A01.10_Geotechnical_Report_15_June_15.pdf

U.S. Army Corps of Engineers

GEOTECHNICAL INVESTIGATION REPORT

PROPOSED USFS RELOCATED FACILITIES

ISABELLA LAKE DAM SAFETY MODIFICATION PROJECT

LAKE ISABELLA

KERN COUNTY

CALIFORNIA

Prepared For:

MFDB/KASL A+E CONSULTANTS, LLC

111 Scripps Drive

Sacramento, California 95825

Prepared By:

GENTERRA CONSULTANTS, INC.

Irvine and Sacramento, California

Project No. 363-KAS-COE-TO3

June 15, 2015

Geotechnical Investigation June 15, 2015 USFS Relocated Facilities, Isabella DSMP

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TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY ................................................................................................................ ii

1.0 SCOPE OF WORK

2.0 SITE CONDITIONS

3.0 PROJECT DESCRIPTION

4.0 FIELD EXPLORATION

5.0 GEOLOGY

5.1 GEOLOGIC SETTING

5.2 GEOLOGIC MATERIALS

5.3 GROUNDWATER

5.4 FAULTS

5.5 GEOLOGIC-SEISMIC HAZARDS

5.6 CONCLUSIONS REGARDING GEOLOGIC HAZARDS

6.0 RECOMMENDATIONS

6.1 GENERAL

6.2 FOUNDATIONS

6.3 SEISMIC DESIGN CRITERIA

6.4 FLOOR SLAB SUPPORT

6.5 RETAINING WALLS

6.6 SHORING DESIGN

6.7 FILL AND CUT SLOPES

6.8 PAVING

6.9 GRADING

6.10 GEOTECHNICAL OBSERVATION AND TESTING

7.0 LIMITATIONS AND BASIS FOR RECOMMENDATIONS

8.0 REFERENCES

FIGURES

FIGURE 1 Vicinity Map FIGURE 2-1 Site Plan, Proposed Administration and Warehouse Buildings FIGURE 2-2 Site Plan, Proposed Fire Station FIGURE 3 Regional Geologic Maps FIGURE 4 Regional Fault Map

APPENDICES

APPENDIX A – RESULTS OF FIELD EXPLORATION AND LABORATORY

TESTING

APPENDIX B – PERCOLATION TEST RESULTS

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EXECUTIVE SUMMARY

GENTERRA Consultants, Inc. (GENTERRA) has completed the geotechnical investigation of the sites of the proposed U.S. Forest Service (USFS) Relocated Facilities to be located within two project sites known as the Kernville Work Center site (Kernville, CA) and the Lake Isabella “Triangle” site (Lake Isabella, CA) in Kern County, California.

USFS administration and warehouse buildings will be located at the Kernville Work

Center (KWC) site and a fire station building will be located at the Lake Isabella

“Triangle” site. It is anticipated that all proposed buildings will be wood-framed with slab-on-grade and supported on continuous strip footings along the perimeter and isolated columns (if needed).

The locations of the proposed USFS relocated facilities are shown on Figure 1, Vicinity

Map. The locations of the proposed project features are shown on Figure 2-1, Site Plan, Proposed Administration and Warehouse Buildings and Figure 2-2, Site Plan, Proposed

Fire Station. The locations of GENTERRA’s hollow-stem auger borings and percolation test borings are also shown on Figures 2-1 and 2-2.

The proposed development within the Kernville Work Center site consists of a new one-story administration building with a building footprint of about 6,000 square feet and a new one-story warehouse building with a building footprint of about 2,600 square feet.

The structural load on the perimeter footings is anticipated to be one kip per lineal foot or less and the column load is anticipated to be about 15 kips or less. Based on information provided by MFDB/KASL, the finish floor elevation of the proposed administration building is about 2,681.10 feet above mean sea level (NAVD88) and the finish floor elevation of the proposed warehouse building is about 2,680.80 feet above mean sea level

(NAVD88). Vertical elevations quoted in this report refer to the North American Vertical

Datum of 1988 (NAVD88).

The proposed development within the Lake Isabella “Triangle” site consists of a new two-bay, one-story Fire Station Building with a building footprint of about 4,000 square feet.

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The structural load on the perimeter footings is anticipated to be one kip per lineal foot or less and the column load is anticipated to be about 20 kips or less. Based on information provided by MFDB/KASL, the finish floor elevation of the proposed fire station building is about 2609.35 feet above mean sea level.

The site of the proposed administration and warehouse buildings within the Kernville

Work Center site was explored by GENTERRA by drilling 10 borings (BH-1 through BH-

10) to depths of about 11½ to 51½ feet below the existing grade. The proposed leach field area within the Kernville Work Center site was explored by drilling three (3) borings (BP-

1 through BP-3) to depths of about 5 feet each. Fill soils, ranging in thickness of from 1 to

2 feet thick, were encountered in two of the ten borings. Deeper and/or poorer quality fill could occur between boring locations. In Boring BH-3, groundwater was encountered at a depth of about 43 feet below existing grade. Based on materials encountered in our geotechnical explorations, as well as our review of other published materials, the Kernville

Work Center site is believed to be underlain by artificial fill, alluvial materials consisting of silty sand, silty sand with gravel, poorly graded sand with silt, and poorly graded sand with silt and gravel. The on-site materials within the Kernville Work Center site are mildly corrosive to ferrous metals and would have negligible sulfate attack on concrete.

Therefore, normal cement (Type II) can be used for this project.

The site of the proposed fire station building within the Lake Isabella “Triangle” site was explored by drilling 9 borings (BH-11 through BH-19) to depths of about 4 to 24 feet below the existing grade. The erratic nature and depths of the boring refusals appears to indicate that the refusals may be on cobbles or boulders. The proposed leach field area within the Lake Isabella “Triangle” site was explored by drilling two (2) borings (BP-4 and

BP-5) to depths of about 4 feet each. Fill soils were not encountered during our exploration.

Based on materials encountered in our geotechnical explorations, as well as our review of other published materials, it is believed that the Lake Isabella “Triangle” site is underlain by alluvial and colluvial materials consisting of silty sand, silty sand with gravel, poorly graded sand with silt, cobbles, boulders and highly weathered granodiorite bedrock to less weathered granodiorite bedrock. This granodiorite bedrock is highly variable in its

363-KAS-COE-TO3-LakeIsabellaFacilities_GeoInvestRpt_061515_Final iv weathering patterns and rock strength, ranging from decomposed to slightly weathered, and extremely weak to strong. Certain portions of the project site are covered with a granite boulder field. The on-site materials within the Lake Isabella “Triangle” site are

Based on available historical data regarding groundwater in the area of the project sites, groundwater is expected to be deeper than 16 feet within project limits. It is our opinion that groundwater will not have an impact on the construction of the foundation system for the proposed buildings and any other related earthwork. For purposes of design of project features at the Kernville Work Center site, a design groundwater elevation of 2,665 feet

(NAVD88) was selected for engineering analysis (this corresponds to the highest groundwater elevation reported on the website of the State of California, Department of

Water Resources for a well near the Kernville Center site). At the Lake Isabella “Triangle” site, the depth to bedrock is shallow and perched groundwater (if any) is not expected to have an impact on the proposed design features.

The Kern Canyon Fault runs through the right abutment of the Auxiliary Dam of Lake

Isabella Dam but it is well away from both project sites. Based on the available geologic data, active or potentially active faults with the potential for surface fault rupture are not known to be located beneath or projecting towards the project sites. In our opinion, the potential for surface rupture at the site due to fault plane displacement propagating to the ground surface during the design life of the project is considered low. Although the site could be subjected to strong ground shaking in the event of an earthquake, this hazard is common in Southern California and the effects of ground shaking can be mitigated by proper engineering design and construction in conformance with current building codes and engineering practices. The Kernville project site is relatively level and the Lake

Isabella “Triangle” site bounded by an ascending mild slope to the east and a descending mild slope to the west. If recommendations provided in this report are implemented during the design and construction of the project, potential impacts of boulder flow towards the

Lake Isabella “Triangle” site during strong ground shaking could be precluded. The

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Kernville Work Center site could experience up to about one (1) inch of liquefaction induced settlement. Liquefaction potential within the Lake Isabella “Triangle” site is very low. The potential for other geologic hazards such as seismic-induced dry settlement, tsunamis, inundation, seiches, flooding, and subsidence affecting the site is considered low to nonexistent.

Based on the results of our investigation, both project sites are suitable, from a geotechnical engineering standpoint, for the proposed development provided that our recommendations presented in this report are implemented during the design and construction of this project. If grading recommendations in this report are implemented, the proposed buildings at both project sites may be supported on shallow continuous and/or spread footings and the floor slabs may be supported on grade.

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1.0 SCOPE OF WORK

This report provides geotechnical design recommendations by GENTERRA to the

MFDB/KASL design team for the proposed USFS Relocated Facilities in Kern County, California. GENTERRA performed this work as an approved Subconsultant to

MFDB/KASL on this Contract Number W91238-11-D-0009, Task Order 0003 for the

Sacramento District of the U.S. Army Corps of Engineers (USACE). This investigation was conducted in general accordance with the USACE Statement of Work dated 12 August

2014.

Map. The locations of the proposed project features are shown on Figure 2-1, Site Plan, Proposed Administration and Warehouse Buildings and Figure 2-2, Site Plan, Proposed

Fire Station. The locations of GENTERRA’s hollow-stem auger borings and Percolation

Test Borings are also shown on Figures 2-1 and 2-2.

This geotechnical investigation was authorized to evaluate the characteristics of the soils at both project sites of the proposed USFS relocated facilities, and to provide geotechnical recommendations for the design of proposed features.

The assessment of general site environmental conditions for the presence of contaminants in the soils and groundwater of the site was beyond the scope of this investigation.

Our recommendations are based on our geotechnical explorations performed for the proposed USFS relocated facilities and our review of published information for the project area, together with our engineering analyses.

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2.0 SITE CONDITIONS

The Kernville Work Center project site is located on the southwest corner area of the intersection of Kernville Road and Sierra Way in Kernville, Kern County California. The project site is bounded by Kernville Road to the north, existing buildings on the east and south and a fence on the west. The site was predominantly vacant at the time of our exploration except the area for proposed warehouse building site that was occupied by an existing building. The project site is relatively level, except around the area of the proposed warehouse building site. The existing grade within the proposed project limits varies between approximately Elevation 2,670 feet above mean sea level (NAVD88) and approximately Elevation 2,697 feet above mean sea level. The existing grade within the footprint of the proposed administration building varies between approximately Elevation

2,676 feet above mean sea level (NAVD88) and approximately Elevation 2,684 feet above mean sea level. The existing grade within the footprint of the proposed warehouse building is relatively level and is at approximately Elevation 2,680 feet above mean sea level. There are several utility lines that traverse the project site.

The Lake Isabella “Triangle” project site is located south of the left abutment of the Lake

Isabella Auxiliary Dam and south of Lake Isabella Boulevard in Lake Isabella, Kern

County California. This triangular shaped project site is bounded by Lake Isabella

Boulevard to the north and west, existing buildings on the south and vacant land on the east. The site was predominantly vacant at the time of our exploration and covered with sparse brush and boulder fields. The project site is bounded by an ascending mild slope to the east and a descending mild slope to the west. The existing grade within the proposed project limits varies between approximately Elevation 2,597 feet above mean sea level

(NAVD88) and approximately Elevation 2,629 feet above mean sea level. The existing grade within the footprint of the proposed fire station building varies between approximately Elevation 2,608 feet above mean sea level (NAVD88) and approximately

Elevation 2,616 feet above mean sea level. When GENTERRA contacted Underground

Service Alert (USA) prior to the field exploration for utility clearance, flags with

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“Verizon” label were placed by the USA in the Lake Isabella “Triangle” site to indicate the presence of “Verizon” lines. There may be Verizon lines and other utility lines traversing the far northwest corner area of the site, just outside the footprint of any proposed project improvements (see Figure 2-2). The boundaries of the leach field should be located at least

5 feet away from existing utilities so that the potential for undermining and/or damaging existing utility lines can be prevented. Based on available information, no other utility lines are known to traverse the project site. Since locating of utilities is beyond our scope of work, we recommend that the following sentence be added to the plans and/or specifications of the project, “The Contractor shall contact Underground Service Alert

(USA) and seek assistance of a subcontractor who specializes in underground utility locating services to locate the existing utilities within the project limits before starting construction”.

3.0 PROJECT DESCRIPTION

The Isabella Lake Dam Safety Modification Project is a Dam Safety Action Class (DSAC)

I Dam and one of the highest risk dams in the USACE inventory. The risk arises from significant hydrologic, seismic, and seepage deficiencies that menace the integrity of the dam’s structure, with a significant downstream population in the path of potentially catastrophic flooding. Both the Main and Auxiliary Dams will be raised up to sixteen feet to address dam safety deficiencies. In addition to the dam raises, an emergency spillway will be constructed to pass the Probable Maximum Flood (PMF).

To accommodate the emergency spillway, the existing U.S. Forest Service (USFS) Isabella

Lake Ranger Station complex will be demolished and relocated to two separate parcels.

Current plans are to design and build a two-bay fire station on a USFS managed parcel

(Kern County APN# 485-010-078), also known as the “Lake Isabella “Triangle” site. The

USFS administration building and warehouse will be designed and constructed on the existing USFS Kernville Work Center (KWC) site located in Kernville, California (Kern

County APN# 082-35-009).

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Map. The locations of the proposed project features are shown on Figure 2-1, Site Plan, Proposed Administration and Warehouse Buildings and Figure 2-2, Site Plan, Proposed

Fire Station.

The proposed development within the Kernville Work Center site consists of a new one-story administration building with a building footprint of about 6,000 square feet and a new one-story warehouse building with a building footprint of about 2,600 square feet.

The structural load on the perimeter footings is anticipated to be one kip per lineal foot or less and the column load is anticipated to be about 15 kips or less. Based on information provided by MFDB/KASL, the finish floor elevation of the proposed administration building is about 2,681.10 feet above mean sea level (NAVD88) and the finish floor elevation of the proposed warehouse building is about 2,680.80 feet above mean sea level

(NAVD88). Vertical elevations quoted in this report refer to the North American Vertical

Datum of 1988 (NAVD88).

The proposed development within the Lake Isabella “Triangle” site consists of a new two-bay, one-story fire station building with a building footprint of about 4,000 square feet.

The structural load on the perimeter footings is anticipated to be one kip per lineal foot or less and the column load is anticipated to be about 20 kips or less. Based on information provided by MFDB/KASL, the finish floor elevation of the proposed fire station building is about 2609.35 feet above mean sea level.

It is our understanding that structural design of proposed features will be performed by

USACE in-house design staff. It is also our understanding that, due to the accelerated nature of this requirement, the Government intends to bypass a 65% design submittal.

Thus 10%, 35% and options for 95% and bid set submittals will be used.

The goal is to have the USFS Isabella Lake mission completely relocated to their new facilities no later than December 2016 in preparation of a January 2017 dam modification construction contract award.

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4.0 FIELD EXPLORATION

GENTERRA explored the Kernville Work Center site by drilling ten (10) hollow stem auger borings (BH-1 through BH-10) to depths ranging from 11½ feet to 51½ feet below existing ground using a truck-mounted CME 75 drill rig equipped with an 8-inch-diameter hollow-stem auger. Approximate boring location, boring number and depth of each boring are shown on Figure 2-1, Site Plan, Proposed Administration and Warehouse Buildings. In addition, three (3) shallow borings (BP-1 through BP-3) were drilled to a depth of approximately 5 feet each using a truck-mounted drill rig equipped with an 8-inch-diameter hollow stem auger to perform percolation tests within the proposed leach field area in accordance with Kern County soils percolation test requirements published as a

PDF, http://psbweb.co.kern.ca.us/EH_Internet/pdfs/land/landInfo/SoilsPercolation.pdf. In these shallow borings, percolation tests were performed by a professional Civil Engineer to obtain the percolation rate for the design of a septic system. Approximate boring location, boring number and depth of each boring are shown on Figure 2-1, Site Plan, Proposed

Administration and Warehouse Buildings.

GENTERRA explored the Isabella “Triangle” site by drilling nine (9) hollow-stem auger borings (BH-11 through BH-19) to depths ranging from 4 feet to 24 feet below existing ground using a truck-mounted CME 75 drill rig equipped with an 8-inch-diameter hollow stem auger. Approximate boring location, boring number and depth of each boring are shown on Figure 2-2, Site Plan, Proposed Fire Station. In addition, two (2) shallow borings (BP-4 and BP-5) were drilled to a depth of approximately 4 feet using a truck-mounted drill rig equipped with an 8-inch-diameter hollow stem auger to perform percolation tests within proposed leach field area in accordance with Kern County soils percolation test Requirements that are discussed in the above paragraph. In these shallow borings, percolation tests were performed by a professional Civil Engineer to obtain the percolation rate for the design of a septic system. Approximate percolation test boring location, boring number and depth of each boring are shown on Figure 2-2, Site Plan, Proposed Fire Station. In anticipation of a Kern County requirement to widen Lake

Isabella Blvd, pavement improvements may ultimately be required. GENTERRA located

363-KAS-COE-TO3-LakeIsabellaFacilities_GeoInvestRpt_061515_Final 6 one boring (BH-19) adjacent to Lake Isabella Blvd to evaluate subsurface conditions, specifically to determine the California Bearing Value (CBR) value of the subsurface materials for pavement design associated with the highway widening project.

GENTERRA conducted all drilling and sampling in accordance with the applicable

American Society for Testing Materials (ASTM) standards. GENTERRA performed

Standard Penetration Tests (SPTs) in all borings at 5-foot intervals, and samples were collected at every 2½ feet to create a nearly continuous sampling in at least the upper 15 feet. SPTs and Modified California Samplers were used in an alternative manner to collect samples. Bulk samples of upper soils were collected for compaction tests. Samples collected with both disturbed and undisturbed methods were used to perform laboratory testing to determine the pertinent static physical characteristics of the subsurface materials within project limits. The results of hollow-stem auger borings are presented in Appendix

A.

All soil borings were backfilled starting at the bottom of the hole to within 6 inches of the ground surface with a low strength (compressive strength of 200 psi or less) soil-cement slurry mixture. The soil-cement slurry was made using local soil, which contains up to 20-

25% non-plastic or slightly plastic fines. The cement content was around 3-6% by dry mass of the soil (about 1 to1 ½ 90-pound bags of cement per cubic yard of soil).

Laboratory tests were assigned by GENTERRA on selected samples obtained from the borings to aid in the classification of the soils and to determine the pertinent engineering properties of the foundation soils.

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The following tests were assigned and completed:

Sieve Analysis Percent Passing No. 200 Sieve Moisture Content Unit Weight Atterberg Limits Direct Shear Consolidation Compaction Expansion Index Sand Equivalent CBR-Value Chemical tests

All testing, except chemical tests, was done in general accordance with applicable ASTM specifications. Chemical tests were performed in general accordance with Caltrans Test

Methods. Laboratory test results are presented in Appendix A.

Based on our evaluation of the results of percolation tests performed in shallow borings located within the limits of proposed leach field, the existing soil conditions within both leach field sites (leach field within Kernville Work Center site and leach field within Lake

Isabella “Triangle” site) can be classified as California Plumbing Code (CPC) Soil Type 3.

Please note that excavation for an infiltration trench may be difficult due to the potential for large cobbles within the footprint of the proposed leach field area.

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5.0 GEOLOGY

5.1 GEOLOGIC SETTING

5.1.1 Regional Geologic Setting

The project sites are located at or in the close vicinity of the mountains, in the southernmost portion of the Sierra Nevada geomorphic province of California. The Sierra

Nevada geomorphic province separates the Great Basin geomorphic province to the east from the Great Valley geomorphic province to the west. The Sierra Nevada geomorphic province is considered a westerly-tilted fault block extending 400 miles in a northwesterly direction from the Mojave Desert in the south to the Cascade Range in the north. The mountain range is about 70 miles east-to-west. The extensive uplift of the block on its eastern border has created much steeper relief on the eastern side of the range and relatively long and gentle relief on the western side. Consequently, drainages on the eastern flank tend to be steeper and narrower than those on the western flank. Altitudes along the west slope of the Sierra Nevada vary from the few hundreds of feet above mean sea level in the foothill areas of the Sacramento and San Joaquin Valleys to 14,494 feet above mean sea level at Mount Whitney. The rocks that form the backbone of the Sierra

Nevada are mostly granitic rocks that formed during the Mesozoic Era. At that time, an arc-shaped chain of volcanoes, similar to the present-day Cascade volcanic arc, erupted where the Sierra Nevada now stands. Approximately 20 million years ago, crustal extension associated with the Basin and Range geomorphic province caused extensive volcanism in the area of the Sierra Nevada. Approximately 4 million years ago, the Sierra

Nevada started to form as the block of crust between the Coast Range and the Basin and

Range geomorphic province started to tilt to the west. A series of ice ages began approximately 2.5 million years ago. Glaciers associated with the ice ages carved out characteristic U-shaped canyons throughout the Sierra Nevada. The combination of river and glacier erosion exposed the uppermost portions of the plutons emplaced millions of years before, leaving only remnants of metamorphic rock referred to as roof pendants on

363-KAS-COE-TO3-LakeIsabellaFacilities_GeoInvestRpt_061515_Final 9 top of some Sierra Nevada peaks and deposited glacial debris as ice advanced and retreated.

5.1.2 Local Geologic Setting

The majority of the surface materials in the project area have been mapped by the

California Geological Society (CGS) as Holocene age alluvial deposits (Figure 3). These deposits developed and continue to develop from erosion of the surrounding granitic hills in the area.

In the Lake Isabella “Triangle” site, numerous cobbles and boulders are present in the surface alluvial soils with size and frequency increasing up-gradient of the alluvial fan, toward the foothills located east of the project site.

5.2 GEOLOGIC MATERIALS

The site of the proposed administration and warehouse buildings within the Kernville

Work Center site was explored by GENTERRA by drilling 10 borings (BH-1 through BH-

10) to depths of about 11½ to 51½ feet below the existing grade. The proposed leach field area within the Kernville Work Center site was explored by drilling three (3) borings (BP-

1 through BP-3) to depths of about 5 feet each. Fill soils, ranging in thickness of from 1 to

2 feet thick, were encountered in two of the ten borings. Deeper and/or poorer quality fill could occur between boring locations. In Boring BH-3, groundwater was encountered at a depth of about 43 feet below existing grade. Based on materials encountered in our geotechnical explorations, as well as our review of other published materials, the Kernville

Work Center site is believed to be underlain by artificial fill, alluvial materials consisting of silty sand, silty sand with gravel, poorly graded sand with silt, and poorly graded sand with silt and gravel. The on-site materials within the Kernville Work Center site are

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The site of the proposed fire station building within the Lake Isabella “Triangle” site was explored by drilling 9 borings (BH-11 through BH-19) to depths of about 4 to 24 feet below the existing grade. The erratic nature and depths of the boring refusals appears to indicate that the refusals may be on cobbles or boulders. The proposed leach field area within the Lake Isabella “Triangle” site was explored by drilling two (2) borings (BP-4 and

BP-5) to depths of about 4 feet each. Fill soils were not encountered during our exploration. Based on materials encountered in our geotechnical explorations, as well as our review of other published materials, it is believed that the Lake Isabella “Triangle” site is underlain by alluvial and colluvial materials consisting of silty sand, silty sand with gravel, poorly graded sand with silt, cobbles, boulders and highly weathered granodiorite bedrock to less weathered granodiorite bedrock. This granodiorite bedrock is highly variable in its weathering patterns and rock strength, ranging from decomposed to slightly weathered, and extremely weak to strong. Certain portions of the project site are covered with a granite boulder field. The on-site materials within the Lake Isabella “Triangle” site are mildly corrosive to ferrous metals and would have negligible sulfate attack on concrete.

5.3 GROUNDWATER

Based on available historical data regarding groundwater in the area of the project sites, groundwater is expected to be deeper than 16 feet within project limits. It is our opinion that groundwater will not have an impact on the construction of the foundation system for the proposed buildings and any other related earthwork. For purposes of design of project features at the Kernville Work Center site, a design groundwater elevation of 2,665 feet

(NAVD88) was selected for engineering analysis (this corresponds to the highest groundwater elevation reported in the website of the State of California, Department of

Water Resources for a well near the Kernville Center site). At the Lake Isabella “Triangle” site, the depth to bedrock is shallow and perched groundwater (if any) is not expected to have an impact on the proposed design features.

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5.4 FAULTS

There are no known faults identified trending across or towards the project sites. However, the Kern Canyon Fault is located approximately 3,900 and 3,200 feet from the Lake

Isabella “Triangle” site and Kernville Work Center site, respectively (Figure 3). The project sites are not mapped in an Alquist-Priolo Earthquake Fault Zone. The Alquist-

Priolo Special Studies Act of 1972 requires that zones along active faults be established to restrict construction of structures for human occupancy to mitigate the hazard of surface rupture. Under the Alquist-Priolo criteria an active fault is defined as one that has experienced surface displacement within the last 11,000 years (Holocene age). Numerous

Late Quaternary (within the last 700,000 years) faults have been mapped in the region of the site (Figures 3 and 4).

Several significant fault zones border the south end of the Sierra Nevada Mountains. The north trending Sierra Nevada Fault Zone is located approximately 30 miles east of the project. This Holocene fault zone extends along almost the entire portion of the eastern boundary of the mountain range. The south end of the Sierra Nevada Mountains terminate at the northeast trending Garlock Fault Zone. Other late Quaternary and Holocene faults in the region include the close proximity Kern Canyon Fault, Kern Gorge Fault and White

Wolf Fault. Seismic activity produced from these active faults will likely produce ground shaking at the project site. A major structural feature of the southern Sierra Nevada

Mountains is the northerly trending Kern Canyon Fault. It extends for more than 80 miles from the Walker Basin on the south to the Kings-Kern Divide on the north. Until recently, the Kern Canyon Fault was thought to be inactive. However, studies by Kelson et al

(2010) have revealed that the fault has produced multiple surface-rupturing earthquakes within the past several thousand years, contrary to early interpretations of fault inactivity.

The Kern Canyon Fault passes under the right abutment of the Auxiliary dam at Isabella

Lake, and is now considered capable of generating significant earthquakes with surface-rupturing. (Figure 3)

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5.5 GEOLOGIC-SEISMIC HAZARDS

Fault Rupture

Based on available information from the California Geological Survey’s Official Maps of the Alquist-Priolo Earthquake Fault Zones, no map has been prepared for the project area.

Considering that the site is not within currently established Alquist-Priolo Earthquake

Fault Zones for surface fault rupture hazards, and no known active or potentially active faults with the potential for surface fault rupture are known to be located directly beneath or projecting toward the site, the potential for surface fault rupture at the site is considered to be low. While fault rupture would most likely occur along previously established fault traces, future fault rupture could occur at other locations.

Seismicity

The project sites could be subjected to strong ground shaking in the event of an earthquake. However, this hazard is common to California and the effects of ground shaking can be mitigated by proper engineering design and construction in conformance with current building codes and engineering practice.

Boulder Flow

Based on the geological conditions and topography of the Lake Isabella “Triangle” site, a low to moderate potential for boulder flow exists at this site. Such a boulder flow event has higher probability during heavy storm events and seismic events. Some remedial mitigation, such as a 6-foot-high reinforced retaining wall or a 6-foot-high gabion retaining wall or a 6-foot-high reinforced soil buttress wall constructed using wrapped around geogrids and geotextiles or a 6-foot-high barrier constructed using boulders and cobbles to be excavated within project limits, is necessary to protect the proposed facilities within the

Lake Isabella “Triangle” site. The remedial mitigation is needed only along the eastern perimeter of the project limits where ascending slopes exist. Once a preferred alternative for remedial mitigation is selected, GENTERRA can provide necessary recommendations.

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This hazard does not exist within the Kernville Work Center site.

Slope Stability

The Kernville project site is relatively level and the Lake Isabella “Triangle” site is bounded by an ascending mild slope to the east and a descending mild slope to the west.

The sites are not within an area having a potential for slope instability. There are no known landslides at the sites nor are the sites in the path of any known landslides.

Based on our evaluation, the potential for slope instability at the project site is considered to be low. If recommendations provided in this report are implemented during the design and construction of the project, potential impacts of boulder flow towards the Lake Isabella

“Triangle” site during strong ground shaking could be precluded.

Proposed cut and fill slopes that are needed for the proposed project will be stable under static and seismic conditions, provided that our recommendations are implemented during the design and construction of the cut and fill slopes.

Liquefaction and Seismic-Induced Settlement

Liquefaction potential is greatest where the ground water level is shallow, and where submerged loose, fine sands occur within a depth of about 50 feet or less. Liquefaction potential decreases as grain size increases and as clay and gravel contents increase. As ground acceleration and shaking duration increase during an earthquake, liquefaction potential increases.

To evaluate the liquefaction potential of the Kernville Work Center site, we selected the peak ground acceleration (PGA) for the ground motion with a 10% probability of exceedance in 50 years. This ground motion, which is designated as the Design Basis

Earthquake (DBE), corresponds to a Predominant Earthquake Magnitude of 6.1.

According to the United States Geological Survey (USGS) website, the PGA for the ground motion with a 10% probability of exceedance in 50 years is reported as 0.28g for

363-KAS-COE-TO3-LakeIsabellaFacilities_GeoInvestRpt_061515_Final 14 the project site. This information was used in our liquefaction evaluation. The historic high groundwater table for our liquefaction analysis was assumed to be at Elevation 2,665 feet (NAVD88) (this corresponds to the highest groundwater elevation reported in the website of the State of California, Department of Water Resources for a well near the

Kernville Center site).

The liquefaction potential was computed using the recorded SPT data imported into the software program, LiquefyPro by CivilTech Software, in accordance with procedures described in Youd and Idriss, 1997 (NCEER Technical Report 97-0022) consensus publication on liquefaction evaluation, and Youd et al., 2001 summary report from 1996

NCEER and 1998 NCEER/NSF workshop on evaluation of liquefaction resistance of soils.

Based on our engineering analyses, the loose sand layers at depths ranging from about 40 feet below existing grade to about 44 feet below existing grade, at the location of proposed

Administration Building site, are potentially liquefiable.

Seismic-induced ground settlement may occur as the result of the densification of loose to medium-dense granular soils during ground shaking. Dry and partially saturated soils are subject to seismic-induced settlement. Based on the available information, seismic-induced ground settlement from densification of the soils above the groundwater table is expected to be low.

We estimate that potential liquefaction-induced total settlement is about one inch for existing soil conditions without any mitigation. Liquefaction of the underlying soils at the site will not induce lateral spreading due to site conditions.

Tsunamis, Inundation and Flooding

The project sites are not in a coastal area. Therefore, tsunamis (seismic sea waves) are not considered to be a significant hazard at the sites.

The Kernville Work Center site is not located downslope of any large bodies of water that could adversely affect the site in the event of earthquake-induced dam failures or seiches

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(wave oscillations in an enclosed or semi-enclosed body of water). Even though Lake

Isabella “Triangle” site is located downstream of the Auxiliary Dam of Lake Isabella, it is well away from the potential flow path of earthquake-induced dam failures or seiches, therefore Lake Isabella “Triangle” site will not be adversely affected by such events.

According to FEMA website, the sites are not in an area of potential flooding. Both project sites are outside the limits of 500-year floodplains.

Subsidence

The proposed project sites are not within an area of known subsidence associated with fluid (groundwater or petroleum) withdrawal, peat oxidation or hydroconsolidation.

5.6 CONCLUSIONS REGARDING GEOLOGIC HAZARDS

Based on the available geologic data, active or potentially active faults with the potential for surface fault rupture are not known to be located beneath or projecting towards the project sites. In our opinion, the potential for surface rupture at the sites due to fault plane displacement propagating to the ground surface during the design life of the project is considered low. Although the sites could be subjected to strong ground shaking in the event of an earthquake, this hazard is common in Southern California and the effects of ground shaking can be mitigated by proper engineering design and construction in conformance with current building codes and engineering practices. The Kernville project site is relatively level and the Lake Isabella “Triangle” site is bounded by an ascending mild slope to the east and a descending mild slope to the west. If recommendations provided in this report are implemented during the design and construction of the project, potential impacts of boulder flow towards the Lake Isabella “Triangle” site during strong ground shaking could be precluded.

The Kernville Work Center site could experience up to about one (1) inch of liquefaction-induced settlement. Liquefaction potential within the Lake Isabella “Triangle” site is considered to be very low to nonexistent.

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The potential for other geologic hazards such as seismic-induced dry settlement, tsunamis, inundation, seiches, flooding, and subsidence affecting the sites is considered low to nonexistent.

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6.0 RECOMMENDATIONS

6.1 GENERAL

Based on our investigation, up to two feet of non-engineered fill is expected within the footprint of the proposed features at the Kernville Work Center site. All existing fill soils should be removed and replaced as properly compacted fill soils. To mitigate the potential for unacceptable differential settlement, and to provide uniform support for the proposed

Buildings and paving features, we recommend that remedial grading be performed to place at least a 2-foot-depth of properly compacted fill consisting of relatively non-expansive materials underneath concrete slabs-on-grade and paving. All existing fill soils should be removed and replaced with properly compacted fill. The excavations should be deepened as necessary so as to provide at least a 3-foot-depth of compacted fill soils, or a depth of compacted fill equal to the maximum dimension of the width of the footing, whichever is greater, beneath the footings. The lateral extent of removal and replacement should be at least equal to the removal depth below footings.

In the Lake Isabella “Triangle” site, to mitigate the potential for unacceptable differential settlement, and to provide uniform support for the proposed fire station building and paving features, we recommend that remedial grading be performed to remove top soils, natural soils, cobbles and boulders in the upper 4 feet and placement of at least a 4-foot-depth of properly compacted fill consisting of relatively non-expansive materials underneath concrete slabs-on-grade and paving. Due to the nature of subsurface materials at the Lake Isabella “Triangle” site and to provide better performance for paving, we recommended at least a 4-foot-depth of properly compacted fill consisting of relatively non-expansive materials underneath the paving. However, this requirement can be reduced to a 2-foot-depth of properly compacted fill consisting of relatively non-expansive materials underneath the paving, provided that similar materials (all sandy materials without significant number of boulders) with similar consistency (medium dense to dense) exist after removal of the upper 2 feet of existing materials within the paving area.

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If the remedial grading recommendations in this report are implemented, and an adequate slope to finish grade or proper drainage systems are installed to drain surface water away from the foundations, the proposed buildings may be supported on shallow continuous/spread footings, and the floor slabs may be supported on grade.

We also recommend that a retaining wall be constructed to protect the proposed buildings within the Lake Isabella “Triangle” site from the potential impacts of boulder flow during strong ground shaking. Recommendations for design of retaining walls are given in the section below.

6.2 FOUNDATIONS

The proposed buildings at both project sites may be supported on continuous and/or isolated spread footings established in properly compacted fill soils and extending at least two feet below the lowest adjacent grade or top of the floor level, whichever is lower.

In order to minimize settlement and/or expansion of onsite soils when saturated, we recommend that good drainage of surface water, away from the proposed buildings and improvements, should be provided by providing adequate slopes to all graded and paved surfaces.

Bearing Value, Settlement and Lateral Resistance that are discussed below are applicable to both project sites.

6.2.1 Bearing Value

Continuous footings carried at least two feet below the lowest adjacent grade or top of the floor level, whichever is lower, may be designed to impose a net dead-plus-live load pressure of 2,500 pounds per square foot. The excavations should be deepened as necessary to extend into satisfactory soils. The width of the footings should not be less than two feet.

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A one-third increase in bearing value may be used for wind or seismic loads. The recommended bearing value is a net value, and the weight of concrete in the footings may be taken as 50 pounds per cubic foot; the weight of soil backfill may be neglected when determining the downward loads.

Footings for minor structures (minor retaining walls and free-standing walls) that are structurally separate from the structures may be designed to impose a net dead-plus-live load pressure of 1,000 pounds per square foot at a depth of 1½ feet below the lowest adjacent grade. Such footings may be established in undisturbed or properly compacted fill soils.

6.2.2 Settlement

Based on our analysis using the structural load provided by MFDB/KASL, we estimate that the static settlement of the proposed buildings, supported on continuous footings in the manner recommended, will be up to about ½ inch and differential settlement is expected to be about ¼ inch or less.

Please note that buildings within the Kernville Work Center site may experience up to about one inch of liquefaction-induced settlement, and differential settlement due to liquefaction is expected to be ¼ inch or less.

6.2.3 Lateral Resistance

Lateral loads may be resisted by soil friction and by the passive resistance of the soils. A coefficient of friction of 0.4 may be used between the footings and the floor slab and the supporting compacted fill soils. The passive resistance of properly compacted fill soils may be assumed to be equal to the pressure developed by a fluid with a density of 250 pounds per cubic foot. A one-third increase in the passive value may be used for wind or seismic loads. The frictional resistance and the passive resistance of the soils may be combined without reduction in determining the total lateral resistance.

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6.3 SEISMIC DESIGN CRITERIA

Kernville Work Center Site – Administration and Warehouse Buildings

Based on a review of the local soil and geologic conditions, the Kernville Work Center site may be classified as Site Class D in accordance with Table 1613.5.2 in Section 1613 of

2013 California Building Code (CBC) and 2012 International Building Code (IBC).

The 2012 IBC seismic parameters were estimated using the Java application provided on the USGS website. This application takes site latitude, site longitude, and a site class as input parameters. The 2012 IBC seismic parameters were calculated to be:

SS = 0.972g

S1 = 0.328g

SMS = 1.080g

SM1 = 0.572g

SDS = 0.720g

SD1 = 0.381g

Lake Isabella “Triangle” Site – Fire Station Building (Critical Facility)

Based on a review of the local soil and geologic conditions, the Lake Isabella “Triangle” site may be classified as Site Class C in accordance with Table 1613.5.2 in Section 1613 of

2013 California Building Code (CBC) and 2012 International Building Code (IBC).

The 2012 IBC seismic parameters were estimated using the Java application provided on the USGS website. This application takes site latitude, site longitude, and a site class as input parameters. The 2012 CBC seismic parameters were calculated to be:

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SS = 1.011g

S1 = 0.348g

SMS = 1.011g

SM1 = 0.506g

SDS = 0.674g

SD1 = 0.337g

6.4 FLOOR SLAB SUPPORT

If the subgrade is prepared as recommended in Section 6.9 - Grading, the floor slabs of proposed buildings may be supported on grade.

Construction activities and exposure to the environment can cause deterioration of the prepared subgrade. Therefore, we recommend that a Government field representative observe the condition of the final subgrade soils immediately prior to slab-on-grade construction and, if necessary, perform further density and moisture content tests to determine the suitability of the final prepared subgrade.

If vinyl or other moisture-sensitive floor covering is planned, we recommend that the floor slab in those areas be underlain by a capillary break consisting of a vapor-retarding membrane over a 4-inch-thick layer of gravel. A 2-inch-thick layer of sand should be placed between the gravel and the membrane to decrease the possibility of damage to the membrane. We suggest the following gradation for the gravel:

Sieve Size Percent Passing ¾ 90–100

No. 4 0–10 No. 100 0–3

A low-slump concrete should be used to reduce possible curling of the slab. A 2-inch-thick layer of coarse sand may be placed over the membrane to reduce slab curling. If this sand

363-KAS-COE-TO3-LakeIsabellaFacilities_GeoInvestRpt_061515_Final 22 bedding is used, care should be taken during the placement of the concrete to prevent displacement of the sand. The concrete slab should be allowed to cure properly before placing vinyl or other moisture-sensitive floor covering.

6.5 RETAINING WALLS

Lateral Earth Pressure

For design of cantilevered retaining walls, where the surface of the backfill is level, it may be assumed that drained soils will exert a lateral pressure equal to that developed by a fluid with a density of 30 pounds per cubic foot.

In addition to the recommended earth pressure, retaining walls adjacent to areas subject to vehicular traffic should be designed to resist a uniform lateral pressure of 100 pounds per square foot, acting as a result of an assumed 300 pounds per square foot surcharge behind the walls due to normal vehicular traffic. If the traffic is kept back at least 10 feet from the walls, the traffic surcharge may be neglected. Retaining walls should also be designed to resist any applicable surcharges due to any other vertical surcharge loads behind the walls.

For preliminary design, a uniform lateral pressure equal to one-third of the vertical surcharge pressure may be used.

If the retaining wall is more than 12 feet in height, it should also be designed to resist seismic lateral earth pressure. GENTERRA can provide that recommendation upon request.

If a reinforced retaining wall is selected as the preferred alternative to mitigate boulder flow into the Lake Isabella ‘Triangle” site, then this wall should be designed to withstand impact from potential boulder flow.