HomeMy WebLinkAboutTract 6916 Sewer StudyTable of Contents
I. Introduction ....................................................................................... 1
A. Background and Scope
B. Phasing
C. City Standards
II. Proposed Sewer Improvements ....................................................... 1
A. City Flow Projection Formulas
B. General Flow Diagram
C. Line Sizing
III. Connection to Existing Sewer System ............................................ 2
A. Existing System
B. Proposed Discharge Locations
IV. Future Connection ............................................................................ 3
V. Conclusion ......................................................................................... 4
References
Figures
1. Vicinity Map
2. Project Location
3. Phasing Exhibit
4. Sanitary Sewer Master Plan
Appendices
A. Calculations
B. City of Bakersfield Standards for Sanitary Sewers
C. Tract 6916 Conditions of Approval
SEWER STUDY
FOR
TRACT 6916
I. Introduction
A. Background and Scope
Tract 6916 is a proposed 2-phase residential community to be developed
by Lennar Homes. The 40-acre tract is located in the City of Bakersfield
approximately 1,500 ft south of the intersection of Panama Lane and
Mountain Vista Drive. More specifically, it is located within the Southwest
Quarter of the Northeast Quarter of Section 30, Township 30 South,
Range 27 East. The vicinity and location maps are shown in Figures 1 and
2. The development will consist of 150 single-family homes. Located in
the Southwest part of Bakersfield, the site ranges in elevation between
343 ft to 349 ft.
Tract 6916 is in the City of Bakersfield Wastewater Treatment plant #3
service area that has been analyzed and designed accordingly.
The Objective of this study is to:
1. Describe the proposed sewer collection system to serve the new
development.
2. Analyze the existing sewer collection system which serves the City in
this area.
3. Develop a master sewer plan that will effectively address and manage
sewage flows generated by the new development.
The proposed sewer system within Tract 6916 will be operated and
maintained by the City of Bakersfield.
B. Phasing
As noted above, Tract 6916 will be developed in 2 phases. Figure 3 shows
the limits of each phase and the number of lots that will be developed. It is
anticipated that each phase will be implemented numerically.
Tract 6916 Sewer Study Page 2 of 4
C. City Standards
The sewer system proposed for Tract 6916 will be designed and
constructed per City of Bakersfield Standards and the Subdivision and
Engineering Design Policy Manual.
II. Methodology
The sewer collection system hydraulic analysis was performed using the
Manning’s equation. The average sewer generation duty factor for single-
family dwellings and the peak factors were determined per Section 1.2.1
of the City of Bakersfield Subdivision and Engineering Design Manual.
The following is a list of assumptions used in our analysis:
1. Manning coefficient of 0.011 for PVC pipes.
2. A maximum d/D ratio of 50% for the proposed sewer pipes.
3. The minimum design velocity of 2 feet/second for pipes flowing full
or half-full (minimum pipe slopes are calculated according to this
criteria).
4. The maximum distance of 400 feet between manholes
5. One tenth foot energy drop is allowed for flow through manholes
with a deflection of 45o or more.
6. Invert elevation of varying size pipes leading into and out of
manholes are set by matching elevations of the eight-tenths depth.
Invert elevations of equal size pipes leading into an out of
manholes without deflection are equal.
7. The sanitary sewer alignment is generally located 5 feet away from
the roadway centerline.
8. The depth of building sewer shall provide a minimum of two and
one-half feet of cover at the gutter flow line and two and one-
quarter of cover at the property line.
9. Minimum line size used for any sewer main is eight inches.
10. Minimum line size used for dead-ends and cleanouts is six inches.
III. Proposed Sewer Improvements
A. City Flow Projection Formulas
The City of Bakersfield requires the use of the following formulas to
determine the design sewage flows for new subdivisions.
Average population per single family dwelling unit = 2.6 persons
Average daily discharge of domestic sewage per person = 100 gallons
Design discharge = Peak factor x Cumulative Average discharge
Tract 6916 Sewer Study Page 3 of 4
The Peak Factor = 2.65 x (Avg. Discharge)-0.1 (in cubic feet per seconds,
cfs)
For Tract 6916, the average daily sewage discharge per residential lot is:
2.6 persons / lot x 100 gallons / person-day = 260 gallons / day per lot.
This is equivalent to 4.02 x 10-4 cfs
B. General Flow Diagram
The proposed sewage flow directions are shown in Figure 4. The sewage
flow directions were designed according to the existing topography and
the proposed grading of Tract 6916. All proposed sewers within Tract
6916 will be gravity lines.
Figure 4 also lists the design flow for all sewer main pipe segments in
each street. The design flows are based on the estimated discharge from
each service area.
C. Line Sizing
Appendix A includes the calculations used to determine the sewer line
sizes for Tract 6916. The calculations list the design flows for each of the
sewer mains shown on Figure 4. Based on the design flows, each sewer
main has been sized per the guidelines listed in the City of Bakersfield
Subdivision and Engineering Design Policy Manual. All in-tract line sizes
are designed to be 8-inch and 10-inch.
The on-site sanitary sewer system is designed for minimum cleaning
velocity of 2 feet per second per Section 1.2.1.2 of the City of Bakersfield
Subdivision Design Manual. Sewer inverts are designed to have a
minimum of 3.5 feet of cover over the majority of the pipes in the system.
IV. Connection to Existing Sewer System
A. Existing Survey
Recent topographic survey information for Tract 6916 indicates that there is
an existing 8” sewer line that is stubbed 9’ east of the intersection of Alondra
Drive and Mountain Vista Drive. A sewer study for Tract 6328 shows a
second 12” stub located at the intersection of Pointe Royal Drive and
Mountain Vista Drive. The invert elevations were obtained from the
topographic survey conducted in the area.
Tract 6916 Sewer Study Page 4 of 4
B. Proposed Discharge Locations
Sewer discharges from Tract 6916 will connect to the existing 12” line
stubbed from Point Royale Drive of Tract 6328 approximately 625 ft north of
the intersection of Broad Avenue and Mountain Vista Drive. The existing
stub will eventually lead to the main line on Buena Vista Road and to the
treatment facility.
V. Future Connection
A 10” cleanout at the east end Broad Avenue will be constructed as a future
point of connection for Tract 6825.
VI. Conclusion
Tract 6916 is estimated to generate a total peak flow of 0.214 cfs. Tract
6825 is estimated to contribute a total peak flow of 0.182 cfs to the system.
The pipe within the development has been properly designed to carry the
total peak flow. The main along Buena Vista Road is at capacity, and the
City of Bakersfield is looking at measures to increase this capacity, but this
discussion is beyond the scope of this study.
The supporting calculations and summary of results are presented in
Appendix A. An exhibit of the proposed manholes, pipe locations, proposed
sizes, and elevations is attached. Based on the hydraulic analysis, the
recommended pipe sizes are adequate for the sewer collection servicing
Tract 6916.
References
1. City of Bakersfield. Department of Public Works. Subdivision and Engineering
Design Manual. Bakersfield, CA: City of Bakersfield.
Appendix A
Calculations
Ennis Land Development, LLC
Tract 6916
Sewer Study
3/4/14
DESIGN CLEANING VELOCITY =2.00 fps
ROUGHNESS COEFFICIENT (n ) =0.011 (For PVC Sewer)
Service
Area
Pipe
Segment
Dwelling
Units
Average
Flow, cfs
Cumulative
Average Flow,
cfs
Peak
Factor
Total
Design
Flow, cfs
U.S.
Manhole
D.S.
Manhole
Pipe
Diameter
Pipe
Length
Min Slope
Require
Full Flow
Capacity
A
A-1 11 0.004 0.004 4.56 0.020 1 2 8 400 0.35%0.71
A-2 9 0.004 0.007 4.34 0.031 3 2 8 240 0.35%0.71
A-3 7 0.003 0.004 4.65 0.017 4 3 8 240 0.35%0.71
A-4 2 0.001 0.001 5.40 0.004 25 4 8 121 0.35%0.71
A-5 1 0.000 0.000 5.79 0.002 24 9 8 150 0.35%0.71
A-6 0 0.000 0.001 5.19 0.006 2 7 8 310 0.35%0.71
A-7 3 0.001 0.061 3.50 0.396 6 5 10 224 0.25%1.10
A-8 9 0.004 0.025 3.83 0.278 7 6 10 291 0.25%1.10
A-9 10 0.004 0.010 4.21 0.223 8 7 10 305 0.25%1.10
A-10 10 0.004 0.006 4.45 0.207 9 8 10 305 0.25%1.10
A-11 3 0.001 0.001 5.19 0.188 SSCO1 9 10 183 0.25%1.10
A-12 4 0.002 0.035 3.71 0.130 10 6 8 295 0.35%0.71
A-13 5 0.002 0.027 3.80 0.103 13 10 8 300 0.35%0.71
A-14 5 0.002 0.019 3.95 0.073 16 13 8 310 0.35%0.71
A-15 7 0.003 0.010 4.20 0.042 19 16 8 310 0.35%0.71
A-16 7 0.003 0.006 4.39 0.028 11 10 8 223 0.35%0.71
A-17 6 0.002 0.006 4.39 0.028 14 13 8 223 0.35%0.71
PIPE DESIGN CALCULATION
L:\Projects\2013\130205.01\ACAD\DESIGN\SEWER STUDY\130205.01 - SS Calcs.xls 1 of 2
Ennis Land Development, LLC
Tract 6916
Sewer Study
3/4/14
DESIGN CLEANING VELOCITY =2.00 fps
ROUGHNESS COEFFICIENT (n ) =0.011 (For PVC Sewer)
Service
Area
Pipe
Segment
Dwelling
Units
Average
Flow, cfs
Cumulative
Average Flow,
cfs
Peak
Factor
Total
Design
Flow, cfs
U.S.
Manhole
D.S.
Manhole
Pipe
Diameter
Pipe
Length
Min Slope
Require
Full Flow
Capacity
PIPE DESIGN CALCULATION
A-18 6 0.002 0.006 4.39 0.028 17 16 8 223 0.35%0.71
A-19 8 0.003 0.007 4.34 0.031 20 19 8 230 0.35%0.71
A-20 9 0.004 0.004 4.65 0.017 12 11 8 214 0.35%0.71
A-21 10 0.004 0.004 4.60 0.019 15 14 8 213 0.35%0.71
A-22 10 0.004 0.004 4.60 0.019 18 17 8 213 0.35%0.71
A-23 10 0.004 0.004 4.60 0.019 21 20 8 598 0.35%0.71
TOAL S 152 0.061 0.061 3.50 0.396 6 5
L:\Projects\2013\130205.01\ACAD\DESIGN\SEWER STUDY\130205.01 - SS Calcs.xls 2 of 2
Appendix B
City of Bakersfield Standards for Sanitary Sewers
Appendix C
Tract 6916 Conditions of Approval