbles, and bounders over alluvial fan deposits consisting of gravels with cobbles and boulders. They report groundwater was not encountered during their investigations. The consultants utilized boring information from two hollow-stem auger borings drilled to a maximum depth of 50 feet, and four test pits to a maximum depth of about 7 feet.

8. Geologic Cross Sections: Adequately addressed.

9. Geotechnical Testing of Representative Samples: Adequately addressed.

10. Consideration of Geology in Geotechnical Engineering Recommendations: Adequately addressed. The consultants recommend the structures be supported on conventional strip and spread footings with reinforced concrete slabs for building bearing entirely within undisturbed native soils or upon a uniform thickness of engineered fill.

11. Conditional Geotechnical Topics: Not applicable.

Seismology & Calculation of Earthquake Ground Motion

12. Evaluation of Historic Seismicity: Adequately addressed. The consultants provide a summary of historical seismicity in the region.

13. Classify the Geologic Subgrade (Site Class): Adequately addressed. The consultants classify the site soil profile as Site Class D, Stiff Soil, based on field investigation and literature review, which appears to be reasonable based on the data in the boring logs presented.

14. General Procedure Ground Motion Analysis: Adequately addressed. The consultants report the following parameters derived from a map-based analysis:

SS = 1.373 and S1 = 0.498

CGS Application No. 04-CGS4354

15. Site-Specific Ground Motion Hazard deterministic and probabilistic MCE spectra appear reasonable based on comparison with results from the National Seismic Hazard Model (from Petersen and others, 2014). The consultants report their site-specific seismic design parameters are: SDS = 1.0250g and SD1 = 0.9406. Alternatively, Sa values presented in the column K in Appendix C Table 1 may be used with the equivalent lateral force procedure, per ASCE 7, §21.4. The site-specific ground motion analysis presented appears to be reasonable and in accordance with ASCE 7-16.

16. Deaggregated Seismic Source Parameters: Adequately addressed.

17. Time Histories of Earthquake Ground Motion: Not applicable.

Fault Rupture Hazard Evaluation

18. Active Faulting & Coseismic Deformation Across Site: Adequately addressed. The consultants report about 2.4 miles northeast. They conclude the potential for ground rupture is considered relatively low. The data appears to support their conclusion.

Liquefaction/Seismic Settlement Analysis

19. Geologic Setting for Occurrence of Liquefaction: Adequately addressed. The consultants report the site is underlain by dense alluvium composed of gravels with cobbles and boulders to a depth greater than 50 feet and the depth to the historic-high groundwater level is greater than 50 feet below ground surface. They conclude the potential for liquefaction is considered to be relatively low. The historic-high depth to groundwater data presented appear to support this conclusion.

20. Seismic Settlement Calculations: Not applicable.

21. Other Liquefaction Effects: Not applicable.

22. Mitigation Options for Liquefaction/Seismic Settlement: Not applicable.

Slope Stability Analysis

23. Geologic Setting for Occurrence of Landslides: Adequately addressed. The consultants report the surface of the project site and vicinity is gentle and no significant slope breaks of any substantial relief are located within or adjacent to the site. They also report no landslides are mapped within the project site or vicinity. They conclude landsliding in the form of traditional rotational/translational failures is considered low. The data presented appears to support this conclusion.

24. Determination of Static and Dynamic Strength Parameters: Not applicable.

25. Determination of Pseudo-Static Coefficient (Keq): Not applicable.

26. Identify Critical Slip Surfaces for Static and Dynamic Analyses: Not applicable.

27. Dynamic Site Conditions: Not applicable.

28. Mitigation Options/Other Slope Failure: Not applicable.

Other Geologic Hazards or Adverse Site Conditions

29. Expansive Soils: Adequately addressed. The consultants report the soils encountered consist of sands and gravels with low plasticity indices (< 10), and the San Diego County General Plan indicates the site is not located within an area of mapped expansive soils.

They conclude the risk of adverse consequences related to expansive soils is low, which appears to be reasonable based on the data presented.

30. Corrosive/Reactive Geochemistry of the Geologic Subgrade: Adequately addressed. The consultants report site soils are classified as non-corrosive, which appears the be reasonable based on the laboratory test results presented.

31. Conditional Geologic Assessment: Selected geologic hazards addressed by the consultant are listed below:

C. Flooding: Adequately addressed. The consultants report the alluvial deposits at the site are related to high-energy floods and debris flows in the distant pass. They also report no floods or debris flows are known to have impacted the site in more recent time, but that there is a potential the site could be impacted by debris flows in future extreme climatic/geologic event. They conclude the risk of debris flow events occurring is interpreted as being relatively low and appears to have been partially mitigated by past grading operations associated with Yuima Creek. These conclusions appear to be reasonable based on the data presented.

Report Documentation

32. Geology, Seismology, and Geotechnical References: Adequately addressed.

33. Certified Engineering Geologist: Adequately addressed.

Donald Lindsay, Certified Engineering Geologist #2323

34. Registered Geotechnical Engineer: Adequately addressed.

Donald Lindsay, Registered Geotechnical Engineer #3097

Rincon FFS

Preliminary Geotechnical Investigation

Rincon FFS

San Diego County, California

Table of Contents

INTRODUCTION

PROJECT SCOPE

SITEANDPROJECTDESCRIPTION

GEOLOGICSETTING

SOILS

FAULTING

Site Conditions Surface Conditions Subsurface Conditions

Groundwater

Laboratory Testing

Discussion of Geologic Hazards Landsliding Ground Rupture Ground Shaking Liquefaction, lateral Spreading, and Seismic-induced settlement flooding AND DRAINAGE Tsunamis Seiches Expansive Soils Naturally occuring asbestos Radon Volcanic Hazards Corrosivity

Conclusions and Recommendations General Procedure Ground Motion Analysis Site-Specific Ground Motion Analysis Site Preparation and Grading considerations

Clearing and Grubbing Undocumented Fills Finished cut and fill slopes Transition Areas

ENGINEERED FILL

On-Site Soil Materials Imported Fill Materials - General Placement and Compaction

FOUNDATION CONSIDERATIONS

Over excavation

Minimum Footing Embedment and Dimensions Allowable Bearing Pressures Sliding and Passive Resistance Settlement

INTERIOR CONCRETE FLOOR SLABS SUPPORTED ON-GRADE

Retaining Wall Considerations

General Design Parameters Seismic loads Retaining Wall Drainage

Surface Drainage Considerations Construction Considerations

Excavatability Temporary slopes and shoring Dewatering Equipment Limitations Adjacent to Steep Slopes and Structures

Limitations

Appendix A

Tables Table 1 – Pertinent Published Soil Parameters Table 2 – Pertinent Faults within 50 miles of Site Table 3 – Generalized Stratigraphic Column of Native Soils Table 4 – Soil Chemistry Results Table 5 – Seismic Design Criteria Table 6 – Summary of Site-specific Ground Motion Analysis Table 7 – Imported Engineered Fill Table 8 – Presumptive load-bearing values

Figures Figure 1 – VicinityMap Figure 2 – Preliminary Site Plan Figure 3a –Geologic Map Figure 3b – Geologic Map Explanation Figure 4 – Fault Location Map Figure 5 – Transition Lot Overexcavation Figure 6 – Approximate Test Pit and Bore Hole Location Map Figure 7a – Cross Section A – A’ Figure 7b – Cross Section B – B’

Appendices Appendix A – Field Exploration Appendix B – Laboratory Testing Program Appendix C – Site-specific Ground Motion Analysis

Rincon FFS 4

INTRODUCTION

The Rincon Forest Fire Station (FFS) is an existing California Forestry and Fire Protection (CAL FIRE) facility that is proposed to be reconstructed. The Rincon FFS is on the south side of State Highway 76 (Hwy 76), approximately 0.2 miles west ofValley Center Road, near the community of Rincon, San Diego County, California. The site address is 16971 Hwy 76, San Diego County, California, 92061. The site is located in the southwest quarter of Section 23, Township 10 south, Range 1 west (San Bernardino Baseline and Meridian) and has site coordinates oflatitude 35.288103o North, and longitude -116.961797 o West.

The approximate location of the site is shown on Figure 1.

According to CAL FIRE, the replacement FFS facility will include a stand-alone, two-story, wood-framed building that will house a twelve-bed barracks, a 3-bay apparatus building, an administration office, and a battalion chief’s office. Ancillary improvements associated with the replacement FFS will include the construction of a generator building, a storage building, a trash enclosure, and two <5-foot tall dry-stack rock retaining walls. Approach aprons providing access from Hwy 76 will be covered in asphaltic pavement and the travel lanes and parking areas inside the site will be covered in reinforced concrete pavement.

Preliminary site development plans and layout are presented in Figure 2.

This report presents the results of a preliminary geotechnical investigation for the proposed FFS facility. The purpose of this investigation was to explore the surface and near-subsurface site conditions, evaluate the materials encountered, and provide preliminary recommendations related to geotechnical aspects of the design and construction of the facility. It is anticipated that the recommendations provided may need to be amended and/or additional studies performed and new recommendations formulated to meet the requirements of the project as the plans are finalized and the project is constructed.

PROJECT SCOPE

The following work was completed as part of this geotechnical investigation:

Reviewed existing available geotechnical data for the project site, including geologic, soils, seismic, and topographic information;

Performed a surface reconnaissance of the site;

Explored and sampled the near-subsurface conditions beneath the site using four exploratory test pits and two exploratory borings;

Coordinated geotechnical laboratory testing on representative soil samples to provide data to evaluate the geotechnical design characteristics of the site foundation soils;

and

Prepared this report, which includes:

A description of the proposed project;

A description of site surface and subsurface conditions encountered during the field investigations;

A summary of the field exploration and laboratory testing programs;

Rincon FFS 5

An evaluation of potential geohazards that might affect the development; and

Presenting preliminary geotechnical recommendations for:

Ground motion parameters for seismic design for use with the current 2019

California Building Code (CBC);

Site preparation and grading;

Engineered fill;

Foundation design and construction;

Retaining wall design and construction;

Site Drainage; and

Construction Considerations.

SITE AND PROJECT DESCRIPTION

The Rincon FFS (site) occupies an irregular shaped parcel that is about 2.8 acres in size and is bounded on the north by Hwy 76, and to the east, south and west by citrus plantations (Figure 1). The site is at an elevation of about 980 feet above mean sea level (msl) and is positioned on an alluvial fan created by fluvial/colluvial deposits that were shed off a prominent, northwest-trending mountain range to the east referred to as the Agua Tibia Mountains. Palomar Mountain, at an elevation of about 6,140 feet above msl, forms a prominent high point in the Agua Tibia Mountains and is approximately 5.3 miles northeast of the site. The alluvial fan that the site is located on slopes gently (about 10%) to the southwest, is bounded to the north and southeast by bedrock-controlled ridges, and is currently drained by several ephemeral swales that flow into one of two mapped watercourses that include Potrero Creek, about 1,200 feet southeast of the site, and Yuima Creek, about 300 feet southeast of the site. These two creeks are tributary to the San Luis Rey River that flows northwest through Pauma Valley, a prominent valley bottom at an elevation of about 800 feet above msl about 4,000 feet southwest of the site.

Due to the site’s location along the foot of the Agua Tibia Mountains (i.e. orographic effect) in the northern part of San Diego County, the climate in the area is classified as “Mediterranean” with an average annual temperature of about 62 degrees Fahrenheit and an average annual precipitation of 24.6 inches1.

The site is currentlyoccupied byexisting facilities that include a single-story barracks and office building, a metal apparatus building, and various ancillary structures and improvements, including a roughly 16-inch diameter water well that was advanced to an undetermined depth in the far southeast corner of the site (see additional discussion under

GROUNDWATER).

The site is vegetated with ornamental grasses, shrubs, and trees, the latter of which include large-diameter palm, pine, oak, and sycamore trees (see Photo 1). The site topography has been altered through grading operations resulting in a surface that generally slopes to the southwest at roughly 5% and is drained mostly by sheet flow.

1 Weather data obtained at: http://www.weatherbase.com/weather/weather-summary.php3?s=232940&cityname=Rincon%2C+California%2C+United+States+of+America&units= http://www.weatherbase.com/weather/weather-

Rincon FFS 6

Photo 1: View looking south from Hwy 76 at existing Rincon FFS proposed to be replaced.

Through discussions with CAL FIRE engineer, Mr. Gregory Vincent, P.E., it is understood the proposed facility will be constructed as a conventional wood-framed building with foundations comprised of slab-on grade with perimeter and interior footings. Parking and high use traffic lanes will be covered in Portland cement concrete. The proposed <5-foot tall, dry-stacked rock retaining walls will have horizontal backfills with no additional surcharge loads due to vehicle parking or structural influences.

GEOLOGIC SETTING

The site is located within the central portion ofthe Peninsular Range geologic and geomorphic province. The Peninsular Range geologic and geomorphic province is comprised of a series of northwest-oriented mountain ranges extending from Baja California north to the Transverse Ranges, including the Santa Ana, San Jacinto and Santa Rosa mountains. Faulting within the province consists of numerous northwest oriented strike slip faults, including the Elsinore and San Jacinto fault zones, both of which are known to be historically active (Last 200 years). The province is drained primarily to the Pacific Ocean by several rivers including the San Diego, Santa Ana and San Luis Rey Rivers (Harden, 2004).

A review of published geologic maps indicates that the site is located along a mapped contact between Quaternary-aged alluvial fan deposits (Qf) and young alluvial fan deposits (Qyf), both of which are composed of unconsolidated to poorly consolidated mixtures of silts, sands, gravels, cobbles and boulders (Kennedy, 2014). Ridges that confine the alluvial fan to the north and southeast of the site are composed of bedrock described as Cretaceous-age, medium- to course-grained, hornblende-biotite tonalite (similar to a granite) extensively intruded by pegmatite dikes (Kennedy, 2014). The geology of the project site and vicinity is shown in Figures 3a and 3b.

Rincon FFS 7

SOILS

Available soil maps (USDA, 2016) show the project site to be underlain primarilybythe Soboba stony loamy sands (slopes 9-30 percent). The soil type is generallydescribed as well-drained silty gravels and silty sands. Table 1 lists pertinent published soil parameters for the Soboba stony loamy sand, including the plasticity index, the percent clay content, the concrete corrosion potential, and the Unified Soil Classification System (USCS) classification.

Table 1 - Pertinent Published Soil Parameters (USDA, 2016)

Soil Name Plasticity

Index

Percent

Clay (%)

Concrete

Corrosion

Potential

USCS

Classification

Soboba stony loamy sand NA <5

Moderate to Low GM, SM

1 See ASTM D4318 for description (ASTM, latest addition) 2 See ASTM D2487 for description (ASTM, latest addition) NA-Not Applicable

FAULTING

The California Geologic Survey (CGS) evaluates the activity rating of a fault in fault evaluation reports (FER). In general, faults that show evidence of Historic (last 200 years) or Holocene (last 11,000 years) rupture are considered “active”, faults that show Late Quaternary (last 700,000 years) or Quaternary (last 1.6 million years) rupture are often referred to as “potentially active”, and faults that show Pre-Quaternary (older than 1.6 million years) rupture are considered “inactive”. Quaternary Faults that are active are typically incorporated into an Earthquake Fault Zone map in accordance with the Alquist- Priolo (AP) Earthquake Fault Zoning Act. The AP Earthquake Fault Zoning Act requires a site-specific fault investigation to be performed to locate faults where planned improvements are proposed inside designated Earthquake Fault Zones.

The site is not located within a currentlydesignated San Diego County Special Study Fault Zone (San Diego County, 2007) or State ofCalifornia Earthquake Fault Zone (Bryant and Hart, 2007). Based on regional geologic mapping, there are no known active faults projecting toward or extending across the project site (Kennedy, 2014; Jennings and Bryant, 2010) (Figure 4). However, the site is situated in a seismically active region and, as is the case for most areas of western California, ground shaking resulting from earthquakes associated with nearby and more distant faults may occur at the project site. During the life of the project, seismic activity associated with active faults can be expected to generate moderate to strong ground shaking at the site, (California Seismic SafetyCommission, 2003). Table 2 presents a list of pertinent active and potentiallyactive faults within approximately 46 miles of the FFS site that are considered by the CGS to be the most capable of producing high ground motion within the site vicinity. Additional information on each fault is presented in the CGS fault database (Bryant, 2005:

https://www.conservation.ca.gov/cgs/Pages/Publications/QuaternaryFaults_ver2.aspx).

https://www.conservation.ca.gov/cgs/Pages/Publications/QuaternaryFaults_ver2.aspx

Rincon FFS 8

Table 2 - Pertinent Faults within 46 miles of Site

Fault Name Fault

Type1

Approximate

Distance and

Direction from

Site

Slip Rate

(mm/yr) Mmax2 Activity

Elsinore Fault Zone (EFZ), (Julian Section) rl-ss 3.2 miles north 5.0 + 2.0 7.7 Active

EFZ (Temecula) rl-ss

4.5 miles northwest

5.0 7.7 Active

San Felipe Fault rl-ss

10.9 miles northeast

NA 6.3 Active

Murrieta Hot Springs n 18.7 miles north NA 6.3 Active

EFZ, (Julian Section- Earthquake valley fault) rl-ss

23.2 miles southeast

2.0 + 1.0 6.7 Active

San Jacinto Fault Zone (SJFZ), Anza Section rl-ss

26.9 miles northeast

12.0 + 6.0 7.7 Active

SJFZ, Coyote Creek Section rl-ss 27.5 miles east 4.0 + 2.0 7.3 Active

Rose Canyon fault zone (Oceanside Section) rl-ss

27.8 miles southwest

1.5 + 0.5 6.8 Active

Rose Canyon fault zone (Del Mar section) rl-ss

28.7 miles southwest

2.0 6.8 Active

SJFZ, San Jacinto Valley Section (Hot Springs Fault) rl-ss

28.4 miles northeast

12.0 + 6.0 7.7 Active

Newport-Inglewood (offshore) rl-ss 29.2miles northeast

1.5 + 0.5 6.9 Active

EFZ, (Glen Ivy) rev rl-ss

29.7 miles northwest

5.0 7.7 Active

San Jacinto (San Jacinto Valley- Southern Extension) rl-ss 32.4 miles north 18.0 7.7 Active

Rose Canyon fault zone (San Diego Section) rl-ss

34.7 miles southwest

2.0 6.8 Active

Rincon FFS 9

Table 2( Continued) - Pertinent Faults within 46 miles of Site

Fault Name Fault

Type1

Approximate

Distance and

Direction from

Site

Slip Rate

(mm/yr) Mmax2 Activity

Rose Canyon fault zone (Silver Stand section-Spanish Bight Fault) rl-ss 39.6 miles south 2.0 6.8 Active

Point Loma fault zone rl-ss 39.7 miles south NA 6.3 Potential Active

Rose Canyon fault zone (Silver Strand section-Downtown Graben Fault) rl-ss 40.6 miles south 2.0

6.8 Active

Rose Canyon fault zone (Silver Strand section-Silver Strand Fault) rl-ss 40.9 miles south 2.0 6.8 Active

Rose Canyon fault zone (Silver Strand section-Coronado fault) rl-ss 41.6 miles south 2.0 6.8 Active

Beaumont Plain fault zone n 41.6 miles north NA 6.0 Potentially

Active

Coronado Bank (alt2) rl-ss

43.6 miles southwest

3.0 + 1.0 7.4 Active

San Gorgonio Pass r 44.5 miles north 1.8 6.7 Active

Elsinore (Coyote Mountains) rl-ss

44.7 miles southeast

3.0 7.7 Active

San Jacinto (Borrego- South) rl-ss 45.0 miles east 5.0 7.3 Active

San Jacinto (Borrego- North) rl-ss 46.0 miles east 5.0 7.3 Active

San Andreas (San Gorgonio Pass- Garnet hill) rl-ss 46.0 northeast 10.0 6.7 Active

1Right-lateral, strike-slip (rl-ss), normal (n), reverse (r).

2Maximum Moment Magnitude from Jennings and Bryant (2010), Cao et al. (2003), or Caltrans

Fault Database V2 (2012).

3 (NA) not available

Rincon FFS 10

SITE CONDITIONS

Field work performed as part of this investigation was conducted between June 13-14, 2017, and included conducting surface and shallow subsurface field observations using backhoe-excavated test pits, as well as advancing and observing two exploratory borings to evaluate deeper subsurface conditions.

As mentioned, the improvements associated with the proposed new facility are located within the same general footprint of the existing FFS facility that is to be dismantled.

Based on the natural topography of the site, it appears the existing FFS facility was constructed on a transitional building pad with the northeast portion of the pad underlain by cut slopes and the southwest portion of the pad underlain by 3 to 4 feet of undocumented fill. Based on the location of the perceived transition line between cut and fill, it appears the existing FFS facility is founded entirely within native (i.e. cut) soils. However, the proposed replacement FFS facility will likely span the transition line and will require additional measures to mitigate the undocumented fill (see CONCLUSIONS AND

RECOMMENDATIONS).

Areas of additional undocumented fill were observed along the western and southwestern site boundary. This fill was observed to range from 1 to 8 feet thick and was placed to create a more level site. No structures, either current or proposed, are founded within this area of recognized undocumented fill. However, the area underlain by this fill is the site of an existing and proposed leach field.

The locations of undocumented fill relative to the proposed site development plan are provided in Figure 6.

To explore the subsurface conditions in the area of the proposed improvements, four test pits were excavated to a maximum depth of about 7 feet bgs using a backhoe (John Deere 310k equipped with a 2-foot wide bucket) and two exploratory borings (B1 and B2) were advanced to a maximum depth of about 50 feet bgs (Boring B1) using a Marl Technologies Inc., M-5, tuck-mounted drill rig (equivalent to a CME-75) equipped with an 8-inch-outside-diameter hollow-stem auger. The locations of the test pits and exploratory borings relative to the proposed site development plan are provided in Figure

6. Individual test-pit and boring logs are provided in Appendix A. All test pits were backfilled loose with excavated spoils. The test pits should be relocated during grading and the loose backfill soils should be removed to the final excavated depth shown on the Logs of Test Pits, presented in Appendix A, and replaced as compacted fill (See

CONCLUSSIONS AND RECOMMENDATIONS).

Subsurface conditions encountered in the test pits and exploratory borings were visually examined, classified and logged in general accordance with the Unified Soil Classification System (USCS) for soil designations (ASTM, 2488). In general, the native soils encountered consist of sandy gravels (GM) with abundant cobbles and boulders (Photo 2).

Based on the presence of large diameter boulders, both encountered in the test pits and

Rincon FFS 11 observed placed in a windrow along the western site boundary (Photo 3), it is likely boulders up to about 6 feet in diameter may be encountered during grading operations.

Table 3 provides a general description of the ‘native’ materials anticipated within the footprint of the proposed new facility. Figure 7 provides a cross-section through the center of the site showing inferred subsurface conditions.

Based on results of the subsurface exploration and our experience, some variations in the vertical and horizontal continuity and nature of subsurface conditions within the project site should be anticipated. Because of the uncertainties involved in the nature and depositional characteristics of the earth material at the site, care should be exercised in interpolating or extrapolating subsurface conditions between or beyond the test pit locations.

Photo 2: Photo showing typical native soil profile in upper six feet. Note the range in clast size from sand to boulder size.

Rincon FFS 12

Photo 3: Photo of boulders up to 6 feet in diameter windrowed along western site boundary.

Table 3 – Generalized Stratigraphic Column of Native Soils Beneath Proposed Barracks/Apparatus Building.

Depth first encountered below ground surface

Range of strata thickness

(ft.)

Material description1

0 feet (at surface)

0.5 Disturbed Soil: Silty SAND (SM) with gravel, dark

brown, moist, non-plastic, loose (easy to dig with round-point shovel), up to 3-inch diameter round to sub-angular clasts composed of granite (tonalite) and gneiss.

0.5 to 1.5 feet

2.5 to 3 Alluvial fan deposits (Qf/Qyf): Silty to Sandy

GRAVEL (GM to GP) with cobbles and boulders, dark brown, moist, dense to very dense (difficult to dig with backhoe), non-plastic, up to 6-foot diameter sub-round boulders composed of granite (tonalite), abundant roots up to 4 inches in diameter where adjacent to trees.

3.5 feet >8 Sandy Gravel (GW) with cobbles and boulders, dark brown, moist to dry, dense to very dense, non-plastic, up to 3-foot diameter clasts composed of granite

(tonalite) and gneiss.

1 Soil descriptions follow ASTM 2488 (latest version).

Rincon FFS 13

GROUNDWATER

Groundwater was not encountered in the test pits or exploratory borings advanced to a maximum depth of about 50 feet below ground surface for this investigation. In addition, sounding of the on-site, 16-inch diameter well determined that it had been grouted (sealed) to within about 120 feet below ground surface, thus depth to groundwater could not be determined using the well. No records pertaining to the on-site well could be obtained.

In order to assess the historic high groundwater table anticipated beneath the site, depth to groundwater information and general stratigraphy was obtained through the review of driller’s logs reported on adjacent wells in the vicinity.

According to Howes (1955), a well identified as “Rincon Ranch 2” was drilled in June

1946. The location of this well is reportedly located just north of the site at an elevation of

1,015 feet. According to the Driller’s log, alluvial fan deposits were encountered from 0 to

104 feet below ground surface (bgs), followed by decomposed granite to a depth of 304 feet bgs before stopping in very hard granite at a depth of 306 feet bgs. The depth to static water level in this well after drilling was 110 feet bgs and corresponded to the alluvium/bedrock contact.

According to groundwater data provided by the Yuima Municipal Water District, the static water level in “Well no. 22”, positioned about 2,000 feet southeast of the site at an elevation of 1,005 feet above msl, has ranged from about 176 feet bgs in January 2009, to as low as

235 feet bgs in January 2017.

Through interpolation of the recorded water depths within these two wells that straddle the site, the static long-term water level below the site is likely to be at depths greater than 100 feet bgs. However, there is the possibility for isolated areas of seasonally-perched groundwater present at shallower depths.

LABORATORY TESTING

Laboratory tests were performed in accordance with generally accepted test methods of the

American Society for Testing of Materials (ASTM) or other suggested procedures.

Laboratory tests consisting of in-situ dry density and moisture content, grain size distribution, and corrosion potential were performed on soil samples selected as being representative of the site conditions. The laboratory testing was performed by Ninyo &

Moore, in San Diego, California. The results of the laboratory tests are provided in

Appendix B and summarized in the following:

Gradation: Native soil: 3% passing the #200 sieve (0.075mm) and 41% passing the

#4 sieve (4.75mm). Undocumented fill: 4% passing the #200 sieve and 88% passing the #4 sieve.

Atterberg limits: Samples collected were non-plastic.

Average dry density: 116.4 pcf at 25 feet bgs

Average moisture content: 7.7% at 25 feet bgs

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DISCUSSION OF GEOLOGIC HAZARDS

Landslide potential is partiallydriven byslope gradient and topographic relief. The surface ofthe project site and vicinity is gentle (<10%) and no significant slope breaks of any substantial relief are located within or adjacent to the site. No landslides are mapped within the project site or vicinity (Kennedy, 2014) and according to the San Diego County General Plan (San Diego County, 2011), the project site is not located within an area mapped as having a potential for landslides. For these reasons, landsliding in the form of traditional rotational/translational failures is considered low.

However, the FFS site is positioned on an alluvial fan that is a semi-conical landform composed of stream deposits and debris flow materials that often occur in response to episodic geologic and climatic conditions commonly associated with flooding and seismic events (shaking and uplift). Deposits encountered on and beneath the site include well-graded (poorly-sorted) deposits of sand and boulders up to about 6 feet in diameter.

Deposits of this type and size appear to be associated with early Holocene and late Pleistocene alluvial deposits (Qyf) and suggest that the site had been impacted by high-energy floods and debris flows in the distant pass (~10 to 15 thousand years ago).

Although no such floods or debris flows are known to have impacted the site in more recent time (~100 years), there is a potential that the site could be impacted by floods and debris flows in the future that avulse out of Yumia Creek during an extreme climatic/geologic event. The risk of such an event occurring is interpreted as being relatively low and appears to have been partially mitigated by past grading operations that have straightened and armored the banks of Yuima Creek in the vicinity of the site. The improvements performed along Yuima Creek have effectively increased the channel’s gradient and reduced its sinuosity, thereby increasing the capacity of the channel to convey water and debris without alvulsing. See additional discussion under FLOODING AND

DRAINAGE.

The FFS site is not within a currently established State of California Earthquake Fault Zone for surface fault rupture hazards and the closest mapped fault is the “potentially active” Elsinore Fault Zone about 2.4 miles northeast. As a result, the potential for ground rupture is considered relatively low.

The FFS site is located in a seismically active region of southern California with several active and potentially active faults within 50 miles of the site (see Table 2). An earthquake on one of the surrounding faults could cause moderate ground motion. According to the CGS’s 2008 Ground Motion Interpolator (2016), the anticipated peak ground acceleration at the site with a 10 percent probability of being exceeded in 50 years (475-year return period) is about 0.369 times the acceleration of gravity. This is based on an estimated shear wave velocity in the upper 100 feet (V s

30) of the soil column of 270 meters per second (Site Class

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D – stiff soil). Thus, the project site could be subject to moderate to strong ground shaking in the event of an earthquake. This hazard, however, is common in this part of California and the effects of ground shaking can be mitigated by proper engineering design and construction in conformance with current building code requirements and sound engineering practices (see CONCLUSIONS and RECOMENDATIONS section).

San Diego County identifies the area beneath the FSS site as a potential liquefaction area (San Diego County, 2007).

Liquefaction is described as the sudden loss of soil shear strength due to a rapid increase in soil pore water pressures caused by cyclic loading from a seismic event. In simple terms, it means that a liquefied soil acts more like a fluid than a solid when shaken during an earthquake. In order for liquefaction to occur during a seismic event, the following are needed:

Granular soils (sand, silty sand, sandy silt, and some gravels);

A high groundwater table; and

A low density in the granular soils underlying the site.

If those criteria are present and strong ground motion occurs, then those soils could liquefy, depending upon the intensity and duration of the strong ground motion.

Liquefaction that produces surface effects generally occurs in the upper 50 feet of the soil column, thus, the potential for liquefaction to have an adverse effect would generally require the criteria above to persist within 50 feet below the surface.

The site is generally underlain by dense2 alluvium composed of Silty to Sandy GRAVEL (GM-GP) with cobbles and boulders to a depth greater than 50 feet. In addition, the depth to the historic-high groundwater level is documented to be greater than 50 feet bgs (see Groundwater section). In consideration of these site conditions, the potential for liquefaction and its associated adverse effects (settlement, lateral spreading, lurch cracking etc.) is considered to be relatively low.

The Federal Emergency Rate Map (FEMA) Flood Insurance Rate Map (FIRM) and the San Diego County General Pan indicates that the project site is not located within a flood hazard zone (FEMA, 2012, and San Diego County, 2011).

Dams or other water-retaining structures may fail as a result of several factors including large earthquakes. The Lake Henshaw Regional Dam is located approximately 15 miles upstream of the site. A review of the San Diego County Dam Inundation Hazards map

2 Corrected blow counts, (N1)60, can normally be used to quantify the in-place density of underlying sediments. However, due to the high percent of cobble- to boulder-sized material encountered, the recorded blow counts, N, are considered unreliable and may over-estimate the soil density. For this reason, the density of the underlying soils beneath the site was conservatively estimated to be dense rather than very dense.

Rincon FFS 16 indicates that the project site is not located within a mapped flood inundation zone associated with the Henshaw Dam (San Diego County, 2011).

As discussed, the site is located on an alluvial fan that was built-up over time through episodic flood and debris flow events. Yuima Creek drains a portion of the alluvial fan and is located about 300 feet east of the site. If floodwater or a debris flow migrates down Yuima Creek, it is possible that the creek could jump its bank and flow toward the site.

The risk of this occurring, however, is considered relatively low, particularly since the upper watershed of Yuima Creek has been developed and now supports a dense cover of agricultural crops, which decrease runoff through an increase in interception, evapotranspiration and surface roughness. Moreover, the banks of Yiuma Creek have been made more resilient and less prone to overtopping through the construction of local levees and armored banks. Consequently, provided the vegetative cover remains relatively consistant upstream and the channel improvements along Yiuma Creek are maintained, the risk of flooding at the site is considered relatively low. If, however, significant changes within the watershed occur, such as a large wildfire that can increase runoff and debris flow potential by removing the vegetative cover and altering the infiltration capacity of the soils, the risk of flooding and debris flow would increase.

In regard to local drainage conditions within the site limits, sheet flow and concentrated runoff from upslope will likely flow across the site. Provided the site is developed in compliance with pertinent grading, stormwater, and building regulations and ordinances, it is anticipated that adverse impacts related to local drainage conditions would be mitigated.

Tsunamis are large waves generated in open bodies of water by fault displacement or major ground movement. Based on the inland location of the site, tsunamis do not pose a hazard to the site.

Seiches are large waves generated in enclosed bodies of water in response to ground shaking. There are no large bodies of water adjacent to or up gradient of the site. The closest body of water is Lake Henshaw. A review of the San Diego County Dam Inundation Hazards map indicates that the project site is not located within a mapped flood inundation zone associated with Lake Henshaw (San Diego County, 2011). This, combined with the elevation of the site above the San Luis Rey River (about 60 foot elevation difference), the potential for flooding due to a seiche is considered low.

The potential for clay-rich soils to swell and shrink with variations in soil moisture content is correlated to the plasticity index of the soil, with expansive soils generally having a high plasticity index. Because the on-site soils encountered in our investigation were found to consist of sands and gravels with low plasticity indices (< 10), we conclude the risk of adverse consequences related to expansive soils is low. This conclusion is in general agreement with published results and testing performed by the soils survey (Table 1). In addition, the San Diego County General Plan indicates that the

Rincon FFS 17 project site is not located within an area of mapped expansive soils (San Diego County, 2011).

NaturallyOccurring Asbestos (NOA) is the term applied to the natural geologic occurrence ofasbestos that is related to the chemistryofrocks in an area and the different geologic processes that have acted on those rocks through time. NOA is common in ultramafic and serpentine rock, and less common in metavolcanic rock throughout California.

A review of the General Location Guide for Ultramafic Rocks in California-Areas More Likely to Contain Naturally Occurring Asbestos (Churchill and Hill, 2000), indicates that the project site is not located within an area known to contain ultramafic rocks. In addition, the project site is underlain by alluvial deposits associated with the Potrero and Yuima Creeks, and no mapped ultrmafic rocks occur within the upstream watershed.

It is our opinion the risk of NOA through the development of the site is low.

Radon is a radioactive gas that occurs naturally as a by-product of decaying uranium.

Uranium is naturally present in the earth’s crust with higher concentrations in certain types of rock, such as granite and shale.

According to a USEPA Radon Zones Map (USEPA, 2017), the project site is mapped in an area with low potential for indoor radon levels above 2 PicoCuries per liter (pCi/L).

As a result, adverse effects from Radon gas at the site are considered to be low. To ensure Radon does not exist, testing would be necessary.

The closest volcanic areas to the site include the Lavic Lake and Coso Volcanic Fields.

The Lavic Lake Field is about 90 miles northeast of the site and the Coso Volcanic Field is about 200 miles north-northeast of the site. According the USGS3, the Lavic Lake Field last erupted about 10,000 years ago and has a low to very low threat potential; the Coso Volcanic Field last erupted about 40,000 years ago and has a moderate threat potential.

Separating these two volcanic fields from the site is a topographic divide formed by the Agua Tibia Mountains. Due to the large distance between the site and these two volcanic fields, their low to moderate threat potential, and the presence of a significant topographic divide separating the site from the volcanic fields, it is unlikely the site would experience any impacts from volcanic-induced ground deformation or volcanic flows (e.g lava, pyroclastic and lahar flows). The site may, however, be impacted by air fall deposits that could deposit a layer of ash or tephra over the site; however, the volume of deposited material would likely me small and would not present a substantial impact to the site.

3 Volcanic hazard information obtained from USGS Volcanic Hazards Program web site, accessed 7/2017, at:

https://volcanoes.usgs.gov/observatories/calvo/ https://volcanoes.usgs.gov/observatories/calvo/

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One (1) soil sample was tested for soil corrosion parameters with respect to common construction materials such as concrete and steel. Tests were performed for pH, sulfate and chloride content, and saturated minimum electrical resistivity in accordance with California Test Methods 643, 422 and 417. The test results are discussed below and are presented in Appendix B, Laboratory Testing Program.

Table 4 - Soil Chemistry Results Sample

I.D./Depth Minimum

Resistivity (Ohm-cm) pH Chloride Content (ppm)

Sulfate Content (ppm)/(%)

Tp-1/1.5-6.0 feet. 6,900 7.6 30 10/0.001

In accordance with Caltrans Corrosion Guidelines, Version 2.0 (Caltrans, 2012), a site is considered corrosive to foundation elements if one or more of the following conditions exist: the chloride concentration is greater than or equal to 500 ppm, the sulfate concentration is greater or equal 2,000 ppm, or the pH is 5.5 or less. Furthermore, a site is considered corrosive to ferrous metals in contact with the soil where: the minimum resistivity is less than or equal to 2,000 Ohm-cm, the chloride concentration is greater than or equal to 250 ppm, sulfate concentration is greater or equal to 500 ppm, or the pH is <

5.5 or >10.0. In comparing the soil chemistry data in Table 4 to these threshold conditions, the results indicate that the site soils are non-corrosive.

CONCLUSIONS AND RECOMMENDATIONS

Based on the findings from our literature review and field exploration, we conclude that the project is feasible with respect to geologic and geotechnical conditions, provided that the recommendations included in this report are followed. We consider the major geotechnical issues for this project to be:

The presence of large boulders within the near surface materials that may challenge site grading and foundation excavations, Undocumented fill up to about 4 feet in thickness along the southwest corner of the propose FFS barracks/apparatus building, and

Transition lots where proposed structures span a transition line from cut to fill.

Based on our field investigation and literature review (Kennedy, 2014; Howes, 1955), we classify the site in accordance with the California Building Code (CBC, 2019) and ASCE 7-16 (ASCE, 2016) as Site Class D (stiff soil). The following provides a summary of the California Building Code seismic design criteria obtained using the site coordinates (latitude 33.288oN, longitude -116.962o W) and the OSHPD Seismic Design Maps web interface tool available at: https://seismicmaps.org/.

https://seismicmaps.org/

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Table 5 - Seismic Ground Motion Values (CBC 2019, ASCE 7-16) Site Class D

Ss – MCER, Site Class B at 0.2 sec. 1.373

S1 – MCER, Site Class B at 1.0 sec. 0.498

Fa – Site Coefficient for Site Class D at 0.2 sec. 1.000

Fv – Site Coefficient for Site Class D at 1.0 sec. Null*

SMS – Site-modified spectral acceleration value, Site Class D at 0.2 sec. 1.373

SM1 – Site-modified spectral acceleration value, Site Class D at 1.0 sec. Null*

SDS – Design SRA, Site Class D at 0.2 sec. (= 2/3SMS) 0.915

SD1 – Design SRA, Site Class D at 1.0 sec. (= 2/3SM1) Null*

PGA – MCEG peak ground acceleration 0.606

FPGA – Site amplification factor at PGA 1.1

PGAM – Site modified peak ground acceleration 0.667

TL – Long-period transition period in sec. 8

CRS – Mapped value of the risk coefficient at short periods 0.896

CR1 – Mapped value of the risk coefficient at a period of 1 sec. 0.903

*See requirements for site-specific ground motions ASCE 7-16 section 11.4.8, discussed below.

According to Section 1604A.5 of CBC 2019, the Risk category for an essential facility (fire station) is designated as IV. With a Risk category of IV and the Design Spectral Response Accelerations listed above, the site would have a Seismic Design Category of D.

Site-specific design and MCER ground motion spectra characterize the intensity and frequency content of ground motions at the site in terms of peak…