CITY OF STOCKTON DELTA WATER SUPPLY PROJECT
RAW WATER PIPELINE ALIGNMENT RECOMMENDATIONS TECHNICAL MEMORANDUM
CITY OF STOCKTON DELTA WATER SUPPLY PROJECT
MARCH 2005
Raw Water Pipeline
Phase II Tasks
RAW WATER PIPELINE ALIGNMENT RECOMMENDATIONS TECHNICAL MEMORANDUM
CITY OF STOCKTON DELTA WATER SUPPLY PROJECT
MARCH 2005
Raw Water Pipeline
Phase II Tasks
CITY OF STOCKTON DELTA WATER SUPPLY PROJECT Raw Water Pipeline Alignment Recommendations Technical Memorandum Table of Contents CHAPTER 1
INTRODUCTION ............................................................................................ 1
1.1. BACKGROUND AND PURPOSE .......................................................................................... 1
CHAPTER 2
DESIGN CONSIDERATIONS ........................................................................ 4
2.1. DESIGN FLOWS AND PIPE SIZING..................................................................................... 4 2.2. PIPELINE APPURTENANCES............................................................................................... 5 2.2.1. Blowoffs ....................................................................................................................... 5 2.2.2. Air Vacuum/Air Release Valves .................................................................................. 5 2.2.3. Intertie Stations ............................................................................................................ 6 2.2.4. Access Manways .......................................................................................................... 6 2.3. MINIMUM DEPTH OF COVER ............................................................................................. 6 2.4. TRENCH SECTIONS............................................................................................................... 6 2.5. REQUIRED CONSTRUCTION CORRIDOR ......................................................................... 7
CHAPTER 3
ALIGNMENT ANALYSIS AND RECOMMENDATIONS......................... 10
3.1. DISCUSSION OF INDIVIDUAL ALIGNMENT SECTIONS.............................................. 10 3.1.1. Empire Tract from Intake Facility to West Eight Mile Road ..................................... 11 3.1.2. Empire Tract Along West Eight Mile Road ............................................................... 11 3.1.3. King Island Along Eight Mile Road........................................................................... 12 3.1.4. Undeveloped (West) Portion of Bishop Tract ............................................................ 13 3.1.5. Developed Areas of Bishop Tract West of Interstate 5 .............................................. 13 3.1.6. East of Interstate 5 Along Oak Grove Park ................................................................ 14 3.1.7. Eight Mile Road East of Oak Grove Park to North Thornton Road........................... 15 3.1.8. North Thornton Road to Davis Road ......................................................................... 15 3.1.9. Davis Road to Pixley Slough Crossing ...................................................................... 16 3.1.10. Pixley Slough – Eight Mile Road to Lower Sacramento Road .................................. 16 3.1.11. Lower Sacramento Road ............................................................................................ 17
CHAPTER 4
CONSTRUCTION CONSIDERATIONS ...................................................... 18
4.1. SUBSURFACE CONDITIONS.............................................................................................. 18 4.2. DEWATERING REQUIREMENTS ...................................................................................... 18 4.2.1. Coefficient of Permeability ........................................................................................ 19 4.3. CONSTRUCTION EQUIPMENT AND CREW SIZE .......................................................... 19 4.4. ESTIMATED TRUCK TRIPS................................................................................................ 20 4.5. CONSTRUCTION STAGING AREAS ................................................................................. 21
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Tables Table 1. Major Construction Equipment Required for DWSP Raw Water Pipeline Construction .............19 Table 2. Approximate Crew Size for DWSP Raw Water Pipeline Construction ........................................19
Figures Figure 1. Delta Water Supply Project Vicinity Map ....................................................................................1 Figure 2. Parallel Pipeline Total Dynamic Head (TDH) at 160 mgd ............................................................5 Figure 3. Typical Trenching Operation .........................................................................................................7 Figure 4. Ideal Construction Corridor Width ................................................................................................8 Figure 5. Minimum Construction Corridor Width ........................................................................................9 Figure 6. Estimated Construction Truck Trips per Week for the DWSP Raw Water Pipeline ...................21
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CHAPTER 1 INTRODUCTION 1.1.
BACKGROUND AND PURPOSE
The purpose of this technical memorandum is to evaluate and recommend an alignment for the City of Stockton’s Delta Water Supply Project (DWSP) raw water pipeline in support of the environmental permitting process. This memorandum evaluates the potential alignments along Eight Mile Road and recommends a conceptual level alignment for the raw water pipeline. The pipeline will convey water from the intake on the southwest corner of Empire Tract adjacent to the Stockton Deep Water Channel to the City’s planned new treatment facility located off Lower Sacramento Road (See Figure 1).
Figure 1. Delta Water Supply Project Vicinity Map
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The pipeline will be built in two phases—an initial 54-inch pipeline followed in the future by a parallel 72inch pipeline when additional capacity is needed. Objectives considered during the alignment evaluation include: •
Minimizing overall project cost
•
Minimizing construction risk to the City of Stockton
•
Choosing an alignment that is unlikely to adversely impact the schedule
•
Choosing an alignment that can be adequately maintained for the pipeline’s service life
•
Minimizing impacts to the public during construction
The alignment recommended will consider construction of both the initial and future parallel pipelines, although this memorandum will focus on the 54-inch pipeline. The initial pipeline alignment will be routed to allow construction of the future pipeline without crossings between the two pipelines. A preliminary pipeline route was previously identified in the City of Stockton Delta Water Supply Project Feasibility Report dated January 2003 (Feasibility Report). The pipeline route heads north from the intake structure approximately 6,600 feet to Eight Mile Road, then heads east parallel to Eight Mile Road for approximately 48,000 feet to one of the three Water Treatment Plant Site “C” alternatives. After the Feasibility Report was published, the City of Stockton purchased a 127-acre parcel for constructing the Water Treatment Plant (WTP) located at 11373 North Lower Sacramento Road. The site purchased by the City of Stockton is further away from the intake facility than the Site “C” alternatives described in the Feasibility Report. The additional distance adds approximate 2.5 miles in length to the raw water pipeline. The approximate length of the raw water pipeline is 67,000 feet. A conceptual-level set of raw water pipeline drawings is included with this technical memorandum. Alignment alternatives are shown in cross-section view at the back of the drawing set. Key assumptions incorporated into the recommended alignment include the following: •
The recommended pipeline alignment uses existing public right-of-way where available.
•
Except for special crossings, open cut trenching construction is anticipated.
•
Where minor ditch crossings (water surface less that 15 feet in width) are required, it is assumed that the ditch will be temporarily dammed to install the pipeline using open cut trenching, and then restored after completion of the crossing to currently existing conditions.
•
Where right-of-way acquisition will be required for construction of the 54-inch pipeline, it is preferred that the entire right-of-way acquisition for both the initial and future pipeline be acquired.
•
Where right-of-way will only be necessary for the future pipeline, acquisition will be deferred to a later date.
Limitations on the accuracy and completeness of the alignment analysis include the following: •
Utility search is not part of the scope for this conceptual-level effort.
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•
No right-of-way (ROW) engineering has been performed. In some cases, information was readily available indicating the width of the ROW; however, the exact limits of the ROW were not determined by survey, and the limits shown are only approximate.
•
A detailed survey was not performed. Elevations in other areas are estimated using USGS 7.5-minute maps and surface features identified during field investigation. Pipeline stationing is approximate.
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CHAPTER 2 DESIGN CONSIDERATIONS This section discusses the design issues considered when evaluating the various alignment alternatives. Although some design criteria are discussed, a formal Basis of Design Report should be prepared as part of the final design.
2.1.
DESIGN FLOWS AND PIPE SIZING
Near-term water demands require an initial design capacity of the DWSP WTP of 30 million gallons per day (mgd). This initial capacity will be increased incrementally as necessary to meet long-term potable water demands within the City of Stockton Metropolitan Area (COSMA). Long-term demands include the nearterm demands as well as an assumed constant municipal growth rate of 1.9 percent from 2015 to 2050. These water demands are assumed to occur within the general Plan Boundary within and outside of the Urban Services Area. The required capacity of the DWSP to meet long-term demands is 160 mgd. To address both near and long-term demands, the raw water facilities will consists of an initial 54-inch diameter pipeline, (to meet near-term demand and provide for some future demand) and a 72-inch pipeline to provide the required long-term demand capacity. The timing of the design and construction of the 72-inch pipeline is dependent on future needs and is not a part of the initial project. A conceptual level system curve of the dual raw water pipeline is shown in Figure 2. In addition to the recommended 54-inch/72-inch dual pipe combination, a 54-inch/60-inch commination was also considered. As shown in the figure, under long-term operating conditions the 54-inch/60-inch combination would require approximately 100 feet of additional hydraulic head to operate, resulting in considerable additional operations and maintenance costs over the useful life of the facilities and increased wear and tear of the intake pumps. Design flow velocities in the 54-inch/72-inch system would be about 5 and 6 feet per second, respectively, which is considered appropriate. Design flow velocities in the 54-inch/60-inch system would be 6.6 and 7.2 feet per second, respectively, which is considered to be higher than optimum.
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Figure 2. Parallel Pipeline Total Dynamic Head (TDH) at 160 mgd 300 TDH (feet) 54-inch C = 100
250
TDH (feet) 60-inch C = 100
TDH (feet) 72-inch C = 100
TDH (feet)
200
150
100
50
0 0
10
20
30
40
50
60
70
80
90
100
110
120
Flow (mgd)
2.2.
PIPELINE APPURTENANCES
In order to properly operate and maintain the raw water pipeline, appurtenant facilities are required. Appurtenant facilities for the DWSP raw water pipeline will include blowoffs, air vacuum/air release valves, intertie stations, and access manways. Standard details and preliminary locations for these facilities are included in the attached recommended alignment drawings. A brief discussion of the function of these facilities is provided in the following subsections. 2.2.1.
Blowoffs
Blowoffs will need to be included along the pipeline to enable dewatering of the pipeline. Blowoffs will be located at all low elevations in the pipeline and on the upstream side of isolation valves. A blowoff consists of a bottom outlet tee (sized for the pipe volume to be drained) with a shutoff valve on the branch leg of the tee that can be operated to allow removal of water from the system. 2.2.2.
Air Vacuum/Air Release Valves
There are generally two types of air valves: air and vacuum valves and air release valves. Air and vacuum values are used to admit air into a pipe to prevent formation of vacuum that may be a result of valve operations, rapid draining such as a line break, a column separation, or other causes. Without air vacuum valves, a vacuum can cause the pipe to collapse from atmospheric pressure. Air release valves are required at
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high points along a pipe to release any air buildup in the pipeline. Air escapes from water within the pipe 1) while filling the pipeline, 2) at low-pressure zones created by partially open valves, 3) at locations of cascading flow in a partially filled pipe, 4) because of variations in flow velocity caused by changing pipe diameters and slopes, and 5) at changes in pipeline elevations. In reducing the accumulation of air within a pipe, air release valves increase the flow rate of water (by enlarging the cross-sectional flow area) and decrease headloss in the pipeline. 2.2.3.
Intertie Stations
Intertie stations connect the two pipelines periodically along the alignment and allow for isolation of a portion of either pipeline for maintenance or repair without taking the entire pipeline out of service. A maximum spacing of 2.5 miles is recommended. Since the raw water pipelines will be constructed in phases, the intertie stations for the initial phase will be limited to two isolation valves, a tee, and a blind-flange oriented in the direction of the future parallel pipeline. 2.2.4.
Access Manways
Access manways allow access into the pipeline for inspection, maintenance, and repair. Access points consist of a flanged outlet oriented vertically. Removal of the flange is required for access. Typically manways are located adjacent to or combined with other appurtenances and should be provided at approximately 2,000-foot intervals. Due to the preliminary nature of the recommended alignment, manways have not been shown on the attached drawings, but should be incorporated during final design.
2.3.
MINIMUM DEPTH OF COVER
Selection of a minimum depth of cover is a balance between cost and risk. Generally, the deeper a facility is buried, the more costly construction becomes. Typical minimum covers for small diameter (non-gravity) utilities range from 3.5 to 5 feet. By installing the raw water pipeline deeper than 5 feet, potential conflicts with many existing and future adjacent utilities is avoided. In agricultural areas where the pipeline will not be in road right-of-way, farming operations, including construction of irrigation canals, tilling, and deep-ripping, must be considered. To minimize risk of damage to the raw water pipeline, and to provide a vertical corridor for future small diameter utilities, a minimum cover of 7 feet was used.
2.4.
TRENCH SECTIONS
Trenches for this size pipeline typically need to be excavated to about 1 foot below the invert of the pipe. Bedding should be installed beneath the pipe and then backfilled with imported material to 1 foot above the top of pipe. In areas where soil conditions permit (and suitable shoring is provided), trench sections can be constructed vertically with 1- to 1.5-foot clearances from pipe springline to shoring. The resulting trench widths should range from 7 to 8 feet for the 54-inch pipe and 8.5 to 9.5 feet for future parallel pipeline. Conceptual standard trench sections are shown in the drawing set. Where more space is available, such as unimproved areas, the trench section walls need not be vertical above the pipe zone. Consideration was also given to the minimum recommended clearance between the 54-inch and future 72inch pipelines. To allow for the future construction of the 72-inch pipeline with minimal interference from the 54-inch pipeline, and to allow for maintenance and operation of both pipelines, and minimum distance of 10.5 feet (about two pipe diameters) is assumed.
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2.5.
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REQUIRED CONSTRUCTION CORRIDOR
Typical pipeline construction for this size raw water facility consists of trench excavation, pipe installation, and backfill operations (see Figure 3). A dewatering operation in advance of trench excavation will also be required for pipeline construction west of Interstate 5. Generally, the more room a contractor has to stage for and construct a pipeline, the more efficient the operation will be. For example, in areas of limited available construction corridor, the contractor will have to haul soil excavated from the trench (spoil) away from the trenching operation and haul it back during the backfill operation. In areas with wider available construction corridors, the contractor would typically cast the spoil off to the side of the trench, install the pipe, and backfill the trench using the piled soil. In areas of limited construction corridor, the pipe will be unloaded directly from delivery trucks. In areas where more construction corridor is available, the pipe could be staged along the alignment in advance of the pipe installation operation. It is estimated that in open areas, where sufficient room is available, the contractor would use an 80-foot wide corridor to maximize construction efficiency (see Figure 4).
Figure 3. Typical Trenching Operation
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Figure 4. Ideal Construction Corridor Width
In areas encumbered by existing improvements, high-volume roadways, or environmentally sensitive areas and narrower construction corridor will be necessary. The minimum practicable construction corridor is estimated to be 47 feet (see Figure 5). This corridor provides for the width and turning movement of a 320L Mass excavator and assumes all other construction equipment (i.e., spoil haul trucks, pipe laying crane, pipe delivery trucks) will share the remaining corridor width.
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Figure 5. Minimum Construction Corridor Width
Where sufficient corridor width is available and traffic volumes warrant (i.e. Eight Mile Road east of Interstate 5) the design alignment should allow one 12-foot wide lane of traffic in each direction. In other areas with less traffic volumes, one lane of alternative traffic may be acceptable. An encroachment permit and/or maintenance agreement will be required from the City of Stockton and San Joaquin County for utilization of, and construction work within, the right-of-way maintained by the respective municipalities.
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CHAPTER 3 ALIGNMENT ANALYSIS AND RECOMMENDATIONS For the purposes of analysis, the project is divided into sections with similar characteristics and issues affecting the pipeline alignment. The 10 segments used for the alignment analysis are listed below, followed by a narrative discussion of the specific issues related to each section in Section 3.1. •
Empire Tract from Intake Facility to West Eight Mile Road
•
Empire Tract along West Eight Mile Road
•
King Island Along Eight Mile Road
•
Undeveloped (West) Portion of Bishop Tract
•
Developed Areas of Bishop Tract West of Interstate 5
•
Developed area of Bishop Tract east to Interstate 5
•
East of Interstate 5 along Oak Grove Park
•
Eight Mile Road East of Oak Grove Park to North Thornton Road
•
North Thornton Road to Davis Road
•
Davis Road to Pixley Slough Crossings
•
Pixley Slough – Eight Mile Road to Lower Sacramento Road
•
Lower Sacramento Road
In addition to the individual alignments, there are several key crossings the pipeline will have to make, all located along West Eight Mile Road. These include: •
A large drainage ditch/pump station at the western terminus of Eight Mile Road
•
Honker Cut, between Empire Tract and King Island
•
Bishop Cut, between King Island and Bishop Tract
•
Interstate 5
•
Thornton Road
•
Davis Road
•
Western Pacific Railroad tracks
These crossings are discussed in this technical memorandum only as they affect alignment.
3.1.
DISCUSSION OF INDIVIDUAL ALIGNMENT SECTIONS
This section discusses the requirements and restrictions to constructing the pipeline along the individual sections. It also recommends a preferred alignment alternative.
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3.1.1.
Phase II Tasks
Empire Tract from Intake Facility to West Eight Mile Road
The Empire Tract levee is the largest physical feature affecting construction along this segment of pipeline. In addition, there are several small irrigation ditches that must be crossed. The alignment must be located a safe distance east of the toe of the levee. Reclamation District 2029 (RD-2029) owns the first 150 feet extending landward from the centerline of the levee and has jurisdiction over an additional 100 feet landward. The centerline of the levee, although not well-defined, is assumed to be the centerline of the road in the area of concern. The levees in the area are substandard and seepage of water is consistently observed. If funds become available, the levees will likely be upgraded. If this were to happen, the levee would be enlarged on the landward side and a pipeline built too close to the toe of the levee could have significant quantities of fill placed atop it. Such action would make maintenance of the pipeline impractical and necessitate future relocation of the pipeline. In addition, the pipeline would likely not be designed to handle the earth loads imposed by the additional fill. The toe of the levee ranges from approximately 125 feet to 160 feet from the center of the levee road. There is a series of drainage canals that collect runoff and convey it westerly to canals that run roughly parallel to the levee near the levee toe. Approximately 1,700 feet southerly of Eight Mile Road, the canals run roughly parallel to the levee, with some larger canals collecting the runoff to the base of the levee in a westerly direction. Locating the pipelines easterly of the canals would place the alignment in most cases over 200 feet from the middle of the levee. In order to avoid delays due to review and conditions imposed by RD-2029 and to construct the pipeline a sufficient distance away from the levee to avoid levee integrity and seepage issues, it is recommended that the alignment be located at least 250 feet from the levee centerline. An 80-foot wide strip of easement will be required from the end of the intake facility property to West Eight Mile Road. The pipeline can be constructed with the standard 7 feet of cover along the alignment, except where the irrigation must be crossed. The recommended alignment is shown on Drawings C1, C2, and C3 of the attached set of conceptual drawings. 3.1.2.
Empire Tract Along West Eight Mile Road
This section of pipeline is approximately 11,000-linear-feet long and will extend from a drainage ditch crossing at the western end of Eight Mile Road to Honker Cut. Eight Mile Road is a two-lane road in this section with an average total paved width of approximately 23 feet. It is assumed that the road will be widened to two lanes in each direction during the pipeline’s design life. A large drainage ditch (approximately 25 feet wide at the water surface) runs parallel to the road on the south side. The pipeline will have to be located on the north side of the large drainage ditch in order to have access for maintenance. The existing right-of-way is believed to be 90 feet wide, beginning near the north edge of the ditch and extending northward (based on County Survey No. 4218.) The exact ROW boundary is still to be determined. Potential locations for the pipelines include the following: •
Between (south of) the road and the ditch
•
Under the road
•
North of the road
Approximately 20 feet is available between the road and the ditch. This is only sufficient to construct one phase of the pipeline in this location.
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The paved road width in this area averages approximately 23 feet. In order to construct both pipelines under the road, the trenches would extend slightly onto the shoulder of each side. North of the road lies farmland with no physical limitation to construction except a few ditch crossings. Both pipelines could be constructed north of the road; however, it remains to be determined exactly where the existing ROW ends. It appears probable that at least one pipeline could be constructed with the entire trench within the existing ROW, although some additional ROW might be needed for construction. The Phase 2 pipeline most likely will have a portion of the trench beyond the existing ROW, with a portion of the construction zone beyond the existing ROW. Both pipelines can likely be installed within the existing ROW alongside the road, saving the significant cost of road reconstruction, minimizing traffic control expenses, and allowing higher productivity. It is therefore recommended that both the 54-inch and future 72-inch pipelines be constructed to the north of the road. The Phase 1 pipeline will be constructed closer to the road to minimize the ROW requirement. The 54-inch pipeline will be constructed closer to the road to minimize the ROW requirement. The initial pipeline should be designed to handle additional earth load as a result of potential future road widening (approximately 6 additional feet of cover). At the eastern end of Empire Tract, the pipeline will have to be routed through Honker Cut to King Island. Honker Cut is approximately 425 feet wide. Empire Tract and King Island both have levees that route northsouth along Honker Cut. On the south side of Eight Mile Road is a large drainage ditch on Empire Tract and a marina on the King Island side. A drainage ditch slightly smaller than that on Empire Tract begins approximately 100 feet east of the center of the King Island levee. The pipeline cannot be routed under Eight Mile Road because of the bridge structure. Several farming structures exist to the north, beginning approximately 375 feet west of the levee and continuing approximately 400 feet north of Eight Mile Road on Empire Tract. There are no apparent obstructions to the north of Eight Mile Road on King Island immediately east of the Honker Cut Levee. It is therefore recommended that the pipeline route to the north of Eight Mile Road around the farm structures for the Honker Cut crossing. The routing also includes several advantages: •
The alignment eliminates the need to cross the road for the Honker Cut crossing, since the pipeline to the west is already on the north side of the road.
•
The alignment allows for sufficient staging area for the microtunneling operation away from existing improvements.
•
The alignment avoids the buildings and marina structures to the south of Eight Mile Road on the King Island side. 3.1.3.
King Island Along Eight Mile Road
This section of pipeline is approximately 11,200 linear feet (LF) and will extend from Honker Cut to Bishop Cut. Eight Mile Road is a two-lane road in this section with an average total paved width of approximately 22.5 feet. A large drainage ditch (approximately 12 feet wide at the water surface) runs parallel to the road on the south side for much of the alignment. Utility poles run parallel to the road on the north side for the entire alignment. The pipeline will have to be located north of the large drainage ditch in order to have access for maintenance. The existing right-of-way is 90 feet wide, begins near the north edge of the ditch, and extends northward, but the exact ROW boundary is still being determined. The approximate ROW was determined from a survey map by Albert Sanguinetti in 1973. Potential locations for locating the pipelines include the following:
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•
Under the road
•
North of the road, north of the existing utility poles
There is not sufficient space to safely construct a pipeline between the drainage ditch to the south and the road without removing some pavement. Sufficient space exists to construct each phase under the road, particularly if some of the space between the road and the drainage ditch to the south is utilized. The presence of utility poles makes construction immediately north of the road infeasible, in addition to a small drainage ditch (approximately 2 feet wide and 1.5 feet deep) where the poles are located. Because of the poles, any alignment to the north would be more likely to be beyond the existing ROW, especially if both phases were sited in this location. It is possible that one phase might be within the existing ROW. It is recommended that the first phase be constructed north of the telephone poles (within existing the ROW) if possible. This will reduce costs due to eliminating pavement restoration and reducing traffic control; it will also avoid crossing Eight Mile Road after the pipeline is installed under Honker Cut. It is recommended that the 72-inch pipeline be constructed to the north of the 54-inch pipeline; it is likely that the ROW will have to be acquired for the future pipeline. 3.1.4.
Undeveloped (West) Portion of Bishop Tract
This portion of pipeline is still within agricultural lands and extends from Bishop Cut eastward approximately 3,200 feet. The paved roadway is approximately 31 feet wide and the existing ROW is 80 feet wide through this area. This portion of the pipeline can be seen on Sheets C13 and C14 of the Plan and Profile drawings and Sheet X1 of the Cross-Section drawings. During summer 2004, small ditches were observed on each side of the road within the farmed areas, but the ditches were not present during the October 2004 field visit. Potential locations for the pipeline route include the following: •
Under the paved roadway
•
North of the paved roadway
•
South of the paved roadway.
Constructing beyond the paved roadway can minimize construction cost and impacts to the public. Therefore, a practical route beyond the paved roadway is desirable. Because the pipeline from King Island will cross Eight Mile Road on the north side of the road, it is recommended that the pipeline be routed north of the paved roadway in this section. To be consistent with the other sections considered, the initial pipeline should be located closer to the road and the future pipeline north of the initial pipeline. 3.1.5.
Developed Areas of Bishop Tract West of Interstate 5
This portion of the pipeline comprises approximately 9,000 LF and heads through areas with significant recent, current, and future development, including the following: •
A housing development (Spanos Park West) recently completed on the south side of Eight Mile Road.
•
An outdoor shopping mall with minimal existing road frontage is still being developed on the south the south side of the road.
•
A completed golf course on the north side of Eight Mile Road.
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A new housing development (Westlake at Spanos Park West) has been proposed on the south side of Eight Mile Road immediately west of the Spanos Park West housing development.
Currently the western 3,300-foot portion has a similar undeveloped layout as the portion of Bishop Tract immediately west (shown on Section 3 on Drawing X1), except that there is a defined ditch paralleling the road along the south end, and there is a depression that would probably not be considered a roadside ditch along the north side of the road. The eastern 5,700 feet has significant development and wider pavement, as shown on Section 4 on Drawing X1. The plan and profile for the western portion of this area appears on Sheets C14 and C15, while that for the eastern portion appears on Sheets C15 through C17. If no development occurs in the eastern portion prior to the initial 54-inch pipeline construction, it is recommended that the pipeline follow the alignment recommended in Section 3.1.4 for the undeveloped portion of Bishop Tract. The ultimate ROW width will be 134 feet, but currently the known ROW is 80 feet in the western portion. In the newly developed areas (beginning at the Spanos Park housing development), the existing ROW may currently be more than 80 feet wide. Here the paved roadway is wide enough to potentially construct each phase under lanes on a single half of the street. South of the road exists significant landscape associated with the housing development, which probably has significant utility infrastructure. To the north of the road are several light poles and a utility pole corridor. Several mounds exist between the light poles and utility poles. Construction outside the paved roadway is likely impractical due to the existing utilities and layout of the land. Therefore, each pipeline should be constructed under pavement barring a change in conditions due to further development. Construction would have the least impact, and a future pipeline could avoid crossing the initial pipeline by locating the initial pipeline just north of road centerline, then locating the future pipeline north of the initial pipeline. Locating the pipelines on the north side of the road will also minimize traffic impacts when constructing near the Interstate 5 crossing, which was previously determined to be located on the north side of Eight Mile Road due to development on the south side of the road. If there is sufficient ROW and there are no interfering utilities, it may be possible to construct the Phase 2 pipeline to the north of the existing pavement to save on construction cost, but such evaluation should be performed during future design of said pipeline. 3.1.6.
East of Interstate 5 Along Oak Grove Park
This section of Eight Mile Road has a single lane in each direction with a current total paved width of approximately 32.5 feet. On the south side of the road there is gravel nearly to the fence line for Oak Grove Park, 35 feet beyond the edge of existing pavement. To the north is 10 feet of unimproved, uneven ground for approximately 25 feet to a row of mature trees, and then vineyards north of the trees. The existing and ultimate ROWs for this section are 80 and 134 feet wide, respectively, and there is sufficient space to construct each pipeline phase under pavement or on either side of the existing paved roadway. A portion of the shoulder will have to be removed and repaired if each pipeline is located within the area immediately north of the road and the existing trees, if the trees are not to be removed. Since it has already been determined that the pipeline will be routed under Interstate 5 on the north side of Eight Mile Road, it is recommended that the Phase 1 pipeline be routed just beyond the north edge of the pavement. The corridor would allow two-way traffic to be maintained in each direction without removing the mature trees. The Phase 2 pipeline location may be greatly affected by future development, including road widening. Tentatively it is recommended that the pipeline be located with the north end of the trench 5 feet clear of the row of trees to the north, which provides about 7 feet of clearance from the Phase 1 pipeline. If
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the trees are to be removed as a result of development, the pipeline can be moved further north to increase the clearance. 3.1.7.
Eight Mile Road East of Oak Grove Park to North Thornton Road
This section of Eight Mile Road has a housing development on the south side and agricultural land to the north. According to the Eight Mile Road Specific Plan by Omni-Means (approved February 16, 1994), the roadway has a current ROW of 80 feet and will have an ultimate ROW of 134 feet. The ROW widens to 160 feet for the approach to the North Thornton Road intersection. The ROW appears to be centered on the paved median approaching North Thornton Road. Beginning at the south edge of pavement, the existing roadway consists of a paved shoulder approximately 18.5 feet wide and two eastbound lanes totaling 32.5 feet in width. The traveled lanes are divided by a 12-foot wide asphalt median. North of the median is a single westbound lane and paved shoulder 14.75 feet in width. Several alignment options are possible given the available space: •
Locate each pipeline under the eastbound traffic lanes.
•
Locate one under the paved shoulder on the south side and the other under an eastbound lane.
•
One pipeline could be placed under the median and the other under the westbound lane.
•
Locate one pipeline under the westbound lane and the other north of the paved section of the road.
•
Place both pipelines north of the paved roadway.
It is recommended that the Phase 1 pipeline be located beyond the north edge of the pavement. This will allow construction without pavement restoration and with minimal traffic control. Most of the construction corridor is within the existing ROW, although a portion may be within the planned ultimate ROW and require some efforts to secure for construction. The Phase 2 pipeline should be tentatively located 10 feet clear to the north of the Phase 1 pipeline. 3.1.8.
North Thornton Road to Davis Road
The portion from North Thornton Road to Davis Road is approximately 5,400 LF long . The paved roadway is approximately 40 feet wide, with one lane in each direction and utility poles located approximately 18 feet south of the edge of pavement. A small ditch is located approximately 6 feet beyond the north edge of the pavement. Construction has begun on a housing development on the south side of Eight Mile Road, approximately 2,700 feet east of North Thornton Road. The housing development currently takes up approximately 1,200 feet of road frontage. The existing ROW is 80 feet wide and centered approximately on the road centerline; the ultimate ROW per the Eight Mile Road Specific Plan is 134 feet. It would be possible to construct each pipeline under existing pavement or on either side of existing pavement. In order to avoid the utility poles and housing development, an alignment south of the paved roadway is not recommended. If located north of the road without disturbing the ditch, the Phase 1 pipeline would likely be located within the existing ROW but within the ultimate ROW; therefore, some ROW acquisition would probably be required. It would also be possible to construct the first and second phase under each of the existing lanes. It is recommended that the Phase 1 pipeline be constructed north of the small ditch on the north side of the road to minimize pavement restoration and traffic control costs. The alignment will also minimize the impact
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to the public during construction. The tentative location for the Phase 2 pipeline should be to the north of the Phase 1 pipeline with 10 feet of clearance between each pipeline. 3.1.9.
Davis Road to Pixley Slough Crossing
The portion of the pipeline from the Davis Road crossing to where Pixley Slough crosses under Eight Mile Road is approximately 5,300 LF. Approximately 500 feet east of Davis Road, Pixley Slough begins to run parallel to Eight Mile Road on the south side, and is separated from the road by a floodwall. The total paved width of the two lanes totals approximately 38.5 feet in this area. A utility pole parallels the road on the north side, approximately 21 feet beyond the edge of pavement. Approximately 2,200 feet east of Davis Road, the pipeline will cross the Union Pacific Railroad tracks. The Eight Mile Road Specific Plan indicates an existing ROW of 120 feet extending approximately 40 feet north of road centerline, with the ultimate ROW extending at least 129 feet north of road centerline for the entire length, and as far as 278 feet north of road centerline at the railroad track crossing. Due to the floodwall, the only practical locations for the pipeline are under the roadway to the north of the existing pavement. The Phase 1 pipeline could be constructed north of the existing pavement with the edge of trench 10 feet clear of the utility poles. This alignment would allow construction of the pipeline with the following benefits: •
Within existing ROW.
•
No pavement restoration.
•
Limited traffic control and no lane closures. Approximately 14 feet of the north lane could be closed off for construction and there would be about 24.5 feet of pavement available for two-way traffic. If necessary, a portion of the gravel shoulder, over 20 feet in width, could be used for traffic lanes.
Because of the above benefits, it is recommended that the pipeline be constructed north of the paved portion of Eight Mile Road as shown on Section 4 of Drawing X2. For Phase 2, the recommendation is to tentatively place the pipeline further north as shown on the section, but development, including road widening and/or relocation of the utility pole, may change the construction conditions when the second pipeline is needed. 3.1.10. Pixley Slough – Eight Mile Road to Lower Sacramento Road The pipeline alignment will meet up with Pixley Slough approximately 1,300 feet west of Lower Sacramento Road. The floodwall on the south side of Eight Mile Road ends here, where the slough crosses the road. In this area, Pixley Slough drains in a southwesterly direction and due to increased elevation does not continually contain large volumes of water; its flow is more like a creek. Options for routing the pipeline include the following: •
Crossing under Pixley Slough and continuing east approximately 1,300 LF to the intersection with Lower Sacramento Road, then routing north parallel to Lower Sacramento Road for approximately 1,000 LF, including a second crossing of Pixley Slough. Total length of this alternative is 2,300 LF and includes two jacking operations to cross Pixley Slough totaling approximately 500 feet.
•
Routing the pipeline in a northwesterly direction parallel to Pixley Slough for a total length of approximately 1,700 feet.
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The second option would be significantly less expensive, provides the least risk and easiest maintenance access by eliminating the slough crossings, and would avoid a lengthy permitting process to jack under the slough. The pipeline would be routed through a vineyard area that would require new ROW acquisition, but the time required to obtain the ROW would likely be comparable to or less than that for permitting crossing Pixley Slough twice. It is therefore recommended that the pipeline be routed parallel to Pixley Slough in this area. Considerations to align the pipeline in this area include the proximity to a flood control levee. The design slope on the landward side of the levee is 2.0 to 1.0 horizontal to vertical and excavation may not extend into the projection of the landward slope. A contractor could have restrictions on use of a patrol road alongside the levee during wet months when the roads are used to inspect the levees. The width of the patrol road generally ranges from 9.5 to 13.0 feet. Given the levee slope and that the trench of the Phase 1 pipeline will be approximately 9.5 feet deep, the pipeline will have to be located beyond the patrol road, at least 19 feet from the levee toe. The best construction option is to use the patrol road to transport materials to and from the site. The recommended alignment and location for Phases 1 and 2 is shown on Drawings C24 and C25, with a representative cross section on Section 1 of drawing X1. 3.1.11. Lower Sacramento Road After routing past Pixley Slough, the raw water pipelines will route parallel to Lower Sacramento Road for approximately 4,000 LF to a new treatment facility. It is important is to allow sufficient corridor for the treated water transmission line to be routed south from the treatment plant along Lower Sacramento Road to the distribution system. It is assumed that the treated water pipeline will be 30 inches in diameter to match the pipe at the planned connection point. The existing ROW in this stretch of Lower Sacramento Road is 80 feet wide and roughly centered on the road centerline. The “Lower Sacramento Road Special Purpose Plan” by Mark Thomas and Company, 1997, increases the ROW by 40 feet to the east for a planned expansion of the road to an expressway with two lanes in each direction and a 20-foot median. Because the road will be expanded to the east, an alignment to the west side of Lower Sacramento Road will allow for the easiest maintenance by placing the pipelines clear of traffic to the greatest extent possible. In order to avoid crossing the raw water pipelines, it is recommended that the treated water pipelines be routed to the east of the raw pipelines. It is therefore recommended that the Phase 1 pipeline be placed under the existing west (southbound) lane of traffic and the Phase 2 pipeline be placed on the flat shoulder just beyond the edge of pavement as shown on Section 2 of Drawing X1. The alignment also prevents the Phases 1 and 2 waterlines from crossing each other. The recommended alignment and location for Phases 1 and 2 is shown on Drawings C25 and C26.
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CHAPTER 4 CONSTRUCTION CONSIDERATIONS 4.1.
SUBSURFACE CONDITIONS
Subsurface conditions along the proposed pipeline were explored and evaluated by drilling 14 borings (B-1 through B-14), extending to depths of 21.5 to 41.5 feet below ground surface. The results of the field exploration program indicate that the subsurface conditions consist of generally medium dense sands, silty clayey sands, and stiff silty and sandy clays and silts. A layer of soft to medium stiff peat was encountered in borings drilled west of Interstate 5 extending to depths of 7 to over 23 feet below ground surface. The peat was overlain by 1 to 7 feet of fill soils. The peat generally increased in thickness towards the west. Groundwater levels were measured at depths ranging from 8 to 12 feet below ground surface corresponding to elevations -6 to -23 feet in Borings B-6 through B-13 and Boring B-19 drilled west of Interstate 5, along the pipeline and below the proposed on-shore intake structure. Groundwater was not encountered in borings drilled east of Interstate 5. Additional details on subsurface conditions are contained in the Delta Water Supply Project Preliminary Geotechnical Report.
4.2.
DEWATERING REQUIREMENTS
Minor to moderate dewatering may be required for construction of the pipeline. The proposed invert elevation of the pipeline will range from +11 to -27 feet, and the bottoms of the jacking and receiving pits will be at lower elevations, extending below -30 feet. Groundwater levels vary throughout the year. Between December and June, maximum groundwater levels are likely to be higher than those encountered in our field exploration program. For five months, between July and November, the groundwater levels are likely to be about elevation -6 feet or higher. The contractor should be responsible for selecting the appropriate range of groundwater levels for design of the dewatering system and for providing an adequate dewatering system during construction. A properly designed, installed, and operated dewatering system should: •
Lower the water table inside the excavation or intercept seepage that will emerge from the sides or the bottom of the excavation
•
Improve the stability of the excavation and prevent disturbance of the bottom of the excavation
•
Provide a reasonably dry working area in the bottom of the excavation
•
Provide for collection and removal of surface water and rainfall
It is recommended that the water level be maintained below the bottom of the excavations until the pipelines are placed and backfilled.
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Water collected during dewatering should be tested for contamination prior to disposal. The potential for contamination of groundwater has not been evaluated as part of this study. However, it is the responsibility of the contractor to obtain the proper permits and dispose of the discharged water. 4.2.1.
Coefficient of Permeability
To aid in the design of dewatering systems, we evaluated the coefficient of permeability of the soils, based on the results of laboratory grain size distribution (sieve analyses) tests. Samples of sandy soils drilled for this study indicate that the percentages of fines in materials that will be in dewatering areas are quite variable. Hazen’s formula (Lambe and Whitman, 1979), which estimates permeability from the grain size represented by the 10 percent fraction by weight, was used to estimate permeability. Based on the results of our analyses, it is recommended that coefficients of permeability of 10-2 centimeters per second (cm/sec), 5 x 10-4 cm/sec, and 10-5 cm/sec be used in analyses of groundwater flow for sandy, silty, and clayey soils, respectively. A coefficient of permeability 10-5 cm/sec is recommended for the peat layers at the site. Additional details on expected groundwater and dewatering requirements are contained in the Delta Water Supply Project Preliminary Geotechnical Report.
4.3.
CONSTRUCTION EQUIPMENT AND CREW SIZE
The major construction equipment and approximate crew size required to perform the pipeline construction operation shown in Figure 3 are presented in Tables 1 and 2 respectively.
Table 1. Major Construction Equipment Required for DWSP Raw Water Pipeline Construction Equipment CAT 325L Mass Excavator CAT 956F Wheel Loader 10-wheel Water Truck 30 Ton RT530 Grove Crane CAT CS-323 Smooth Drum Vibratory Compactor
Quantity 2 1 1 1 1
Table 2. Approximate Crew Size for DWSP Raw Water Pipeline Construction Typical Pipe Laying Crew Foreman/Superintendent Grade Setter Operators Laborers/Pipe Fitters Welder
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Quantity 1 1 4 6 2
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The anticipated pipeline construction sequence for the raw water pipeline is as follows: •
Construction staking
•
Dewatering system installation (where required)
•
Trench excavation
•
Trench bedding installation and preparation
•
Pipe installation
•
Joint welding
•
Joint diaper installation
•
Initial backfill (imported material)
•
Excavated native soil classification, segregation, and moisture conditioning
•
Final backfill (with appropriate backfill material)
•
Surface restoration (pavement replacement where required)
•
Removal of dewatering system
•
Testing and Startup
4.4.
ESTIMATED TRUCK TRIPS
In addition to the construction equipment and crew identified in Tables 1 and 2, the raw water pipeline will generate truck trips to and from the construction site. The types of trucks traveling to the construction site include dump trucks to transport excavated material to and from the construction area, flatbed semi trucks and trailers to transport pipe, concrete ready-mix trucks to transport controlled density fill and concrete, and other miscellaneous trucks to support the construction activities. An estimated pattern of truck trips has been prepared and is shown in Figure 6. A trip is defined as a roundtrip to and from the construction site. The pattern assumes sufficient construction corridor width west of Interstate 5 to stockpile spoil adjacent to the trench excavation. The average production rate west of Interstate 5 is assumed to be 350 feet per day. The assumed average production rate east of Interstate 5 is 200 feet per day. The reduced production is attributable to narrower available construction corridors, higher traffic volumes, and more utilities. With the assumed production rates, the pipeline construction is expected to take approximately 54 weeks. This duration does not include initial pipe manufacturing in advance of construction.
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Figure 6. Estimated Construction Truck Trips per Week for the DWSP Raw Water Pipeline
1,000 900
Truck Trips per Week
800 700 600 500 400 300 200 100 0 1
3
5
7
9
11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53
Time (weeks) Mobilization and Demobilization
Spoil Truck
Import Truck
CDF Trucks
Pipe Truck
Backfill Trucks
Additional Miscellenous Truck Trips
4.5.
CONSTRUCTION STAGING AREAS
In addition to the construction corridor identified on the plan and profile drawings, the contractor will need periodic staging areas along the 12.7-mile pipeline alignment. The staging areas will be used to store equipment and materials, process backfill, and provide space for a construction office trailer. It is estimated that up to four staging areas along the alignment will be required. Each area could be up to several acres in size. The actual number, size, and location of the staging areas should be determined by the contractor.
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CITY OF STOCKTON DELTA WATER SUPPLY PROJECT
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RAW WATER PIPELINE ALIGNMENT RECOMMENDATIONS TECHNICAL MEMORANDUM
CITY OF STOCKTON DELTA WATER SUPPLY PROJECT
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CITY OF STOCKTON DELTA WATER SUPPLY PROJECT Raw Water Pipeline Alignment Recommendations Technical Memorandum Table of Contents CHAPTER 1
INTRODUCTION ............................................................................................ 1
1.1. BACKGROUND AND PURPOSE .......................................................................................... 1
CHAPTER 2
DESIGN CONSIDERATIONS ........................................................................ 4
2.1. DESIGN FLOWS AND PIPE SIZING..................................................................................... 4 2.2. PIPELINE APPURTENANCES............................................................................................... 5 2.2.1. Blowoffs ....................................................................................................................... 5 2.2.2. Air Vacuum/Air Release Valves .................................................................................. 5 2.2.3. Intertie Stations ............................................................................................................ 6 2.2.4. Access Manways .......................................................................................................... 6 2.3. MINIMUM DEPTH OF COVER ............................................................................................. 6 2.4. TRENCH SECTIONS............................................................................................................... 6 2.5. REQUIRED CONSTRUCTION CORRIDOR ......................................................................... 7
CHAPTER 3
ALIGNMENT ANALYSIS AND RECOMMENDATIONS......................... 10
3.1. DISCUSSION OF INDIVIDUAL ALIGNMENT SECTIONS.............................................. 10 3.1.1. Empire Tract from Intake Facility to West Eight Mile Road ..................................... 11 3.1.2. Empire Tract Along West Eight Mile Road ............................................................... 11 3.1.3. King Island Along Eight Mile Road........................................................................... 12 3.1.4. Undeveloped (West) Portion of Bishop Tract ............................................................ 13 3.1.5. Developed Areas of Bishop Tract West of Interstate 5 .............................................. 13 3.1.6. East of Interstate 5 Along Oak Grove Park ................................................................ 14 3.1.7. Eight Mile Road East of Oak Grove Park to North Thornton Road........................... 15 3.1.8. North Thornton Road to Davis Road ......................................................................... 15 3.1.9. Davis Road to Pixley Slough Crossing ...................................................................... 16 3.1.10. Pixley Slough – Eight Mile Road to Lower Sacramento Road .................................. 16 3.1.11. Lower Sacramento Road ............................................................................................ 17
CHAPTER 4
CONSTRUCTION CONSIDERATIONS ...................................................... 18
4.1. SUBSURFACE CONDITIONS.............................................................................................. 18 4.2. DEWATERING REQUIREMENTS ...................................................................................... 18 4.2.1. Coefficient of Permeability ........................................................................................ 19 4.3. CONSTRUCTION EQUIPMENT AND CREW SIZE .......................................................... 19 4.4. ESTIMATED TRUCK TRIPS................................................................................................ 20 4.5. CONSTRUCTION STAGING AREAS ................................................................................. 21
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Tables Table 1. Major Construction Equipment Required for DWSP Raw Water Pipeline Construction .............19 Table 2. Approximate Crew Size for DWSP Raw Water Pipeline Construction ........................................19
Figures Figure 1. Delta Water Supply Project Vicinity Map ....................................................................................1 Figure 2. Parallel Pipeline Total Dynamic Head (TDH) at 160 mgd ............................................................5 Figure 3. Typical Trenching Operation .........................................................................................................7 Figure 4. Ideal Construction Corridor Width ................................................................................................8 Figure 5. Minimum Construction Corridor Width ........................................................................................9 Figure 6. Estimated Construction Truck Trips per Week for the DWSP Raw Water Pipeline ...................21
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CHAPTER 1 INTRODUCTION 1.1.
BACKGROUND AND PURPOSE
The purpose of this technical memorandum is to evaluate and recommend an alignment for the City of Stockton’s Delta Water Supply Project (DWSP) raw water pipeline in support of the environmental permitting process. This memorandum evaluates the potential alignments along Eight Mile Road and recommends a conceptual level alignment for the raw water pipeline. The pipeline will convey water from the intake on the southwest corner of Empire Tract adjacent to the Stockton Deep Water Channel to the City’s planned new treatment facility located off Lower Sacramento Road (See Figure 1).
Figure 1. Delta Water Supply Project Vicinity Map
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The pipeline will be built in two phases—an initial 54-inch pipeline followed in the future by a parallel 72inch pipeline when additional capacity is needed. Objectives considered during the alignment evaluation include: •
Minimizing overall project cost
•
Minimizing construction risk to the City of Stockton
•
Choosing an alignment that is unlikely to adversely impact the schedule
•
Choosing an alignment that can be adequately maintained for the pipeline’s service life
•
Minimizing impacts to the public during construction
The alignment recommended will consider construction of both the initial and future parallel pipelines, although this memorandum will focus on the 54-inch pipeline. The initial pipeline alignment will be routed to allow construction of the future pipeline without crossings between the two pipelines. A preliminary pipeline route was previously identified in the City of Stockton Delta Water Supply Project Feasibility Report dated January 2003 (Feasibility Report). The pipeline route heads north from the intake structure approximately 6,600 feet to Eight Mile Road, then heads east parallel to Eight Mile Road for approximately 48,000 feet to one of the three Water Treatment Plant Site “C” alternatives. After the Feasibility Report was published, the City of Stockton purchased a 127-acre parcel for constructing the Water Treatment Plant (WTP) located at 11373 North Lower Sacramento Road. The site purchased by the City of Stockton is further away from the intake facility than the Site “C” alternatives described in the Feasibility Report. The additional distance adds approximate 2.5 miles in length to the raw water pipeline. The approximate length of the raw water pipeline is 67,000 feet. A conceptual-level set of raw water pipeline drawings is included with this technical memorandum. Alignment alternatives are shown in cross-section view at the back of the drawing set. Key assumptions incorporated into the recommended alignment include the following: •
The recommended pipeline alignment uses existing public right-of-way where available.
•
Except for special crossings, open cut trenching construction is anticipated.
•
Where minor ditch crossings (water surface less that 15 feet in width) are required, it is assumed that the ditch will be temporarily dammed to install the pipeline using open cut trenching, and then restored after completion of the crossing to currently existing conditions.
•
Where right-of-way acquisition will be required for construction of the 54-inch pipeline, it is preferred that the entire right-of-way acquisition for both the initial and future pipeline be acquired.
•
Where right-of-way will only be necessary for the future pipeline, acquisition will be deferred to a later date.
Limitations on the accuracy and completeness of the alignment analysis include the following: •
Utility search is not part of the scope for this conceptual-level effort.
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•
No right-of-way (ROW) engineering has been performed. In some cases, information was readily available indicating the width of the ROW; however, the exact limits of the ROW were not determined by survey, and the limits shown are only approximate.
•
A detailed survey was not performed. Elevations in other areas are estimated using USGS 7.5-minute maps and surface features identified during field investigation. Pipeline stationing is approximate.
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CHAPTER 2 DESIGN CONSIDERATIONS This section discusses the design issues considered when evaluating the various alignment alternatives. Although some design criteria are discussed, a formal Basis of Design Report should be prepared as part of the final design.
2.1.
DESIGN FLOWS AND PIPE SIZING
Near-term water demands require an initial design capacity of the DWSP WTP of 30 million gallons per day (mgd). This initial capacity will be increased incrementally as necessary to meet long-term potable water demands within the City of Stockton Metropolitan Area (COSMA). Long-term demands include the nearterm demands as well as an assumed constant municipal growth rate of 1.9 percent from 2015 to 2050. These water demands are assumed to occur within the general Plan Boundary within and outside of the Urban Services Area. The required capacity of the DWSP to meet long-term demands is 160 mgd. To address both near and long-term demands, the raw water facilities will consists of an initial 54-inch diameter pipeline, (to meet near-term demand and provide for some future demand) and a 72-inch pipeline to provide the required long-term demand capacity. The timing of the design and construction of the 72-inch pipeline is dependent on future needs and is not a part of the initial project. A conceptual level system curve of the dual raw water pipeline is shown in Figure 2. In addition to the recommended 54-inch/72-inch dual pipe combination, a 54-inch/60-inch commination was also considered. As shown in the figure, under long-term operating conditions the 54-inch/60-inch combination would require approximately 100 feet of additional hydraulic head to operate, resulting in considerable additional operations and maintenance costs over the useful life of the facilities and increased wear and tear of the intake pumps. Design flow velocities in the 54-inch/72-inch system would be about 5 and 6 feet per second, respectively, which is considered appropriate. Design flow velocities in the 54-inch/60-inch system would be 6.6 and 7.2 feet per second, respectively, which is considered to be higher than optimum.
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Figure 2. Parallel Pipeline Total Dynamic Head (TDH) at 160 mgd 300 TDH (feet) 54-inch C = 100
250
TDH (feet) 60-inch C = 100
TDH (feet) 72-inch C = 100
TDH (feet)
200
150
100
50
0 0
10
20
30
40
50
60
70
80
90
100
110
120
Flow (mgd)
2.2.
PIPELINE APPURTENANCES
In order to properly operate and maintain the raw water pipeline, appurtenant facilities are required. Appurtenant facilities for the DWSP raw water pipeline will include blowoffs, air vacuum/air release valves, intertie stations, and access manways. Standard details and preliminary locations for these facilities are included in the attached recommended alignment drawings. A brief discussion of the function of these facilities is provided in the following subsections. 2.2.1.
Blowoffs
Blowoffs will need to be included along the pipeline to enable dewatering of the pipeline. Blowoffs will be located at all low elevations in the pipeline and on the upstream side of isolation valves. A blowoff consists of a bottom outlet tee (sized for the pipe volume to be drained) with a shutoff valve on the branch leg of the tee that can be operated to allow removal of water from the system. 2.2.2.
Air Vacuum/Air Release Valves
There are generally two types of air valves: air and vacuum valves and air release valves. Air and vacuum values are used to admit air into a pipe to prevent formation of vacuum that may be a result of valve operations, rapid draining such as a line break, a column separation, or other causes. Without air vacuum valves, a vacuum can cause the pipe to collapse from atmospheric pressure. Air release valves are required at
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high points along a pipe to release any air buildup in the pipeline. Air escapes from water within the pipe 1) while filling the pipeline, 2) at low-pressure zones created by partially open valves, 3) at locations of cascading flow in a partially filled pipe, 4) because of variations in flow velocity caused by changing pipe diameters and slopes, and 5) at changes in pipeline elevations. In reducing the accumulation of air within a pipe, air release valves increase the flow rate of water (by enlarging the cross-sectional flow area) and decrease headloss in the pipeline. 2.2.3.
Intertie Stations
Intertie stations connect the two pipelines periodically along the alignment and allow for isolation of a portion of either pipeline for maintenance or repair without taking the entire pipeline out of service. A maximum spacing of 2.5 miles is recommended. Since the raw water pipelines will be constructed in phases, the intertie stations for the initial phase will be limited to two isolation valves, a tee, and a blind-flange oriented in the direction of the future parallel pipeline. 2.2.4.
Access Manways
Access manways allow access into the pipeline for inspection, maintenance, and repair. Access points consist of a flanged outlet oriented vertically. Removal of the flange is required for access. Typically manways are located adjacent to or combined with other appurtenances and should be provided at approximately 2,000-foot intervals. Due to the preliminary nature of the recommended alignment, manways have not been shown on the attached drawings, but should be incorporated during final design.
2.3.
MINIMUM DEPTH OF COVER
Selection of a minimum depth of cover is a balance between cost and risk. Generally, the deeper a facility is buried, the more costly construction becomes. Typical minimum covers for small diameter (non-gravity) utilities range from 3.5 to 5 feet. By installing the raw water pipeline deeper than 5 feet, potential conflicts with many existing and future adjacent utilities is avoided. In agricultural areas where the pipeline will not be in road right-of-way, farming operations, including construction of irrigation canals, tilling, and deep-ripping, must be considered. To minimize risk of damage to the raw water pipeline, and to provide a vertical corridor for future small diameter utilities, a minimum cover of 7 feet was used.
2.4.
TRENCH SECTIONS
Trenches for this size pipeline typically need to be excavated to about 1 foot below the invert of the pipe. Bedding should be installed beneath the pipe and then backfilled with imported material to 1 foot above the top of pipe. In areas where soil conditions permit (and suitable shoring is provided), trench sections can be constructed vertically with 1- to 1.5-foot clearances from pipe springline to shoring. The resulting trench widths should range from 7 to 8 feet for the 54-inch pipe and 8.5 to 9.5 feet for future parallel pipeline. Conceptual standard trench sections are shown in the drawing set. Where more space is available, such as unimproved areas, the trench section walls need not be vertical above the pipe zone. Consideration was also given to the minimum recommended clearance between the 54-inch and future 72inch pipelines. To allow for the future construction of the 72-inch pipeline with minimal interference from the 54-inch pipeline, and to allow for maintenance and operation of both pipelines, and minimum distance of 10.5 feet (about two pipe diameters) is assumed.
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2.5.
Phase II Tasks
REQUIRED CONSTRUCTION CORRIDOR
Typical pipeline construction for this size raw water facility consists of trench excavation, pipe installation, and backfill operations (see Figure 3). A dewatering operation in advance of trench excavation will also be required for pipeline construction west of Interstate 5. Generally, the more room a contractor has to stage for and construct a pipeline, the more efficient the operation will be. For example, in areas of limited available construction corridor, the contractor will have to haul soil excavated from the trench (spoil) away from the trenching operation and haul it back during the backfill operation. In areas with wider available construction corridors, the contractor would typically cast the spoil off to the side of the trench, install the pipe, and backfill the trench using the piled soil. In areas of limited construction corridor, the pipe will be unloaded directly from delivery trucks. In areas where more construction corridor is available, the pipe could be staged along the alignment in advance of the pipe installation operation. It is estimated that in open areas, where sufficient room is available, the contractor would use an 80-foot wide corridor to maximize construction efficiency (see Figure 4).
Figure 3. Typical Trenching Operation
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Figure 4. Ideal Construction Corridor Width
In areas encumbered by existing improvements, high-volume roadways, or environmentally sensitive areas and narrower construction corridor will be necessary. The minimum practicable construction corridor is estimated to be 47 feet (see Figure 5). This corridor provides for the width and turning movement of a 320L Mass excavator and assumes all other construction equipment (i.e., spoil haul trucks, pipe laying crane, pipe delivery trucks) will share the remaining corridor width.
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Figure 5. Minimum Construction Corridor Width
Where sufficient corridor width is available and traffic volumes warrant (i.e. Eight Mile Road east of Interstate 5) the design alignment should allow one 12-foot wide lane of traffic in each direction. In other areas with less traffic volumes, one lane of alternative traffic may be acceptable. An encroachment permit and/or maintenance agreement will be required from the City of Stockton and San Joaquin County for utilization of, and construction work within, the right-of-way maintained by the respective municipalities.
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CHAPTER 3 ALIGNMENT ANALYSIS AND RECOMMENDATIONS For the purposes of analysis, the project is divided into sections with similar characteristics and issues affecting the pipeline alignment. The 10 segments used for the alignment analysis are listed below, followed by a narrative discussion of the specific issues related to each section in Section 3.1. •
Empire Tract from Intake Facility to West Eight Mile Road
•
Empire Tract along West Eight Mile Road
•
King Island Along Eight Mile Road
•
Undeveloped (West) Portion of Bishop Tract
•
Developed Areas of Bishop Tract West of Interstate 5
•
Developed area of Bishop Tract east to Interstate 5
•
East of Interstate 5 along Oak Grove Park
•
Eight Mile Road East of Oak Grove Park to North Thornton Road
•
North Thornton Road to Davis Road
•
Davis Road to Pixley Slough Crossings
•
Pixley Slough – Eight Mile Road to Lower Sacramento Road
•
Lower Sacramento Road
In addition to the individual alignments, there are several key crossings the pipeline will have to make, all located along West Eight Mile Road. These include: •
A large drainage ditch/pump station at the western terminus of Eight Mile Road
•
Honker Cut, between Empire Tract and King Island
•
Bishop Cut, between King Island and Bishop Tract
•
Interstate 5
•
Thornton Road
•
Davis Road
•
Western Pacific Railroad tracks
These crossings are discussed in this technical memorandum only as they affect alignment.
3.1.
DISCUSSION OF INDIVIDUAL ALIGNMENT SECTIONS
This section discusses the requirements and restrictions to constructing the pipeline along the individual sections. It also recommends a preferred alignment alternative.
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3.1.1.
Phase II Tasks
Empire Tract from Intake Facility to West Eight Mile Road
The Empire Tract levee is the largest physical feature affecting construction along this segment of pipeline. In addition, there are several small irrigation ditches that must be crossed. The alignment must be located a safe distance east of the toe of the levee. Reclamation District 2029 (RD-2029) owns the first 150 feet extending landward from the centerline of the levee and has jurisdiction over an additional 100 feet landward. The centerline of the levee, although not well-defined, is assumed to be the centerline of the road in the area of concern. The levees in the area are substandard and seepage of water is consistently observed. If funds become available, the levees will likely be upgraded. If this were to happen, the levee would be enlarged on the landward side and a pipeline built too close to the toe of the levee could have significant quantities of fill placed atop it. Such action would make maintenance of the pipeline impractical and necessitate future relocation of the pipeline. In addition, the pipeline would likely not be designed to handle the earth loads imposed by the additional fill. The toe of the levee ranges from approximately 125 feet to 160 feet from the center of the levee road. There is a series of drainage canals that collect runoff and convey it westerly to canals that run roughly parallel to the levee near the levee toe. Approximately 1,700 feet southerly of Eight Mile Road, the canals run roughly parallel to the levee, with some larger canals collecting the runoff to the base of the levee in a westerly direction. Locating the pipelines easterly of the canals would place the alignment in most cases over 200 feet from the middle of the levee. In order to avoid delays due to review and conditions imposed by RD-2029 and to construct the pipeline a sufficient distance away from the levee to avoid levee integrity and seepage issues, it is recommended that the alignment be located at least 250 feet from the levee centerline. An 80-foot wide strip of easement will be required from the end of the intake facility property to West Eight Mile Road. The pipeline can be constructed with the standard 7 feet of cover along the alignment, except where the irrigation must be crossed. The recommended alignment is shown on Drawings C1, C2, and C3 of the attached set of conceptual drawings. 3.1.2.
Empire Tract Along West Eight Mile Road
This section of pipeline is approximately 11,000-linear-feet long and will extend from a drainage ditch crossing at the western end of Eight Mile Road to Honker Cut. Eight Mile Road is a two-lane road in this section with an average total paved width of approximately 23 feet. It is assumed that the road will be widened to two lanes in each direction during the pipeline’s design life. A large drainage ditch (approximately 25 feet wide at the water surface) runs parallel to the road on the south side. The pipeline will have to be located on the north side of the large drainage ditch in order to have access for maintenance. The existing right-of-way is believed to be 90 feet wide, beginning near the north edge of the ditch and extending northward (based on County Survey No. 4218.) The exact ROW boundary is still to be determined. Potential locations for the pipelines include the following: •
Between (south of) the road and the ditch
•
Under the road
•
North of the road
Approximately 20 feet is available between the road and the ditch. This is only sufficient to construct one phase of the pipeline in this location.
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The paved road width in this area averages approximately 23 feet. In order to construct both pipelines under the road, the trenches would extend slightly onto the shoulder of each side. North of the road lies farmland with no physical limitation to construction except a few ditch crossings. Both pipelines could be constructed north of the road; however, it remains to be determined exactly where the existing ROW ends. It appears probable that at least one pipeline could be constructed with the entire trench within the existing ROW, although some additional ROW might be needed for construction. The Phase 2 pipeline most likely will have a portion of the trench beyond the existing ROW, with a portion of the construction zone beyond the existing ROW. Both pipelines can likely be installed within the existing ROW alongside the road, saving the significant cost of road reconstruction, minimizing traffic control expenses, and allowing higher productivity. It is therefore recommended that both the 54-inch and future 72-inch pipelines be constructed to the north of the road. The Phase 1 pipeline will be constructed closer to the road to minimize the ROW requirement. The 54-inch pipeline will be constructed closer to the road to minimize the ROW requirement. The initial pipeline should be designed to handle additional earth load as a result of potential future road widening (approximately 6 additional feet of cover). At the eastern end of Empire Tract, the pipeline will have to be routed through Honker Cut to King Island. Honker Cut is approximately 425 feet wide. Empire Tract and King Island both have levees that route northsouth along Honker Cut. On the south side of Eight Mile Road is a large drainage ditch on Empire Tract and a marina on the King Island side. A drainage ditch slightly smaller than that on Empire Tract begins approximately 100 feet east of the center of the King Island levee. The pipeline cannot be routed under Eight Mile Road because of the bridge structure. Several farming structures exist to the north, beginning approximately 375 feet west of the levee and continuing approximately 400 feet north of Eight Mile Road on Empire Tract. There are no apparent obstructions to the north of Eight Mile Road on King Island immediately east of the Honker Cut Levee. It is therefore recommended that the pipeline route to the north of Eight Mile Road around the farm structures for the Honker Cut crossing. The routing also includes several advantages: •
The alignment eliminates the need to cross the road for the Honker Cut crossing, since the pipeline to the west is already on the north side of the road.
•
The alignment allows for sufficient staging area for the microtunneling operation away from existing improvements.
•
The alignment avoids the buildings and marina structures to the south of Eight Mile Road on the King Island side. 3.1.3.
King Island Along Eight Mile Road
This section of pipeline is approximately 11,200 linear feet (LF) and will extend from Honker Cut to Bishop Cut. Eight Mile Road is a two-lane road in this section with an average total paved width of approximately 22.5 feet. A large drainage ditch (approximately 12 feet wide at the water surface) runs parallel to the road on the south side for much of the alignment. Utility poles run parallel to the road on the north side for the entire alignment. The pipeline will have to be located north of the large drainage ditch in order to have access for maintenance. The existing right-of-way is 90 feet wide, begins near the north edge of the ditch, and extends northward, but the exact ROW boundary is still being determined. The approximate ROW was determined from a survey map by Albert Sanguinetti in 1973. Potential locations for locating the pipelines include the following:
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•
Under the road
•
North of the road, north of the existing utility poles
There is not sufficient space to safely construct a pipeline between the drainage ditch to the south and the road without removing some pavement. Sufficient space exists to construct each phase under the road, particularly if some of the space between the road and the drainage ditch to the south is utilized. The presence of utility poles makes construction immediately north of the road infeasible, in addition to a small drainage ditch (approximately 2 feet wide and 1.5 feet deep) where the poles are located. Because of the poles, any alignment to the north would be more likely to be beyond the existing ROW, especially if both phases were sited in this location. It is possible that one phase might be within the existing ROW. It is recommended that the first phase be constructed north of the telephone poles (within existing the ROW) if possible. This will reduce costs due to eliminating pavement restoration and reducing traffic control; it will also avoid crossing Eight Mile Road after the pipeline is installed under Honker Cut. It is recommended that the 72-inch pipeline be constructed to the north of the 54-inch pipeline; it is likely that the ROW will have to be acquired for the future pipeline. 3.1.4.
Undeveloped (West) Portion of Bishop Tract
This portion of pipeline is still within agricultural lands and extends from Bishop Cut eastward approximately 3,200 feet. The paved roadway is approximately 31 feet wide and the existing ROW is 80 feet wide through this area. This portion of the pipeline can be seen on Sheets C13 and C14 of the Plan and Profile drawings and Sheet X1 of the Cross-Section drawings. During summer 2004, small ditches were observed on each side of the road within the farmed areas, but the ditches were not present during the October 2004 field visit. Potential locations for the pipeline route include the following: •
Under the paved roadway
•
North of the paved roadway
•
South of the paved roadway.
Constructing beyond the paved roadway can minimize construction cost and impacts to the public. Therefore, a practical route beyond the paved roadway is desirable. Because the pipeline from King Island will cross Eight Mile Road on the north side of the road, it is recommended that the pipeline be routed north of the paved roadway in this section. To be consistent with the other sections considered, the initial pipeline should be located closer to the road and the future pipeline north of the initial pipeline. 3.1.5.
Developed Areas of Bishop Tract West of Interstate 5
This portion of the pipeline comprises approximately 9,000 LF and heads through areas with significant recent, current, and future development, including the following: •
A housing development (Spanos Park West) recently completed on the south side of Eight Mile Road.
•
An outdoor shopping mall with minimal existing road frontage is still being developed on the south the south side of the road.
•
A completed golf course on the north side of Eight Mile Road.
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•
Phase II Tasks
A new housing development (Westlake at Spanos Park West) has been proposed on the south side of Eight Mile Road immediately west of the Spanos Park West housing development.
Currently the western 3,300-foot portion has a similar undeveloped layout as the portion of Bishop Tract immediately west (shown on Section 3 on Drawing X1), except that there is a defined ditch paralleling the road along the south end, and there is a depression that would probably not be considered a roadside ditch along the north side of the road. The eastern 5,700 feet has significant development and wider pavement, as shown on Section 4 on Drawing X1. The plan and profile for the western portion of this area appears on Sheets C14 and C15, while that for the eastern portion appears on Sheets C15 through C17. If no development occurs in the eastern portion prior to the initial 54-inch pipeline construction, it is recommended that the pipeline follow the alignment recommended in Section 3.1.4 for the undeveloped portion of Bishop Tract. The ultimate ROW width will be 134 feet, but currently the known ROW is 80 feet in the western portion. In the newly developed areas (beginning at the Spanos Park housing development), the existing ROW may currently be more than 80 feet wide. Here the paved roadway is wide enough to potentially construct each phase under lanes on a single half of the street. South of the road exists significant landscape associated with the housing development, which probably has significant utility infrastructure. To the north of the road are several light poles and a utility pole corridor. Several mounds exist between the light poles and utility poles. Construction outside the paved roadway is likely impractical due to the existing utilities and layout of the land. Therefore, each pipeline should be constructed under pavement barring a change in conditions due to further development. Construction would have the least impact, and a future pipeline could avoid crossing the initial pipeline by locating the initial pipeline just north of road centerline, then locating the future pipeline north of the initial pipeline. Locating the pipelines on the north side of the road will also minimize traffic impacts when constructing near the Interstate 5 crossing, which was previously determined to be located on the north side of Eight Mile Road due to development on the south side of the road. If there is sufficient ROW and there are no interfering utilities, it may be possible to construct the Phase 2 pipeline to the north of the existing pavement to save on construction cost, but such evaluation should be performed during future design of said pipeline. 3.1.6.
East of Interstate 5 Along Oak Grove Park
This section of Eight Mile Road has a single lane in each direction with a current total paved width of approximately 32.5 feet. On the south side of the road there is gravel nearly to the fence line for Oak Grove Park, 35 feet beyond the edge of existing pavement. To the north is 10 feet of unimproved, uneven ground for approximately 25 feet to a row of mature trees, and then vineyards north of the trees. The existing and ultimate ROWs for this section are 80 and 134 feet wide, respectively, and there is sufficient space to construct each pipeline phase under pavement or on either side of the existing paved roadway. A portion of the shoulder will have to be removed and repaired if each pipeline is located within the area immediately north of the road and the existing trees, if the trees are not to be removed. Since it has already been determined that the pipeline will be routed under Interstate 5 on the north side of Eight Mile Road, it is recommended that the Phase 1 pipeline be routed just beyond the north edge of the pavement. The corridor would allow two-way traffic to be maintained in each direction without removing the mature trees. The Phase 2 pipeline location may be greatly affected by future development, including road widening. Tentatively it is recommended that the pipeline be located with the north end of the trench 5 feet clear of the row of trees to the north, which provides about 7 feet of clearance from the Phase 1 pipeline. If
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the trees are to be removed as a result of development, the pipeline can be moved further north to increase the clearance. 3.1.7.
Eight Mile Road East of Oak Grove Park to North Thornton Road
This section of Eight Mile Road has a housing development on the south side and agricultural land to the north. According to the Eight Mile Road Specific Plan by Omni-Means (approved February 16, 1994), the roadway has a current ROW of 80 feet and will have an ultimate ROW of 134 feet. The ROW widens to 160 feet for the approach to the North Thornton Road intersection. The ROW appears to be centered on the paved median approaching North Thornton Road. Beginning at the south edge of pavement, the existing roadway consists of a paved shoulder approximately 18.5 feet wide and two eastbound lanes totaling 32.5 feet in width. The traveled lanes are divided by a 12-foot wide asphalt median. North of the median is a single westbound lane and paved shoulder 14.75 feet in width. Several alignment options are possible given the available space: •
Locate each pipeline under the eastbound traffic lanes.
•
Locate one under the paved shoulder on the south side and the other under an eastbound lane.
•
One pipeline could be placed under the median and the other under the westbound lane.
•
Locate one pipeline under the westbound lane and the other north of the paved section of the road.
•
Place both pipelines north of the paved roadway.
It is recommended that the Phase 1 pipeline be located beyond the north edge of the pavement. This will allow construction without pavement restoration and with minimal traffic control. Most of the construction corridor is within the existing ROW, although a portion may be within the planned ultimate ROW and require some efforts to secure for construction. The Phase 2 pipeline should be tentatively located 10 feet clear to the north of the Phase 1 pipeline. 3.1.8.
North Thornton Road to Davis Road
The portion from North Thornton Road to Davis Road is approximately 5,400 LF long . The paved roadway is approximately 40 feet wide, with one lane in each direction and utility poles located approximately 18 feet south of the edge of pavement. A small ditch is located approximately 6 feet beyond the north edge of the pavement. Construction has begun on a housing development on the south side of Eight Mile Road, approximately 2,700 feet east of North Thornton Road. The housing development currently takes up approximately 1,200 feet of road frontage. The existing ROW is 80 feet wide and centered approximately on the road centerline; the ultimate ROW per the Eight Mile Road Specific Plan is 134 feet. It would be possible to construct each pipeline under existing pavement or on either side of existing pavement. In order to avoid the utility poles and housing development, an alignment south of the paved roadway is not recommended. If located north of the road without disturbing the ditch, the Phase 1 pipeline would likely be located within the existing ROW but within the ultimate ROW; therefore, some ROW acquisition would probably be required. It would also be possible to construct the first and second phase under each of the existing lanes. It is recommended that the Phase 1 pipeline be constructed north of the small ditch on the north side of the road to minimize pavement restoration and traffic control costs. The alignment will also minimize the impact
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to the public during construction. The tentative location for the Phase 2 pipeline should be to the north of the Phase 1 pipeline with 10 feet of clearance between each pipeline. 3.1.9.
Davis Road to Pixley Slough Crossing
The portion of the pipeline from the Davis Road crossing to where Pixley Slough crosses under Eight Mile Road is approximately 5,300 LF. Approximately 500 feet east of Davis Road, Pixley Slough begins to run parallel to Eight Mile Road on the south side, and is separated from the road by a floodwall. The total paved width of the two lanes totals approximately 38.5 feet in this area. A utility pole parallels the road on the north side, approximately 21 feet beyond the edge of pavement. Approximately 2,200 feet east of Davis Road, the pipeline will cross the Union Pacific Railroad tracks. The Eight Mile Road Specific Plan indicates an existing ROW of 120 feet extending approximately 40 feet north of road centerline, with the ultimate ROW extending at least 129 feet north of road centerline for the entire length, and as far as 278 feet north of road centerline at the railroad track crossing. Due to the floodwall, the only practical locations for the pipeline are under the roadway to the north of the existing pavement. The Phase 1 pipeline could be constructed north of the existing pavement with the edge of trench 10 feet clear of the utility poles. This alignment would allow construction of the pipeline with the following benefits: •
Within existing ROW.
•
No pavement restoration.
•
Limited traffic control and no lane closures. Approximately 14 feet of the north lane could be closed off for construction and there would be about 24.5 feet of pavement available for two-way traffic. If necessary, a portion of the gravel shoulder, over 20 feet in width, could be used for traffic lanes.
Because of the above benefits, it is recommended that the pipeline be constructed north of the paved portion of Eight Mile Road as shown on Section 4 of Drawing X2. For Phase 2, the recommendation is to tentatively place the pipeline further north as shown on the section, but development, including road widening and/or relocation of the utility pole, may change the construction conditions when the second pipeline is needed. 3.1.10. Pixley Slough – Eight Mile Road to Lower Sacramento Road The pipeline alignment will meet up with Pixley Slough approximately 1,300 feet west of Lower Sacramento Road. The floodwall on the south side of Eight Mile Road ends here, where the slough crosses the road. In this area, Pixley Slough drains in a southwesterly direction and due to increased elevation does not continually contain large volumes of water; its flow is more like a creek. Options for routing the pipeline include the following: •
Crossing under Pixley Slough and continuing east approximately 1,300 LF to the intersection with Lower Sacramento Road, then routing north parallel to Lower Sacramento Road for approximately 1,000 LF, including a second crossing of Pixley Slough. Total length of this alternative is 2,300 LF and includes two jacking operations to cross Pixley Slough totaling approximately 500 feet.
•
Routing the pipeline in a northwesterly direction parallel to Pixley Slough for a total length of approximately 1,700 feet.
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The second option would be significantly less expensive, provides the least risk and easiest maintenance access by eliminating the slough crossings, and would avoid a lengthy permitting process to jack under the slough. The pipeline would be routed through a vineyard area that would require new ROW acquisition, but the time required to obtain the ROW would likely be comparable to or less than that for permitting crossing Pixley Slough twice. It is therefore recommended that the pipeline be routed parallel to Pixley Slough in this area. Considerations to align the pipeline in this area include the proximity to a flood control levee. The design slope on the landward side of the levee is 2.0 to 1.0 horizontal to vertical and excavation may not extend into the projection of the landward slope. A contractor could have restrictions on use of a patrol road alongside the levee during wet months when the roads are used to inspect the levees. The width of the patrol road generally ranges from 9.5 to 13.0 feet. Given the levee slope and that the trench of the Phase 1 pipeline will be approximately 9.5 feet deep, the pipeline will have to be located beyond the patrol road, at least 19 feet from the levee toe. The best construction option is to use the patrol road to transport materials to and from the site. The recommended alignment and location for Phases 1 and 2 is shown on Drawings C24 and C25, with a representative cross section on Section 1 of drawing X1. 3.1.11. Lower Sacramento Road After routing past Pixley Slough, the raw water pipelines will route parallel to Lower Sacramento Road for approximately 4,000 LF to a new treatment facility. It is important is to allow sufficient corridor for the treated water transmission line to be routed south from the treatment plant along Lower Sacramento Road to the distribution system. It is assumed that the treated water pipeline will be 30 inches in diameter to match the pipe at the planned connection point. The existing ROW in this stretch of Lower Sacramento Road is 80 feet wide and roughly centered on the road centerline. The “Lower Sacramento Road Special Purpose Plan” by Mark Thomas and Company, 1997, increases the ROW by 40 feet to the east for a planned expansion of the road to an expressway with two lanes in each direction and a 20-foot median. Because the road will be expanded to the east, an alignment to the west side of Lower Sacramento Road will allow for the easiest maintenance by placing the pipelines clear of traffic to the greatest extent possible. In order to avoid crossing the raw water pipelines, it is recommended that the treated water pipelines be routed to the east of the raw pipelines. It is therefore recommended that the Phase 1 pipeline be placed under the existing west (southbound) lane of traffic and the Phase 2 pipeline be placed on the flat shoulder just beyond the edge of pavement as shown on Section 2 of Drawing X1. The alignment also prevents the Phases 1 and 2 waterlines from crossing each other. The recommended alignment and location for Phases 1 and 2 is shown on Drawings C25 and C26.
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CHAPTER 4 CONSTRUCTION CONSIDERATIONS 4.1.
SUBSURFACE CONDITIONS
Subsurface conditions along the proposed pipeline were explored and evaluated by drilling 14 borings (B-1 through B-14), extending to depths of 21.5 to 41.5 feet below ground surface. The results of the field exploration program indicate that the subsurface conditions consist of generally medium dense sands, silty clayey sands, and stiff silty and sandy clays and silts. A layer of soft to medium stiff peat was encountered in borings drilled west of Interstate 5 extending to depths of 7 to over 23 feet below ground surface. The peat was overlain by 1 to 7 feet of fill soils. The peat generally increased in thickness towards the west. Groundwater levels were measured at depths ranging from 8 to 12 feet below ground surface corresponding to elevations -6 to -23 feet in Borings B-6 through B-13 and Boring B-19 drilled west of Interstate 5, along the pipeline and below the proposed on-shore intake structure. Groundwater was not encountered in borings drilled east of Interstate 5. Additional details on subsurface conditions are contained in the Delta Water Supply Project Preliminary Geotechnical Report.
4.2.
DEWATERING REQUIREMENTS
Minor to moderate dewatering may be required for construction of the pipeline. The proposed invert elevation of the pipeline will range from +11 to -27 feet, and the bottoms of the jacking and receiving pits will be at lower elevations, extending below -30 feet. Groundwater levels vary throughout the year. Between December and June, maximum groundwater levels are likely to be higher than those encountered in our field exploration program. For five months, between July and November, the groundwater levels are likely to be about elevation -6 feet or higher. The contractor should be responsible for selecting the appropriate range of groundwater levels for design of the dewatering system and for providing an adequate dewatering system during construction. A properly designed, installed, and operated dewatering system should: •
Lower the water table inside the excavation or intercept seepage that will emerge from the sides or the bottom of the excavation
•
Improve the stability of the excavation and prevent disturbance of the bottom of the excavation
•
Provide a reasonably dry working area in the bottom of the excavation
•
Provide for collection and removal of surface water and rainfall
It is recommended that the water level be maintained below the bottom of the excavations until the pipelines are placed and backfilled.
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Water collected during dewatering should be tested for contamination prior to disposal. The potential for contamination of groundwater has not been evaluated as part of this study. However, it is the responsibility of the contractor to obtain the proper permits and dispose of the discharged water. 4.2.1.
Coefficient of Permeability
To aid in the design of dewatering systems, we evaluated the coefficient of permeability of the soils, based on the results of laboratory grain size distribution (sieve analyses) tests. Samples of sandy soils drilled for this study indicate that the percentages of fines in materials that will be in dewatering areas are quite variable. Hazen’s formula (Lambe and Whitman, 1979), which estimates permeability from the grain size represented by the 10 percent fraction by weight, was used to estimate permeability. Based on the results of our analyses, it is recommended that coefficients of permeability of 10-2 centimeters per second (cm/sec), 5 x 10-4 cm/sec, and 10-5 cm/sec be used in analyses of groundwater flow for sandy, silty, and clayey soils, respectively. A coefficient of permeability 10-5 cm/sec is recommended for the peat layers at the site. Additional details on expected groundwater and dewatering requirements are contained in the Delta Water Supply Project Preliminary Geotechnical Report.
4.3.
CONSTRUCTION EQUIPMENT AND CREW SIZE
The major construction equipment and approximate crew size required to perform the pipeline construction operation shown in Figure 3 are presented in Tables 1 and 2 respectively.
Table 1. Major Construction Equipment Required for DWSP Raw Water Pipeline Construction Equipment CAT 325L Mass Excavator CAT 956F Wheel Loader 10-wheel Water Truck 30 Ton RT530 Grove Crane CAT CS-323 Smooth Drum Vibratory Compactor
Quantity 2 1 1 1 1
Table 2. Approximate Crew Size for DWSP Raw Water Pipeline Construction Typical Pipe Laying Crew Foreman/Superintendent Grade Setter Operators Laborers/Pipe Fitters Welder
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Quantity 1 1 4 6 2
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The anticipated pipeline construction sequence for the raw water pipeline is as follows: •
Construction staking
•
Dewatering system installation (where required)
•
Trench excavation
•
Trench bedding installation and preparation
•
Pipe installation
•
Joint welding
•
Joint diaper installation
•
Initial backfill (imported material)
•
Excavated native soil classification, segregation, and moisture conditioning
•
Final backfill (with appropriate backfill material)
•
Surface restoration (pavement replacement where required)
•
Removal of dewatering system
•
Testing and Startup
4.4.
ESTIMATED TRUCK TRIPS
In addition to the construction equipment and crew identified in Tables 1 and 2, the raw water pipeline will generate truck trips to and from the construction site. The types of trucks traveling to the construction site include dump trucks to transport excavated material to and from the construction area, flatbed semi trucks and trailers to transport pipe, concrete ready-mix trucks to transport controlled density fill and concrete, and other miscellaneous trucks to support the construction activities. An estimated pattern of truck trips has been prepared and is shown in Figure 6. A trip is defined as a roundtrip to and from the construction site. The pattern assumes sufficient construction corridor width west of Interstate 5 to stockpile spoil adjacent to the trench excavation. The average production rate west of Interstate 5 is assumed to be 350 feet per day. The assumed average production rate east of Interstate 5 is 200 feet per day. The reduced production is attributable to narrower available construction corridors, higher traffic volumes, and more utilities. With the assumed production rates, the pipeline construction is expected to take approximately 54 weeks. This duration does not include initial pipe manufacturing in advance of construction.
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Figure 6. Estimated Construction Truck Trips per Week for the DWSP Raw Water Pipeline
1,000 900
Truck Trips per Week
800 700 600 500 400 300 200 100 0 1
3
5
7
9
11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53
Time (weeks) Mobilization and Demobilization
Spoil Truck
Import Truck
CDF Trucks
Pipe Truck
Backfill Trucks
Additional Miscellenous Truck Trips
4.5.
CONSTRUCTION STAGING AREAS
In addition to the construction corridor identified on the plan and profile drawings, the contractor will need periodic staging areas along the 12.7-mile pipeline alignment. The staging areas will be used to store equipment and materials, process backfill, and provide space for a construction office trailer. It is estimated that up to four staging areas along the alignment will be required. Each area could be up to several acres in size. The actual number, size, and location of the staging areas should be determined by the contractor.
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