HomeMy WebLinkAboutAMEND 2024-0008; INNS OF AMERICA; SEWER CAPACITY STUDY; 2025-05-08Joh
SEWER CAPACITY STUDY FOR:
PRELIMINARY CARLSBAD COMMONS
INNS OF AMERICA
APN: 210-090-52
5010 A VENIDA ENCINAS
CARLSBAD, CA 92008
AMEND: 2024-0008/CUP 2024-0009/PUD 2024 2024-0009
Prepared By:
RCE 80667
Van Ryn Engineering, Inc.
16766 Bernardo Center Dr., Ste 115
San Diego, CA 92128
"~ VAN RVN
Prepared for:
Community Development Department
Engineering Division
1635 Faraday Avenue
Carlsbad, CA 92008
May 8, 2025
EXP: 3-31-27
CITY OF CARLSBAD
MAY 2 2 2025
PLANNING DIVISION
SEWER STUDY-5010 AVENIDA ENCINAS MAY2025
TABLE OF CONTENTS
1. INTRODUCTION ................................................................................................................................... 3
1.1 Purpose .......................................................................................................................................... 3
1.2 Land Use ........................................................................................................................................ 3
1.3 Vicinity Map ................................................................................................................................... 3
1.4 Site Map ......................................................................................................................................... 5
2. METHODOLOGY .................................................................................................................................. 6
2.1 Sewer Collection Method ............................................................................................................. 6
2.2 Design Criteria And Abbreviations .............................................................................................. 6
3. CALCULATIONS/RESULTS ................................................................................................................... 7
3.1 Projected Sewer Flows .................................................................................................................. 7
3.2 Peak Sewer Flow Rates ................................................................................................................. 7
3.3 Offsite Sewer Ca lculation ............................................................................................................. 7
3.4 Onsite Sewer Calculation .............................................................................................................. 7
4. CONCLUSION ....................................................................................................................................... 7
Appendix 1 ............................................................................................. Reference Material
SEWER STUDY -5010 A VENIDA ENCINAS MAY2025
1. INTRODUCTION
1.1 Purpose
This Sewer Study Report has been prepared for the proposed project located at 5010 Avenida
Encinas in the City of Carlsbad, California. The project proposes new hardscape areas on the
northwestern end of the site with new landscaping scattered in and around the proposed hardscaping.
The existing hotel on-site will remain undisturbed. However, the project is proposing to convert the
existing 98-room hotel into a 98-unit multi-family apartment building, therefore modifying the sewer
generation rates and densities. The following study will show that the existing 8" VCP sewer main
in A venida Encinas and the 8" sewer lateral currently serving the existing site are adequately sized to
accommodate the proposed change in building use. This report will also indicate that the proposed
sewer flows generated because of final construction are less than the City of Carlsbad: Sewer Master
Plan Update -2019 flows allocated to the site. The purpose of this Sewer Study is to:
i) Size the proposed sewer line intended to be constructed/ connected to the existing sewer main
in the existing roadway.
ii) Show that the proposed sewer generation for the proposed development is consistent with the
2019 City of Carlsbad Sewer Master Plan.
iii) Show that the proposed flows downstream of the project site are less than or equal to the
flows per the City of Carlsbad: Sewer Master Plan Update -2019.
1.2 Land Use
5010 Avenida Encinas is lo~ated at the comer intersection of Avenida Encinas and Cannon Road,
approximately 200 feet west of the 5 (San Diego Parkway), located in the City of Carlsbad. The lot's
total area is 111,738 sq.-ft (~2.7, acres). The existing site is within the Planned Industrial (P-M) zone
in the City of Carlsbad, part of the Planned Industrial General Plan. The current land use is Hotel/Motel
and the proposed land use is Multi-family. Per City of Carlsbad: Engineering Standards -2022 Ed., an
equivalent dwelling unit (EDU) generates an average daily flow of 200 gpd/ ADF. Per Carlsbad
Municipal Code Table 13.10.020(c)(5) for EDU conversion, each room of a hotel, motel, or other
multiple dwelling designed for sleeping accommodations has an equivalent EDU of 1.00 (w/ cooking
facilities). Therefore, Hotel/Motel & Multi-Family land use flows are based on identical sewage
generation rates, approximating to 200 gpd/EDU/Unit (Total of 98 units existing & proposed).
3
SEWER STUDY -5010 AVENIDA ENCINAS
1.3 Vicinity Map
-
""O '"Jt!.
-~
MAY2025
z,a.;_~l
4
SEWER STUDY -5010 AVENJDA ENCINAS MAY2025
1.4 Site Plan,
5
SEWER STUDY -5010 AVENIDA ENCINAS MAY2025
2. METHODOLOGY
2.1 Sewer Collection System
The proposed CARLSBAD COMMONS -INNS OF AMERICA multi-family apartment building lies in
the Agua Hedionda Creek Watershed (Figure 1.4_Carlsbad Watershed Basins) within the Carlsbad Sewer
Service Area (Figure 1.3_Sewer Service Area) located in the City of Carlsbad (Figure 1.l_Location Map).
As-built dra,wings for the project site obtained from the City of Carlsbad do show a current 8" sewer lateral
connection sloped down at 4.4% to the street's 8" PVC sewer main and manhole (Grading Plan-Sewer
Connection). Any wastewater collected within the existing 8" sewer lateral pipe that drains to the existing
8" PVC sewer main in Avenida Encinas, then north to the 24" VCP sewer main along Cannon Road, then
southwest into the 42" RCP Vista/Carlsbad Interceptor System. Once there, sewage is conveyed south via
the City of Carlsbad gravity main to the Encina Water Pollution Control Facility (Figure 2.2_Existing
Interceptor System).
2.2 Design Criteria and Abbreviations
The list below illustrates the criteria necessary for sewer system analysis. Values were obtained from the
City of Carlsbad: Sewer Master Plan Update -2019 & the City of Carlsbad Engineering Standards Vol. 1,
2022 Ed ..
• Equivalent Residential EDU= 200 gpd, ADF (Chapter 6, Section 1, Page 42; 2022 Ed.)
• Hotel/Multi-Family EDU Conversion w/ cooking Facilities= 1.0 (Table 13.10.020(c))
• Peak Flow Factor= 2.5 (Average Daily Flow less than 100,000 gal/day).
• Manning's "N" Value:
o All Pipes= 0.013
• 0.50 dn/D for any diameter, gravity sewer pipes (Chapter 6, Section 1, Page 42; 2022 Ed.)
• 0.75 dn/D for any diameter, gravity sewer pipes (Chapter 6, Section 1, Page 42; 2022 Ed.)
• Minimum Design Velocity= 2.0 ft/sec (Gravity Main)
• Maximum Design Velocity= 12 ft/ sec (Gravity Main)
• Gpd = Gallons per Day
• GPM = Gallons per Minute
• MGD = Million Gallons per Day
• EDU = Equivalent Dwelling Units
• ADF = Average Daily Flow Rate
Sewer mains, unable to sustain a minimum velocity of 2 ft/s at peak flow shall be designed to have a
minimum slope of that listed in the City of Carlsbad Engineering Standards -2022 Ed., 6.5(A). Volume 1.
Public sewer mains are to be at an 8" minimum. Sewer laterals are to be at a 4" minimum. Maximum
velocities greater than 12 ft/s should be avoided.
6
SEWER STUDY -5010 AVENIDA ENCINAS MAY2025
3. CALCULATIONS/RESULTS
3.1 Projected Sewer Flow Rates
The project site is located within the Northwest Quadrant Facility Management Zone (Figure_l.7-Local
Facility Management Zone), as part of the Carlsbad Sewer Service Area, and utilizes the Vista/Carlsbad
Interceptor pipeline system. South of the Agua Hedionda Lift Station, an ex. 8" PVC sewer pipe in
Avenida Encinas per drawing number: 333-2GE1, conveys sewage to an existing 24" PVC sewer main
• '
per drawing number: 333-2GE1 in Cannon Road before flowing into a 42" RCP sewer interceptor (VC
13 via Table _2.4 Vista/Carlsbad Ownership) gravity main and discharges south through the remaining
pipeline reaches (VC14-16) to the Encinas Wastewater Treatment Plant. The current full flow capacity for
the 42" RCP gravity main pipe (pipeline reach VC13) flowing to the Encinas Wastewater Treatment Plant
is 20.5 mgd, with an_ average flow of 4.65 mgd, and a current capacity of 30.9%. For the existing hotel,
the gpd of the DWP is estimated to generate an average flow rate of 19,600 gpd (98 Hotel Units x 1.0 x
200 gpd/ EDU), and a peak dry weather rate.of 49,000 gpd (98 Jf: 1.0 x 2.5 x 200) based off the existing
structure's 98 units, 1.0 Conversion Factor, 200 gpdper capita for Equivalent Dwelling Units, and a Peak
Factor of 2.5. For the multi-family apartments, the gpd of the DWF is estimated to generate an average
flow rate of 19,600 gpd (98 Multi-Family Units x 200 gpd/ EDU), and a peak dry weather rate of 49,000
(98 x 2.5 x 200 x 1.0) gpd based off the proposed structure's 98 units, 1.0 Conversion Factor, 200 gpd per
capita for Equivalent Dwelling Units, and a Peak Factor of 2.5. The final flow rate of 49,000 (98 x 2.5 x
200) gpd was determined for the proposed condition at 5010 Avenida Encin~s (approximately 34.03 gpm
or 0.076 cfs).
3.2 Peak Sewer Flow Rates
To determine the Ratio of Peak to Average Sewage flow needed for the sizing of the onsite sewer pipe,
the equivalent popul~tion was calculated using the ratio of peak dry weather flow to average dry weather
flow. Depending on the equivalent population within the tributary area, peak weather flow factor was
calculated using page 43 of the City of Carlsbad Engineering Standards -2022 Ed., Chapter 6, Voiume 1.
Based on the site's equivalent population of average daily flow less than 100,000 gpd, a Peak Factor of
2.5 was determined. P~r design sewer criteria in the City of Carlsbad: ,Sewer Master Plan Update-2019
(and the EDU factoring of the Hotel Units to Multi-Family Units (Table_13.10.020(c)), the gpd per EDU
remained the same, and the proposed change in building use should have no new impacts on the existing
sewer main or interceptor system
7
SEWER STUDY -5010 AVENJDA ENCINAS MAY2025
3.3 Offsite Sewer Calculations
Population Data
Proposed total flow rate = 19,600 gpd
Peaking Factor= 2.5
Total Peak Plow= (Q)= 2.5 * 19,600 gpd = 49,000 gpd
I gal/day= 1.547 * 10-6 cfs
(Q) = 49,000 * (1.547 * 10-6) = 0.076 cfs
Pipe Characteristics
PVC Pipe, n = 0.013
Diameter = 8"
Capacity= 30.9%
(Q) = 0.076 cfs
(S) Slope = 0.32%
Hydraulic Radius (R) =(A -Flow Area/P-Wetted Perimeter)= ((0.349) I (2.09)) = 0.17'
Manning's Eqn. (QMAX) = (1.49/n)* A *R213*S 112) = (l.49/0.013)*(0.349)*(0.17)213*(.0032)112 = 0. 7 cfs
Velocity (V) = (Q/A) = (0.7 / .349) = 2.01 fps < 12 fps, 2.01 fps > 2.0 fps, velocity is OK.
QMAX>Q
Depth of flow
QI QMAX= (0.076 I 0.7) = (0.1 I)
Current d/D (depth/ diameter) in existing 8" Pipe= ~0.206'
Proposed Capacity= ~0.32 < .5' ., additional Capacity is OK.
8
SEWER STUDY -5010 AVENIDA ENCINAS MAY2025
3.4 Onsite Sewer Calculations
Pipe Characteristics
PVC Pipe, n = 0.013
Diameter = 8"
(S) Slope= 4.4%
Hydraulic Radius (R) =(A -Flow Area/P-Wetted Perimeter)= ((.349) / (2.09)) = 0.17'
Manning's Eqn. (QMAX) = (1.49/n)* A *R213*S 112) = ( 1.49/0.013)*0.349*(.17)213*(.044) 112 = 2.57 cfs
QMAX > Q => Existing 8" Sewer Lateral has capacity for demands
Velocity (V) = (Q/A) = (2.57 / .349) = 7.37 fps < 12 fps, 7.37 > 2 fps, velocity in accepted limits: OK.
4. CONCLUSION
The approved City of Carlsbad: Sewer Master Plan Update -2019 identified the proposed project site area
of 5010 Avenida Encinas as flowing into the Vista/ Carlsbad Interceptor, and ultimately the Encina Water
Po llution Control Facility. With the proposed building use change of the 98 hotel units to 98 multi-family
apartments, Carlsbad Commons -Inns of America has an anticipated total anticipated flow rate of 49,000
gpd, same as the existing use. The analysis of the existing, offsite 8" sewer main that has a 0.32% slope
within Avenida Encinas Street confinned the piping has adequate capacity to convey the proposed
wastewater flow rate of 49,000 gpd, an estimated velocity of 2.01 fps, and a consistent depth of ~32.0%.
The analysis of the onsite, existing 8" lateral has an existing slope of 4.4% with a velocity of 7 .3 7 fps and
a set, maximum depth of 50%.
9
SEWER STUDY -5010 A VENIDA ENCINAS MAY2025
APPENDIX!
REFERENCE MATERIALS
10
Figure 1-1. Location Map
Cities
• City of Carlsbad
□ City of Oceanside
□ City of Encinitas
□ City of Vista
□City of San Marcos
Sewer Master Plan Update L "'\~
City of Carlsbad r .,/ ~
City of
Carlsbad
C ii 11 for n I 1,
1
MILES
Document Path: C:\Projects\Carlsbad\SewerMasterPlan_ 10046316\Jon_Figures\Jan _27 _ mapdocs\Carlsbad_ City.mxd
June 2019 I 1-3
Figure 1-3. Carlsbad Sewer Service Area
Sewer Service Areas
• Carlsbad Sewer Service Area
•Buena Sanitation District
CJ City of Encinitas
CJ City of Oceanside
• City of Vista
Leucadia Wastewater District
□Vallecitos Water District
Sewer Master Plan Update L "''"\
City of Carlsbad r .I~
tewater District
City of
Carlsbad
C1llfornl1
1 Uon_ 1gures an_ _mapdocs\ ewer_ eNtce.mx
1
MILES
June 2019 I 1-7
Figure 1-3. Carlsbad Sewer Service Area
Sewer Service Areas
• Carlsbad Sewer Service Area
• Buena Sanitation District
City of Encinitas
□City of Oceanside
• City of Vista
Leucadia Wastewater District
□Vallecitos Water District
Sewer Master Plan Update
City of Carlsbad
City of
Carlsbad
( I JI f Or n I I
1 MILES
Vallecitos
Water
District
June2019 I 1-7
Figure 1-7. Local Facility Management Zones
Quadrants
•Northwest
Northeast
Southwest
•Southeast
CILFMP Zones
Sewer Master Plan Update
City of Carlsbad
0
City of
Carlsbad Cali fornia
,
MILES 2
Document Path: C:IProjects\Carlsbad\SewerMasterPlan_ 10046316\Jon _Figures\Jan_27 _mapdocs\Carlsbad _ City_LFMP.mxd
June 20 19 I 1-13
Sewer Master Plan Update
City of Carlsbad
Figure 2-1. Existing Lift Stations and Force Mains
Chinqua
LS
·-'. '
' ' ~
Lift Stations
[§1 1n Service
~Recently Removed
-Force Mains
, J
Boundaries
_...,.., , I
~. #Jr' __,,
I
-j /j
• f ~ -I,
/ -( I
/ f I
c.·,carlsbad Sewer Service Area
Gravity Mains ~
0 1
MILES
City of 1-~"'\ Carlsbad ·~ ~
Ca 11 f or n 1 ii
Document Path: C:\ProjeclslCarlsbad\SewerMasterPlan_10046316\Jon_Figures\Jan_27 _mapdocs\Ca~sbad_Ex_LS_FM.mxd
2-6 I June 2019
Sewer Master Plan Update
City of Carlsbad
Figure 2-2. Existing Interceptor System
Interceptors Facilities
-Vista/ Carlsbad I!]] Lift Stations
-North Agua Hedionda ~ Encina Water Pollution Control Facility
-south Agua Hedionda
••Buena Boundaries
-Vallecitos ~iCarlsbad Sewer Service Area
-North Batiquitos
Collection System
-Gravity Mains
ocument ath: ures an_ _mapdocs\ utab _lnterceptors_v .mxd
2-10 I June 2019
City of
Carlsbad
Ca l ifornia
1
MILES
Figure 2-3. Vista/Carlsbad Interceptor
V
VC1il~-
\
' VC12 & VC13 -4
Interceptor System
-Gravity Mains
-Force Mains
VC1ll
• Delineating Manholes
lb§] Lift Stations
vc
VC16
~ Encina Water Pollution Control Facility
Collection System
-Gravity Mains
Boundaries
Sewer Master Plan Update
City of Carlsbad
c ,Carlsbad Sewer Service Area
0 0.5 MILES
□tyof 1-)"\ Carlsbad ~
C1 l lfo r nl1
I , ;.__..,
June 2019 I 2-13
Sewer Master Plan Update
City of Carlsbad
Table 2-4. Vista/Carlsbad Interceptor Ownership
Buena
Vista LS 2
vc4 2
vc5 2
VC6 2
vc1 2
vc8 2
vc9 2
VC10 2
VC11A 2
VC11B 3
Agua
Hedionda
LS
VC12
VC13
VC14
VC15 3
VC16 4
2x24 (FM)
2x18 (FM)
2
30 (FM) 3
42 2
30 (FM) 3
42 2
54 3
2-14 I June 2019
23.1
23.1
33.0
21 .0
21 .0
20.5
21 .0
20.5
30.3
46.3
84.0
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
10.38
City of Vista
96.6
93.4
89.6
89.6
89.6
89.6
81 .9
79.4
79.4
75.5
74.7
69.1
69.1
69.1
69.1
69.1
56.1
56.1
50.2
14.2
14.5
11 .5
17.0
26.0
42.2
4.65
8.11
8.13
10.28
City of Carlsbad
1.0
2.2
2.0
2.4
2.4
3.3
5.7
6.5
6.5
7.0
7.2
6.3
10.2
10.2
30.9
43.9
43.9
49.8
Sewer Master Plan Update I..:),
City of Carlsbad ~ ~
Table 2-4. Vista/Carlsbad Interceptor Ownership
I
Full City of Vista City of Carlsbad
Flow
Pipe Average Capacity Average Capacity
Pipeline Pipe Size Capacity Flow 6 Percent Rights 8 Flow 6 Percent Rights 8
Reach (inches) (mgd) 5 (mgd) Capacity7 (mgd) (mgd) Capacity7 (mgd)
Notes:
1 Per February 2002 Ownership, Operation, and Maintenance Agreement with the City of Vista agreement, as
amended on June 11 , 2013 and May 20, 2014.
2 Per the February 2002 Agreement for Ownership, Operation, and Maintenance of the Vista/ Carlsbad
Interceptor Sewer. In this agreement average flow rates were obtained from the October 1997 Sewer Master
Plan Update for the City of Carlsbad. The Master Plan Update used a peaking factor of 2.0 for the Vista
Carlsbad Interceptor System. The percent capacity for each pipeline reach is based on the ratio of average
flow to total flow.
3 Per the 2011 Agreement for Planning and Design Phase Services for the Agua Hedionda Sewer Lift Station and
Vista/ Carlsbad Interceptor Sewer, Reaches VC11B-VC15.
4 A separate multiagency agreement was prepared for Reach VC16, now referred to as the West Encina Influent
Sewer.
5 Pipe capacity is based on a depth of flow (D) to pipe diameter (d) ratio of one and Manning's "n" value of 0.013
except for VC5 through VC10 which were assigned n=0.012 for PVC-lined pipe.
6 Average flow rates were obtained from the October 1997 Sewer Master Plan Update for the City of Carlsbad.
7 Percent capacity based on ra tio of agency's average flows shown in this table.
8 Capacity rights based on percent capacity multiplied by fu ll flow pipe capacity.
FM=force main; LS=lift station; mgd=million gallons per day
June 2019 I 2-15
Table 2-3. Summary of Existing Lift Stations
Name
Agua
Hedionda
--
Buena
Vista
Cannon
Road
El Fuerte
Foxes
Landing
II
Operated
and
Maintained
by
(Interceptor
System
Discharge)
EWA (V/C)
EWA (V/C)
Carlsbad
(SAHi)
Carlsbad
(NAHi)
Constructio
n/
Rehabilitatio
n Date
2019
1975, 1994,
2018
2005, 2007,
2017
2001
2009
2001,2018
Quantity
Lift Side:
4
FM Side:
4
4
3
3
-
Pump/Motor Information
I
i
Motor
Size
(Horse-
power)
100
300
105
7.5
50
38.7
I
Motor
Type
VFO
VFO
CSO
CSO
CSO
VFD
Design
Point
Lift Side:
4860 gpm
X 30'
FM Side:
3820 gpm
x40'
6000 gpm
X 142'
1420 gpm
X 200'
360 gpm
x50'
970 gpm
X 127'
1500 gpm
X 61'
Firm Station
Capacity1
(gpm) (mgd)
22,900 33.0
II
14,900 21 .5
2,440 3.5
360 0.5
970 1.4
2,600 3.7
ii
Sewer Master Plan Update L '"'\""'
City of Carlsbad r .I~
Forcemain
Diameter
(inches)
FM Side:
30
24"
24"
14"
6"
8"
16"
Material
HOPE
--
HOPE
CIPP
lined DIP
HOPE
PVC
HOPE
HOPE
Comments
Replaced in
2018
Upgrades
ongoing in
2018
Flygt NP3301
1 duty and 1
standby
.J
Reconstructio
n ongoing to
be completed
in 2019
including
addition of
redundant
______ .,........__ ____________ ~•~--~~---------•----.. ---•------'-----force mains
Home 2012 20 VFO Plant
Knots 1999 10 CSD Lane
North Carlsbad 1997,2008 100 CSD Batiquitos (NBI)
800 gpm 8"
10" (back X 70' up)
355 gpm 6" x44'
1210 gpm 14" X 164'
HOPE
PVC
2 duty and 1
standby
PVC 1 duty and 1
____ standby
PVC 172,300 gal
overflow tank
June 2019 I 2-7
Sewer Master Plan Update
City of Carlsbad
4.2 Design Criteria
The City of Carlsbad General Engineering Standards, Volume I, Chapter 6, Design
Criteria for Gravity Sewer Lines and Appurtenances, provides design guidelines for the
design of sewer gravity mains, lift stations, and forcemains. New sewer improvement
plans must be reviewed and approved by the City Engineer.
4.2.1 Engineering Standards Design Criteria
The design criteria from City's Engineering Standards are shown in Table 4-1. Criteria to
be reconsidered in this Master Plan update, highlighted in Table 4-1 , include sewer
generation rates, as lower water demands per capita due to voluntary and mandated
water conservation measures are also reflected in lower wastewater flows.
Table 4-1 . Sewer Design Criteria
Parameter
Sewer Generation Rate
Residential, Single Family
Residential, Multi-Family
Commercial,
Industrial or
Institutional
Peak Daily Flow Factor
d/D Ratio for Gravity Mains
For sewer mains s 12-inch
For sewer mains> 12-inch
For all sewer mains
Engineering Standard Criteria
(Volume 1, Chapter 6) Recommended Revised Criteria
220 gpd/EDU 200 gpd/EDU
176 gpd (80 percent of 220 gpd/EDU) 160 gpd (80 percent of 200 gpd/EDU)
Flow projections for future schools, No change
resort hotels, and certain industrial
uses are based on EDU conversions
documented in the Carlsbad Municipal
Code (Table 13.10.020c).
2.5 x Average Daily Flow No change
0.50 at peak hour dry weather flows
0.75 at peak hour dry weather flows
0.90 at peak hour wet weather flows
No change -----------No change
Manning's Roughness Coefficient
For all other pipes
Velocity for Gravity Mains
Minimum allowable velocity
Maximum allowable velocity
Velocity for Force Mains
Notes:
0.013 No change
2 feet per second No change
12 feet per second No change
2.5 feet per second No change
8 feet per second No change
d/D=depth-to-diameter ratio; EDU=equivalent dwelling unit; V/C=Vista/Carlsbad
4-10 I June 2019
4.2.2
Sewer Master Plan Update
City of Carlsbad
The most important evaluation criteria for gravity sewers is the depth of flow, which is
calculated in the hydraulic model based on Manning's Equation. The capacity of each
gravity sewer is based on the relative depth of flow within the respective pipeline reach .
Sewer interceptors are not typically designed to flow full , as unoccupied space at the top
of the pipe is required for conveyance of sewage gasses and to provide contingent
capacity for wet weather inflow and infiltration. Interceptor sizing is typically based on the
pipeline flowing 75 percent full at the PWWF if the pipe is larger than 12-inches in
diameter (Did = 0. 75). If the pipeline is 12-inches in diameter or smaller, a Did factor of
0.50 is used.
Friction factors for pipelines are a required input to the model. The factors vary with the
material and the age of the pipe . A roughness factor as indicated by a Manning's'
coefficient ("n") of 0 .013 is typically used to evaluate existing interceptors and for
projection of future sizing needs. Previous studies have shown that this value typically
accounts for most pipe roughness, joints, and fouling that occur after several years of
operation . At the direction of City staff, a Manning's coefficient of 0.012 was used in the
evaluation of the PVC-lined RCP and centrifugally cast fiberglass reinforced plastic
mortar pipeline sections of the V/C installed in 2002 (reaches VC5 through VC11 A).
In the design of sewer lift stations, it is required that spare pumping units be included for
mechanical reliability. A wastewater facility must be capable of conveying PWWFs with
the largest operating unit out of service. Lift stations are typically equipped with a
minimum of two pumps and have a secondary or emergency power source, consisting of
either installed generators or a connection for a portable generator. Forcemains are
evaluated based on maintenance of a minimum or maximum allowable flow velocity,
varying between 2.5 and 8.0 feet per second. Velocities less than 2.5 feet per second
can result in deposition in the forcemain, while velocities greater than 8.0 feet per second
can damage the pipeline through excessive abrasion.
Existing System Capacity Evaluation Criteria
As stated in the previous section, the design criteria for gravity sewers provides
unoccupied space at the top of the pipe for conveyance of sewage gasses and to provide
contingent capacity for wet weather inflow and infiltration. In this Master Plan, the PWWF
analysis assumes peak l&I rates coincide with the peak dry weather flow, and the
duration of the PWWF condition is brief. When gravity pipelines are evaluated to
determine if there is adequate capacity under the PWWF condition, a separate pipeline
evaluation criteri a is often used to determine the permissible flow level before the
pipeline should be upsized. This criteria is often referred to as "trigger" criteria.
The 2012 Sewer Master Plan used a design storm from 2005 to estimate inflow and
infiltration during wet weather flows. The 1.5 inch rainfall event on Wednesday, February
23, 2005 was therefore selected as the basis for PWWF. For this 2018 Master Plan
update, the December 2010 storms will be used as the basis for PWWFs. This storm
was a 10-year design storm event and is consistent with the assessment by the City of
Vista in its 2017 Comprehensive Sewer Management Plan, which shares sewer
interceptor systems that convey wastewater to the EWPCF. In addition , the 2012 Sewer
Master Plan allowed for gravity sewers to flow up to 90 percent full under PWWF
conditions before improvement projects were required. This same approach was used in
the 2018 Master Pla n Update for the large diameter interagency interceptor gravity
June 2019 I 4-11
Sewer Master Plan Update
City of Carlsbad
mains. A different approach was used in the 2018 Master Plan Update for the Carlsbad
collection system which is made up of smaller diameter gravity mains.
Figure 4-3 shows the d/D ratios and the corresponding flow/maximum or full flow (Q/Qr)
ratios for circular pipes with a constant friction factor as used in the existing system
capacity analysis.
Figure 4-3. Comparison Depth Flow Relationship
a ti
a: ~ ~ -< ....
0
0 I-
~ ,Q.
,0
1'
0 -,1-~
VALUE S OF" ...:L A.NO _IL
f f n if
1,0 .2 1,4 1,S 1-8 2,0 2,2 2,4 2•~ 2,8 3,0 3.2 3,4 3,6
t.O
0,9
0,8
O,i
o.s
o.s
M/..NNJ NG
o . .,
0.3
0,2
0,,
0
-----
\ ' I I I ,~~ --·--n.f VARIABLE ' ' I \\ --· n.f CONSTA T . I I
\\ -·-·· INDE PENDANT Of n,f ~ I ' ~ ' -'1 1 I
\ r\. D~RC Y-l~[S8, ~.CH V --~ J }
\ F , 1 CTr lN FAI TOR. f h' ,,., ,./ I I I
\ . ~ v· ,,. V 'I ' '
l. -. '\: -D-IS PH.ARO ~· /
/ ,,., I · / ' ' ./
\ \ ~-
V ,, / / , ~ I/ _.,.;,
I,.~,,, '/ ~-
~>O /4 V .h HYDR, UL.IC ~ l'l-... ocn, . v-, J'I''
v-,,.,. RAl)Jt S, R
~,,, ,.,·•~·\ V ~y~ /
~ / ~ '· .
I " L 'ARU " ~ ,.//
,I' ,A'-. 1/ 8 ,,
I/
v..:--I/"'-,, .
1 ........ "-11.. ~-~ /
/¼
~ ,.,.. ·-.,., --~ ~-~ ::;------( ,---
o 0.1 o.i o,3 o.◄ o,s o.6 o.t o.& 0,9 1.0 1,1 1.2 1.3
HYORAUl lC £LEM£ TS v, 0, ~, ANO R
V-f O;. Af R-f
As indicated in red, the pipe is flowing at 99 percent of its full pipe flow capacity when the
depth is 80 percent of full pipe. In areas between 80 percent and 100 percent of depth the
hydraulic regime is unstable. The use of the 0.80 value is considered more conservative
than the 0.85 value.
The lnfoSWMM model reports the partial flow ratio of full flow using the equation Q/Qr. In
instances where the d/D is greater than 0.980 and the Q/Qr< 0.99 the line is surcharging
because of a downstream restriction. In this Master Plan Update, improvement projects
were triggered in the existing system when pipes had both a d/D >0.80 and Q/Qr>0.99.
Pipelines that had only one or the other of these constraints were put on a "watch" list.
4-12 I June 2019
Sewer Master Plan Update L ""°"'
City of Carlsbad r J ~
Using a d/O ratio of 0.5 for small diameter pipes and 0.75 for larger diameter pipes for
peak dry weather flow has been considered. However, with the potential for ROIi, using a
d/O ratio of 0.80 for capacity evaluation of the system during PWWF is a conservative
approach. If ROIi is reduced significantly in future years, the alternative standard may
become appropriate.
June 2019 I 4-13
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EXHIBIT 1
ORDINANCE NO. CS-2QZ
AN ORDINANCE OF THE CITY COUNCIL OF THE CITY OF
CARLSBAD, CALIFORNIA, AMENDING THE CARLSBAD MUNICIPAL
CODE, TITLE 13 -SEWERS AND TITLE 18 -BUILDING CODES AND
REGULATIONS, TO CLARIFY SEWER AND TRAFFIC FEES RELATED
TO OUTDOOR DINING AREAS
The City Council of the City of Carlsbad, California, hereby ordains as follows:
SECTION 1: That Title 13, Chapter 13.10, Section 13.10.20, subsection (c) of the
Carlsbad Municipal Code is amended to read as follows:
13.10.020-Equivalent dwelling units.
(c) Table 13.10.020(c) shall be used to determine equivalent dwelling units.
TABLE 13.10.020(c)
Type of Building, Structure or Use Equivalent Dwelling
Units
(1) Each space of a trailer court or mobilehome park 1.00
(2) Each duplex 2.00
(3) Each separate apartment in an apartment house 1.00
(4) Each housing accommodation designed for occupancy by a single 1 :oo
person or one family, irrespective of the number actually occupying such
accommodation
(5) Each room of a lodginghouse, boardinghouse, hotel, motel or other
multiple dwelling designed for sleeping accommodations for one or more
individuals
Without cooking facilities 0.60
With cooking facilities 1.00
(6) Churches, theaters and auditoriums, per each unit of seating 1.33
capacity (a unit being one hundred fifty persons or any fraction thereof)
(7) Restaurants
No seating 2.67
Seating (See Note) 2.67 plus 1.00 per
each 7 seats or
fraction thereof
Delicatessen or fast food, using only disposable tableware:
No seating 2.67
Seating (See Note) 2. 76 plus 1.00 per
each 21 seats' or
fraction thereof
(8) Automobile service stations:
Not more than four gasoline pumps 2.00
More than four gasoline pumps 3.00
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(9) Self-service laundries, per each washer . 75
(10) Office space in industrial or commercial establishments not listed Divide the gross
above and warehouses floor area of the
building in square
feet by 1800
(11) Schools:
Elementary schools
For each .sixty pupils or fraction thereof 1.00
Junior high schoots
For each fifty pupils or fraction thereof 1.00
High schools
For each thirty pupils or fraction thereof 1.00
(12) In the case ofall commercial, industrial and business
establishments not included in subdivisions· .1 through· 10, inclusive, of
this· subsection, the ·number of equivalent dwelling units shall be
determined in each case by the utilities director and shall be based upon
his estimate of the volume and type of wastewater to be discharged into
the sewer. The provisions of Chapter 13.16 shall apply to all cases under
this subsection and an industrial waste permit shall be required. Any
such permit, issued for any use hereunder, shall include a specific
volume of sewage authorized for such use. If said amount is exceeded, it
shall be grounds for revocation of the permit
(13) Theme park (LEGOLAND California) per acre 17.00
Note: Seats allowed iri incidental outdoor dining areas pursuant to Section 21.26.013, and
seats allowed without any parking requirement in outdoor, sid~walk or curb cafes, as defined
by and pursuant to the ·Carlsbad Village Master Plan.and Design Manual and the City Council,
shall not count towards. the generation of equivalent dwelling units. However, any
. combination of outdoor seats which exceeds the number of indoor seats and therefore is
required to be parked, shall count towards the generat,ion of equivalent dwelling units."
SECTION 2: That· Title 18, Chapter 18.42, Section 18.42.020, subsection (e) of
the Carlsbad Municipal Code is amended to read as follows:
18.42.020 -Definitions.
24 (e) "Trip" means an arrival at or a departure from a proj.ect by any motor vehicle averaged
over a one-day period (12:01 a.m. to 11:59 p.m.) as determined according to Table
18.42.020(e}. In using this table, the sq·uare footage of the building, structure or use shall
include all interior floor area of a building or structure, and all usable ground area of a
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use without ,a structure, except any designated open space area. Where the table
establishes traffic generation for a project o~ the basis of square footage, acreage, or
some other unit, the unif establishing the greatest number of trips shall be utilized. When
a project has more than one use the number of trips shall be calculated by adding
.. J
CHAPTER 6 -DESIGN CRITERIA FOR SEWER FACILITIES
Prior to preparation of improvement plans, Engineer of Work shall submit a preliminary layout
of the sewer system for review and approval by the City Engineer. Basis of design shall be
demonstrated for the development type and density and corresponding sewer flow generation
factors and the following design criteria.
6.1 SEWER FLOW GENERATION FACTORS
A. Flow Rate Generation -The values in the latest adopted Sewer Master Plan shall govern:
1) An Equivalent Dwelling Unit (EDU) = 200 gal/day, Average Daily Flow (ADF)
2) For ADF less than 100,000 gal/day, a peaking factor (PF) of 2.5 multiplied times the
ADF shall be used to determine Peak Daily Flow (PDF). PDF = ADF x 2.5
a) Residential: Single Family and Multi-Family Residence= 1 EDU
b) Commercial Property: 1 EDU/1,800 square feet of building space
i) To convert raw land to square feet of building space, assume 30%
coverage. This could vary significantly dependent development
constraints.
ii) To convert improved pads to square feet of building space, assume 40%
of coverage.
c) Industrial Property:
i) 1 EDU/5,000 square feet of warehouse space
ii) 1 EDU/1,800 square feet of office space
iii) To convert raw land to square feet of building space, assume 30%
coverage. This could vary significantly dependent issues such as
environmental restrictions.
iv)· To convert improved pads to square feet of building space, assume 40%
of coverage.
v) Assume 60% of building space is warehouse, and 40% is office space.
6.2. SEWER MAIN DEPTH AND SIZE
A. Sewer main depth and size shall be as shown below unless approved by the City Engineer,
B. Minimum depth, finish grade to top of pipe: 6 feet
C. Maximum depth, finish grade to top of pipe: 15 feet
D. Design calculations shall be submitted as a basis for pipe size and bedding design.
(Manning's "n" for all types of pipe shall be = 0.013).
E. Minimum pipe diameter of sewer main shall be 8 inches. A 6-inch sewer main may be
allowed on cul-de-sac streets with a maximum of 10 units.
F. A decrease in the pipe diameter in the downstream direction of flow will not be allowed
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without hydraulic calculations and prior approval of the City·Engineer.
G. Residential (multiple-unit single-family and multi-family), commercial and industrial
developmer:,ts shall complete wastewater hydraulic modeling as required by the City
Engineer prior to discretionary project approval. Any sewer main shown to be deficient at or
downstream of the development's connection point shall be replaced with larger diameter
pipe as indicated by hydraulic modeling.
' H. All sewer laterals and gravity sewer main invert elevations shall be shown in profile on the
improvement plans. Show stationing of manholes and laterals, invert elevations at
manholes and lateral connections, and the distance, pipe size, pipe type, standard
dimension ratio and pipe slope of sewer main segments.
I. All sewer mains 15" and greater pipe diameters shall require special design subject to City
Engineer approval.
6.3 SEWER LATERALS
A. Use 4" minimum drameter pipe for each seier lateral to single-family residences.
B. Use 6" minimum diameter pipe for sewer laterals for all other development types and sized
for the drainage fixture units in accordance with the latest adopted California Plumbing
Code or for the proposed industrial use water demand.
C. Sew!3r lateral depth at the property line shall be 5 feet (top of pipe to finish grade @ top of
curb). ,
D. Sewer laterals shall be constructed in accordance with the Carlsbad Standard Drawings.
The minimum horizontal distance from water services, fire hydrants, driveways, light
standards, electrical utilities, etc. is 1 O feet. Special approval is required for horizontal
clearance less than specified herein.
1) Install at a right angle or radial to the main.
2) Laterals shall not be located in driveways.
3) No connections shall be permitted on laterals other than as allowed by the Standard
Drawings.
4) Location of property cleanout: See Standard Drawing No. S-7.
5) If the lowest sanitary sewer fixture in a building structure is lower than 2-feet above
the nearest upstream manhole cover, then the owner must provide a backwater
valve on the sewer lateral to prevent sewage backflow into the structure. The valve
must be installed in a valve box for accessibility and be visible from the public right-
of-way. The property owner shall be responsible for the installation and maintenance
of the backwater valve. The backwater valve shall be shown on the precise grading
and improvement plans.
6) Install sewer laterals using wye fittings, or manholes as required, sized and located
as shown on the Approved Plans.
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7) Laterals shall . be bedded, backfilled and compacted in the same manner as the
sewer main they are connected to. •
8) Sewer laterals cannot be connected to gravity mains of equal or lesser diameter.
Sewer lateral diameter that meets or exceeds the gravity main shall require upsizlng
of the gravity main as required by the City Engineer. •
6,4 MATERIALS FOR PIPE AND FITTINGS
A. . Gravity sewer pipe and fittings shall be PVC conforming to ASTM 03034 for diameters 4"
through 15" and ASTM F679 for 18" through 24" with integral bell and gasketed joints
(gasket and spigot end joint design). Pipe shall be made of PVC plastic having a cell
classification of 12454-B or 12364-B as defined in ASTM 01784 and shall have SOR of
35 or thicker, and a minimum stiffness of 46 psi according to ASTM 02412.
B. • All fittings and accessories shall be as manufactured and finished by the pipe
manufacturer with joints or joining systems compatible with that of the pipe.
C. PVC pipe joints shall be elastomeric gasket joints conforming to Standard Specifications
for Public Works (Greenback) most recent edition. Rubber gaskets shall be factory
installed and conform to ASTM F417. Pipe joints shall have been tested and meet
watertight performance requirements of ASTM 03212, "Joints for Pipe Using Flexible
Elastomeric Seals".
0. PVC pressure pipe conforming to AWWA C900 or HOPE pipe conforming to AWWA C906
shall be used for gravity sewer pipelines with depths of 30 feet or greater or as required
by the City Engineer for special installations. Engineering calculations shall be submitted
for approval to demonstrate that the pipe material and wall thickness will accommodate
the anticipated earth and live loads.
E. Service connections to the sewer main shall be watertight and not protrude into the sewer
pipe. All materials used to make the service connections shall be compatible with the pipe
materials to be joined and shall be corrosion proof.
F. Couplings used. for repair or transition to dissimilar pipe materials shall be ·approved by
the City Engineer and provide a corrosion proof watertight sec;tl.
G. Use of other pipe and fitting materials and types may be required by the City Engineer for
special designs for accessibility constraints of adjacent improvements, deep installations,
trenchless construction methods or other site conditions. Refer to the Approved Materials
List in Volume 2 for alternative materials.
6.5 DESIGN CRITERIA FOR PIPE VELOCITY, SLOPE AND FLOW DEPTH
A. Gravity sewer pipelines shall be designed for a minimum velocity of 2 feet/second.
Velocity, unless otherwise stated, shall be calculated from peak dry weather flow.
B. Pipe slope shall be established to satisfy the minimum velocity criterion. Maximum
velocities greater than 12 ft/second should be avoided.
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Slopes for 6-through , 12-inch diameter pipe, unless otherwise approved by the City
Engineer:
1) 6" pipe, minimum slope = 2%
2) 8" pipe, minimum slope = 0.50%
3) 1 O" pipe, minimum slope = 0.40%
4) 12" pipe, minimum slope= 0.30%
Pipe slope for 12-inch diameter or larger pipe shall be designed to meet flow and velocity
criteria and shall be approved by the City Engineer. Pipelines with horizontal curvature
may require increases slope to achieve minimum required velocities.
C. • Gravity sewer mains of any diameter shall convey peak hour dry weather flow at depths
of 50% of pipe diameter (d/D = 0.5) or less. Existing sewer mains not meeting this criterion
shall be replaced with larger diameter pipe.
D. Gravity sewer mains of any diameter shall convey peak wet weather flow at flow depths
of 75% of pipe diameter (d/D = 0.75) or less. Existing sew~r mains not meeting this
criterion shall be replaced with larger diameter pipe.
E. Peak sewer flow rates do not include infiltration or inflow (1/1). Infiltration is defined as the
addition of groundwater into the sewer collection system and inflow is the addition of storm
water into the sewer collection system. Because sewer collection system 1/1 is dependent
on many factors including season, age of system, pipe material and joint types, root
intrusion, and presence of storm water flow, 1/1 flow rate estimates will vary. The design of
sewer mains connecting to sewer systems known to have 1/1, or are susceptible to 1/1, shall
utilize peak wet weather flow estimates from the latest adopted Sewer Master Plan or
perform wet weather flow monitoring as directed by the City Engineer.
6.6 HORIZONTAL AND VERTICAL LAYOUT
A. Streets: See City of Carlsbad Standard Drawing No. GS-6 for location.
B. Alley: The centerline offset between the alley and the sewer main shall be three feet (3')
minimum.
C. Private Street: Sewer mains in private streets shall require special design consideration
for access.
D. Horizontal Curves: SOR 35, PVC pipe may be curved horizontally through longitudinal
bending with the following limitations:
Min. Radius
PiE!e Diameter of Curvature
6-inch 150 feet
8-inch 200 feet
10-inch 250 feet
12-inch 300 feet
15~inch 375 feet
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