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Preliminary Design Report

Shackelford CrossingCity of Modesto

September 1, 2009

Prepared under the responsible charge of

Randall ODell, P.E.

C29547

1165 Scenic Drive, Suite AModesto, CA 95350


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ODell Engineering Preliminary Design Report

September 2009 i City of ModestoShackelford Crossing

Table of Contents

1.0 Introduction 1

1.1 Background 11.2 Summary of Work and Approach 1

1.3 Authorization 4

2.0 Condition Assessment 4

2.1 Field Investigation 42.2 Condition Assessment 82.3 Topographic Survey 82.4 Geotechnical Investigation 92.5 FEMA Flood Zone 9

3.0 Construction Alternatives 9

3.1 No project 93.2 Open Cut 9

3.3 Trenchless Construction Alternatives 103.3.1 Microtunneling 103.3.2 Horizontal Directional Drilling 11

4.0 Design Concepts /Design Criteria 14

4.1 Existing Utilities and River 144.2 Design Flows 144.3 Pipe Materials and Properties 14

4.3.1 Open Cut 154.3.2 Microtunneling 154.3.3 HDD 15

4.4 Construction Flow Bypass 164.5 Maintenance 174.6 Right of Way 17

5.0 Construction Considerations 18

5.1 Open Cut Design Concept 185.1.1 Open Cut Risks and Mitigation 185.1.2 Geotechnical Considerations

5.2 Microtunneling Design Concept 195.2.1 Microtunneling Risks and Mitigation 195.2.2 Geotechnical Considerations 20

5.3 HDD Design Concept 205.3.1 HDD Risks and Mitigation 25

5.3.1.1 Hydrofracture and Inadvertent Fluid Returns 25

5.3.1.2 Conductor Casing 255.3.2 Geotechnical Considerations 26

5.4 Schedule Implications 265.4.1 Open Cut 275.4.2 Microtunneling and HDD 27

5.5 Construction Easements 275.5.1 Open Cut 275.5.2 Microtunneling 275.5.3 HDD 28


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September 2009 ii City of ModestoShackelford Crossing

5.6 Permanent Easements 325.6.1 Open Cut 325.6.2 Microtunneling 325.6.3 HDD 32

5.7 Golf Course Operations 365.8 Recommended Alignment 36

5.8.1 Open Cut 365.8.2 Microtunneling 365.8.3 HDD 37

5.9 Operations 375.9.1 Flow Control 37

6.0 Geotechnical Investigation 38

6.1 Report 386.2 Boring Logs 38

7.0 Permitting and CEQA Considerations 38

7.1 Project CEQA Needs 38

7.2 Resource Agencies 387.3 NPDES Permit for Stormwater Discharges Associated with Construction

Activity 397.4 City Encroachment Permit 39

8.0 Construction Cost Estimate 39

9.0 Project Schedule 39

10.0 Comparison of Alternatives 39

10.1 Open Cut 3910.2 Microtunneling 39

10.3 HDD 3910.4 Evaluation Criteria 41

11.0 Recommended Project 43

11.1 Summary of Design Conditions and Solutions 4311.2 Total Project Cost Summary 4311.3 Recommended Project 44

Appendix A - Preliminary Design Drawings

Appendix B - Preliminary Geotechnical Report

Appendix C - Opinion of Probable Construction Cost

List of Figures

Figure 1-1 Vicinity Map 2Figure 1-2 Existing Sewer Facilities 3Figure 2-1 (Photo) Tuolumne River at approximate location of crossing (facing north) 5Figure 2-2 (Photo) Tuolumne River at approximate location of crossing (facing east) 5


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September 2009 iii City of ModestoShackelford Crossing

Figure 2-3 (Photo) Abandoned Modesto Tallow Company Plant (from rough off ofDryden Municipal Golf Course second fairway) 6

Figure 2-4 (Photo) Tuolumne River and Dryden Municipal Golf Course (fromabandoned Modesto Tallow Company plant) 6

Figure 2-5 (Photo) Abandoned Modesto Tallow Company plant (facing northeast) 7Figure 2-6 (Photo) Abandoned Modesto Tallow Company plant (facing east towards

Zeff Road) 7Figure 2-7 (Photo) Existing sanitary sewer manholes (from abandoned Modesto

Tallow Company plant) 8Figure 3-1 Schematic of a Microtunneling Operation 10Figure 3-2 Conceptual Microtunneled Crossing Alternative 11Figure 3-3a HDD Pilot Bore Schematic 12Figure 3-3b HDD Reaming and Pullback Schematic 12Figure 3-4 Conceptual HDD Crossing Alternative 13Figure 5-1 Open Cut Proposed Sewer Facilities 22Figure 5-2 Microtunneling Proposed Sewer Facilities 23Figure 5-3 HDD Proposed Sewer Facilities 24Figure 5-4 Open Cut Temporary Construction Easements 29Figure 5-5 Microtunneling Temporary Construction Easements 30Figure 5-6 HDD Temporary Construction Easements 31

Figure 5-7 Open Cut Permanent Easement or Lease 33Figure 5-8 Microtunneling Permanent Easement or Lease 34Figure 5-9 HDD Permanent Easement or Lease 35Figure 10-1 Rating Matrix 42

List of Tables

Table 9-1 Project Schedule 39

List of Acronyms

CCFRPMP Centrifugally Cast Fiberglass Reinforced Polymer Mortar Pipe

CEQA California Environmental Quality ActCSM Cutter Soil MixedDR Dimension ratioEDM Electronic Distance MeasurementFPS Feet per secondFPVC Fusible Polyvinyl ChlorideHDD Horizontal Directional DrillingHDPE High Density PolyethyleneLF Lineal FeetMGD Million Gallons per DayMH ManholeMTBM Microtunnel Boring MachineNOAA National Oceanic and Atmospheric Administration

NOI Notice of IntentNPDES National Pollutant Discharge Elimination SystemOD Outside DiameterPCP Polymer Concrete PipePDR Preliminary Design ReportPVC Polyvinyl ChlorideRCP Reinforced Concrete PipeRWQCB Regional Water Quality Control BoardSWPPP Storm Water Pollution Prevention PlanSWRCB State Water Resources Control Board


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September 2009 iv City of ModestoShackelford Crossing

USA Underground Service AlertUSACE United States Army Corps of EngineersWCSMP Wastewater Collection System Master Plan


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September 2009 1 City of ModestoShackelford Crossing

1.0 Introduction

1.1 Background

The existing City of Modesto sanitary sewer system crosses under the Tuolumne River ata location approximately 1,000 feet west of the intersection of Crows Landing Road andZeff Road. The existing crossing commences on a private property which was formerlyused as a rendering plant by the Modesto Tallow Company on the east side of the river.Flows are conveyed in a pipeline to the west side where it connects to the 66-inch Drydensanitary sewer trunk located in fairway number two of the Dryden Municipal GolfCourse, a City owned and operated facility. See the Vicinity Map (Figure 1-1) for an

overview of the project area. The existing crossing consists of a 400lineal foot (l.f.) 18-inch inverted siphon which was constructed in the 1970s and is reportedly at the end ofits expected useful service life. A previous pipeline crossing was abandoned in place atthe time the existing siphon was constructed. Figure 1-2 (Existing Sewer Facilities)provides an illustration of the existing crossings.

The City of Modesto is planning to replace the existing 18-inch siphon with a newpipeline crossing. A diversion box or manhole would be constructed to control flows asnecessary for maintenance or in the event of failure of the main siphon. The project was

identified in the 2007 Wastewater Collection System Master Plan (WCSMP) as theShackelford Crossing.

1.2 Summary of Work and Approach

This Preliminary Design Report (PDR), prepared by ODell Engineering and BennettTrenchless Engineers, summarizes the results of field investigations, identifies andassesses design alternatives, and recommends a preferred alternative. The following is asummary of the Scope of Work as presented in Exhibit A of the Agreement forPreliminary Design Report for Shackelford Crossing between the City of Modesto andODell Engineering.

Topographic SurveyA field survey to obtain existing topographic data was performed on February 19th,2009. The findings of the topographic survey are discussed further in Section 2.3.

Geotechnical ReportPreliminary borings were performed on March 4thand 5th, 2009 and a preliminarygeotechnical report was prepared. These items are discussed in Section 6 of thisPDR and the full preliminary geotechnical report is included in Appendix B.

Concept ResearchTo facilitate the assessment of the potential design concepts and constructionalternatives for the Shackelford Crossing, the topographic survey, preliminarygeotechnical report, field site investigation, existing City documents and plans, and

City master plans were reviewed and the findings were presented to City staff at ameeting on April 7, 2009. Upon consideration of this data the projects designconstraints were defined. Section 3.0 of this PDR identifies and describes theconstruction alternatives including the no project alternative. Section 4.0addresses design concepts and criteria, section 5.0 provides a discussion ofconstruction considerations, and section 10.0 contains a comparison of alternatives.


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Resource Permitting and CEQA DocumentationPermitting considerations and CEQA (California Environmental Quality Act)documentation are addressed in Section 7. A list of resource agencies which mayneed to be consulted is included. This section also provides commentary on CEQAdocumentation which will be prepared by the City.

Right of Way and Easement AcquisitionsA list of potentially necessary right of way acquisitions and easements is included inSection 4.6. Additionally, construction easements and permanent easements arediscussed in Sections 5.5 and 5.6, respectively.

Cost EstimateAn opinion of probable construction cost was prepared and is presented in AppendixC.

ScheduleA preliminary project schedule was prepared and is included in Section 9.

Preliminary Design ReportThis entire document constitutes the Preliminary Design Report.

1.3 Authorization

The Agreement for Preliminary Design Report for Shackelford Crossing between theCity of Modesto and ODell Engineering was authorized by the City Council on February10, 2009.

2.0 Condition Assessment

2.1 Field Investigation

Site visits were undertaken in February 2009. Figures 2-1 through 2-7 are sitephotographs in the vicinity of the crossing. The existing 400 l.f. crossing extends fromthe east side to the west side. At the time of the survey, approximately 115 l.f. (29%) ofthe crossing length was under the water surface. Approximately 26 l.f. (6%) was underconcrete on the east side, and approximately 259 l.f. (65%) was under the riversidehabitat corridor. See photo, Figure 2-4. Approximately 94% of the overall length of theexisting crossing is through environmentally sensitive areas (river or habitat).

During the field investigation, tentative limits were determined for surveying andlocations were selected for the geotechnical investigation borings.

The work site has physical access on the east side through private property over a paveddriveway to Zeff Road; on the west side, access is available through City property

directly through the golf course, or preferably via a dirt road east of the driving range toNeece Drive. These approaches can provide all-weather access for constructionequipment on both sides of the river.


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Figure 2-5 Abandoned Modesto Tallow Company plant (facing northeast)

Figure 2-6 Abandoned Modesto Tallow Company plant (facing east towards Zeff Road)


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Figure 2-7 Existing sanitary sewer manholes (from abandoned Modesto Tallow Company plant)

2.2 Existing Condition

The existing Shackelford Crossing consists of an 18-inch concrete pipe siphon which wasconstructed in the 1970s. City staff has indicated that this crossing is approaching the

end of its useful service life.

The existing acting siphon has not been inspected or assessed. Mechanical or visualaccess to the pipeline is not feasible since the pipeline is in continuous service. It ispossible that this existing siphon could be retained as a redundant pipeline. Afterconstruction of a new siphon, the existing siphon could be assessed for its potential tocontinue in service as a redundant pipeline.

The crossing which was used prior to the currently active crossing has been abandoned inplace, and is not available to provide redundant service in the event of failure of theactive crossing.

Failure of the existing siphon could result in service interruption, risks to public health,and adverse environmental consequences, as well as associated enforcement actions andfines.

2.3 Topographic Survey

A topographic survey was performed on February 19th, 2009 and a supplemental surveywas performed on March 26th, 2009. This survey included existing features extending200 feet beyond each end of the assumed limits of work. The results of the survey areincluded in Appendix A. A boundary survey has not been prepared but it isrecommended that one be completed during the final design of construction documents.


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3.3 Trenchless Construction Alternatives

Two trenchless construction methods were evaluated for the crossing: horizontaldirectional drilling (HDD) and microtunneling. Descriptions of each method areprovided in the following sections.

3.3.1 Microtunneling

Microtunneling is a specialized pipejacking method that can be used to construct apipeline by sequentially jacking pipes horizontally from a jacking shaft to a receptionshaft. Soil is excavated using a microtunnel boring machine (MTBM). The MTBM is aremote-controlled, guided, slurry shield that can provide continuous support to theexcavation face using both mechanical and hydraulic support. The MTBM is operatedfrom a control container located on the ground surface near the jacking shaft. Theguidance system consists of a laser or theodolite and electronic distance measurement(EDM) device mounted in the jacking shaft communicating a reference line to a targetmounted inside the MTBMs articulated steering head. The MTBM is advanced byhydraulic jacks in the jacking shaft. As tunneling proceeds, pipes are placed behind theMTBM and jacked into place until the MTBM reaches the reception shaft. A schematicof the microtunneling process is shown in Figure 3-1.

Figure 3-1

Schematic of a Microtunneling Operation.

Excavated soil is forced into a chamber behind the MTBM face where it is mixed withwater to form thickened slurry. Pumps cycle the slurry to the surface where a soilseparation plant removes the solids. The recycled slurry is then returned to the face. Theslurry system operates as a closed system of pumps and hoses. Because of the remoteoperation and the closed spoil removal system, routine personnel entry into the pipeline isnot required for microtunneling. The slurry used to convey spoil typically consists

simply of water; however, it may contain additives such as bentonite for suspension andtransport of solids, and to provide gel strength to prevent the slurry from permeatinggranular soils at the heading. The slurry system is pressurized and provides stability tothe excavation face by counterbalancing earth and hydrostatic pressures. The ability toprovide a stabilizing slurry pressure at the face makes microtunneling a preferred methodfor unstable soils, when surface settlements must be minimized, when ground conditionsare loose or soft, or when substantial groundwater is expected.

Microtunneling can be used to install pipes ranging from 18 inches to 102 inches orgreater in diameter. For this project, the two smaller siphons could be installed most

Control container

Separation plantJacking pipe

Reception shaft

Shaft seal

Groundwater level

Jacking shaft

Launch seal

Slurry feed pipeSpoils pipe

Plan view of

jacking shaft

Spoil pump

Jacking pipeLaser

MTBMLaser

Jacking frame

Slurry

pump

Laser target


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efficiently inside a single larger microtunneled casing pipe in a separate operation. Themost likely casing pipe material would be steel, but other choices for jacking pipe includereinforced concrete pipe (RCP), polymer concrete pipe (PCP), and centrifugally castfiberglass reinforced polymer mortar pipe (CCFRPMP). The annular space between thecasing pipe and the installed product pipes would be grouted to eliminate the need toprotect the casing from future corrosion and to restrain the siphon pipes.

Microtunneling drives must be straight-line segments with typical slope limits of lessthan twelve percent. Therefore vertical shafts are typically necessary on each side of thefeature to be crossed. Typical shaft dimensions are approximately 12 to 20 feet wide by20 to 30 feet long for jacking shafts and 10 to 16 feet wide by 12 to 20 feet long forreception shafts. The depths are based partially on the required clearance below thefeature. For the anticipated ground conditions on this project the shafts could beconstructed using interlocking steel sheetpiles, auger drilled casings, secant piles, orcutter soil mixed (CSM) panels.

The vertical shafts necessary for a microtunneled crossing would allow for a shorteroverall siphon length for this project, as the shafts could be constructed immediatelyadjacent to the connection points. However, this option requires that the siphon beconstructed with vertical riser legs on both ends. A conceptual microtunneled crossing

for this project is illustrated in Figure 3-2.

Figure 3-2

Conceptual Microtunneled Crossing Alternative

3.3.2 Horizontal Directional Drilling

HDD is a trenchless construction method whereby a pipeline is installed along an arcingdrill path, beginning and ending at the ground surface, and passing under the conflictingfeature in between. As illustrated in Figure 3-3a, a drill rig is set up on one side of thecrossing and begins by drilling a pilot bore to the exit point. The alignment typicallybegins with a 5 to 20 degree tangent section that transitions to a vertical curve with aradius between 600 and 6,000 feet, depending on drill pipe size, product pipe diameter,product pipe material, and required alignment. After passing beneath the obstacle, the

alignment will rise to the surface at a typical angle of 5 to 18 degrees.


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Figure 3-3a

HDD Pilot Bore Schematic

The pilot bore is then reamed in one or more passes to obtain the required diameterneeded for pullback of the prefabricated pipe string. To provide adequate space in thebore for the pullback of the product pipe string, the bore is reamed to a diameter largerthan the product pipe diameter. For product pipe diameters less than 8 inches, the bore istypically reamed 4 inches larger than the product outer diameter. For product pipesbetween 8 and 24 inches, the bore is typically reamed to 1.5 times the product pipe outerdiameter. For product pipes larger than 24 inches, the bore is typically reamed 12 incheslarger than the product pipe outer diameter. Once reaming is complete, the drill pipe isconnected to the product pipe with a swivel and pulling head at the exit side of thealignment, and pulled into place in one continuous operation, as illustrated in Figure 3-3b.

Figure 3-3b

HDD Reaming and Pullback Schematic

During the pilot bore steering is accomplished using a slanted-face bit and rotating drillpipe. To advance the bore in a straight line, the bit is rotated and advancedsimultaneously. To turn, the operator aligns the slanted face of the bit and advances thedrill stem without rotating. As the bit is advanced, soil resistance develops against theslanted face and deflects the bit in the intended direction.

Guidance of the system for a typical river crossing is accomplished by the use of adownhole wireline steering tool located in a non-magnetic drill pipe, immediately behindthe bit. This tool measures the pitch, clock face position, and magnetic azimuth of the bitand sends the data back to the surface to the drill rig operator. The position of the bit iscalculated after each successive drill pipe has been pushed using the pipe length, averagepitch, and average azimuth angle reported for that reach. Accuracy of the downholewireline system can be improved with the use of an energized surface coil such as theTruTracker or ParaTrack system. These systems create a magnetic field at the groundsurface that can be detected and interpreted by the downhole tool to triangulate theposition of the drill head. An eight to ten gauge copper wire coil must be laid on the


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surface around the bore path with a width between the wire grid equal to at least twice thedepth of the bore. The corners and any bends of the coil are then surveyed prior todrilling so that the induced magnetic field can be predicted. Line and grade tolerances fora typical HDD installation using a downhole steering tool and surface coil are on theorder of plus or minus 2 to 10 feet over the length of the bore.

Drilling fluids consisting of a mixture of water, bentonite and/or polymers are

continuously pumped to the drilling tool during all phases of the installation process.These fluids are used to stabilize the bore, assist the drilling/reaming processes, cool thecutting tools, and lubricate the pipe string. The generated soil cuttings are mixed with theinjected drilling fluids to create a slurry that is removed from the bore using a drillingfluid induced pressure gradient. The bore is filled with the drilling fluid/soil cuttings at alltimes.

HDD can be used in most soil conditions and rock. Additionally, it can be used to installpipelines below the water table and is therefore well suited for river crossings. Cobbles,boulders, and clean gravel soils can cause problems with HDD installations due topotential loss of drilling fluid and collapse of the borehole. However, special designfeatures can be used to reduce risks and accomplish bores through these soils if the lengthof bore through the problem soils can be limited.

HDD is capable of installing cables and pipes ranging from 2 inches to 54 inches indiameter. HDD is often used for river crossings and has been used to install pipelines aslong as 7,000 feet. The equipment can be categorized into three size categories: small,medium, and large rigs. The cost, staging area required, and construction durationincreases as rig size increases. Small HDD rigs are generally used for product pipes up toapproximately 8 inches in diameter, or bundles of smaller 2 to 4-inch pipes. Medium sizerigs can install single pipes or bundles of pipe up to approximately 18 inches in diameterand large rigs are used for larger pipes up to approximately 54 inches, or for very longbores that have high pullback forces. The average required staging area for each of thesize classes is approximately 1,500, 15,000, and 35,000 square feet, respectively. TheShackelford project will likely require a drill rig in the upper medium size range or lowerlarge size range. During final design, detailed calculations will be performed for thedesign bore that will allow for a more precise determination of necessary rig size.

An additional consideration for HDD projects is the risk of inadvertent fluid returns(often referred to as hydrofractures or frac-outs). Inadvertent fluid returns can occurwhen excess drilling fluid pressures cause fluids to escape the bore and surface throughgranular soils, cracks in cohesive soils, or along other natural or man-made conduits.While the drilling fluid is generally a non-toxic mixture of water and bentonite clay,drilling fluid spills are typically viewed as an environmental risk, especially for rivercrossings. Therefore, it is important to design HDD projects to reduce the risks ofinadvertent returns. These risks and measures to minimize them are discussed further inSection 5.3.1.

Figure 3-4

Conceptual HDD Crossing Alternative


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4.0 Design Concepts /Design Criteria

4.1 Existing Utilities and River

The following utility companies were contacted in an effort to determine the location ofutilities in and around the project area:

City of Modesto PG&E AT&T Modesto Irrigation District Kinder Morgan Energy Partners Comcast Level 3 Communications Time Warner Telecommunications Turlock Irrigation DistrictResponses to these inquiries were incorporated into the results of the topographic survey(see Appendix A). The survey also located surface features and Underground ServiceAlert (USA) markings to identify the location of underground utilities. There are severalexisting underground and overhead utilities within the project area, particularly on theeast side of the river at the former tallow plant site. Underground utilities in this areainclude numerous gas, sewer, and, storm drain lines as well as several utility polessupporting various overhead lines. There are two sanitary sewer trunk lines on the westside of the river traversing the golf course property as well as a storm drain line whichdischarges to the river.

The Tuolumne River is approximately 225 feet wide at the location of the crossing (as

measured between the top of bank on each side). The top of bank is approximately 36feet above the river bottom on the east side and 14 feet above the river bottom on thewest side. As measured on February 19, 2009, the river was approximately 2.5 3.5 feetdeep. In addition to the currently active 18-inch sewer siphon crossing the river, thepreviously used siphon consisting of 6-inch, 10-inch, and 18-inch pipes was abandoned inplace beneath the river bed.

4.2 Design Flows

The Shackelford Crossing will carry sewage flows from Areas 8 and 9 of the 2007WCSMP across the Tuolumne River to the 66-inch Dryden trunk line. Per CarolloEngineers, the author of the WCSMP, the ultimate peak flow rate for the crossing is 5.2

million gallons per day (MGD). This flow rate will be used as the design flow for thisproject.

4.3 Pipe Materials and Properties

This project has unusually high risk implications in the event of pipeline or constructionfailure. Each of the alternatives discussed below have preferred pipeline materials notnecessarily included in City Standards.


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4.3.1 Open Cut

Ductile iron pipe is recommended for open cut construction. The DIP should be linedwith an inert material to resist corrosion. A high strength specification, such as C151 isappropriate to this river crossing location.


A jacking pipe casing, most likely steel, is required. The carrier pipe to be installedwithin the casing could be almost any material available in the necessary size including:ductile iron (DIP), high-density polyethylene (HDPE), (CCFRPMP), or polymer concrete(PCP). Lining of the carrier pipeline may be necessary for corrosion resistance in someof the suggested pipe materials. It is recommended that the annular space between thecasing pipe and the carrier pipes is grouted to isolate and protect the siphons and toeliminate the need for corrosion protection for the casing. A preliminary recommendedsize for the casing pipe is 60 diameter to provide adequate room for installing the twinsiphons and annular space grout. Additional commentary on pipe materials for

microtunneled construction is contained in section 3.3.1.

4.3.3 HDD

The primary pipe materials used for HDD installations are high-density polyethylene(HDPE), fusible polyvinyl chloride (FPVC), and steel. Additionally, ductile iron pipewith special flexible joints capable of supporting significant tensile load are available foruse on HDD projects. This pipe material has been successfully used on HDD projects,but is not a common option. HDPE and FPVC are generally preferred for sanitary sewerapplications due to higher flexibility, corresponding tight allowable bend radii, andcorrosion resistance. Steel is generally used for high pressure gas pipelines and for longor deep bores where tensile pullback capacity or buckling collapse of the product pipe isa concern, or when extra protection of a carrier pipe is necessary. The main

disadvantages of steel are its susceptibility to corrosion and the large bend radii requiredto avoid excessive bending stresses. Ductile iron pipe typically has lower pull strengththan steel pipe, and may suffer corrosion if not protected be external means, but has amuch tighter allowable bend radius than steel pipe.

Steel pipe is strong and resistant to rough handling. However, it has some disadvantagesfor use on a sanitary sewer HDD project. First, unlined steel is subject to corrosion. Toimprove corrosion resistance steel pipe can be lined and coated with mortar, coal tar, orepoxy. For small-diameter HDD installations, however, linings cannot be patched aftersections are welded together. Coatings may also become damaged during pullbackthrough granular soils. Therefore, steel is often not practical for use as a sanitary sewercarrier pipe. Unlined steel could be used as a casing pipe with corrosion-resistant carrierpipes installed inside, however this would require a much larger bore and a more costly

two-pass installation. Additionally, HDPE and FPVC can be installed directly to providea corrosion-resistant pipe without the need for a casing.

A second disadvantage of steel pipe relates to the allowable bend radius of the bore. Thedrill path for the HDD bore would follow a large radius arc in passing beneath the river.Therefore, the entrance and exit points must be set back from the banks to allow the pipeto reach the proper depth before passing beneath the river. The radius of this arc controlshow far back the entry and exit points must be located, and the radius is largelydetermined by the type and diameter of the pipe being installed. Steel pipe cannot bebent through short radius curves without risk of yield in bending. The rule of thumb for


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steel pipe is that the minimum allowable bend radius in feet is equal to 100 times the pipediameter in inches. Therefore for an 18-inch pipe, the required minimum bend radiuswould be 1,800 feet. ASCE Manual of Practice No. 108 provides specific guidance onevaluation of steel pipe bending stresses for HDD Installation. If HDPE, FPVC, orductile iron pipe were used, the minimum pipe material bend radius would not be an issuebecause of the much lower stiffness of the plastic pipe materials and the flexible jointring of ductile iron. In practice the minimum bend radius for a plastic pipe or ductile ironinstallation is dictated by the steel HDD drill pipe, which is approximately 750 feet forthe rig size necessary for this project. The space available, for this project, is notpractical for the required setback distance associated with a 1,800-foot bend radius.Additionally, the use of steel pipe would increase the overall crossing lengthsignificantly, adding to maintenance challenges and overall project cost.

Ductile iron pipe suitable for use on an HDD project is produced by one manufacturer inthe United States. American Ductile Iron Pipes Flex-Ring pipe is available in diametersfrom 14 to 48 inches with allowable pull loads and minimum bend radii that would likelybe compatible with the recommended bore design for this project. The Flex-Ring joint iscapable of supporting significant tensile load and allowing the deflections necessary foruse in a curved bore. Therefore, DIP avoids the bore geometry difficulties that steel pipeis susceptible to. However, depending on the owners experience and preferences and the

corrosivity of the native soils, DIP may require corrosion protection measures to ensurereasonable design life. Additionally, the sole-source nature of this pipe material couldlead to increased cost unless DIP is bid alongside HDPE and/or FPVC pipe as an option.

HDPE and FPVC are flexible, corrosion-resistant pipe materials that are well-suited toboth HDD construction and sanitary sewer conveyance. Butt-fusion welded HDPE has along history of successful use on HDD projects. More recently, PVC resins have beendeveloped that allow for butt-fusion welding, increasing PVCs usefulness for HDDapplications. FPVC is a stiffer material than HDPE, allowing for slightly thinner wallsections for the same application, but is also more susceptible to potential brittle failure.While FPVC is fairly new to the HDD market, numerous projects throughout the UnitedStates have been completed with this material.

To ensure that the HDPE or FPVC pipe has adequate pipe strength, pullback capacity,and long-term buckling resistance, calculations must be performed to determine thenecessary dimension ratio (DR) for the pipes. Both pipes come in varying DRsdepending on the interior and exterior pressure requirements. As part of the final design,a full set of installation and long-term service load calculations must be performed todetermine the required DR necessary to prevent buckling or other failure duringinstallation or later during service. Based on past experience with HDD bores of similardiameter and geometry, the required pipe stiffness will likely be DR 11 for HDPE orDR21 for FPVC. Additionally, it is recommended that the pipe be mandrel tested andhydrostatically tested after installation to ensure that the pipe was not damaged duringpullback. To provide an extra layer of security, the prefabricated pipe string can be testedon the ground surface prior to pullback.

4.4 Construction Flow Bypass

West Side:During construction, sewage flows will be rerouted to allow for the connection to existingfacilities. To construct a new manhole on the existing Dryden trunk line, sewage flowsmay be temporarily rerouted to the 60-inch cannery segregation line which is locateddirectly east of the Dryden trunk. If the cannery segregation line is not available, abypass system with pumping can be used.

East Side:


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Connection to an existing manhole on the former tallow plant site will require flows to beblocked in the manholes directly upstream and pumped around to the most downstreammanhole east of the river.

4.5 Maintenance

The installation of two siphons, each capable of handling the design flow independently,will allow for either line to be closed for maintenance without a disruption in service.There are no unusual maintenance issues associated with either HDPE or FPVC pipematerials. The siphons should be designed to achieve a minimum velocity of three feetper second (fps) in order to avoid sedimentation in the line which would mandate morefrequent maintenance.

The pipeline crossings will be constantly submerged with sewage flows. The routinestatic water elevation for the crossing segments will never be lower than the outletelevation. This results in the pipeline being constantly submerged, which presents achallenge for routine cleaning, access, and visual inspection.

Routine cleaning, if required, can be accomplished by pigging the line. A pipeline pigis a device that fits within the pipeline, and is sent through the pipeline by water pressure.

The pig has a slightly smaller diameter than the inside diameter of the pipeline, andeffectively pushes and scrapes debris downstream to the receiving manhole. The pipelinewould be flushed with clean water before and after the pigging operation.

Video cameras can function while submerged in clean water. If desired, the pipeline canbe periodically cleaned and televised for a permanent inspection record.

Complete evacuation of fluid from the pipeline would require a pump to be inserted inthe pipeline, and pushed or pulled to the low point of the profile. It is not expected thatpumping of the pipeline would be a routine necessity. It is possible that pumping of thepipeline may never be required.

4.6 Right of Way

The City currently has easements over the existing pipeline facilities east of the river. Anew permanent easement will be required over all new facilities constructed on privateproperty (Tallow side).

A permanent access easement on the east side should also be required. It appears thataccess historically has been via the paved driveway from Zeff Road. The permanentaccess easement could be flexible to allow the private property latitude for re-development.

The property on the west side of the Tuolumne River is owned by the City of Modesto,and is currently occupied by the Dryden Golf Course. Since the property is City owned,

permanent easements and temporary construction easements are not necessary. Neither isan access easement necessary, since physical access is available through City ownedproperty from the project area to Neece Drive, the nearest public street.

The State Lands Commission has purview for the Tuolumne River. The Commissionwill likely require an amended lease with conditions for the final alignment.

Permanent easements for open cut, Microtunneling, and HDD are shown on Fig. 5-7 to 5-9. Section 5.6 contains discussion of permanent easements.


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Temporary construction easements are shown on Fig. 5-4 to 5-6. Section 5.5 containsdiscussion of temporary construction easements

5.0 Construction Considerations

5.1 Open Cut Design Concept

Please refer to Fig. 5-1 for an overview of the proposed open cut alignment. Open cutwould involve installation of two 18 ductile iron pipes, with new connections to existingpipelines at each end.

Since the pipeline functions as a siphon under pressure, the pipelines can be constructedto follow the existing vertical profile at minimum depths. An exception is the literal riverwater crossing where agency requirements and potential river scour actions dictategreater depths to protect the pipeline.

Open cut construction allows the new connection points on each end of construction to be

approximately same as existing.

Staging areas would be required on both sides of the river crossing. Access issues frompublic streets are similar to other alternatives.

5.1.1 Open Cut Risks and Mitigation

Open cut trenching through an active river and streamside habitat contains risks. Themost serious is weather related. If the construction operation is overwhelmed byunexpected high river flows, the consequences could include unplanned environmentaleffects or damage, permit penalties, and construction delays.

The resource agency permit conditions are not yet known, but it is likely that the permits

will contain rigorous schedules and mitigation factors and costs. A risk associated withopen cut is that unexpected construction difficulties could result in a wider constructionfootprint than anticipated by the permits. Reacting to unforeseen occurrence is a riskassociated with this alternative.

Mitigation for open cut construction should include a sufficiently broad and conservativeconstruction area.

5.1.2 Geotechnical Considerations

The open cut construction method is compatible with nearly any type of soil and rockcondition. Since the open cut method is relatively shallow (8 to 20 feet), only the near-surface soils are a factor in the construction.

On the west side, the soils types are silty sands to a depth of 40 feet. On the east side, thesoil types are silty sands and lean clay to a depth of 40 feet. Soil types below the riversegment are expected to be similar. In these soil types, the open cut method is feasible.For depths greater than 5 feet, a shoring system will be required.

As described in Section 3.2, the open cut method will require a phased cofferdam system.The soil types present are compatible with the cofferdam system. The cofferdam systemdetails would be determined during final design phase.


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The existing soils types would be compatible as backfill on the west side (golf course)and through the river segment. At the east side, during final design, a determination ofappropriate backfill will be made, since this area is private property, and may be subjectto regular vehicular traffic.

5.2 Microtunneling Design Concept

Please refer to Fig. 5-2 for an overview of the proposed Microtunneling alignment. Adetailed discussion of the Microtunneling concept is described in Section 3.3.1.

Staging areas would be required on both sides of the river crossing. This alternativewould include vertical riser shafts at each end of the tunnel. These risers would beconnected to the existing facilities at each end. Access issues from public streets aresimilar to other alternatives.

5.2.1 Microtunneling Risks and Mitigation

A microtunneled crossing for this project would consist of the twin siphon pipes installedwithin a single casing pipe beneath the Tuolumne River. Based on the currenttechnology available in the United States, microtunneling drives are limited to straightsegments with maximum inclination of approximately 12 percent. Because of thelimitations on slope and the requirement for straight drives, microtunneled crossingsrequire vertical shafts for launching and receiving of the tunnel. The advantage ofvertical shafts is the potential ability to begin and end a crossing close to the boundariesof the feature to be crossed, shortening the overall trenchless crossing length. The shorterdrives lengths can help offset the higher unit cost of microtunneling when compared toHDD, but the added cost of the shafts themselves often uses up this savings.Potential settlement resulting from the shaft construction must be considered as a risk tonearby existing facilities, requiring some horizontal separation from the existing buriedutilities. It is important during design to evaluate possible shaft construction methods

available, and provide specifications to the contractor that list only those methods that areappropriate for the project conditions. The plan dimensions and depth of the requiredshafts combined with the saturated ground conditions preclude the use of some commonshaft support types such as speed shores, trench boxes, slide rails systems, and soldierpiles and lagging. For this project appropriate shaft construction methods would likelyinclude interlocking steel sheetpiles, auger drilled shafts, secant pile shafts, cutter soilmixed shafts, and sunken concrete caissons. If appropriate shaft support and excavationmethods are used, risks associated with shaft construction can be minimized.

Microtunneling can provide positive support of the excavation face at all times and alsouses a relatively small annular overcut, reducing the overall settlement potential.However, given the relatively large diameter of the proposed casing pipe (approximately60 inches) it is still prudent to provide approximately 10 feet of vertical cover beneath the

existing sanitary sewers on the west side of the crossing to minimize the risk of damage.During final design a detailed settlement analysis will be completed to fully evaluate therisk of damage and optimize the clearance beneath the existing sewers.

Portal stabilization is another important consideration for microtunneled crossings. Formany shaft types the shaft wall must be breached during launch and retrieval of theMTBM. Supplemental stabilization of the ground outside the shaft is necessary toprevent inflows of soil or groundwater into the shaft during the penetration that couldlead to surface settlement or shaft flooding. Depending on the shaft type, portalstabilization can be provided by many different methods including grouting or other


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ground improvement, double shoring walls, or concrete launch blocks. Some shaft typesthat use concrete or soilcrete walls like secant piles and concrete caissons do not needadditional portal stabilization methods as the MTBM can excavate through the walldirectly. Portal stabilization requirements must be included in the specifications.The vertical siphon risers that would be required with a typical microtunneled crossingcan complicate the flow characteristics of the siphons and present maintenancechallenges at the downstream vertical riser leg. It is possible to construct inclined riserson the downstream end of the siphons to reduce maintenance issues; however this wouldadd additional cost, construction risk, and disruption to the golf course facilities.

Clearance beneath the river bottom is affected by a few factors including hydrofracturerisk, scour protection, and regulatory requirements. The hydrofracture risk for amicrotunnel bore is typically much lower than for HDD construction. Microtunnelingoperations use lower volumes of drilling fluid at much lower pressures, and primarilycontained within the MTBMs slurry chamber. Often as little as 10 feet of cover can beadequate. A detailed hydrofracture analysis will be performed during the final designphase to determine the required depth to minimize hydrofracture risk for this crossing.Scour protection requirements vary based on many flow characteristics of the river andthe particular flood level being designed for. We are not aware of any scour analysiscompleted for the Tuolumne River near the Shackelford crossing. This issue will need to

be coordinated further with the City during final design. Finally, the various regulatoryagencies may have minimum required clearances that must be met. However, we havehad success on previous projects in justifying reasonable clearance limits based onhydrofracture and scour calculations. To provide a conservative depth for planningpurposes, we have proposed a 20-foot vertical clearance in the conceptual design.


The microtunneling method was developed to provide a pipejacking system capable ofoperating in soft and/or loose saturated ground conditions. Since its originaldevelopment many improvements have also been made to allow for construction in

harder ground, and even in full-face rock. Ground conditions that are problematic formicrotunneling include large quantities of cobbles and boulders in a soft ground matrix,soils very high in gravel content, and very soft/loose ground with blow counts below 2blows per foot. Additionally, soils that may contain fill debris such as reinforcedconcrete, steel, or large chunks of wood can pose an obstruction to an MTBM. Theground conditions encountered in the geotechnical investigation do not include theproblematic soils described above and are generally well suited to microtunneling.

5.3 HDD Design Concept

Please refer to Fig. 5-3 for an overview of the proposed sewer facilities. This alternativewould entail the construction of twin siphon pipelines beneath the Tuolumne River tocarry sewage flows from an existing manhole (MH1), located on the east side of the riverin the Modesto Tallow Company property to the existing 66-inch Dryden trunk sewer

located on the west side of the river on the Dryden Golf Course property.

Specific design features related to the site topography and geometry limitations of anHDD installation warrant discussion. The entry and exit angles must be withinreasonable limits. The minimum bend radius that can be achieved in the vertical curvesection of the bore must be compatible with the bending and combined stresses exertedon the drill pipe and product pipe. For the size of rig necessary for this project, theminimum bend radius that can reasonably be achieved based on the drill pipe is 750 feet.For HDPE, FPVC, and DIP the minimum bend radius for the pipe is lower than 750 feetand therefore does not control. Further, to minimize the risk of inadvertent fluid returns


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to the river and to provide future protection from scour, the bore should be sited 30 feetor more below the deepest portion of the river channel. These constraints, combined withthe steep eastern river bank and the proximity of MH1 to the slope, preclude exit of anHDD bore immediately adjacent to the intended manhole. That is, the required clearancebeneath the river, bend radius, entry angle, and allowable drill pipe stresses cannot besatisfied if the HDD bore exits at MH1. The recommended solution to these constraintsis a bore that is designed to surface as close to the east river bank as possible. Thissolution will then require a short section of open-cut gravity sewer to carry flow fromMH1 to a junction box (MH13) located further east on the tallow plant property.

The two existing City of Modesto sanitary sewer lines on the golf course property presenta different constraint. Because the HDD method requires the drilling of a bore largerthan the product pipe diameter to be installed, there is a potential risk of settlementdamage to underground utilities or other facilities that are within close proximity abovethe bore. Further, the sensitive riparian habitat on the west bank of the river precludes asolution where the bore surfaces east of the existing sewers. These factors combine torequire a crossing design that passes beneath the two existing sewers and surfaces on thegolf course property. To mitigate the risk of settlement to the existing sewers andminimize the distance the siphons extend into the golf course property, oversized steelconductor casing should be installed along the intended bore path passing beneath the

existing utilities. This casing should be approximately 110 feet long to support the boreand contain the drilling fluid in the shallow portion of the bore, thereby minimizingsettlement and hydrofracture risk. To ensure that the installation of the conductor casingdoes not cause any damage to the existing sewers, a minimum clearance of five feet isrecommended between the outside diameter of the conductor casing and the invert of the66-inch sanitary sewer. Manholes (MH10 and MH11) will be constructed west of theexisting sewers to direct flow to a short segment of gravity pipe which will connect to anew manhole (MH9) to be constructed on the 66-inch Dryden trunk sewer.


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5.3.1 HDD Risks and Mitigation

5.3.1.1 Hydrof racture and Inadvertent Fluid Returns

Hydrofracture or inadvertent drilling fluid returns to the river channel are aserious concern for any HDD river crossing. Resource agencies are oftenconcerned about the environmental impacts of drilling fluid entering sensitivehabitats. For this crossing, measures are available to reduce this risk, to theextent possible. However, it is understood that this risk cannot be entirelyeliminated. The preliminary depth of the bore was determined based on pastexperience and review of the preliminary geotechnical information to minimizerisk. To further reduce risk, detailed calculations analyzing the potential forhydrofracture should be performed during final design to determine whether thedepth should be adjusted. Additionally, we recommend that a Frac-Out andSurface Spill Contingency Plan be prepared during final design that detailscontractor contingency measures to contain, clean-up, document, and report anyincidents. This plan would be a contract document provided to the contractor

detailing contingency measures in the event of a spill or fluid return. Thecontingency plan is a proactive solution which would facilitate a swift responseand containment of drilling fluid should any reach the surface. Past experiencesuggests that the engineer is in the best position to coordinate with permittingagencies, address their concerns, and ensure the contractor is informed.

To reduce the risk of hydrofracture and inadvertent fluid returns, the HDD boreentry and exit locations should be set back sufficiently from the river channel toprevent any fluid returns at entry and exit from reaching the river. Hay bales,silt fencing, berms, and small entry and exit pits should be used to contain andconfine drilling fluids to a small area. The minimum clearance beneath the riverbottom for the recommended alignment will be approximately 40 feet; this depthof bore further reduces the risks of hydrofracture and inadvertent fluid returns.

Experience suggests that there is some potential for fluid returns very near theentry and exit of the bore, where the surficial layer of soil is loose silty sand.Detailed calculations should be performed during final design to verify this anddetermine the extent of this potential. However, this risk can be minimized onthe entry side with the installation of the recommended conductor casing.

5.3.1.2 Conductor Casing

A conductor casing can be used to alleviate the risks associated with boringthrough the surficial layer of loose silty sand. On the entry side, steel conductorcasing can be installed along the proposed bore path prior to beginning the pilotbore. This consists of driving (usually by pipe ramming) a steel casing pipe,slightly larger than the final planned bore diameter, through the upper layer of

soil to stabilize the soils and prevent loss of circulation or inadvertent fluidreturns. This casing pipe is then augered out and the pilot bore is advancedthrough the casing into the denser soils below. Additionally, the conductorcasing would help to prevent settlement of the exiting 66-inch and 60-inch sewerlines by creating a stable bore with no potential for collapse.

On the exit side, conductor casing cannot be practically used for the pilot bore.Because of the somewhat limited accuracy of HDD, it is not practical to steerthe pilot bore into the end of a preinstalled conductor casing. However, on theexit side only 10 feet of loose silty sand overlay the denser soils, as opposed to


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the 25 feet of loose silty sand on the entry side. Also, even if an inadvertentfluid return does occur near the exit point it can easily be contained within theformer tallow plant site with very low risk of drilling fluid impacting the river orriparian habitat.


The HDD method is compatible with a wide range of soil and rock conditions.Additionally, the bentonite drilling fluid used to support the bore and remove the cuttingsis heavier than water and therefore makes HDD suitable for use below the water table.Ground conditions that are problematic for HDD include very loose, soft, squeezing, orflowing soils that are not self supporting and highly permeable, large-grainedcohesionless soils and fractured rock where drilling fluid losses are high. Specializeddesign features and construction methods can be used to minimize the risks associatedwith these types of ground conditions to allow the use of HDD in certain cases.

For this project, the ground conditions are generally well-suited to an HDD bore. Thesoils encountered in the two borings drilled for the geotechnical investigations consistedprimarily of clean to silty sand with some thin layers of gravel and sand with gravel. Theupper 25 feet of material on the west side of the river consisted of very loose to loose

silty sand. On the east side of the river the very loose to loose silty sand wasapproximately 10 feet thick. Below the loose surficial materials, the consistency of thesoils increased from medium dense to very dense.

Overall, these soils are favorable for drilling. However, the loose materials near thesurface could present some difficulties related to bore stability, settlement, andinadvertent drilling fluid returns. These problematic soil layers are both thicker andlooser consistency on the west side of the crossing. Additionally, the presence of twoexisting sanitary sewers and sensitive riparian habitat on the west side requires that stepsbe taken to mitigate the risk of inadvertent fluid returns and settlement. As previouslydiscussed, it is recommended that steel conductor casing be used to support the bore atthe entry and contain drilling fluids during drilling. After the bore is complete, tremiepipes should be used to pump grout into the annulus between the casing and carrier pipeto fill the space to minimize the risk of future settlement. The exit location on the eastside of the crossing has less than 10 feet of loose soils which pose far lower risks.Therefore, conductor casing is not necessary for this side of the crossing. However, theannulus should be grouted for 100 to 150 feet from the exit to reduce risks of settlementand restrain the pipe.

5.4 Schedule Implications

Scheduling construction during the winter months would avoid the peak golf season andreduce disruption to the golf course. Additionally, construction occurring during thewinter would allow the 60-inch cannery segregation line to be used as a bypass while theconnections are made to the existing 66-inch sewer. Use of the cannery segregation lineduring construction would not be possible during summer canning season.

Construction during winter months could result in more stringent runoff mitigationrelative to the river.

Winter construction could result in more golf course remediation than during dryweather. Wet weather construction mitigation measures such as laying down rock ormats may be required to allow the heavy equipment to move around the job site.

Schedule issues related specifically to the construction alternatives are discussed below.


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5.4.1 Open Cut

Open cut construction is not necessarily restricted to a particular season; however, thepotential for rainfall and unpredictable elevated river flows suggests that the peak rainyseason should be avoided. It is also possible that resource agencies permits would restrictconstruction to a particular time of year.

Temporary cofferdam construction, included in this alternative, is less feasible duringwinter high river flows. Open cut construction is likely to be most feasible duringsummer months, when conditions are dry and river flows are lowest.

The estimated construction time is 75 working days.

5.4.2 Microtunneling and HDD

Microtunneling and HDD are not restricted to a particular construction season andtherefore the work could be scheduled for any time during the year. However therewould be significant difference in the construction duration for HDD construction versusmicrotunneling. While the overall drive length for a microtunnel would be shorter and

only a single bore would be completed, the time required to construct and then to backfillthe shafts, and the time for installation of the carrier pipe and annular space grout wouldincrease the construction duration for the microtunneled alternative by approximately 30to 50 percent.

The estimated construction times for Microtunneling and HDD are 120 and 100 workingdays, respectively.

5.5 Construction Easements

Permanent easements are discussed in Section 5.6. In addition to the permanenteasements, temporary construction easements will be required. The constructioneasements must be sufficient for construction access and staging the work.

An issue common to each construction alternative is access. Since the work is notadjacent to existing public streets, access will be required through private property andthe golf course.

Construction easements particular to each alternative are described below. Constructioneasement and construction access are illustrated on Figs. 5-4 through 5-7.

5.5.1 Open Cut

This alternative will require a construction footprint in the river and through adjacenthabitat areas. A corridor, estimated at 80 wide would allow room for constructionequipment, material transport, excavated spoils, and cofferdam construction and

restoration. Staging areas on both sides of the river will be required. Easementsnecessary for this alternative are shown on Fig. 5-4.


This alternative requires staging areas on both sides of the river. Unlike the open cutalternative, no construction easement in the main river corridor or embankment isnecessary.


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Section 3.3.1 contains commentary on the construction operation. This techniqueeliminates the need for heavy equipment and materials in the river and habitat corridor.The staging areas on either side must be of sufficient size to install the permanent shafts,risers and connection to existing.

Easements necessary for this alternative are shown on Fig. 5-5.

5.5.3 HDD

This alternative requires staging areas on both sides of the river. Unlike the open cutalternative, no construction easement in the main river corridor or embankment isnecessary, except control points for pipeline tracking. HDD methods require a lay-downsurface area for the assembled pipeline, and a more robust staging area on the golf courseside. Easements necessary for this alternative are shown on Fig. 5-6.

A medium to large size horizontal directional drill rig requires approximately 15,000square feet (sq. ft.) of work space on the entry side. There must be 60 to 70 feet availablebehind the entry point to provide space for the rig. Therefore, the entry site for thisproject requires a rectangular work site with minimum dimensions of approximately 150feet in the east-west direction by 50 feet in the north-south direction. This area would

extend from the eastern edge of the golf course property approximately 100 feet into thefairway of the second hole centered on the twin bore alignments. This area wouldprovide sufficient width for the two bores to be drilled with 20 feet of separation betweenthem. The shape of the remainder of the required work area is flexible. Because accessto the site will most likely be from the road which wraps around the tee-box of the secondhole, it is suggested that most of this space be provided as a long strip on the east side ofthe second fairway north of the entry points with sufficient area to the south to completethe open-cut tie-in to the existing 66-inch sewer. It appears that a strip approximately 50to 60 feet wide and 150 feet long to the north of the previously described rectangular areaand 50 to 60 feet wide and approximately 50 feet long to the south of the rectangular areacould remain in the rough and minimize damage to the fairway.

On the exit side, the temporary construction easement should be large enough to allow

the pipe to be laid out as a single string. For this project a strip 800 feet long and 50 feetwide would be required to provide sufficient space for the fabrication of both pipestrings. An ideal location for this would be along the extension of Zeff Road that runsinto the former Modesto Tallow Company plant.

It is recommended that the HDD contractor use a wireline tracking system for steeringguidance of the two bores. This system requires a thin coil of wire be laid along thealignment, offset up to 100 feet from the centerline. To lay and later remove the wire,workers on foot would need limited access to walk the bore alignment at the beginningand conclusion of the job. A temporary construction easement is not necessarilyrequired; however, the request for this access may impact the permitting process due topart of it being within the riparian habitat. The riparian habitat would be disturbed to theextent that workers would walk through the area and lay a small (typically 6 to 8 gauge)

insulated wire and survey its location. Upon completion of the bores, access would berequired again for removal of the wire. Some bushes may have to be trimmed to allowsurveying of the coils position. If a permit or access agreement could not be obtained, itwould be possible, though not preferred, to use the wireline system with the wire laidonly on the east side. However, steering would be more accurate if wire could be placedon both sides of the river. The coil does not need to be placed across the river channel.


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5.6 Permanent Easements

Permanent easements are required for the City to access and maintain the new facilities.Permanent easements are anticipated on the east side on private property (former Tallowsite), and possibly on the west side on the City owned golf course.

The Tuolumne River is under purview of the State Lands Commission. An application tothe State for an amended lease will be required. If granted, the lease will containconditions of use. Although not technically an easement, the lease will serve as a long-term right for the City to operate the facility in accordance with the conditions. Otherleases of this nature have sunset dates, and a renewal will be necessary in the future.

Permanent easements particular to each alternative are described below.

5.6.1 Open Cut

A minimum width of 40, centered on the pipelines is recommended. Easementsnecessary for this alternative are shown on Fig. 5-7.


A minimum width of 40, centered on the pipelines is recommended. Easementsnecessary for this alternative are shown on Fig. 5-8.

5.6.3 HDD

Line and grade accuracy limitations of the HDD installations dictate that 20 feet ofseparation be provided between the twin bores and at least 10 feet of easement beprovided on either side of the bore centerlines. Therefore it is recommended that a 50-foot width of permanent easement be obtained along the new siphon alignment.Easements necessary for this alternative are shown on Fig. 5-9.


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5.7 Golf Course Operations

The west side of the project, where the siphon will connect to the Dryden trunk is locatedwithin the second fairway of the City owned Dryden Municipal Golf Course. Temporaryclosure of a portion or all of this hole will likely be required to accommodateconstruction. The time period varies depending on the construction alternative.

The construction times for open cut, Microtunneling and HDD are 75, 120, and 100working days, respectively.

The golf course hole might be able to remain open and playable during construction. Atemporary tee box could be created south of the construction zone, which would shortenthe hole by approximately half its normal playing length.

During the final design and construction phase, close coordination with the Parks,Recreation and Neighborhoods Department will be necessary. Constructionspecifications will be developed to address manhole structure placement, constructionaccess, golf course turf and irrigation remediation, closure time frames, safety ofconstruction workers, golf course maintenance crews, and the golfing public.

If this work is scheduled during the winter months, disruption of the golf courseoperations could be minimized. Appropriate signage and construction fencing should beutilized to ensure the safety of golfers as well as workers during construction. Seesection 9.0 for discussion of schedule.

5.8 Alignment

Alignments for each of the alternatives are discussed below. Alignments were selected toavoid existing facilities and habitat areas, where possible.

5.8.1 Open Cut

The alignment for open cut is through the least cluttered habitat area, primarily to avoidremoval of existing mature trees in the habitat corridor. The proposed alignment isessentially a direct line from the existing manhole on the east side to a new connection onthe westerly 66 trunk line.

The open cut construction technique will require a construction easement corridor toprovide working room on both sides of the pipeline alignment. Work will occur in theriver for coffer dam, river diversion, and trenching and backfill. The alignment for thisalternative is shown in Fig. 5-1.


The alignment for Microtunneling is not affected substantially by the habitat corridor.

The tunneling can occur along the most efficient construction corridor, considering thatvertical shafts are required at both ends, and new connections to existing facilities arenecessary. The alignment for this alternative is shown in Fig. 5-2.

The jacking shaft would be located on the east side of the river to take advantage of thespace and access available at the abandoned tallow plant site. Temporary easementwould be required on the west side for construction of the reception shaft, retrieval of theMTBM, and construction of the riser and connections. The jacking shaft site wouldrequire significantly more space for setup of the microtunneling equipment and jackingpipe. The vertical shafts used with microtunneling would allow for shorter connections


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to the existing facilities, but would create difficulties with sediment transport of thesanitary sewer flows.

5.8.3 HDD

The alignment for this alternative is shown in Figure 5-3. The total length of each HDDbore is approximately 735 feet. The proposed bores reach maximum depth at anapproximate elevation of -15 feet to ensure that there is adequate clearance below theriver channel to minimize the risk of hydrofracture. The final reamed diameter of eachbore will be approximately 32 inches to accommodate the 22-inch OD (~18-inch ID)HDPE DR 11 siphons.

It is recommended that the rig be set up on the west side of the river, within the secondfairway of the Dryden Municipal Golf Course. The HDD operations would require awork area of approximately 15,000 sq. ft.at the entry location. Much of this area isrequired for storage and can be located in the rough on the east side of the fairway. Aroughly rectangular section will have to extend into the second fairway to provide spacefor the HDD rig to set up. The 735-foot pipe strings would be laid out on the east side ofthe river, within the Modesto Tallow Company property. This arrangement results in theleast amount of disruption to the golf course, since the rig setup area would only impact

the second hole, whereas the area required for pipe layout would impact multiple holes.Additionally, this arrangement allows for the installation of 110 feet of conductor casingat the entry point to protect the existing 66-inch and 60-inch sewers against settlementand to minimize risk of inadvertent fluid returns.

The twin 110-foot, 36-inch conductor casings will be driven at the proposed entry angleof 18. This would result in 5 feet of clearance between the conductor casing and theexisting 66-inch sewer. The bores would pass through the conductor casings andcontinue through the 18 straight tangent for approximately 112 feet and then transitionto a vertical curve with a radius of 750 feet. This curve would continue forapproximately 471 feet and then transitions to the exit tangent at an angle of 18 forapproximately 175 feet to the exit point in the former tallow plant property at Station17+20.

On the west side of the river, two manholes, one for each siphon, will be constructed atapproximate Station 10+05. Flows from these manholes will be directed to the existing66-inch Dryden trunk sewer. On the east side of the river, the HDD bores will passbeneath the remnants of buildings of the tallow plant. It is assumed that these remnantsshould have no impact on construction activities and planning as they will be razedbefore or shortly after construction of the new siphons. During final design, whatremains of the foundations of the former tallow plant buildings should be investigated toensure that they will not provide an obstruction to the planned bore path. The HDD boreswill pass below the buildings and exit approximately 210 feet beyond MH 1 on the eastside of the river. Approximately 210 feet of pipe will be required to deliver flow fromMH1 to a junction box (MH13) capable of diverting flow to either of the new siphons.

5.9 Operations

5.9.1 Flow Control

Since the project will result in a redundant pipeline, a method to direct flow to alternativesiphons by valves is required.


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A new flow diversion manhole will be constructed on the east (upstream) side. Thismanhole will contain valves to shut off flow to either pipeline for maintenance oremergency stoppage.

Valves can be manually operated or electrical driven. Either type should be exercisedperiodically. Electrical valves would require a new electrical service application.

Valves under consideration include eccentric plug valves and sluice valves. Eccentricvalves could be installed in conjunction with a standard manhole configuration. Sluicevalves would require an at grade slab at the surface, which then would likely require asecurity fence.

6.0 Geotechnical Investigation

6.1 Report

Blackburn Consulting has prepared a preliminary geotechnical report for the project site.The report includes description of the surface and subsurface conditions and is intendedonly for preliminary planning purposes. To facilitate the final design of this project,further laboratory testing and engineering analysis must be completed. It is intended that

this work will be performed during the final design phase. A copy of the preliminaryreport is included in Appendix B.

6.2 Boring Logs

Two exploratory borings were performed, one on each side of the Tuolumne River.Blackburn Consulting has prepared a boring location map and preliminary boring logswhich are included in Appendix B.

7.0 Permitting and CEQA Considerations

7.1 Project CEQA Needs

The City will conduct the CEQA process. At the present time, it is expected that an

initial study will be prepared, with the adoption of a mitigated negative declaration.

7.2 Resource Agencies

Coordination with resource agencies and necessary permitting for this project will beprovided by the City of Modesto. The following is a list of agencies with whichcoordination may be required:

California Department of Fish and Game - Section 1602 Streambed AlterationAgreement

California Regional Water Quality Control Board - Water Quality Certification California Reclamation Board - Encroachment Permit U.S. Army Corps of Engineers - Section 10 Permit U.S. Fish and Wildlife Service - Section 7 Consultation (if needed) NOAA Fisheries - Section 7 Consultation California State Lands Commission Lease with Conditions


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7.3 NPDES Permit for Stormwater Discharges Associated with ConstructionActivi ty

Construction projects that disturb land greater than one acre but less than five acres arecovered under The National Pollutant Discharge Elimination System (NPDES) GeneralPermit for Storm Water Discharges Associated with Construction Activity (WaterQuality Order 99-08-DWQ). A Notice of Intent (NOI) must be submitted to theCalifornia State Water Resources Control Board (SWRCB) and a Storm Water PollutionPrevention Plan (SWPPP) must be prepared in compliance with the requirements of theGeneral Permit.

7.4 City Encroachment Permit

An encroachment permit must be obtained from the City of Modesto to allow for theconnection to the existing sewer system. The standard conditions for a Cityencroachment permit are listed in Section 2.13 of the Citys Standard Specifications.

8.0 Construction Cost Estimate

Cost estimate were developed based on the labor, equipment, and material costsassociated with each alternative. The following markups were added to the raw

construction costs:Overhead 8%Profit 10%Legal, Administration 10%Design 15%Contingency 20%

Estimates for each alternative are included in Appendix C.

9.0 Project Schedule

Table 9-1 contains a schedule for the alternative construction methods.

The schedule for open cut method is likely to be much longer than the two trenchlessmethods. Due to more extensive environmental review and more lengthy permittingprocess, a schedule for open cut methods could be 6 months to a year longer. Even withthe additional time for permit processing, it cannot be assumed the permitting authoritieswill allow all the required permits.

Table 9-1. Project Schedule

DateTask

HDD Micro Open Cut

Completion Preliminary Design Report August 2009 August 2009 August 2009

Public Review and City Hearing (Complete) October 2009 October 2009 October 2009

Award Final Design Contract October 2009 October 2009 October 2009

Completion of Final Design April 2010 April 2010 Unknown


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Completion of Permitting June 2010 June 2010 Unknown

Estimated (Earliest) Construction Commencement July 2010 July 2010 Unknown

Estimated (Earliest) Completion of Construction November 2010 January 2011 Unknown

10.0 Comparison of Alternatives

This section contains comparison of the three construction alternatives.

10.1 Open Cut

Open cut construction historically has been a preferred method, primarily due to cost andlocally available construction expertise. This alternative is theoretically still a feasiblealternative. However, the permitting by resource agencies is expected to be formidable.

Considerable resistance should be expected from the permitting entities. Environmentalreview is likely to be much more extensive, possibly including a full EIR. Examination

of alternative construction scenarios should be expected. This alternative would have anopen-ended schedule, due to the time required for review, and no early assurance ofpermit issuance for this construction alternative.

10.2 Microtunneling

Microtunneling has the advantage of less rigorous permitting with resource agencies. Noconstruction would occur in the river or habitat corridors. All staging would occuroutside the river and habitat corridors.

From a constructability standpoint, microtunneling does not face significant challengeson this project. The site soils are conducive to both the microtunneling excavation andsupport, and the shaft construction methods typically used. Additionally, the verticalshafts used allow for shorter connections to the existing facilities. Tight control of both

line and grade and excavation face stability reduces the risks associated with settlementdamage to existing facilities and the permanent easement requirements.

While microtunneling provide some benefits with respect to constructability, there aredrawbacks associated with construction cost and schedule. The required vertical shaftsare both time consuming and costly to install and the tunneling equipment is morecomplex and costly than HDD equipment. Even including the shorter overall crossinglength, the cost of a microtunneled alternative would likely be 2 to 2.5 times greater thanthe cost of an HDD alternative. Further, the construction duration for microtunnelingwould also be longer at approximately 1.5 to 2 times longer than an HDD alternative.

Another significant drawback to this alternative is the hydraulic and maintenance issue.This alternative necessitates a vertical shaft on each end. The downstream end of the

siphon would be expected to carry sediment in suspension a considerable verticaldistance. Since sewage pipe flows vary considerably over the diurnal cycle, it will bedifficult to select a specific riser pipe size that will satisfy all flow scenarios. This facilitycould require considerably more maintenance than other alternatives.

10.3 HDD

HDD also has the advantage of less rigorous permitting with resource agencies, since theconstruction staging is located outside the river corridor.


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HDD does not have the hydraulic issue described above for microtunneling. Thebeginning and ending of the siphon are essentially at the grade of the existing connectedfacilities. The smooth flow line of the HDD siphon will better tolerate varying velocities,and the minimum flow rate will likely keep sediment in suspension.

A drawback to the HDD is additional connection facilities on the east side. Bend radiuslimitations for HDD trigger a new gravity pipeline, and thus the overall length of siphonis increased. These facilities also trigger a larger permanent easement requirement.

10.4 Evaluation Criteria

Each of the construction alternatives has its merits. A method to evaluate and weigh thevarious factors is described herein. The factors are arranged in a table, with each factorassigned a relative weight. Factors include permitting, community, constructability,easements, and operations/maintenance. Each factor was assigned a relative weight,essentially a judgment regarding its importance to this particular project relative to otherfactors. Each alternative was then assigned a score from 1 to 3, with 1 being the leastdesirable, and 3 being the most desirable.

Results from the ratings matrix are shown Fig. 10-1. The HDD alternative ranked higherthan other alternatives. The recommended alternative will consider both the ratingsmatrix and total cost of the project in Section 11.0.

Permitting (25%)

Permitting considers impacts to land use and environmental elements. Alternatives thatscore low for this factor require more permitting, or more time consuming permittingcompared to the other alternative. Additional permitting can lead to more constructionmitigation and schedule extension.

Community (5%)

Higher impacts to local residences or businesses near construction rate lower for thisfactor. Construction dust, mud, noise, and disrupted traffic are considered in this factor.

Constructability (30%)

Difficult construction techniques and necessity for specialty subcontractors rate lower forthis factor. Trenchless construction requires specialty subcontractors to perform thework. Difficult construction issues would include presence of the river, deep tunneling ortrenching, groundwater, phasing, river diversions, and environmentally sensitive areas.

Easements (10%)

Alternatives requiring more construction easements and permanent easements rate lower.

Easements must be obtained from private properties and businesses, and can involvedelays and schedule disruptions.

Operations and maintenance (30%)

Alternatives with more mechanical devices, electrical connections, and alternatives withrelatively higher expected maintenance would rate lower for this factor. Alternativeswhich present more difficult access, such as deeper shafts or structure, or more structuresand pipeline length would rate lower for this factor.


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RatingMatrix

Cri

teria

Weight

OpenCut

Unweighted

score

Weighted

score

Microtunneling

Unweightedscore

Weighted

score

HDD

Unweighted

score

Weighted

score

Perm

itting

25%

Requ

ireswork

intheriveran

d

adjacen

tha

bita

tarea.

Requ

iresmoreresource

agencyrev

iew,

an

dmay

trigger

moreex

tens

iveenv

ironmen

tal

documen

tation,

an

dlonger

time

frame

forperm

it

comp

letion.

Requ

ires

amen

dmen

ttoStateLan

ds

Comm

iss

ion

lease.

1

0.2

5

Cons

truc

tionw

illbes

tage

d

ou

tsideriveran

da

djacen

t

ha

bita

t.Cons

truc

tionm

itiga

tion

willbere

lative

lyless

thanopen

cu

t.Requ

iresamen

dmen

tto

StateLan

ds

Comm

iss

ion

lease.

3

0.7

5

Cons

truc

tionw

illbes

tage

d

ou

tsideriveran

da

djacen

t

ha

bita

t.Cons

truc

tionm

itiga

tion

willbere

lative

lyless

thanopen

cu

t.Requ

iresamen

dmen

tto

StateLan

ds

Comm

iss

ion

lease.

3

0.7

5

Commun

ity

5%

Requ

ireswork

inthe

Dry

den

go

lfcourse

fairway.

Depen

ding

onseason,

go

lfcourse

disrup

tionvaries.

Workon

the

eas

ts

ideoccurson

inac

tive

bus

inesspriva

teproperty.

Work

intherivercorr

idormay

have

increase

dpu

blicscru

Documents

Shackelford HDD Crossing