03_140R2024R0017_9_of_19_0003.pdf

Arroyo Canal Fish Screen and Sack Dam Fish Passage Project

Prepared for

Henry Miller Reclamation District #2131

Semptember 2012

2525 Airpark Drive Redding, CA 96001

Project No. 418544

Contents Section Page

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Acronyms and Abbreviations............................................................................................................................... v

1 Introduction......................................................................................................................................... 1 1

1.1 Background...................................................................................................................................... 1 1

1.2 Project Description .......................................................................................................................... 1 2

1.3 Surface Conditions and Water Levels .............................................................................................. 1 2

1.4 Borrow Sources for Fill Material ...................................................................................................... 1 7

2 Field Exploration .................................................................................................................................. 2 1

2.1 Field Exploration .............................................................................................................................. 2 1

2.2 Laboratory Testing........................................................................................................................... 2 2

3 Geologic Setting................................................................................................................................... 3 1

3.1 Regional Geology ............................................................................................................................. 3 1

3.2 Local Geology................................................................................................................................... 3 1

3.3 Seismicity and Seismic Design Criteria ............................................................................................ 3 1

3.4 Subsidence....................................................................................................................................... 3 3

4 Subsurface Conditions.......................................................................................................................... 4 1

4.1 Soil Material..................................................................................................................................... 4 1

4.2 Groundwater ................................................................................................................................... 4 1

4.3 Expansive Soil .................................................................................................................................. 4 1

4.4 Soil Corrosivity ................................................................................................................................. 4 2

5 Analyses .............................................................................................................................................. 5 1

5.1 Liquefaction Potential and Associated Hazards .............................................................................. 5 1

5.2 Consolidation Settlement ................................................................................................................ 5 2

5.3 Stability and Seepage....................................................................................................................... 5 2

5.3.1 Stability Analyses of River and Canal Structures ................................................................ 5 2

5.3.2 Loading Conditions and Resisting Forces for Stability Analyses......................................... 5 3

5.3.3 Seepage and Piping Potential ............................................................................................. 5 4

5.3.4 Summary of Results ............................................................................................................ 5 4

5.4 Pile Capacity..................................................................................................................................... 5 5

5.4.1 Steel Pipe Piles for North and South Bridges...................................................................... 5 5

5.4.2 Steel Pipe Piles for Log Boom ............................................................................................. 5 5

5.4.3 Steel H Piles for Fish Screen Support ................................................................................. 5 6

5.4.4 Steel H Piles for Trash Rack Support .................................................................................. 5 6

6 Recommendations ............................................................................................................................... 6 1

6.1 Seepage Cutoff Depths .................................................................................................................... 6 1

6.2 Lateral Earth Pressures .................................................................................................................... 6 1

6.2.1 Surcharge of Control Building on Canal Wall...................................................................... 6 2

6.2.2 Groundwater Levels for Lateral Earth Pressure Analyses .................................................. 6 2

6.3 Foundation Alternatives .................................................................................................................. 6 2

6.3.1 Shallow Foundations Bearing on Improved Soil ................................................................. 6 2

6.3.2 Support on Deep Foundations............................................................................................ 6 3

6.4 Selected Foundations ...................................................................................................................... 6 3

6.5 Fill and Backfill ................................................................................................................................. 6 4

6.6 Erosion and Scour Protection .......................................................................................................... 6 4

CONTENTS, CONTINUED

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6.7 Subgrade Preparation...................................................................................................................... 6 5

6.7.1 Transport Channel and Fish Ladder .................................................................................... 6 5

6.7.2 Sack Dam and Canal Structures .......................................................................................... 6 5

7 Construction Considerations ................................................................................................................ 7 5

7.1 Dewatering ...................................................................................................................................... 7 5

7.2 Construction Observation and Testing ............................................................................................ 7 5

7.3 Dynamic Testing of Piles .................................................................................................................. 7 5

8 Limitations........................................................................................................................................... 8 5

9 References ........................................................................................................................................... 9 5

Appendixes

A Test Pit Logs B Soil Boring Logs C Subsurface Cross Sections D Laboratory Test Results E Analyses and Calculations

Tables

1 Summary of Nearby Active Faults ................................................................................................................ 3 2

2 Stability Criteria for River and Canal Structures ........................................................................................... 5 2

3 Summary of Stability Analyses for Sack Dam and Trash Rack Structure ...................................................... 5 4

4 Recommended Sheet Pile Cutoff Wall Tip Elevations .................................................................................. 6 1

5 Recommended Lateral Earth Pressures for Moist and Saturated Soil ......................................................... 6 1

Figures

1 Location Map ................................................................................................................................................ 1 3

2 Proposed Project Site Plan............................................................................................................................ 1 5

3 Boring and Test Pit Location Map................................................................................................................. 2 3

4 Test Pit Location Map and Potential Borrow Areas...................................................................................... 2 5

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Acronyms and Abbreviations ASTM American Society of Testing and Materials bgs below ground surface

CCID Central California Irrigation District cfs cubic feet per second

FHWA Federal Highway Administration

HMRD Henry Miller Reclamation District #2131

NGA next generation attenuation

PGA peak ground acceleration

Project Arroyo Canal Fish Screen and Sack Dam Fish Passage Project

RAP Rammed Aggregate Piers

SPT Standard Penetration Test

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SECTION 1

Introduction This report presents the results of the geotechnical exploration for the Arroyo Canal Fish Screen and Sack Dam Fish Passage Project (Project). The purpose of the geotechnical exploration was to observe surface and subsurface soil conditions in the vicinity of the proposed structures and provide geotechnical recommendations to aid in designing and constructing the facilities. To accomplish this, the scope of work included the following:

Performing a subsurface exploration by drilling 10 soil borings using mud rotary techniques, both on land and over the San Joaquin River and Arroyo Canal waters.

Excavating eight test pits within potential borrow sources for fill and backfill material required to construct the Project facilities.

Performing laboratory testing on selected soil samples to evaluate engineering properties of subsurface materials.

Performing engineering analysis of data to support structural design and estimate performance of structures.

Preparing this report summarizing the investigation and providing geotechnical recommendations.

Henry Miller Reclamation District #2131 (HMRD) has contracted with CH2M HILL to provide environmental, permitting, and final engineering design services for the Project improvements, including the geotechnical exploration described herein.

Within this report, the left side or right side of rivers or canals are referenced as looking downstream.

1.1 Background

In 1988, a coalition of environmental groups, led by the Natural Resources Defense Council, filed a lawsuit challenging the renewal of long term water service contracts between the United States and the Central Valley Project Friant Division Contractors. After more than 18 years of litigation, a Stipulation of Settlement (Settlement) was reached. On September 13, 2006, the Settling Parties, including Natural Resources Defense Council, Friant Water Users Authority, and the U.S. Departments of the Interior and Commerce, agreed on the terms and conditions of the Settlement, which was approved by the U.S. Eastern District Court of California on October 23, 2006. The Settlement establishes the following primary goals:

Restoration Goal � To restore and maintain fish populations in �good condition� in the mainstem San Joaquin River below Friant Dam to the confluence with the Merced River, including naturally reproducing and self sustaining populations of salmon and other fish.

Water Management Goal � To reduce or avoid adverse water supply impacts on the Friant Division long term Contractors that may result from the interim flows and restoration flows provided for in the Settlement.

To achieve the Restoration Goal, the Settlement requires channel and structural modifications along the San Joaquin River below Friant Dam, releases of water from Friant Dam to the confluence of the Merced River, and the reintroduction of Chinook salmon.

To achieve the Water Management Goal, the Settlement requires the downstream recapture of restoration flows to replace reductions in water supplies to Friant Division long term Contractors, establishes a Recovered Water Account, and allows the delivery of surplus water supplies to Friant Division long term Contractors during wet hydrologic conditions.

Barriers to migration of anadromous and other fish in the San Joaquin River encompass a wide range of both adult and juvenile fish passage impediments. Fish passage in the San Joaquin River has been blocked since the 1940s, when the river was dewatered below Sack Dam, except during uncontrolled flow releases in wet years. The Settlement requires restoration of flows to the San Joaquin River, improvements in fish passage at various

1 INTRODUCTION

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structures, and actions to prevent fish entrainment at certain structures and sloughs. The Fisheries Management Plan identifies potential actions, consistent with those recommended in the Settlement, to provide fish passage and to reduce entrainment.

The Settlement required improvements at Arroyo Canal and Sack Dam will be designed, built, and operated in accordance with Public Law 111 11 and the Memorandum of Understanding between the Bureau of Reclamation and HMRD.

1.2 Project Description

The Project site is located within Section 12, Township 11 South, Range 13 East, approximately 7 miles east of Dos Palos, California, at the confluence of the Arroyo Canal and the San Joaquin River. The Project location is shown on Figure 1.

The purpose of the existing Sack Dam is to divert water into the Arroyo Canal for irrigation purposes on lands of HMRD. The existing dam will be demolished and replaced with a new dam approximately 100 feet upstream of the current location.

The facilities proposed to improve fish passage and flow management are shown on Figure 2. The following key components are included in the Project:

Construct a new Sack Dam to accommodate fish passage and improve operational control under the scheduled restoration flow regime. The dam will be constructed of concrete slab and piers with pneumatic crest control gates between the piers.

Demolish the existing Sack Dam structure. The river bottom will be graded flat across the location of the existing dam.

Improve stability by constructing an erosion resistant embankment on the right side (east overbank flow area) of the San Joaquin River channel between the east abutment of the proposed Sack Dam and adjacent levee.

The height of the embankment will be equal to the maximum elevation of the proposed Sack Dam gates.

Construct a 700 cubic feet per second positive barrier fish screen structure within Arroyo Canal in a vee configuration. The fish screen will be supported within a rectangular concrete channel structure.

Construct a trash rack structure at the head of Arroyo Canal with an automated raking mechanism. A log boom will also be installed upstream of the trash rack to deflect large floating debris from entering the Arroyo Canal channel.

Construct a transport channel/fish ladder to convey both downstream migrating fish and accommodate upstream migrating fish past Sack Dam. The transport channel and fish ladder will consist of sheet pile walls with a concrete base slab and weirs. The channel will discharge to the San Joaquin River immediately downstream of the new Sack Dam.

Construct a control building to accommodate mechanical, electrical, and instrumentation and control equipment, and an equipment storage building to secure maintenance and operation equipment. These structures will be supported on shallow foundations.

Replace the existing bridge across Poso Canal to accommodate Project operation and maintenance equip ment, and extend the Poso Canal structure. Construct an additional new bridge across the Poso Canal near the termination of Valeria Avenue.

1.3 Surface Conditions and Water Levels

The unlined Arroyo Canal is bounded by levees on each side. The Arroyo Canal levees were reportedly constructed from earth materials excavated from the canal channel. The height of the levees has been increased periodically using sediment dredged from the canal.

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The abutment areas around the existing Sack Dam have been periodically eroded during flood events, and various types of riprap and concrete debris have been used to backfill and protect the eroded areas. A scour hole exists immediately downstream of the existing Sack Dam near the left abutment.

The Poso Canal is owned by Central California Irrigation District (CCID), and crosses over the top of the Arroyo Canal through a concrete flume/bridge structure. The Arroyo Canal headworks structure is located approximately 300 feet downstream (west) of the Poso Canal crossing. The new fish screen will be located between the Poso Canal crossing and the Arroyo Canal headworks. The maximum canal water level considered in design of the Poso Canal is elevation 129.5 feet. Elevations reported within this report are in reference to the CCID vertical datum.

The CCID vertical datum was referenced to the NGS monument located on the Bridge/Poso Canal Flume at elevation 132.25 feet (CCID datum). The CCID vertical datum can be converted to NAVD88 using the following conversion equation:

CCID Datum (132.25 feet) � 2.2 feet = NAVD88.

The water level upstream of Sack Dam and within the approach to the Arroyo Canal headworks is approximately flat, but can vary depending on the flow being passed down the San Joaquin River and the Arroyo Canal. The top of the gates at the proposed dam will be set at a maximum height of elevation 122.0 feet (CCID vertical datum).

At any river flow greater than 45 cubic feet per second (cfs), selective pneumatic crest control gates on Sack Dam will start to lower to maintain a water surface elevation of 121.5 feet upstream of Sack Dam. When the San Joaquin River flow exceeds 1,550 cfs, the dam gates are completely down and the water level becomes uniform upstream and downstream of the dam. The maximum flood level considered in design of the Project is a river flow of 4,500 cfs, resulting in a water surface elevation of 125.6 feet at the proposed Sack Dam.

The critical design condition for the dam and canal structures is when there is a differential water height from upstream to downstream, creating lateral force on the structures from water pressure. The normal operating detained water level used to design Sack Dam is elevation 122.0 feet. For the trash rack structure, the maximum detained water level is elevation 126.0 feet (top of bulkhead) to account for flood conditions with the installed bulkheads. For the Fish Screen structure, the water will be approximately level across the screen except for minor head losses.

1.4 Borrow Sources for Fill Material

The right side levee of the Arroyo Canal has been built up with sediment dredged from the bottom of the canal over the years. The amount of soil available for fill and backfill of the new facilities varies from approximately 1 to 6 feet in thickness across the top of the levee. The soil material consists of fine sand, silt, and clay. The material is acceptable for construction, but may present challenges for achieving compaction. The soil contains clay balls with a high moisture content, and will require mixing or drying prior to compaction.

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SECTION 2

Field Exploration

2.1 Field Exploration

The field exploration was conducted during November, 2011, and consisted of excavating 8 test pits and drilling 10 soil borings at the locations shown on Figures 3 and 4. The locations shown are based on measurements from existing features using a fiberglass tape.

Four test pits were excavated within the east river overbank flow area where shown on Figure 3. The test pits were advanced to a maximum depth of 9 feet, but generally were terminated because of severe caving of the sidewalls. Four additional test pits were excavated within the right levee of the Arroyo Canal, where shown on Figure 4. The purpose of these test pits was to evaluate potential borrow materials for use as fill and backfill material. The east overbank flow area was being considered as a potential borrow source at the time of the field exploration, but has since been removed from consideration. The test pits were backfilled immediately after the materials and conditions encountered were recorded on test pit logs. The test pit logs are included in Appendix A.

The borings were drilled by Gregg Drilling of Martinez, California, using mud rotary methods to a maximum depth of 75 feet below existing ground surface (bgs). The borings within the San Joaquin River and Arroyo Canal were drilled using a CME 45 rig mounted on a barge, and the land borings were drilled using a Failing 1500 truck mounted rig. The floating barge was secured at the drill locations using steel spuds embedded into the riverbed.

In situ testing and soil sampling were performed in borings using the Standard Penetration Test (SPT). The SPT was performed in accordance with American Society of Testing and Materials (ASTM) D1586 at approximately 5 foot intervals. An automatic trip hammer was used. The SPT provides a disturbed sample of the soil and an empirical indication (N value) of the soil density or consistency. A modified California 2.5 inch, split spoon sampler was also used in an attempt to obtain intact samples for laboratory testing of a less disturbed specimen, preserved in brass liners placed within the sampler.

A Shelby tube sampler, which consists of a 3 inch inside diameter, thin wall steel tube, was also was used in fine grained soil materials that were encountered during the subsurface exploration. The steel walls are tapered and sharpened at the base to reduce disturbance to the soil during sampling. Relatively undisturbed samples were obtained by pushing the Shelby tubes for a distance of up to 2.5 feet into the soil, or until refusal, using the drill rig hydraulics.

All field exploration was directed by CH2M HILL geotechnical personnel. The soils encountered were visually classified in the field in general accordance with ASTM D2488 (visual manual procedure for description of soils).

The soil classification description and boring logs are presented in Appendix B. The boring logs summarize the methods used, soil sample intervals, sampling data, laboratory testing, soil types, and conditions encountered.

Where laboratory tests were available, the soil classification was also evaluated in accordance with the Unified Soil Classification System (ASTM D2487), and the soil classifications on the logs were updated if necessary.

The material types encountered are presented graphically on subsurface cross sections within Appendix C. These graphical logs are a simplification of the highly stratified soil material, and the boundaries between different soil types are for visual clarity only, and may not represent the stratifications that may be present between soil sample locations. The test pits are not shown on the graphical cross sections.

The elevation of the ground surface adjacent to each boring was approximated from topographic data from an aerial survey completed in 2011. The elevation of the ground surface or mudline under water was based on the measured water depth at the boring location subtracted from the water elevation that was observed at the existing Sack Dam, and assuming a level water surface from the dam throughout the Project area. The accuracy for all borings is approximately plus or minus 1 foot in elevation.

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2.2 Laboratory Testing

A laboratory test program was implemented to determine soil characteristics of the materials encountered within the soil borings and test pits. Testing included the following:

Atterberg limits (ASTM D4318) Sieve analysis (ASTM D422) Consolidation tests (ASTM D2435) Percent finer than No. 200 sieve (ASTM D1140) Moisture content and dry density (ASTM D2937) Consolidated drained direct shear test (ASTM D3080) Consolidated undrained triaxial shear tests with pore pressure measurements (ASTM D 4767) Moisture density relationship, or compaction curves (ASTM D1557) Unconfined compressive Strength (ASTM D2166) Hydraulic conductivity tests (ASTM D5084) Soil corrosivity suite of tests (minimum resistivity, pH, chloride, sulfate)

Laboratory test results are included in Appendix D.

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SECTION 3

Geologic Setting

3.1 Regional Geology

The Project site is located near the center of the Great Central Valley Physiographic Province of California. The Great Central Valley is a northwest trending basin approximately 450 miles long by 50 miles wide. The Great Central Valley province is divided into the piedmont alluvial plain of the western San Joaquin Valley and the floodbasin of the San Joaquin River.

The floodbasin division underlies the Sack Dam Project area (Lettis, 1982). This division varies in width from 3 to 18 miles wide. The ground surface is gently sloped northwestward at an average gradient of approximately 3 to 5 feet per mile along the axis of the basin and is infilled with floodplain and river channel deposition. In the past under natural conditions, early summer snow melt from the Sierra Nevada to the east caused the San Joaquin River to overtop its banks and flood the basin. These floods are now contained within various impoundments in the foothills of the Sierra Nevada and flow is maintained within the river channels and canals by artificial levees.

The basin is bordered by Mesozoic platonic, volcanic, and metamorphic rocks of the Sierra Nevada mountains on the east and by Mesozoic and Cenozoic metamorphic and sedimentary rocks of the Coast Ranges on the west.

3.2 Local Geology

The Project area is underlain by Holocene deposits of the Dos Palos Alluvium (Lettis, 1982). Beneath Sack Dam and within the San Joaquin River channel, the alluvium is distinguished as generally coarse grained, arkosic channel deposits of Sierra Nevada provenance. Beneath the fish screen and canals, the alluvium is distinguished as fine to coarse grained, arkosic, terrace levee, point bar, and abandoned channel deposits of Sierra Nevada provenance.

The area to the east of the San Joaquin River channel is underlain by the Modesto Formation of Pleistocene geologic age (Lettis, 1982), which consists generally of fine grained, arkosic lower fan deposits of Sierra Nevada provenance.

3.3 Seismicity and Seismic Design Criteria

The Project is subject to ground shaking from earthquakes originating on various California faults and random earthquake sources. Review of the USGS fault and fold database for the Project vicinity (USGS, 2006) indicates that no faults are known to pass through the Project site. A number of fault systems are present at the perimeter of the Central Valley basin and in the adjacent ranges, generally running parallel in a northwesterly direction. The nearest active fault, defined as a fault with evidence of surface displacements within Holocene time, or within about the last 11,000 years, is the Ortigalita Fault, located approximately 19 miles west of the Project site. Active faults within approximately 60 miles of Sack Dam are summarized in Table 1. Characteristic seismic events originating on these active faults are unlikely to produce a peak ground acceleration (PGA) exceeding 0.16g at the Project site, based on a deterministic analysis of wave attenuation over the distance to the Project area, using the Boore Atkinson next generation attenuation (NGA) relationship (Boore et al., 2007). The probabilistic based PGA is slightly higher than the deterministic value as discussed below.

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TABLE 1

Summary of Nearby Active Faults Geotechnical Exploration Report Arroyo Canal Fish Screen and Sack Dam Fish Passage Project

Fault Name Distance from Project (miles and direction)

Characteristic Magnitudea

Slip Rate (millimeters/year)a

Great Valley, Segment 9 19 west 6.6 1.5

Ortigalita 27 west 6.9 1

Foothills Fault System 32 east 6.5 0.01

Quien Sabe 42 west 6.4 1

Calaveras 45 west 6.4 15

San Andreas (creeping section) 47 west 6.5 34

Sargent 53 west 6.8 3

Zayante Vergeles 55 west 6.8 0.1

San Andreas (1906 Rupture segment) 57 west 7.9 24 a Characteristic magnitudes and slip rates are based on values either used by USGS to develop 2002 National Seismic Hazard maps or summarized in USGS, 1996.

A total of 45 earthquakes were identified in earthquake records from the last 200 years that had magnitudes greater than 5.0 (M5.0) within a 60 mile radius around the site. The largest earthquake to affect the Project area was the Coalinga Earthquake that occurred on May 2, 1983, with a magnitude of 6.4. The Coalinga Earthquake originated approximately 52 miles south of Sack Dam. The nearest earthquake event was a magnitude 5.0 event that occurred 31 miles southwest of the Project site in 1926 near Panoche Valley.

Potential strong ground motion at the Project site was estimated using probabilistic data from the national seismic hazard maps (USGS, 2008). The maps indicate that the PGA at the Project site with a 10 percent probability of exceedance in 50 years is 0.18g. This probability corresponds to a return period of about 475 years.

The mapped value is for a soft rock site condition (Site Class B), which needs to be adjusted for the soil site condition encountered at the Project site (a stiff soil site or Site Class D). A site amplification factor of 1.19 was used to result in a design PGA of 0.21g for the Project site.

The USGS deaggregation analyses showed that the dominant earthquake source contributing to the seismic hazard at the site is a magnitude 6.4 event at a distance of approximately 20 miles from Sack Dam. The source for the dominant earthquake was within the area of the Great Valley Fault.

For design of structures subjected to seismic loads, a soil site class of �D� may be used in accordance with the 2009 International Building Code (IBC). The site class was determined based on the standard penetration test (SPT) field N values for the materials encountered within the borings during the field exploration. The mapped spectral accelerations (Site Class B) for short periods and at 1 second period ground motion are 0.78g and 0.29g, respectively. These values should be corrected for site class �D� soil at the Project site to obtain ground surface design values for seismic loads in accordance with the IBC.

The bridges over the Poso Canal will be designed for seismic loads in accordance with Caltrans Seismic Design Criteria (Version 1.6, 2010). In general, the Design Spectrum is defined as the greater of a probabilistic spectrum based on a 5 percent in 50 years probability of exceedance (or 975 year return period), a deterministic spectrum based on the nearby faults, or a minimum spectrum considering a magnitude 6.5 earthquake on a strike slip fault located 12 kilometers from the Project. The deterministically controlling fault is the Great Valley Fault with a maximum earthquake magnitude of 7.0. The probabilistic spectrum exceeded both the minimum spectrum and the deterministic spectrum, with a peak ground acceleration of 0.27g and a maximum spectral acceleration of 0.58g at a period between 0.2 to 0.3 seconds. The site soil profile is Type D based on measured SPT values during site exploration, with an approximate shear wave velocity of 250 meters per second. The bridge structure is short

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and will have a period less than 0.5 seconds; therefore, the standard 5 percent damped Acceleration Response Spectrum curve may be used without modification.

3.4 Subsidence

Subsidence has been ongoing within the San Joaquin valley due to groundwater withdrawal beginning in the mid 1920s, and increasing notably around 1945 (Galloway et al., 1999). In the period from 1926 to 1970, subsidence of approximately 2 feet in the vicinity of Sack Dam was estimated based on surveys by the U.S. Geological Survey (Ireland, 1983). The average rate of subsidence was between ½ to ¾ inch per year during this period.

Some areas of the San Joaquin Valley have experienced much greater rates of subsidence, such as 10 miles southwest of the town of Mendota, where close to 30 feet of subsidence was measured from 1926 to 1981.

Importation of surface water to the San Joaquin Valley began in the 1950s via the Friant Kern Canal and the Delta Mendota Canal. As a result, groundwater levels have recovered within many areas of the San Joaquin Valley, and subsidence has either slowed considerably or become negligible. The storage capacity of the aquifer has decreased due to consolidation, and the groundwater level quickly drops when pumping is resumed during drought years. During periods of drought in 1976 to 1977 and 1987 to 1991, subsidence was observed to increase when groundwater pumping was resumed temporarily.

More recently, in 2004, continuous operating reference stations were installed to monitor subsidence at the Mendota Dam, approximately 15 miles southeast of Sack Dam, and at check structure No. 18 on the Delta Mendota Canal, approximately 10 miles southwest of Sack Dam. Records provided by CCID indicate that these two areas have experienced subsidence of up to an average of 0.5 inch per year. The estimated subsidence from 1926 to 1970 at Mendota Dam was approximately 6 feet, or 1 to 2 inches per year, and at check structure No. 18 was approximately 12 feet, or approximately 3 to 4 inches per year (Ireland, 1983). The recent rate of subsidence appears to have slowed to less than 25 percent of the 1926 to 1970 rates.

For farms on the east side of the San Joaquin River near Sack Dam, surface water delivery is not available to the majority of lands adjacent to, or near, the river. Wells have recently been installed for irrigation, and a significant increase in subsidence in the vicinity of Sack Dam (more pronounced east of the San Joaquin River) has been measured from 2008 to the present time. A network of survey monuments is currently being monitored by the Bureau of Reclamation to record ongoing subsidence as part of the San Joaquin River Restoration Project. The subsidence rate at Sack Dam has been increasing since 2005, and appears to be subsiding at a rate of approximately 0.5 foot per year during the period from 2010 to 2011. The subsidence rate around the perimeter of the HMRD water delivery service area appears to be subsiding at a rate of 0.2 to 1.6 inches per year. If differential subsidence continues at the current rates, it is likely that water delivery will be affected significantly.

The study of subsidence in the vicinity of Sack Dam is ongoing, and conclusions and a plan of action will be developed as more data become available.

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SECTION 4

Subsurface Conditions

4.1 Soil Material

The Project area is underlain by alluvial deposits consisting of mixtures of fine to medium sand, silt, and clay soil materials. The soil is stratified in layers varying in thickness from a couple of inches to greater than 10 feet. Gravel was not encountered within the soil borings. Some hardened clay pieces up to ¾ inches in dimension were present and appeared as gravel on the soil gradation laboratory tests. One cobble up to 6 inches in dimension was observed at the test pit locations on the right side levee of the Arroyo Canal, deposited within the artificial fill material.

The sand material is variable in density, but is generally medium dense to dense except within the upper 10 feet of the Arroyo Canal. The silt and clay layers are generally stiff and over consolidated to some degree. There are localized zones of loose sand or soft clay, but these zones are not continuous between soil boring locations.

The majority of fines are of low plasticity, with a plasticity index less than 12. High plasticity soil, with a liquid limit greater than 50 or a plasticity index greater than 25, was not encountered.

Levees have been constructed along the Arroyo Canal, the Poso Canal, and the San Joaquin River. The levees within the areas explored consist of fine sand, silt, and clay soil, likely borrowed from the canal excavations based on the similarity to the native soil materials. The thickness or depth of artificial fill material on the levees can be approximated by comparing the elevation of the natural ground surface outside of the levees, and varies up to a maximum of approximately 10 feet. The clay material from within the test pit excavations was in the form of clay balls or �chunks� of clay.

4.2 Groundwater

Groundwater was encountered within the soil borings at depths near the water level within the San Joaquin River and Arroyo Canal. The water level within the San Joaquin River and Arroyo Canal varied during the field investigation because the water was being drained from the Mendota Pool, located approximately 23 miles upstream of the Project, during the week of drilling. The water level at Sack Dam was between elevation 119 and 120 feet during the field investigation.

A stabilized groundwater level within the soil borings was not possible to measure because the borings were full of drilling mud continuously, and the holes were grouted immediately after reaching final depth. Free water was visible in some of the soil samples, indicating saturated conditions, which provided an apparent groundwater level between the sampling intervals. The moisture condition is described on the soil boring logs (Appendix B) as �wet� where free water was observed in a soil sample. The degree of saturation was also calculated where moisture and density tests were determined, assuming a specific gravity of 2.7 for the soil, to estimate the phreatic water level.

The apparent water levels at the soil boring locations are shown on the subsurface cross sections included in Appendix C. The apparent groundwater level at the boring locations was within approximately 2 feet above and 5 feet below the water surface elevation in the river and Arroyo Canal. It is likely that saturated conditions above the water level in the river and canal were elevated by capillary action of the fine grained soil materials. In general, groundwater levels are expected to approximately match adjacent water bodies or irrigated fields.

There is a potential for groundwater levels to be elevated adjacent to the Poso Canal due to water infiltration from the unlined portions of the canal. The maximum water level within the Poso Canal is approximate elevation

129.5 feet.

4.3 Expansive Soil

High plasticity clay soil, or fat clay, was not encountered within the soil borings. Out of 46 Atterberg limit test results, only 2 tests had a plasticity index greater than 20. The risk of adverse consequences to the Project from

4 SUBSURFACE CONDITIONS

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expansive soil is low, based on typical ranges in Liquid Limit and Plasticity Index that exhibit expansive behavior (Nelson et al., 1992). No mitigation measures for expansive soil are required.

4.4 Soil Corrosivity

Laboratory testing was performed to determine the pH, resistivity, and chloride and sulfate contents of the native soil. One test was performed on shallow soil from 3 feet beneath the San Joaquin River bottom, and another from beneath the levee on the right side of the Arroyo Canal at a depth of 19 feet. The test results are included in Appendix D. Minimum resistivity of the two samples was low, chloride and sulfate content is significantly low relative to levels of concern, and pH is slightly alkaline. Based on the test results, the native soil should be considered moderately corrosive to buried ferrous metals due to low resistivity. The native soils are not expected to be corrosive toward buried concrete and cement mortar surfaces.

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SECTION 5

Analyses

5.1 Liquefaction Potential and Associated Hazards

Liquefaction is described as the sudden loss of soil shear strength due to a rapid increase of soil pore water pressures from cyclic loading during a seismic event. During seismic shaking, pore water pressure can build up until shear strength is significantly reduced. The potential adverse effects of liquefaction include ground settlement, ground cracking and expulsion of water and sand, the partial loss of bearing and confining forces used to support loads, increased lateral soil pressure, buoyancy, and lateral spreading.

Liquefaction occurs in soils located below groundwater level (saturated). Loose granular soils (sand, silty sand, sandy silt, and some gravels, usually associated with young geologic age) are particularly susceptible to liquefaction. Some clay and silt soils of low plasticity are also susceptible to liquefaction.

The alluvial soils encountered during the field exploration were generally dense or cohesive and not subject to liquefaction from the design ground acceleration (475 year return period), except for the upper 9 to 10 feet of soil material within the Arroyo Canal, where loose sand was encountered. Potential liquefaction of these loose sand deposits is discussed below.

The liquefaction potential was evaluated quantitatively based on SPT sampler penetration resistance (N values) observed in the drilled borings. Penetration resistance indicates the existing relative density or consistency of the underlying soil deposits, which correlates to liquefaction potential. The measured N values were corrected as described below to determine normalized blowcounts for use in the liquefaction analyses.

The liquefaction analyses were performed in accordance with the procedures that were developed by consensus of the participants of National Center for Earthquake Engineering Research workshops (Youd et al., 2001). The potential for liquefaction is estimated by calculating the estimated cyclic stress ratio induced by the design ground motion and compared with the capacity of the soil to resist liquefaction, expressed in terms of the cyclic resistance ratio. A maximum ground acceleration of 0.21g and an earthquake magnitude of 6.5 were used in the analyses, corresponding to the 10 percent probability of exceedance in 50 year ground motion and a characteristic magnitude earthquake event on the nearest faults, respectively. The risk of liquefaction is considered significant where the ratio of cyclic resistance ratio to cyclic stress ratio, or factor of safety, is less than 1.0.

The calculations for liquefaction potential are included in Appendix E. The factor of safety for liquefaction was calculated to be less than 1.0 for four soil samples out of all the soil sampling performed during the field investigation, three of which were within the upper 9 to 10 feet of soil within the Arroyo Canal between the Poso Canal crossing and the Arroyo Canal headworks. Liquefaction of the upper soil within the Arroyo Canal would lead to loss of bearing support and result in total or differential settlement for the fish screen and fish passage structures. The potential settlement of the fish screen in the event of the design earthquake was 5 inches, based on the methods of analysis presented by Tokimatsu and Seed (1987). To limit damage to the proposed fish screen structure, the liquefiable soil materials should be improved in place, replaced with properly compacted soil material, or the foundation should be deepened to be supported on non liquefiable soil materials below 10 feet depth using piles.

One sample from SB 3 on the north side levee of the Arroyo Canal, at a depth of 25 feet bgs, had a high risk of liquefaction for the design earthquake event. Liquefaction in limited pockets of loose sand material is not likely to cause instability to the proposed Project facilities; however, damage could occur to concrete slabs or asphalt concrete paving from resulting sand boils or localized ground depressions. The hard surfacing and any embankment displacement could require repair in the event that liquefaction were to occur.

Lateral spreading can occur when liquefied zones move downslope or areas overlying liquefied zones move downslope. Liquefiable soils were limited to the bottom of the Arroyo Canal and in a localized zone at 25 feet depth within soil boring SB 3, and are not likely to be continuously connected within the highly variable

5 ANALYSES

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subsurface materials. The risk level of damage to the proposed fish screen structure within the Arroyo Canal due to large scale lateral spreading is considered low.

5.2 Consolidation Settlement

A total of seven consolidation tests were performed for soil specimens collected during the field investigation.

Based on the laboratory test results, the preconsolidation pressure exceeded the existing overburden pressure in all of the test specimens.

The bearing pressures beneath the new Sack Dam, trash rack, and canal structures are relatively low. The bearing pressures are estimated to be between 400 to 900 pounds per square foot, well below the allowable bearing capacity of the soil. The estimated settlement beneath the center of these structures is approximately 1 inch due to consolidation settlement.

The largest potential for settlement is for the fill material on either side of the canal walls at the fish screen, and at the approaches to the trash rack structure. The estimated settlement of the fill material proposed within the Arroyo Canal between the canal structures and the existing levees due to consolidation of the underlying soil material is approximately 2.5 inches.

The time for consolidation depends on the thickness of the various clay layers. The soil is highly stratified, and it would be reasonable to estimate a maximum clay layer thickness of 10 feet, bounded by drainage layers at some point within that distance. Assuming drainage both up and down from a 10 foot thick clay layer, the time to achieve 90 percent primary consolidation settlement was estimated to range from 1 to 14 weeks for the various soils that were tested. For the consolidation settlement of the fill material on either side of the canal walls at the fish screen, half of the estimated total consolidation is anticipated to occur with 3 weeks after backfill is completed.

The risk of adverse affects on the proposed Project facilities from consolidation settlement is low, except for the control building and miscellaneous structures founded on the fill material. Some delay is likely between completion of backfill and construction of the control building. A delay of 6 weeks after completion of backfill is estimated to be sufficient to limit post construction settlement to less than approximately 1 inch, which should be considered in the structural design of the control building.

5.3 Stability and Seepage

5.3.1 Stability Analyses of River and Canal Structures

The Sack Dam and trash rack structures were analyzed for stability against sliding, overturning, and piping underneath the structures. The forces that are anticipated to act on the structures include the water pressure from the river on the dam and trash rack gates, uplift from internal water pressure beneath the structures, earthquake forces, and seepage forces. The upward seepage force at the downstream side of the structures, caused by a differential water head across the structure, can cause heaving of the soil if the seepage gradient is too large. The stability criteria used for analyzing the Sack Dam and Arroyo Canal structures are summarized in Table 2.

TABLE 2

Stability Criteria for River and Canal Structures Geotechnical Exploration Report Arroyo Canal Fish Screen and Sack Dam Fish Passage Project

Condition Sliding

Factor of Safety Overturning Factor of Safety

Minimum Base Area in Compression

(percent) Heave at Toe or

Piping Factor of Safety

Normal Operation 2.0 2.5 100 6

Maximum Design Flood 1.5 2.0 100 5

Earthquake 1.1 1.5 50 Not Analyzed

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The stability results are affected by the depth of the sheet pile cutoffs both upstream and downstream of the structures, because of their effect on the uplift pressure. The uplift pressure reduces the effective stress between the concrete floor slab and the subgrade soil, resulting in lower frictional resistance. A range in sheet pile cutoff depths was analyzed to evaluate the effect on the uplift pressure. The uplift pressure was determined from flow nets created for various sheet pile cutoff depths using the steady state finite element seepage model within the computer program SLIDE.

The frictional resistance along the base of the dam and trash rack is equal to the internal friction angle of the soil (33 degrees) times a friction reduction factor to account for the…