HomeMy WebLinkAboutAttachment 3a-15 - Sewer Study redactedCity of Chula Vista
PRELIMINARY SEWER STUDY
For:
Shinohara Business Center
VWP-OP Shinohara Owner, LLC
DR21-0032
517 Shinohara Lane
Chula Vista, CA 91911
APN: 644-040-01
Project Permit # DR21-0032
Prepared By:
12-14-2022
Gregory W. Lang, P.E. RCE 68075 EXP: 06-30-23
Pasco Laret Suiter & Associates, Inc.
535 N. Highway 101, Suite A
Solana Beach, CA 92075
Prepared for:
VWP-OP Shinohara Owner, LLC
2390 East Camelback Road, Suite 305
Phoenix, AZ 85016
February 14, 2022
PLSA Job No. 3690
APPENDIX N
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Table of Contents
Section 1 - Introduction .................................................................................................................... 1
Section 2 – Project Description ........................................................................................................ 1
2.1 Project Location ...................................................................................................................... 1
2.2 Proposed Project ..................................................................................................................... 2
2.3 Study Area .............................................................................................................................. 2
2.4 Sewage Generation Rates ....................................................................................................... 6
Section 3 – Sanitary Sewer Analysis ................................................................................................ 7
3.1 Model Methodology ............................................................................................................... 7
2.2 Hydraulic Analysis Results .................................................................................................... 7
Section 4 – Conclusions ................................................................................................................... 9
Section 5 – Appendices .................................................................................................................. 11
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Figure Index
Figure 2-1 Project Site ...................................................................................................................... 1
Figure 2-2 Proposed Site Layout ...................................................................................................... 3
Figure 2-3 Sanitary System Sewer Map and Study Area ................................................................. 4
Figure 2-4 Sanitary System Node Map ............................................................................................ 5
Figure 3-1 Sanitary Sewer Study Summary (Hydraulic Model Results) ....................................... 10
Table Index
Table 2-1 Sewer Generation Rates based on Lot Area ..................................................................... 6
Table 2-2 Sewer Generation Rates based on Building Square Footage ........................................... 6
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Section 1 – Introduction
This report provides background data, analysis, and a summary of results as part of a preliminary
sanitary sewer system study for the proposed Shinohara Business Center. The purpose of this study
is to ascertain the potential impact of the proposed project on the existing sanitary sewer system
and to verify that sufficient capacity exists within the existing sewer facilities. The design for this
sewer study was completed in accordance with the design criteria listed in the City of Chula Vista’s
Subdivision Manual (Revised 03-13-2012), the City of Chula Vista Wastewater Collection Master
Plan (May 2014), and the Sewer System Management Plan (April 2021).
Section 2 – Project Description
2.1 Project Location:
The proposed Shinohara project is comprised of 9.73 acres, located at 517 Shinohara Lane in the
City of Chula Vista, San Diego County, California (APN 644-040-01). The property is defined as
a portion of Lot 1, Section 19, Township 18 South, Range 1 West, San Bernadino Meridian. The
site is bounded on the north and west by residential properties, and on the east and south by
commercial buildings. The existing site is currently undeveloped. See Figure 2.1 for vicinity map.
Figure 2-1
Vicinity Map
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2.2 Proposed Project:
The proposed project will include the construction of a 177,965 square-foot industrial warehouse
building with associated improvements including utilities, paving, storm water management
facilities, and landscape improvements.
The site is General Plan designated ILP – Limited Industrial and Zoned (IL) Limited Industrial. The
proposed industrial uses include primarily warehouse and manufacturing, assembly, storage, and
warehouse distribution.
Please refer to Figure 2-2 on the following page for schematic site layout.
2.3 Study Area:
The project’s study area, shown in Figure 2-3, generally encompasses existing parcels abutting
Main Street between Brandywine Avenue and Oleander Avenue. The primary zoning in the area
consists of Limited Industrial (IL) per the City’s 2005 General Plan. In accordance with the
requirements specified in the preliminary permit review submittal comments, the proposed project
is required to prepare a sewer system study with manhole-to-manhole calculations performed from
the upstream sewer system reach on Main Street, at the intersection of Main Street and Brandywine
Avenue, downstream to the connection to the existing 10-inch sewer in Main Street, at the
intersection of Main Street and Oleander Avenue. Please refer to Figure 2-4 for Sanitary System
Node Map.
The proposed project will connect to an existing 8-inch VCP gravity sewer main located south of
the project site in an existing 10-foot public sewer and drainage easement. The existing 8-inch VCP
sewer was constructed per City of Chula Vista As-Built Drawing No. 86-481. The existing 8-inch
VCP sewer connects to the existing 10-inch VCP gravity sewer in Main Street (see Figure 2-2).
The 10-inch Main Street sewer flows approximately 650 lineal feet westerly to the manhole located
at the intersection of Main Street and Oleander Avenue. There is additional sanitary flow from the
commercial and residential properties to the north (Main Street). The 10-inch sanitary sewer
continues westerly along Main Street approximately 1,000 lineal feet to the intersection of I-805
and Main Street, and an additional 2,100 lineal feet to the intersection of Otay Valley Road and
Main Street. Refer to the City of Chula Vista CV Mapper website for GIS wastewater systems.
The existing 10-inch sewer in Main Street was constructed during the 1960s and 1970s and is
generally VCP west of Brandywine Avenue. The branch connecting sewers along Main Street
between Brandywine Avenue and Oleander Avenue can be found under Work Order No. 08-70068
Drawing No. 72-17D). The branch connecting sewers along Main Street between Oleander
Avenue and Interstate 805 can be found under Work Order No. 5402 (Drawing No. S-5402-20-7).
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2.4 Sewer Generation Rates:
Preliminary sewer generation rates for the proposed development are based on the planning
requirements provided in the City of Chula Vista Subdivision Design Manual and the City of Chula
Vista Wastewater Collection System Master Plan, May 2014. The Wastewater Master Plan
methodology calculates sanitary flows based on the current or planned parcel zoning, lot area, and
duty factor demands obtained from Table 3-2 of the Wastewater Master Plan. The Average Dry
Weather Flow (ADWF) was calculated for the proposed site as shown in Table 2-1 below. As a
comparison, an alternative method for calculating the ADWF is provided in Table 2-2. The
alternative method utilizes a combination of duty factor demands and known building square
footage. Proposed building area was previously provided in Section 2.2. See alternative method
calculation in Table 2-2.
Table 2-1
Sewer Generation Rates based on Lot Area
Net Acreage = 9.73 ac
Duty Factor = 712 gpd/ac
AVERAGE DRY WEATHER FLOW = Net Acreage (ac) * Duty Factor (gpd/ac)
9.73 ac * 712 gpd/ac
6,928 gpd
Table 2-2
Sewer Generation Rates based on Building Square Footage
Building Square Footage = 177,965 sf
Duty Factor = 80 gpd/1000 sf
ADWF = Building Square Footage (sf) * Duty Factor
gpd/1000 sf)
179,530 sf * 80 gpd/1000 sf
14,237 gpd
AVERAGE DRY WEATHER FLOW = 14,237 gpd
Based on the above methods of calculating the ADWF, the more conservative ADWF of 14,237
gpd will be utilized as the basis of determining equivalent population and sanitary flows from the
proposed site during sewer modeling in Section 3 of this report.
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Section 3 – Sanitary Sewer Analysis
This section of the study report discusses the hydraulic analysis of the existing sewer system with
new flows from the proposed Nirvana Business Park project.
3.1 Model Methodology:
A Microsoft Excel spreadsheet was utilized to perform the hydraulic analysis of the existing
sanitary sewer with the Study Area. Each reach or “Line” of the existing sanitary sewer system
includes the upstream and downstream manhole designations, invert elevations, length, and
diameter of the sewer. Sewer lengths and inverts were obtained from GIS sewer manhole and
sewer main shape files used on the City of Chula Vista GIS website, and from as-built sewer data
also obtained by the City of Chula Vista.
Existing wastewater flows for each reach between manholes were found from Appendix 2 of the
City of Chula Vista Wastewater Collection System Master Plan, May 2014. The Average Dry
Weather Flow (ADWF), the Peak Wet Weather Flow (PWWF), and the Peak Wet Weather Flow
d/D were input into the Microsoft Excel Spreadsheet.
The Average Dry Weather Flow (ADWF) for the proposed development was calculated in Section
2.4. The Peak Wet Weather Flow (PWWF) was calculated for the proposed development by
multiplying the ADWF by the calculated Peaking Factor for Wet Weather Flow. In accordance
with the direction received from the City of San Diego Public Utilities Department, the peaking
factor used was 2.5, found from City of Chula Vista Standard Drawing No. SWR-01. The pipe
capacity was calculated utilizing Manning’s Equation and a Manning’s “n” value of 0.013.
Wastewater flows for the existing pipe reaches downstream of the proposed development were then
calculated by adding the proposed development ADWF and PWWF to the wastewater flows found
in Appendix 2. The summation of the existing and proposed flows are included in the Excel
spreadsheet with an asterisk.
The ratio of actual depth to pipe diameter (d/D) was calculated by using an Excel algorithm to
select the appropriate d/D (to the nearest 0.1 increment) based on the corresponding ratio of
calculated ADWF to full pipe flow (Q/Qfull).
The downstream system has been studied to the point in the system where the projected peak wet
weather flow from the proposed development is less than 10% of the total flow, in accordance with
Section 1.7.1 of the City of San Diego Sewer Design Guide (2013).
3.2 Hydraulic Analysis Results:
The results of the hydraulic analysis model are shown in the Sanitary Sewer Study Summary
provided in Figure 3-1 at the end of this section. The results are summarized as follows:
1. The d/D ratio for existing peak flow along the 10-inch diameter Main Street sanitary sewer,
from just upstream of the project’s point of connection (Line A) is 0.523, per Appendix 2
of the City of Chula Vista Wastewater Master Plan (May 2014). Normal depth is 0.52 feet.
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2. The d/D ratios for proposed peak flows along the 10-inch diameter Main Street sanitary
sewer, from just downstream of the project’s point of connection (Line B through C) range
from 0.63 to 0.65. Normal depth ranges from 0.53 to 0.54 feet.
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Section 4 – Conclusions
The analysis demonstrates that while there is an increase in the planned flow in the existing sewer
main in Main Street with the proposed project, the projected peak wet weather flows in the
analyzed, existing sewer mains do not exceed a d/D of 0.7 as required per Table 4-1 of the City of
Chula Vista Wastewater Collection System Master Plan (May 2014) and per Page 36 of the City
of Chula Vista Sewer System Management Plan (April 2021).
Therefore, it is our opinion that the existing sewer infrastructure located in Main Street has
sufficient capacity to convey the anticipated sewer flows from the proposed project per the criteria
listed in the city’s Wastewater Master Plan. Furthermore, the project should not be required to
upsize the existing sewer main in Main Street since an impact to the existing sewer infrastructure
does not occur in the area analyzed.
DATE: 2/14/2022
BY: PLSA PREPARED BY: MM
JOB NO. REFER TO FIGURE 2-4
MANNING N : 0.013
gpd gpd mgd cfs
A 7278 7277 Main Street N/A N/A N/A N/A N/A 288,042 576,629 0.577 0.89 10 384 0.33 0.24 0.52 0.62 0.523 PDWF provided from Appendix 2(5)
9.73 Industrial 712 6,928 177,965 80 N/A N/A 14,237 14,237 2.50 35,593 0.036 0.06 Project Shinohara
B 7277 6908 Main Street N/A N/A N/A N/A N/A 289,431 579,887 0.580 0.90 10 234 0.33 0.24 0.52 0.62 0.438 PDWF provided from Appendix 2(5)
B*Main Street 615,480 0.615 0.95 10 234 0.33 0.24 0.54 0.65 Inclusion of Project Shinohara sewer flow
C 6908 8675 Main Street N/A N/A N/A N/A N/A 289,431 580,791 0.581 0.90 10 166.5 0.36 0.23 0.50 0.60 0.751 PDWF provided from Appendix 2(5)
C*Main Street 616,384 0.616 0.95 10 166.5 0.36 0.24 0.53 0.63 Inclusion of Project Shinohara sewer flow
Notes
1) Per 2005 General Plan, code designation IL
2) Per Table 3-3: Landuse Zoning Designations of the City of Chula Vista Wastewater Collection System Master Plan (May 2014)
3) Per Table 3-2: Wastewater Duty Factors of the City of Chula Vista Wastewater Collection System Master Plan (May 2014)
4) Wet Weather Peaking Factor from City of Chula Vista Standard Drawing No. SWR-01
5) Appendix 2 of City of Chula Vista Wastewater Collection System Master Plan (May 2014)
6) Uses the more conservative value of ADWF calculated from in-line area and building square footage
Remarks
Pipe
Length
ft)
Design
Slope (%)
Hydraulic
Radius
Rh (ft)
Normal
Depth dn
ft)
PWWF
dn/D
Velocity
ft/sec)
From
MH To MH
In-Line Area
Served
In-Line Area
Acres)Land Use(1)
Cum. Total
Avg. Dry
Weather Flow
ADWF)(6)
Duty Factor
gpd/ac)(2)
Avg. Dry
Weather
Flow (gpd)
Duty Factor
gpd/DU)(3)
Duty Factor
gpd/1000
sf)(3)
Building
Square
Footage (sf)
Avg. Dry
Weather
Flow (gpd)
Wet
Weather
Peaking
Factor(4)
Dwelling
Units
Project Shinohara
Peak Wet Weather Flow
PWWF)Line Size
D (in)
PROJECT SHINOHARA
FIGURE 3-1
PWWF
dn/D(5)
SANITARY SEWER STUDY SUMMARY
3690
PIPE
REACH
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Section 5 – Appendices
1. City of Chula Vista Wastewater Collection System Master Plan, 2014 – Wastewater Duty
Factors and Landuse Zoning Designations (Table 3-2 and Table 3-3, pages 3-9 and 3-10)
2. City of Chula Vista Wastewater Collection System Master Plan, 2014 – Pipeline Design
Criteria (Table 4-1, page 4-1)
3. City of Chula Vista Sewer System Management Plan, April 2021 –Design Criteria (page
36)
4. City of San Diego Sewer Design Guide, 2013 – Chapter 1.7.1 Required Capacity
Downstream of New Gravity Sewers (page 1-13)
5. Peak to Average Sewer Flow, City of Chula Vista Standard Drawing No. SWR-01
City of Chula Vista
Wastewater Collection System Master Plan
May 2014 - FINAL
CHAPTER 4. SEWER COLLECTION SYSTEM DESIGN CRITERIA
4.1 DESIGN CRITERIA BACKGROUND
A hydraulic model is the primary tool for evaluating the capacity of the pipes in a sewer collection system.
An effective hydraulic model accurately represents collection system facilities and collection system flows
for capacity analysis. This chapter describes the selection of system criteria, the development of collection
system facilities, and the calculation of flows in the collection system model for the City.
In analyzing a wastewater system, it is necessary to derive standards regarding the amount of flow that
may be efficiently conveyed by a given wastewater pipeline. In an effort to provide reliable gravity sewer
service while minimizing excessive wear or energy usage through force mains and lift stations, sanitary
sewers shall be designed according to the following criteria:
4.1.1 GRAVITY MAIN DESIGN CRITERIA
Sizing a new pipeline is based on the Manning’s equation and the following design criteria shown in Table
4-1.
Table 4-1: Pipeline Design Criteria
Gravity Main Requirements Design Criteria
1New Pipes 12-inches in diameter and smaller:
0.50 (50%) full at peak wet
weather flow
2New Pipes over 12-inches in diameter: 0.75 full at peak wet weather flow
Minimum velocity: 2 feet per second (1/2 full or full)
Maximum velocity: 10 feet per second
Manning’s n: .013
New Pipe Minimum pipe diameter: 8 in
Force Main Requirements Design Criteria
Minimum Force Main Diameter: 4 inches
Minimum Velocity: 3 feet per second
Maximum Velocity: 5 feet per second
Maximum allowable headloss: 10 feet/1000 feet of pipeline
Maximum desirable headloss: 5 feet/1000 feet of pipeline
Hazen-Williams C factor: 120
Notes:
1) Design plans will be required when d/D reaches 0.60 for existing 12” diameter pipes or smaller, and
improvements will be required once d/D reaches 0.70 at peak wet weather flows.
2) Design plans will be required when d/D reaches 0.75 for existing pipes larger than 12” diameter, and
improvements will be required once d/D reaches 0.85 at peak wet weather flows.
The National Clay Pipe Institute (NCPI) recommends that smaller pipelines (8” and smaller) be designed to
flow at levels not exceeding half-full (d/D=0.50) during peak conditions. For larger pipelines, the tributary
area is larger. Local deviation from design wastewater flows tend to balance one another for larger areas,
resulting in a closer correlation of actual and design wastewater flows. Consequently, the NCPI
recommends that these larger wastewater pipelines should be designed for a d/D not to exceed 0.75.
In analyzing the City’s existing sewer gravity mains, it is unnecessary to allow for an excessive factor of
safety. This is because the City’s sewer basins are largely built out, and future development patterns are
4-1
City of Chula Vista
Wastewater Collection System Master Plan
May 2014 - FINAL
relatively certain. As new major wastewater users apply for wastewater service, they should be evaluated
on a case-by-case basis, including estimated flow rates and impacts to City-owned sewer facilities.
Therefore, City-owned sewer gravity mains may be flowing at levels above a d/D of 0.50 and still be
operating satisfactorily.
Remaining pipeline capacity, above d/D = 0.75 has been reserved to handle emergency flows such as I&I
beyond that planned for in a design storm, and to provide for ventilation within the pipe. This should not be
considered a component of the pipeline capacity.
In an effort to account for the City being mostly built-out and ensure that gravity main segments are replaced
due to capacity and flow constraints, the following describes the City’s replacement criteria:
Maximum Peak Wet Weather Flow for pipelines 12-inch or less, depth-to-Diameter d/D = 0.70
Maximum Peak Wet Weather Flow for pipelines greater than 12-inches, depth-to Diameter d/D = 0.85
All pipes requiring replacement shall be designed in accordance with the City’s design criteria. In the event
that a gravity main satisfies these replacement criteria, but the pipeline immediately upstream requires
upsizing, one (1) additional replacement stipulation may be applicable. The purpose of this replacement
stipulation is to insure that pipe-reaches increase in diameter as they progress downstream, and prevent,
wherever possible, pipe-reaches from fluctuating up and down in diameter. If a gravity main requires
upsizing to a diameter larger than the diameter of the gravity main(s) immediately downstream in the same
pipe-reach, and the downstream pipe(s) are less than 750 ft in length before conveying flow to a gravity
main of equal or larger diameter than the diameter recommended for the deficient upstream gravity main,
then the downstream gravity main(s) of less than 750 ft shall be upsized to the same diameter of the
upstream pipe.
4.1.2 LIFT STATION DESIGN CRITERIA
Lift Stations should be sized for the peak wet weather flow rate plus an additional 20% capacity to account
for wear, miscellaneous debris, etc. that may reduce pumping performance. Lift stations should be capable
of meeting the following criteria with the largest capacity pump serving as standby:
Manufacturers recommended cycling times for pumping equipment.
All lift stations will incorporate dual force mains beginning from pumps and ending at gravity flows.
60 percent pump efficiency should be assumed, except where other information is available.
90 percent motor efficiency should be assumed, except where other information is available.
Wet well sized to minimize retention time such that maximum pump cycling time (usually at ½ design
inflow) is within manufacturer’s recommendations.
Separate from wet well operating volume, emergency storage volume shall be sufficient to
accommodate storage of six-hour pumping volume at average ultimate flow.
4-2