17. ML 1 Draft Geological and Geotechnical Investigation_.pdf

DRAFT GEOLOGIC AND

GEOTECHNICAL INVESTIGATION

REPORT

MILLER LAKE DAM

BEALE AFB

YUBA COUNTY, CALIFORNIA

PREPARED FOR

DOKKEN ENGINEERING, INC.

FOLSOM, CALIFORNIA

MAY 10, 2017

PROJECT NO. S1307-05-01

Project No. S1307-05-01 May 10, 2017

DRAFT VIA ELECTRONIC MAIL

Richard Liptak, PE Dokken Engineering 110 Blue Ravine Road, Suite 200 Folsom, California 95630

Subject: DRAFT GEOLOGIC AND GEOTECHNICAL INVESTIGATION REPORT

MILLER LAKE DAM

BEALE AIR FORCE BASE

YUBA COUNTY, CALIFORNIA

Dear Mr. Liptak:

In accordance with your authorization, we have prepared this geologic and geotechnical investigation report for the Miller Lake Dam at Beale Air Force Base (AFB) located east of Yuba City/Marysville in Yuba County, California.

The purpose of our work was to evaluate subsurface conditions at the site from a geological and geotechnical engineering perspective, identify geologic and geotechnical constraints that may impact project design and construction, and provide geological and geotechnical recommendations to support design and construction of planned repairs at the site. Based on the results of our study, the project is feasible from a geological and geotechnical perspective provided the recommendations of this report and subsequent design-level reports are incorporated into the design and construction of the project.

This draft report is not for use for final design as laboratory testing and evaluation is in progress and may result in revisions to the conclusions and recommendations.

Please contact us if you have any questions concerning the contents of this report. We look forward to reviewing the project plans as they develop further and providing geotechnical engineering and engineering geology consultation as needed.

Sincerely, GEOCON CONSULTANTS, INC.

Ronald E. Loutzenhiser, PE, GE Jeremy J. Zorne, PE, GE Senior Engineer Senior Engineer

John C. Pfeiffer, PG, CEG Senior Geologist

TABLE OF CONTENTS

DRAFT GEOLOGICAL AND GEOTECHNICAL INVESTIGATION PAGE

EXECUTIVE SUMMARY

1.0 INTRODUCTION AND PURPOSE

1.1 Scope of Services

1.2 Report Organization

2.0 PROJECT DESCRIPTION

2.1 Background

2.2 Existing Dam

2.3 Proposed Improvements

3.0 LITERATURE REVIEW SUMMARY

4.0 FIELD EXPLORATION PROGRAM SUMMARY

5.0 SOIL AND GEOLOGIC CONDITIONS

5.1 Regional and Local Geology

5.2 Embankment Fill (Qf)

5.3 Alluvium (Qa)

5.4 Mehrten Formation (MPvc)

5.5 Ione Formation (Ei)

5.6 Groundwater/Seepage

6.0 SUMMARY OF LABORATORY TESTING PROGRAM AND TEST RESULTS

7.0 EVALUATION OF SOIL PROPERTIES FOR CONSTRUCTION

7.1 Existing Dam Embankment Fill and Alluvium

7.2 Formational Material (Ione Formation and Mehrten Cobble Conglomerate)

8.0 MATERIAL SPECIFICATIONS AND EARTHWORK RECOMMENDATIONS

8.1 Materials for Fill

8.2 Excavation Characteristics

8.3 Wet Soil Conditions

8.4 Backfill and Compaction

9.0 STRUCTURE FOUNDATION RECOMMENDATIONS

9.1 Box Culverts / Control Structure Outlet

9.2 Lateral Earth Pressures

10.0 GENERAL CONSTRUCTION RECOMMENDATIONS

10.1 Outlet Pipe Penetration

10.2 Slope Protection / Maintenance

11.0 FURTHER GEOTECHNICAL SERVICES

11.1 Plan Review

11.2 Testing and Observation Services

12.0 LIMITATIONS AND UNIFORMITY OF CONDITIONS

TABLE OF CONTENTS (CONTINUED)

FIGURES

Figure 1, Vicinity Map Figure 2, Site Plan Figure 3, Proposed Repair Plan Figure 4, Topographic and Geologic Map Figure 5, Cross-Section A-A’ (Longitudinal) Figure 6, Cross-Section B-B’ (Transverse)

APPENDIX A

FIELD EXPLORATION

Figure A1, Key to Logs Exploratory Boring Logs

APPENDIX B

LABORATORY TESTING PROGRAM

APPENDIX C

HAMMER ENERGY ANALYSIS

Geocon Project No. S1307-05-01 - 1 - May 10, 2017

DRAFT GEOLOGIC AND GEOTECHNICAL INVESTIGATION

EXECUTIVE SUMMARY

This report presents the results of our geologic and geotechnical investigation for the proposed repairs to the Miller Lake Dam at Beale Air Force Base (AFB) located east of Yuba City/Marysville in Yuba County, California. We understand that the proposed improvements include replacement of the main and secondary spillways as well as the outlet works. The main and secondary spillways will be replaced with multi-cell, precast box culverts. Modifications to the supplementary spillway are not proposed at this time.

In addition, the existing outlet works is to be replaced. The existing outlet works consists of an inlet tower on the reservoir side of the dam and an outlet pipe that extends through the dam cross-section. We understand that the Hazard Potential Classification for the dam is low based on Table B1 in Appendix B of the United States Army Corps of Engineers (USACE) ER 1110-2-1806 (Earthquake Design and

Evaluation for Civil Works Projects).

Soil and geologic conditions at the site consist of existing dam embankment fill overlying a minor amount of stream channel alluvium further underlain by formational material consisting of Eocene-age Ione Formation siltstone and sandstone and Tertiary-age Mehrten Formation Conglomerate. Fill materials generally consist of a mixture of sandy and gravelly clay and clayey sands and gravels with variable cobble content. Cobble content of the embankment fill is variable and estimated to be on the order of up to 10 to 20% based on drilling observations. Formational material generally consists of elastic silt, sandy and gravelly clay, clayey gravel, clayey sand, and silty gravel. Cobble content of the formational material is variable and estimated to be on the order of up to 20% based on drilling observations. Preliminary X- Ray diffraction test results indicate the fine-grained (clay) soils are generally composed of kaolinite, with typically minor to moderate expansion potential.

Excavated soils generated from cut operations in the dam are expected to be suitable for re-use as engineered fill/embankment construction. Larger cobble materials (greater than 6 inches) should be screened from the soil before re-use as engineered fill. Due to the fine-grained nature of the soils and in-situ moisture contents (at least locally) well above optimum, significant drying effort to attain moisture contents suitable for compaction should be anticipated when excavated material is placed as fill.

Use of Caltrans Standard Plan Reinforced Concrete Box Culverts, as detailed on Caltrans Standard

Plan D83A and D83B is considered appropriate for the site. Based on the subsurface conditions encountered in our borings, we anticipate that the box culverts and the control structure outlet will be founded on a combination of existing dam embankment fill and/or undisturbed formational material.

A drainage layer should be provided around the replacement outlet conduit in the downstream zone of the dam embankment. We recommend the use of a filter collar (drainage fill) around the downstream 1/3 length of the conduit. We also recommend using a collector pipe to convey seepage water out of the filter collar.

Geocon Project No. S1307-05-01 - 2 - May 10, 2017

1.0 INTRODUCTION AND PURPOSE

This report presents the results of our geologic and geotechnical investigation for the proposed repairs to the existing Miller Lake Dam at Beale Air Force Base (AFB) located east of Yuba City/Marysville in Yuba County, California. The approximate site location is shown on the Vicinity Map, in Figure 1.

A recent aerial photograph of the site and near vicinity is presented on the Site Plan, Figure 2.

The purpose of our investigation was to evaluate subsurface conditions at the site from a geological and geotechnical engineering perspective, identify geologic and geotechnical constraints that may impact project design and construction, and provide geological and geotechnical recommendations to support design and construction of planned repairs at the site. Additional pending design-level reports for this project include: 1) Seepage and Stability Analyses Report and 2) Material Approval Submittal.

1.1 Scope of Services

Our geologic and geotechnical investigation included the following scope of services:

Attended a kickoff meeting at the site on March 31, 2017 with representatives of the designer (Dokken Engineering), Geocon, and the Air Force. The purpose of the meeting was to discuss project specifics and develop a collaborative geotechnical exploration and analysis plan for the project.

Provided information on Geocon and subcontractor personnel using the Entry Access Listing (EAL) procedure for required security background checks.

Performed a limited geologic literature review to aid in evaluating the geologic conditions present at the sites.

Prepared and submitted a Drilling Program Plan (DPP) in general accordance with the guidelines of ER 1110-1-1807. An Activity Hazard Analysis was also prepared as part of the DPP. The DPP was approved on April 4, 2017.

Performed a site reconnaissance to review project limits, determine exploration equipment access and mark out exploratory boring and test pit locations for subsequent utility clearance.

Notified subscribing utility companies via Underground Service Alert (USA) a minimum of two business days (as required by law) prior to performing exploratory borings at the site. Beale AFB personnel reviewed the proposed boring locations and marked out any potential utility or underground structure conflicts.

Retained the services of Gregg Drilling, Inc. a California C57-licensed drilling subcontractor to perform exploratory borings.

Paid required fees and obtained a subsurface exploration permits from the Yuba County Environmental Health Department (YCEHD).

Performed geologic mapping at the site by a California Certified Engineering Geologist (CEG).

Performed 15 exploratory borings (M1 through M15) located in a zig-zag pattern along the crest of the dam. The borings were spaced at approximate 100-foot intervals along the existing dam and were alternately offset towards the upstream and downstream edges of the crown. Boring depths ranged from approximately 3 to 61 feet.

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Obtained representative disturbed and undisturbed soil samples from the exploratory borings consisting of continuous sampling using a sequence of 3-inch outside diameter (OD), 2.5-inch OD, and 2-inch OD (Standard Penetration Test) split spoon samplers per 5 foot sampling interval. Bulk samples were also collected.

Logged the borings in accordance with the Unified Soil Classification System (USCS). Field logging was performed by a California registered Professional Geologist (PG).

Upon completion, backfilled borings with neat cement grout per YCEHD/USACE requirements.

Performed laboratory tests to evaluate pertinent index and engineering parameters.

Prepared this report summarizing the results of our investigation.

1.2 Report Organization

The approximate site location is shown on the Vicinity Map, Figure 1. Current site configuration and approximate locations of exploratory borings are shown on the Site Plan, Figure 2. Proposed repairs are shown on the Proposed Repair Plan, Figure 3. Topography and surficial geology are shown on the Topographic and Geologic Map, Figure 4. A longitudinal geologic cross-section is presented as Cross-Section A-A’, Figure 5. A transverse geologic cross-section is presented as Cross-Section B-B’, Figure 6. Details of our field exploration program including exploratory boring logs are presented in Appendix A. Details of our laboratory testing program and test results are summarized in Appendix B. A copy of the most recent hammer energy analysis for the drill rig used on this project is included as Appendix C.

2.0 PROJECT DESCRIPTION

2.1 Background

The U.S. Army Corps of Engineers (USACE) performed an inspection of Miller Lake Dam in April 2016 and concluded that the dam was in failed to poor condition and recommended corrective actions of existing deficiencies to assure safe operation and performance. USACE performed another inspection in February 2017 and concluded that the dam is threatened due to the severely deteriorated outlet works.

USACE recommended removal and replacement of the low-level intake structure with gate valve and access bridge and outlet works prior to the next wet season.

We understand that the Hazard Potential Classification for the dam is low based on Table B1 in Appendix B of the United States Army Corps of Engineers (USACE) ER 1110-2-1806 (Earthquake

Design and Evaluation for Civil Works Projects).

2.2 Existing Dam

Details of the existing Miller Lake Dam are based on our field observations, limited information available from the Air Force, and review of information prepared by Dokken Engineering. Specific

Geocon Project No. S1307-05-01 - 4 - May 10, 2017 design, construction, or as-built information for the dam is not available as we understand that these documents were destroyed in a structure fire. We understand that as a federal dam located on a Beale AFB, the Miller Lake Dam is under the regulation and authority of the USACE and is not subject to regulation by the California Division of Safety of Dams. For the purposes of this report, “right” and “left” are referenced looking downstream.

Miller Lake Dam is an earth fill dam located on Beale AFB property approximately one-half mile south of Hammonton Smartsville Road and approximately 1½ miles east of Doolittle Drive. The dam is located in gently rolling terrain typical of the western margin of the Sierra Nevada Foothill region. The approximately 1,300-foot-long earth fill dam was constructed in 1962 across a seasonal creek and ranges in height up to 24 feet. The crest is approximately 27 feet wide and is situated at an elevation of approximately 194 feet referenced to the North American Vertical Datum of 1988 (NAVD 88). The slope inclination of the upstream dam face varies from approximately 1.5H:1V (horizontal:vertical) in the upper portion to 3H:1V in the lower portion of the slope. The slope inclination of the downstream dam face is approximately 1.9H:1V. Rock slope protection is generally present on the upstream and downstream faces of the dam.

When full to the spillway crest (elevation 189.5 feet NAVD 88), the dam impounds approximately 580 acre-feet of water. The dam includes three spillways and an outlet works structure. The primary spillway is a three-cell reinforced concrete box culvert in the left abutment with the invert approximately 4½ feet below the dam crest. The secondary spillway is a three-foot diameter corrugated metal pipe (CMP) in the right abutment. A supplementary spillway was added after dam overtopping events in the 1990’s and consists of a 75-foot long concrete weir structure about 2½ feet below the dam crest near the left abutment.

The reinforced concrete outlet works is located near the center of the dam and consists of a control tower in the lake and associated 18-inch diameter reinforced concrete pipe (RCP) extending under/through the dam.

Features of the Miller Lake Dam are shown on the Site Plan, Figure 2. Topography based on a recent survey by UNICO Engineering is shown on the Topographic and Geologic Map, Figure 4. The dam cross-section geometry (longitudinal and transverse) is shown on Figures 5 and 6.

2.3 Proposed Improvements

As demonstrated by recent overtopping events, the hydraulic capacity of the existing spillways and outlet works is insufficient for the design flows and the outlet works is currently non-functional (clogged) and is experiencing seepage and potential internal erosion around the structure. We understand that the proposed improvements include replacement of the main and secondary spillways as well as the outlet works. The main and secondary spillways will be replaced with multi-cell, precast box culverts. Modifications to the supplementary spillway are not proposed at this time. The outlet works is to be replaced. The proposed improvements may be constructed in one or two construction seasons. The proposed improvements are shown on the Proposed Repair Plan, Figure 3.

Geocon Project No. S1307-05-01 - 5 - May 10, 2017

3.0 LITERATURE REVIEW SUMMARY

Specific design, construction, or as-built information for the dam is not available as we understand that these documents were destroyed in a structure fire. Therefore, our literature review was limited to published geologic literature, regulatory design guidance documents, and related information.

Following is a list of references:

1. Air Force Design Guides/Standards, Air Force Engineering Technical Letters, Air Force

Handbooks, Air Force Instructions, Policies and Guidance for Air Force Design and Construction, Air Force Regulations.

2. California Department of Transportation, Standard Plans, 2015.

3. Federal Emergency Management Agency (FEMA) Technical Manual (FEMA 484), Conduits through Embankment Dams.

4. Saucedo, G.J., and Wagner, D.L., Geologic Map of the Chico Quadrangle, California, California Geological Survey, Regional Geologic Map Series, Map No. 7A, scale 1:250,000, 1992.

5. Unpublished reports, aerial photographs, and maps on file with Geocon.

6. USACE EM 1110-1-1804, Engineering and Design, Geotechnical Investigations.

7. USACE EM 1110-2-1901, Engineering and Design, Seepage Analysis and Control for Dams.

8. USACE EM 1110-2-1902, Engineering and Design, Slope Stability.

9. USACE EM 1110-2-1906, Engineering and Design, Laboratory Soils Testing.

10. USACE EM 1110-2-1911, Engineering and Design, Construction Control for Earth and Rock-Fill Dams.

11. USACE EM 1110-2-1913, Engineering and Design, Design and Construction of Levees.

12. USACE EM 1110-2-2300, Engineering and Design, General Design and Construction Considerations for Earth and Rock-Fill Dams.

13. USACE EM 1110-2-2902, Engineering and Design, Conduits, Culverts, and Pipes.

14. USACE ER 1110-1-1807, Engineering and Design, Drilling in Earth Embankment Dams and

Levees.

15. USACE ER 1110-2-1806, Engineering and Design, Earthquake Design and Evaluation for Civil Works Projects.

16. USACE, Miller Lake Dam, NID CA 10119, Beale Air Force Base, California, Periodic Inspection, April 2016.

4.0 FIELD EXPLORATION PROGRAM SUMMARY

Our field investigation program was performed during the period of April 3 through 13, 2017 and consisted of drilling 15 exploratory borings (M1 through M15) at the approximate locations shown on the Site Plan, Figure 2 and Topographic and Geologic Map, Figure 4.

Geocon Project No. S1307-05-01 - 6 - May 10, 2017

Table 4.0 summarizes the details of our exploratory borings. Location information (latitude, longitude, and elevation) was provided by the project surveyor, UNICO Engineering, Inc. (UNICO). Elevations are based on NAVD 88 as adjusted to National Geodetic Survey Permanent Identifier (NGS PID) KS0774 with an elevation of 93.73 feet. Latitude and longitude are based on the North American Datum of 1983 (NAD83) California Zone 2 Epoch 2010.00 as adjusted to NGS PID DL9191, KS0774, and DL 9143.

TABLE 4.0

SUMMARY OF EXPLORATORY BORINGS – MILLER LAKE DAM

Exploratory borings were performed using a truck-mounted Marl M-10 drill rig equipped with 8-inch outside diameter (OD) hollow stem augers. Soil samples were collected continuously using a sequence of 3-inch outside diameter (OD), 2.5-inch OD, and 2-inch OD Standard Penetration Test (SPT) split spoon samplers per 5-foot boring interval to the total depths explored. Sampling was accomplished using a 140-pound, automatic hammer with a 30-inch drop. The automatic hammer has an overall energy transfer ratio (ETR) of 76% per the most recent energy analysis for this hammer (Appendix C).

The 3-inch OD and 2.5-inch OD samplers were equipped with 6-inch-long brass sample tubes to facilitate sample removal and laboratory testing. The SPT sampler had a uniform inside diameter that did not allow for sample liners. The number of blows required to drive the samplers (blow counts) the last 12 inches of the 18-inch sample drive (or portion thereof) are reported on the boring logs. The blow counts presented on the logs are raw, uncorrected values. The borings were logged by a California registered Professional Geologist (PG). Upon completion, the borings were backfilled borings with neat cement grout per YCEHD/USACE requirements. Draft exploratory borings logs are presented in Appendix A.

Boring ID Approximate Boring Location

Boring Depth (feet) Latitude

(degrees North) Longitude

(degrees West) Elevation

(feet NAVD 88) M1 39.10109884 -121.2411612 198.4 39.5 M2 39.10102317 -121.2411109 194.3 39.5 M3 39.10093558 -121.2410278 193.5 39.5 M4 39.10085597 -121.240947 193.8 39.9 M5 39.10077164 -121.2408936 194.1 61.4 M6 39.10068314 -121.2408013 194.0 38.9 M7 39.10060326 -121.2407542 193.7 38.8 M8 39.10051801 -121.2406601 192.9 37.0 M9 39.10041495 -121.240593 193.6 32.5

M10 39.10032017 -121.2404935 193.0 25.5 M11 39.10022287 -121.2404127 193.5 15.5 M12 39.09598146 -121.2402389 193.7 9.0 M13 39.09593902 -121.2401791 194.7 3.0 M14 39.10072285 -121.2408501 194.0 45.2 M15 39.10081591 -121.2409279 193.7 49.5

Geocon Project No. S1307-05-01 - 7 - May 10, 2017

5.0 SOIL AND GEOLOGIC CONDITIONS

Soil and geologic conditions at the site consist of existing dam embankment fill overlying a minor amount of stream channel alluvium further underlain by formational material consisting of Eocene-age Ione Formation claystone and Tertiary-age Mehrten Formation Conglomerate. Surface geology at site is presented on the Topographic and Geologic Map, Figure 4. Geologic cross-sections (longitudinal and transverse to the dam) are presented as Cross-Sections A-A’ and B-B’, Figures 5 and 6, respectively. Soil descriptions provided below include the Unified Soil Classification System (USCS) symbol where applicable. Table 5 summarizes the approximate thickness of the dam embankment/elevation of formational material contact encountered in our borings.

TABLE 5

DAM EMBANKMENT THICKNESS

5.1 Regional and Local Geology

The site is near the approximate margin of the Great Valley and Sierra Nevada geomorphic provinces.

The Great Valley (Sacramento and San Joaquin Valleys) of California is a long, sediment-filled structural depression or down-warped trough, with the axis of the trough beneath the west side of the valley. In general, the southern portion of the Sacramento Valley is underlain by Quaternary continental deposits (alluvial deposits) and late Tertiary age marine and continental sedimentary rocks.

The Sierra Nevada is a tilted fault block nearly 400 miles long with a high, rugged, multiple-scarp east face contrasting with the gentle western slope that disappears under the sediments of the Great Valley.

The site is in a region where both the Sierran bedrock and overlying Great Valley sedimentary deposits are exposed.

Boring ID Boring Elevation

(feet MSL)

Approximate Dam Embankment Thickness

(feet)

Approximate Formational Material Elevation

(feet MSL) M1 198.4 2 196.4 M2 194.3 10 184.3 M3 193.5 17.5 176.0 M4 193.8 35 158.8 M5 194.1 36 158.1 M6 194.0 32.5 161.5 M7 193.7 32.5 161.3 M8 192.9 26.5 166.4 M9 193.6 21 172.6

M10 193.0 19.8 173.2 M11 193.5 11 182.5 M12 193.7 0.5 193.2 M13 194.7 0 194.7 M14 194.0 30 164.0 M15 193.7 31.5 162.2

Geocon Project No. S1307-05-01 - 8 - May 10, 2017

Regional geologic mapping (California Geological Survey [CGS], 1992) depicts the site underlain by sedimentary materials of the Eocene-age Ione Formation (Ei). Based on our subsurface investigation and geologic reconnaissance, the site is underlain predominantly by Ione Formation materials and volcanic cobble conglomerate of the Tertiary-age Mehrten Formation (MPvc). We also encountered Quaternary-age alluvium (Qa) underlying the dam at the axis of the drainage. The general geologic setting of the site is depicted on Figure 4.

5.2 Embankment Fill (Qf)

Miller Lake Dam is constructed of fill material (see Figure 2) presumably derived from nearby excavations. The fill material is predominantly clayey gravel with sand (GC), clayey sand with gravel (SC), and lean clay (CL) with gravel, all with varying cobble content. It appears to be derived from the adjacent deposits of Mehrten Formation and Ione Formation sediments. Based on our investigation, the dam does not appear to contain different material zones or drainage zones.

5.3 Alluvium (Qa)

Alluvium at the site is unconsolidated sediment deposited by the creek that was impounded by Miller Lake Dam. It consists predominantly of silty clay with sand and silty sand with gravel. We encountered approximately 5 feet of alluvium underlying the embankment fill material in one boring (Boring M4), where it was underlain by completely weathered siltstone of the Ione Formation. We also observed alluvium in the active drainage downstream from the dam, where it overlies Mehrten and Ione Formation materials (Figures 4 and 5).

5.4 Mehrten Formation (MPvc)

At the site, the Tertiary-age Mehrten Formation deposits are a volcanic cobble conglomerate consisting of moderately cemented, rounded andesitic cobble in a reddish-yellow sandstone/siltstone (sandy/clayey) matrix. The cobble conglomerate contained rounded to subrounded gravel and cobble, with trace boulders up to approximately 2 feet in maximum dimension. We generally encountered auger refusal on the Mehrten Formation materials after drilling approximately 3 to 10 feet into the cobble conglomerate using a Marl M-10 drill rig equipped with 8-inch-diameter hollow-stem augers. However, we drilled 15 feet into the conglomerate in one boring (M14) before encountering auger refusal. In Boring M15, we drilled 10 feet through the Mehrten Formation conglomerate and encountered the underlying Ione Formation siltstone.

5.5 Ione Formation (Ei)

Ione Formation deposits at the site consist primarily of white to yellowish-brown or yellowish-gray, highly weathered siltstone and sandstone. The Ione Formation materials excavate variously as weak, blocky elastic silt (MH) with gravel and sand, lean clay (CL), or silty/sandy clay (CL), or silty clayey sand (SC). At the location of Boring M5, the Ione Formation sandstone was loose to medium dense immediately below the Mehrten Formation.

Geocon Project No. S1307-05-01 - 9 - May 10, 2017

5.6 Groundwater/Seepage

At the time of our investigation, April 3 through 13, 2017, the water surface elevation in Miller Lake ranged from approximately 170.9 feet to 172.5 feet. We encountered groundwater in our borings at various depths during drilling as summarized in Table 5.6.

TABLE 5.6

GROUNDWATER SUMMARY

Note: 1. Groundwater depth at the time of drilling, measured to the nearest ½-foot.

Based on the conditions observed in our exploratory borings, it appears that the impounded water in the lake seeps through the dam cross-section. At a minimum, groundwater/seepage should be anticipated during excavation into the lower portion of the dam cross-section particularly during and following the period when the dam is impounding water. Given that the proposed repairs will require excavation and construction at the lowest portion of the dam, dewatering will likely be necessary.

It should be noted that fluctuations in the level of groundwater may occur due to variations in rainfall, temperature, and other factors. Depth to groundwater can also vary significantly due to localized pumping, irrigation practices, and seasonal fluctuations. Therefore, it is possible that groundwater may be encountered during construction.

6.0 SUMMARY OF LABORATORY TESTING PROGRAM AND TEST RESULTS

Our laboratory testing program generally focused on evaluating the index and engineering properties of the dam embankment material and underlying foundation materials per the general recommendations of EM 1110-1-1804 and EM 1110-2-1906. Our in-house laboratory is accredited by the USACE. We performed the following laboratory tests:

Boring ID Date Boring Depth

(feet)

Approximate Groundwater Depth1

(feet)

Approximate Groundwater Elevation

(feet MSL) M1 April 6-7, 2017 39.5 -- -- M2 April 10, 2017 39.5 -- -- M3 April 10-11, 2017 39.5 -- -- M4 April 3, 2017 39.9 28 165.8 M5 April 3-4, 2017 61.4 33 161.1 M6 April 4, 2017 38.9 28½ 165.5 M7 April 5, 2017 38.8 32½ 161.3 M8 April 5, 2017 37.0 -- -- M9 April 11, 2017 32.5 27 166.6

M10 April 11, 2017 25.5 -- -- M11 April 12, 2017 15.5 -- -- M12 April 6, 2017 9.0 -- -- M13 April 6, 2017 3.0 -- -- M14 April 13, 2017 45.2 27 167.0 M15 April 13, 2017 49.5 27 166.7

Geocon Project No. S1307-05-01 - 10 - May 10, 2017

Visual sample classification;

In-situ Moisture/Density, American Society for Testing and Materials (ASTM) D2216 or D4643;

Grain Size Distribution, ASTM D1140 and D422;

Hydrometer Analysis, ASTM D422;

Atterberg Limits, ASTM D4318;

X-Ray Diffraction Analysis (XRD);

Organic Content, ASTM D2974;

Maximum Dry Density/Optimum Moisture Content, ASTM D698;

Double Hydrometer, ASTM D4221, or Pinhole Test, ASTM D4647;

Permeability, Flexible-Wall, ASTM D5084 (Intact/Remolded Samples);

Unconfined Compressive Strength, ASTM D2166;

Consolidated-Undrained Triaxial 3-Point, ASTM D4767 (Intact/Remolded Samples);

Unconsolidated-Undrained Triaxial Staged, ASTM D2850 (Intact/Remolded Samples);

pH and Resistivity, CTM 643;

Sulfate Content, CTM 417;

Chloride Content, CTM 422.

Laboratory test results are presented in Appendix B. Laboratory testing is still underway at the time of this draft report; complete laboratory test results will be included in the final report for this project.

7.0 EVALUATION OF SOIL PROPERTIES FOR CONSTRUCTION

7.1 Existing Dam Embankment Fill and Alluvium

Table 7.1 summarizes pertinent index and engineering properties of the existing dam embankment fill and alluvium encountered in our borings based on the laboratory testing program results to date. Gradation test results do not account for particle sizes greater than approximately 2 inches due to maximum inside sampler diameters used during drilling activities.

Geocon Project No. S1307-05-01 - 11 - May 10, 2017

TABLE 7.1

INDEX AND ENGINEERING PROPERTIES FOR EXISTING DAM EMBANKMENT FILL

Property / Parameter Test Results

Range Average Percent Gravel (larger than No. 4 Sieve), % 3 - 49 30

Percent Sand (between No. 4 and No. 200 Sieves), % 26 - 52 32 Percent Fines (Silt/Clay) (Finer than No. 200 Sieve), % 23 - 47 38

Atterberg Limits Liquid Limit 27 - 41 35 Plasticity Index 11 - 24 16

USCS Soil Classifications CL, CL-ML, GC, GP, MH, ML, SC, SM In-Situ Dry Density, pounds per cubic foot (pcf) 92 - 133 111

In-Situ Moisture Content, % 5 - 26 15 Maximum Dry Density, pcf (ASTM D698), rock corrected 120

Optimum Moisture Content, % (ASTM D698), rock corrected 13 Maximum Dry Density, pcf (ASTM D698), uncorrected 115

Optimum Moisture Content, % (ASTM D698), uncorrected 15 Organic Content, % 3 - 5 4

Minimum Resistivity, ohm-cm

Pending pH Chloride Content, ppm Sulfate Content, ppm

Effective Cohesion, C, psf Saturated Conditions 150 Effective Friction Angle, 30

Unconfined Compressive Strength, tsf 1.2 Saturated Hydraulic Conductivity, cm/sec 1.15 x 10-8

Dispersion Potential Pending

Fill materials generally consist of a mixture of sandy and gravelly clay (CL) and clayey sands (SC) and gravels (GC) with variable cobble content. Gradation of the sampled fill soil indicates gravel content ranging from approximately 3 to 49%, sand content of approximately 26 to 52%, and fined grained soil content of approximately 23 to 47%. Hydrometer testing indicates that the fine grained soils are generally evenly split between silt than clay. The test results for the fill materials indicated the fine-grained soils behave as lean clay (CL), with the highest Liquid Limit (LL) test result of 41. Preliminary X- Ray diffraction test results indicate the fine-grained (clay) soils are generally composed of kaolinite, with typically minor to moderate expansion potential. Cobble content of the embankment fill is variable and estimated to be on the order of up to 10 to 20% based on drilling observations.

7.2 Formational Material (Ione Formation and Mehrten Cobble Conglomerate)

Table 7.2 summarizes pertinent index and engineering properties of the formational material (Ione Formation and Mehrten Cobble Conglomerate) below the dam embankment fill encountered in our borings. The in-situ dry density and moisture content information in Table 7.2 exclude Boring M5 due to the anomalous formational materials encountered at that boring location.

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TABLE 7.2

INDEX AND ENGINEERING PROPERTIES FOR FORMATIONAL MATERIAL

Property / Parameter Test Results

Range Average Percent Gravel (larger than No. 4 Sieve), % 0 - 41 10

Percent Sand (between No. 4 and No. 200 Sieves), % 35 - 78 61 Percent Fines (Silt/Clay) (Finer than No. 200 Sieve), % 22 - 37 28

Atterberg Limits Liquid Limit 53 53 Plasticity Index 19 19

USCS Soil Classifications CL, CL-ML, GC, GM, MH, SC, SC-SM, SM In-Situ Dry Density, pounds per cubic foot (pcf) 121 - 124 123

In-Situ Moisture Content, % 11 - 17 14 Maximum Dry Density, pcf (ASTM D698), rock corrected 96 - 131 114

Optimum Moisture Content, % (ASTM D698), rock corrected 9 - 25 17 Maximum Dry Density, pcf (ASTM D698), uncorrected 94 - 119 106

Optimum Moisture Content, % (ASTM D698), uncorrected 12 - 27 19 Organic Content, %

Pending

Minimum Resistivity, ohm-cm pH

Chloride Content, ppm Sulfate Content, ppm

Effective Cohesion, C, psf Saturated Conditions Effective Friction Angle, Unconfined Compressive Strength, tsf 2.1 – 3.1 2.6

Saturated Hydraulic Conductivity, cm/sec Pending Dispersion Potential

Formational material generally consists of weathered siltstone/cobble conglomerate that excavates as elastic silt (MH), sandy and gravelly clay (CL), clayey gravel (GC), clayey sand (SC), and silty gravel (GM) with gravel content of approximately 0 to 41%, sand content of approximately 35 to 78%, and fine grained soil content of approximately 22 to 37%. Hydrometer testing indicates that the fine grained soils are generally more silt than clay. The test results for the Ione Formation bedrock indicated the fine-grained soils behave as elastic silt (MH), with the highest LL test result of 53. Preliminary X-Ray diffraction test results indicate the fine-grained soils are generally composed of kaolinite, with typically minor to moderate expansion potential. Cobble content of the formational material is variable and estimated to be on the order of up to 20% based on drilling observations.

8.0 MATERIAL SPECIFICATIONS AND EARTHWORK RECOMMENDATIONS

8.1 Materials for Fill

In general, excavated soils generated from cut operations in the dam are expected to be suitable for use as engineered fill/embankment construction provided they do not contain deleterious matter, organic material, or rock/cementations larger than 6 inches in maximum dimension (will require screening of larger cobble/boulder materials). We anticipate that the majority of these materials will consist of

Geocon Project No. S1307-05-01 - 13 - May 10, 2017 mixtures of gravel, sand, and clay with possible cobbles. Periodic sampling and laboratory testing should be performed to verify that the following properties outlined in table 8.1 are met.

TABLE 8.1

RECOMMENDED PROPERTIES FOR DAM EMBANKMENT FILL

Property / Parameter Requirement

Percent Gravel (larger than No. 4 Sieve) 20% Minimum Percent Sand (between No. 4 and No. 200 Sieves) 20% Minimum

Percent Fines (Silt/Clay) (Finer than No. 200 Sieve) 20% Minimum Liquid Limit 50 Maximum

Plasticity Index 7 Minimum, 25 Maximum Acceptable USCS Soil Classifications CL, SC, GC

Total Unit Weight (at 90% relative compaction) 120 pcf Minimum Effective Cohesion, C Saturated Conditions 150 pcf

Effective Friction Angle, 30º Saturated Hydraulic Conductivity 1 x 10-6 cm/sec (or slower)

Per FEMA 484 (Conduits through Embankment Dams), soils placed adjacent to conduits in an impervious zone should have a maximum particle size of 1½ inches, have at least 50% by weight passing the No. 200 sieve (be fine-grained), and have a Plasticity Index between 10 and 30. Such soil should be placed at 1 to 3 percent wet of optimum.

8.2 Excavation Characteristics

Excavation characteristics will vary at the site depending on location and excavation depths. Table 8.2 summarizes anticipated excavation characteristics in each geologic material identified at the site.

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TABLE 8.2

ANTICIPATED EXCAVATION CHARACTERISTICS

Geologic Unit1 Excavation Characteristics

Dam Embankment Fill (Qaf)

Existing dam embankment fill consists predominantly of mixtures of gravel, sand, and clay with some cobble. We anticipate light to moderate excavation effort with conventional, heavy-duty excavating equipment.

We anticipate excavations will generate material predominantly 12 inches and smaller;

however, some boulder-sized material or debris (12 inches and larger) may also be generated.

Alluvium (Qal)

Alluvium in the project area generally consists of unconsolidated clay and sand. We anticipate light to moderate excavation effort with conventional, heavy-duty excavating equipment.

We anticipate excavations will generate material predominantly 12 inches and smaller.

Formational Material

– Ione and Mehrten

Formation (Ei, Ti)

Ione Formation deposits at the site consist primarily of highly weathered siltstone and minor sandstone. We anticipate moderate excavation effort with conventional, heavy-duty excavating equipment. We anticipate excavations will generate material predominantly 12 inches and smaller.

Mehrten Formation deposits are a volcanic cobble conglomerate consisting of moderately cemented, rounded andesitic cobble in a sandstone/siltstone (sandy/clayey) matrix. The cobble conglomerate contained rounded to subrounded gravel and cobble, with trace boulders up to approximately 2 feet in maximum dimension. We generally encountered auger refusal on the Mehrten Formation materials after drilling approximately 3 to 10 feet into the cobble conglomerate using a Marl M-10 drill rig equipped with 8-inch-diameter hollow-stem augers.

We anticipate moderate to heavy effort with typical heavy-duty equipment. Highly weathered metavolcanic bedrock at the site generally consists of moderately weak to strong, intensely fractured rock that readily breaks down to gravel and cobble-sized (12 inches or smaller) fragments when excavated. Weathering and degree of fracturing generally decreases with depth, and moderate ripping will likely be required at depths below 3 to 4 feet. Use of an excavator- or dozer-mounted impact ripper may be required for excavations extending below about 8 to 10 feet. We do not anticipate that blasting will be required.

With some effort, Mehrten conglomerate generally breaks down to cobble-sized fragments (12 inches or less) when excavated; however, zones of less weathered material are common and are more resistant to breaking down. In addition, some boulder size rock (greater than 12 inches) may also be present within the conglomerate.

Notes: See Figures 4, 5, and 6 for approximate vertical and lateral extents of geologic units.

Excavation trenches should be wide enough to allow for compaction equipment to operate parallel to the conduits.

Temporary excavation slopes must meet Cal/OSHA requirements as appropriate. We anticipate the majority of the soils and weathered rock at the site will be classified as Cal/OSHA “Type B” soil. If active seepage is encountered, the classification should be downgraded to “Type C” soil. Trench wall sloping, benching, the use of trench shields, and the placement of trench spoils should conform to the

Geocon Project No. S1307-05-01 - 15 - May 10, 2017 latest applicable Cal/OSHA standards. The contractor should have a Cal/OSHA-approved “competent person” onsite during excavation and pipe placement to evaluate trench conditions and to make appropriate recommendations where necessary. It is the contractor’s responsibility to provide sufficient and safe excavation support as well as protecting nearby utilities, structures, and other improvements which may be damaged by earth movements.

8.3 Wet Soil Conditions

The contractor should be aware of the moisture sensitivity of clayey and fine-grained soils and potential compaction/workability difficulties. In-situ average moisture content of the existing dam embankment fill materials have moisture contents up to approximately 10% higher than optimum based on testing performed to date. For weathered formational material the difference is approximately 14%.

The upstream portion of the embankment fill/formational material is also likely to have higher water content than the downstream portion. Blending/mixing/disking of excavated soil/formational material should be anticipated to facilitate uniform moisture conditioning prior to use as engineered fill. Due to the fine-grained nature of the soils and in-situ moisture contents (at least locally) well above optimum, additional drying effort to attain moisture contents suitable for compaction should be anticipated regardless of the time of year. Significant drying effort should be expected.

8.4 Backfill and Compaction

All earthwork operations should be observed and all fills tested for recommended compaction and moisture content by a representative of our firm. References to relative compaction and optimum moisture content in this report are based on the American Society for Testing and Materials (ASTM) D698 Test Procedure, latest edition.

The proposed repairs will require excavation into the dam embankment cross-section. After construction of improvements, excavated areas should be properly prepared prior to backfilling. Prior to placing backfill, exposed surfaces should be scarified approximately 6 inches, uniformly moisture-conditioned at or up to 3% above optimum moisture content and compacted to at least 95% relative compaction.

Scarification in exposed, hard bedrock areas is not required. Scarification and compaction operations should be performed in the presence of our representative.

Backfill should be benched into existing adjacent cut slopes as the fill is placed. Benches should roughly parallel the temporary excavation contours and extend at least 2 feet into competent material.

Benching criteria may need revision during construction based on temporary cut inclinations, geometry, and the materials encountered during excavation.

Backfill should be compacted in horizontal lifts not exceeding 8 inches (loose thickness) and brought to final design elevations. Each lift should be moisture-conditioned at or up to 3% above optimum moisture content, and compacted to at least 95% relative compaction.

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Backfill should be ramped up against the conduit at a slope of 6H:1V to help force the soil against the conduit during compaction. Compaction equipment should be operated parallel to the conduit. The use of handheld compactors should be avoided if possible and minimized where necessary.

The embankment should be built such that soils are uniformly compacted to at least 95% relative compaction to the finished face of the completed slope. This may require over-building the slopes and cutting them back. Track-walking is not an acceptable means of slope zone compaction.

Culverts shall have at least one foot of fill over the top of the structure.

9.0 STRUCTURE FOUNDATION RECOMMENDATIONS

The main and secondary spillways will be replaced with precast box culverts. We understand that preliminary design calls for four-cell, six-foot by six foot culverts to be used. We anticipate culvert inverts to be at elevation 186 feet or lower for the primary spillway and elevation 188 feet or lower for the secondary spillway.

The existing control structure and associated outlet are anticipated to be replaced with new reinforced concrete structures. The new outlet will extend along the same alignment and invert elevations as the existing outlet (approximate inlet elevation of 171 feet and outlet elevation of 163 feet). The outlet is anticipated to consist of a single reinforced concrete pipe or box culvert.

Additional details regarding the proposed culverts and the control structure/outlet are unknown at this time.

9.1 Box Culverts / Control Structure Outlet

The main and secondary spillways will be replaced with multi-cell, precast box culverts with reinforced concrete wingwalls/headwalls. The the box culverts will be installed in conventional open-cut excavations. We recommend using a Caltrans Standard Plan Precast Reinforced Concrete Box Culvert.

Based on the subsurface conditions encountered in our borings (M1, M2, M6, M12, and M13), we anticipate that the box culverts and the control structure outlet will be founded on a combination of existing dam embankment fill and/or undisturbed formational material. Due to the variable consistency of embankment fill and formational material, if these structures bear on both embankment fill and formational material additional excavation may be necessary to provide more uniform bearing conditions. Excavations should be observed by a representative of Geocon prior to the placement of precast structures or reinforcing steel and concrete. If unanticipated soil conditions are encountered, foundation modifications may be required.

To evaluate the suitability of using Caltrans Standard Box Culverts, we analyzed settlement and bearing capacity using the effective foundation dimensions and design loading shown on Caltrans’ Standard Plan D80 and D83A, dated October 30, 2015. Based on the results of our analyses, assuming

Geocon Project No. S1307-05-01 - 17 - May 10, 2017 that all foundations are underlain by undisturbed formational material or hard/dense embankment fill, a Caltrans Standard Plan Reinforced Concrete Box Culvert, as detailed on Caltrans Standard Plan D83A and D83B is considered appropriate for the site.

Excavation for the box culvert should be performed in accordance with Caltrans’ Standard Plan A62G, dated October 30, 2015, or similar specification. Excavation width must allow for proper compaction of embankment fill. The excavation sidewalls should be sloped or shored as necessary in accordance with OSHA requirements. In embankment fill areas, overexcavation of at least 18 inches will be required for placement of filter material, where present.

Outlet works replacement design is ongoing. We understand the structure may be replaced with a box culvert (or similar) and new intake structure. For preliminary planning purposes, an allowable bearing pressure for structures placed on weathered formational material or hard/dense engineered fill is 3 ksf.

The excavation bottom should be scarified a minimum of 6 inches, moisture conditioned and compacted to a minimum of 95% relative compaction near optimum moisture content. Scarification in exposed, intact rock is not required. Scarification and re-compaction operations should be performed in the presence of a Geocon representative to evaluate performance of the subgrade under compaction equipment loading.

Culvert/structure backfill material should conform to Section 8.1 of this report. Backfill operations should be performed in accordance Section 8.1 of this report. The backfill should be brought up even on each side of the culverts/structures, and the difference in the level of backfill against the outside walls should not exceed 2 feet at any time. Drainage layer material should conform to Section 10.1 of this report, where present.

9.2 Lateral Earth Pressures

Design of earth retaining structures may be based on the allowable lateral earth pressures summarized in Table 9.2.

TABLE 9.2

LATERAL EARTH PRESSURES

Condition Lateral Earth Pressure, Equivalent Fluid Weight (pcf)

Active Pressure 40 At-Rest Pressure 60 Passive Pressure 375

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Retaining walls not restrained from movement may be designed using active earth pressures. Walls restrained from movement should be designed using at-rest earth pressures. The recommended values above assume drained conditions and a level, properly compacted granular backfill material meeting the recommendations of this report.

10.0 GENERAL CONSTRUCTION RECOMMENDATIONS

10.1 Outlet Pipe Penetration

A drainage layer should be provided around conduits in the downstream zone of embankments. We recommend the use of a filter collar (drainage fill) around the downstream 1/3 length of the conduit per EM 1110-2-2902 (Conduits, Culverts, and Pipes), Section 8.5 of EM 1110-2-1913 (Design and

Construction of Levees), and Section 6.5 of FEMA 484 (Conduits through Embankment Dams). Filter material should meet the requirements of Appendix B of General Design and Construction

Considerations for Earth and Rock-Fill Dams. Care should be taken to minimize segregation of filter material during placement. Use of a collector pipe is also recommended to convey seepage water out of the filter collar.

Filter material placed around conduits should be compacted to at least 95% relative compaction per ASTM D698 modified to consist of a 1-point test on oven-dried filter material.

10.2 Slope Protection / Maintenance

Embankment slope protection should be provided in accordance with General Design and

Construction Considerations for Earth and Rock-Fill Dams, Appendix C.

As with any slope, the finished dam embankment will be susceptible to erosion and surficial degradation when exposed to wave action, rain, and surface runoff. Proper surface drainage directing runoff away from the slope face, rock slope protection, erosion control measures, and best management practice (BMP) devices should be maintained to reduce long-term slope degradation from erosion.

Periodic inspections should be performed on a regular basis to identify and address maintenance needs.

In general, localized slumps deeper than about 2 to 3 feet should be excavated/removed and replaced with engineered fill (compacted to at least 90% relative compaction) that is keyed and benched into the existing, intact slope. Significant erosional features such as deep rills and gullies should be re-graded (smoothed, backfilled, and tracked/compacted). Any repaired areas should be re-vegetated as soon as possible.

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11.0 FURTHER GEOTECHNICAL SERVICES

11.1 Plan Review

We should review the construction improvement drawings prior to final submittal to assess whether our recommendations have been properly incorporated and evaluate if additional analysis and/or recommendations are required.

11.2 Testing and Observation Services

The recommendations provided in this report are…