HomeMy WebLinkAboutCT 11-01; ROBERTSON RANCH WEST VILLAGE; SEWER SYSTEM ANALYSIS; 2011-05-1341,
SEWER SYSTEM ANALYSIS
FOR
ROBERTSON RANCH WEST
May 13, 2011
M.
Uj CO No. 61070 *\, Exp.W30111 1*
OF C
Prepared by:
Dexter Wilson Engineering, Inc.
2234 Faraday Avenue
Carlsbad, CA 92008
Job No.: 936-001
DEXTER WILSON ENGINEERING, INC.
DEXTER S. WILSON, P.E.
ANDREW M. OVEN, P.E.
STEPHEN M. NIELSEN, P.E.
DIANE H. SHAUGHNESSY, P.E.
May 13, 2011 936-001
Shapell Homes, Inc.
8383 Wilshire Blvd., Suite 700
Beverly Hills, CA 90211
Attention: Erik Pfahler, Vice President
Subject: Robertson Ranch West Sewer System Analysis
Introduction
This letter-report summarizes our evaluation of the sewer system that will serve the
western portion (Planning Areas 1 through 11) of the Robertson Ranch project. The project
is located along the north side of El Camino Real, just east of Tamarack Avenue. Figure 1
provides a location map for the project.
The proposed land use plan for the site includes single family and multi-family residential,
commercial, park, and open space areas. The onsite sewer system for the site is proposed to
be public to be operated and maintained by the City of Carlsbad.
2234 FARADAY AVENUE • CARLSBAD, CA 92008 • (760) 438-4422 • FAX (760)43&0173
p
Erik Pfahler
May 13. 2011
Sewer Service Design Criteria
Unless otherwise noted, the sewer system planning criteria used in this study are in
accordance with the City of Carlsbad Engineering Standards, Design Criteria for Gravity
Sewer Lines and Appurtenances, last revised June 30, 2008. The criteria pertinent to this
study are summarized below:
Manning's Equation Friction Coefficient, n = 0.011
Commercial Sewer Generation Factor = 1 EDU per 1,800 SF Bldg. Area
Raw land to Commercial SF Conversion = Assume 30% coverage
Generation Factor = 220 gpdIEDU Average Flow
. SF Residential Generation Factor = 220 gpd/unit
MF Residential Generation Factor = 160 gpd/unit (per Sewer Master Plan)
Peak Flow Factor = 2.5 x Average Day Demand
Minimum Pipeline Velocity at Peak Flow = 2.0 ft./s
Maximum dID, new12" and smaller pipes - 0.50
Maximum dID, new 15" and larger pipes - 0.75
Where there is not adequate flow to provide a minimum velocity of 2.0 feet per second, a
minimum pipe slope of 1.0 percent is recommended.
Projected Sewage Flows
Based on the factors presented above, Table 1 summarizes the projected sewer flows for the
project. For non-residential acreage, the assumption of 30 percent building coverage and a
generation rate of 220 gpd per 1,800 square feet result in a generation factor of 1,597 gpd
per gross acre.
DEXTER WILSON ENGINEERING, INC. PAGE 3
Erik Pfahler
May 13, 2011
TABLE 1
ROBERTSON RANCH WEST
PROJECTED SEWAGE FLOWS
Planning Gross Maximum Generation Average Land Use Area Acres Dwelling Units Factor Flow, gpd
1 SF Residential 8.3 32 220 gpdlunit 7,040
2 RV Storage 0.5 --- 1,597 gpd/ac 800
3 SF Residential 17.7 89 220 gpd/unit 19,580
4 Recreation 1.4 --- 1,597 gpd/ac 2,240
5 SF Residential 7.6 24 220 gpd/unit 5,280
r 1'cesictential 14.8 65 220 gpd/unit 14,300
7 MF Residential 7.3 110 160 gpd/unit 17,600
8 MF Residential 16.4 260 160 gpd/unit 41,600
9/10 SF Residential 21.9 78 220 gpd/unit 17,160
11 Commercial 14.9 --- 1,597 gpd/ac 23,800
TOTAL
- - ________
658
- ---
As shown the projected average daily flow is 149,400 gpd and the projected peak flow is
373,500 gpd (Peak Factor = 2.5)
Existing SewerSystem
There are several existing sewer lines in the vicinity of the Robertson Ranch West project.
Figure 2 provides the location of existing facilities in the vicinity of the project. The North
Agua Heclionda Interceptor system has trunk sewer lines west and south of the project.
There is an existing 12-inch sewer line in Kelly Drive that conveys flow south from El
Camino Real. From this line in Kelly Drive, an 8-inch sewer line has been extended
approximately 2,000 feet easterly in El Camino Real. There are also existing 8-inch sewer
lines in Eucalyptus Lane and Crestview Drive, south of El Camino Real. These sewer lines
tie into the North Agua Hedionda sewer line which is located in a canyon south of El
Camino Real.
DEXTER WILSON ENGINEERING, INC. PAGE 4
I
Erik Pfahler
May 13, 2011
To the east of the project there are gravity sewer lines at the intersection of Cannon Road
and El Camino Real that convey flow to the North Agua Hedionda sewer system. To the
north of the project, the Gateshead Sewer Lift Station was constructed to serve 24
residential lots along Gateshead Road. At the time this lift station was constructed, a dry
sewer line was also installed to allow this lift station to be abandoned in the future. This
sewer line was installed in an easement south of Gateshead Road and terminates at a
manhole in Edinburgh Drive.
Sewer System Analysis
Manning's equation was used to analyze the onsite sewer system to the point of connection
to the existing sewer system. Appendix A provides the hydraulic analysis results and
Exhibit A provides the corresponding node diagram. All onsite sewer lines were analyzed
as 8-inch in diameter. Figure 3 provides the recommended sewer system for the project.
Offsite Sewer Alternatives
The western portion of the project will convey flow by gravity to El Camino Real where it
will be connected to the existing system and conveyed to the Kelly Drive sewer line. Three
alternatives were evaluated for serving the eastern portion of the project as described
below.
The first alternative considered was identified in the November 2006 Robertson Ranch
Master Plan and involves constructing an 8-inch sewer line in El Camino Real to convey
flow easterly to the existing sewer at Cannon Road. While this alternative is possible, it
would involve difficult design and construction to make the connection at Cannon Road.
This intersection is crowded with utilities, including a gas line, and the existing sewer line
is deep at this location.
I
DEXTER WILSON ENGINEERING, INC. PAGE 5
r
Erik Pfahler
May 13, 2011
The second alternative considered was to convey sewer across El Camino Real to connect
into the sewer lines in Eucalyptus Lane or Crestview Drive. A review of these as-built
drawings revealed that it would not be possible to stay in the public right-of-way and
connect to these sewer lines by gravity flow. It would be possible to connect to the North
Agua Hedionda sewer in this area, but only by acquiring an easement, installing a sewer
line down a slope, and connecting to a sewer line in a canyon which would involve
disturbing the natural vegetation. This alternative is not considered feasible.
The third alternative considered was to convey this sewer westerly in El Camino Real with
the remainder of the project. The primary consideration for this alternative was the
available capacity in the existing 8-inch line in El Camino Real. As indicated by the
hydraulic analysis in Appendix A, the critical section of this line is the last section of line
prior to the connection to the 12-inch line in Kelly Drive. This section of line is
approximately 300 feet in length and was installed at a slope of 0.40 percent with a drop
manhole at the upstream end to allow the sewer line to be installed below a gas line and
box culvert. There are only a few existing connections to this line and with the addition of
flows from the Robertson Ranch West project, including 24 units from Gateshead Road to
the north, the maximum depth-to-diameter (d/D) ratio in this section of line during peak
flows is 0.58. While new 8-inch sewer lines are to be designed for a maximum d/D ratio of
0.5, it is reasonable to allow an existing gravity sewer to flow at a d/D ratio of up to 0.75
during ultimate peak flows before recommending replacement. This is the recommended
offsite alternative and is shown graphically on Figure 3.
Recommendations
Sewer service can be provided to the Robertson Ranch West property by the City of
Carlsbad. All onsite sewer lines are recommended as 8-inch with connections to the
existing sewer line in El Camino Real. The existing 8-inch sewer line in El Camino Real
will convey flow westerly to the 12-inch line in Kelly Drive and will experience d/D ratios of
0.35 to 0.58 during ultimate peak flows, including flow from 24 units along Gateshead
Road to the north of the project.
DEXTER WILSON ENGINEERING, INC. PAGE 7
L
Erik Pfahler
May 13. 2011
If you have any questions on the information contained herein, please let us know.
Dexter Wilson Engineering, Inc.
Stephen M. Nielsen
SMN:ck
I
DEXTER WILSON ENGINEERING, INC. PAGE 8
EL CAMINO REAL '.
CONNECT TO
EXISTING SEWER
7
1;
"-CONNECT TO
LEGEND EXISTING 80 SEWER
— EXISTING GRAVITY SEWER NOTE: ALL PROPOSED GRAVITY SEWER
-+'- PROPOSED GRAVITY SEWER UNES ARE RECOMMENDED AS 8-IN0i.
A;
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riURE 3
PROPOSED SEWER SYSTEM
a
APPENDIX A
HYDRAULIC ANALYSIS
SEWER STUDY SUMMARY
DATE: 5/3/2011 FOR: Robertson Ranch West Sewer Study
JOB NUMBER: 936-001 BY: Dexter Wilson Engineering
FROM TO IN-LINE
FLOW (gpd)
AVG. DRY
WE
FLOW gp
PEAKING DESIGNLINE
PEAK WET
WEATHER FLOW
(DESIGNFACTOR_______
LINE
SLOPE (%) DEPTH K. (1) dn (feet) dnlD(2) ve?
VELOCITY Remarks
M.G.D. C.F.S.
34 32 11,440 11,440 2.50 0.03 0.04 8 2.00 0.010148 0.07333 0.11 0.05 2.11848 PA 5 + Part PA 6 (28 units)
32 30 13,420 24,860 2.50 0.06 0.10 8 4.00 0.015594 0.08667 0.13 0.06 3.73053 Part PA 3(61 units)
30 16 31,840 56,700 2.50 0.14 0.22 8 4.00 0.035566 0.12667 0.19 0.10 4.79118 PA 4 + 1/2 PA 7 + 1/2 PA 8
24 22 16,280 16,280 2.50 0.04 0.06 8 4.00 0.010212 0.07333 0.11 0.05 3.01477 PA 9 + 24 units (Gateshead Road)
PA 10
Part PA6(37 units)+ 1/2 PA
22 20 6,160 22,440 2.50 0.06 0.09 8 0.40 0.044512 0.14000 0.21 0.12 1.62892
20 18 28,940 51,380 2.50 0.13 0.20 8 1.90 0.046763 0.14000 0.21 0.12 3.72658
18 16 22,350 73,730 2.50 0.18 0.29 8 1.00 0.092497 0.20000 0.30 0.20 3.22469 PA 11
16 14 65,500 139,230 2.50 0.35 0.54 8 1.00 0.174669 0.28667 0.43 0.32 3.75286 1/2 PA 7 + flow from MH 30
14 12 3,360 142,590 2.50 0.36 0.55 8 1.40 0.151185 0.26000 0.39 0.28 4.36065 Existing Trailer Park (21 units)
12 10 6,160 148,750 2.50 0.37 0.58 8 2.40 0.120458 0.23333 0.35 0.25 5.28431 Portion PA 3 (21 Units)
10 8 1,830 150,580 2.50 0.38 0.58 8 2.00 0.133578 0.24667 0.37 0.26 4.96057 Existing Commercial (15,000 SF)
8 6 0 150,580 2.50 0.38 0.58 8 0.80 0.211206 0.31333 0.47 0.37 3.58083
6 4 0 150,580 2.50 0.38 0.58 8 0.80 0.211206 0.31333 0.47 0.37 3.58083
4 2 0 150,580 2.50 0.38 0.58 8 0.40 0.298690 0.38667 0.58 0.48 2.74755
'K' based on n = 0.011
2dn/D using Win Brater King Table 7-14
3 From Brater King Table 7-4 based on dn/D
11
CONNECT TO
EXIS11NG SEVER
i
SCALE 1 a - 400'
PROPOSED GRAVITY SEER LINES ARE RECOMMENDED AS 8—INCH. ç NODE AND PIPE DIAGRAM
CA) COMPUTER MODEL NODE NUMBER EXIS11NG 8 SEWER 'a EXH1131T A
- EXIS11NG GRAVITY SEWER 4..,.)
NOTE: ALL PROPOSED GRAVITY SEWER