The URL can be used to link to this page

Home My WebLink AboutCT 11-01; ROBERTSON RANCH WEST VILLAGE; SEWER SYSTEM ANALYSIS; 2011-12-20I I I I I I I I I I I I I U I I I I I SEWER SYSTEM ANALYSIS FOR ROBERTSON RANCH WEST December 20, 2011 Prepared by: Dexter Wilson Engineering, Inc. 2234 Faraday Avenue Carlsbad, CA 92008 Job No.: 936-001 I I DEXTER WILSON ENGINEERING, INC. U I DEXTER S. WILSON, P.E. ANDREW M. OVEN, P.E. STEPHEN M. NIELSEN, P.E. DIANE H. SHAUGHNESSY, P.E. NATALIE J. FRASCHETTI, P.E. U December 20, 2011 936-001 1 I. Shapell Homes, Inc. 8383 Wilshire Blvd., Suite 700 Beverly Hills, CA 90211 I Attention: Erik Pfahler, Vice President Subject: Robertson Ranch West Sewer System Analysis I Introduction This letter-report summarizes our evaluation of the sewer system that will serve the I 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, I 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. I I I I I 2234 FARADAY AVENUE CARLSBAD, CA 92008 • (760) 438-4422 • FAX (760) 438-0173 v'14V Al 304 OL Is" sow -4 ••,. I lk - Ilk 12 -4 it *Dt sow - - N ' ROBERTSON RANCH WEST 00, I I.- - ft NTS dm N -, - -- - - - - llmNl EL C 4V4 7, mill 04 1. I r Li *71 IK tV4 -ir FIGURE 1 Erik Pfahler December 20, 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 = 176 gpd/unit (per 2010 Draft Sewer Master Plan) Peak Flow Factor = 2.5 x Average Day Demand Minimum Pipeline Velocity at Peak Flow = 2.0 ft./s Maximum dID, new 12" 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. As shown the projected average daily flow is 155,320 gpd and the projected peak flow is 388,300 gpd (Peak Factor = 2.5). DEXTER WILSON ENGINEERING, INC. PAGE 3 I I I I I I I I I I I I I I I I Erik Pfahler December 20, 2011 TABLE 1 ROBERTSON RANCH WEST PROJECTED SEWAGE FLOWS Planning Area' Land Use Gross Acres Maximum Dwelling Units Generation Factor Average Flow, gpd 1 SF Residential 8.3 32 220 gpd/unit 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 6 SF Residential 14.8 65 220 gpd/unit 14,300 7 MF Residential 7.3 110 176 gpd/unit 19,360 8 MF Residential 16.4 260 176 gpd/unit 45,760 9/10 SF Residential 21.9 78 220 gpd/unit 17,160 11 Commercial 14.9 --- 1,597 gpd/ac 23,800 TOTAL 658 155,320 See Figure 3 for planning area locations I Existing Sewer System 1 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 I Agua Hedionda 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 I 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 trunk sewer line which is located in a canyon south of El Camino Real. I H DEXTER WILSON ENGINEERING, INC. PAGE 4 I I I- I I I I I Li I I I Erik Pfahler I December 20, 2011 To the east of the project there are gravity sewer lines at the intersection of Cannon Road I and El Camino Real that convey flow to the South 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 I 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 I manhole in Edinburgh Drive. I Sewer System Analysis 1 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 I 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 I will be connected to the existing system and conveyed to the Kelly Drive sewer line, labeled NAHT1B in the City's Sewer Master Plan. Three alternatives were evaluated for serving the eastern portion of the project as described below. I The first alternative considered was identified in the November 2006 Robertson Ranch I 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 I 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 I 1 DEXTER WILSON ENGINEERING, INC. PAGE 5 I * * 4 t 3 * I I , N i r R LIFT TWEAD SEWE STATION (TO BE AB Alp Ai ANDONED) Aj -mb 46 - . I riz_ Al vk I / Ak ABANDONED LIFT STATION TO Dtt DT PKI DAkII'U WEST BE REMOVED BY DEVELOPER F\1'J1sF1 VL I / NTS )01 .' tv qftft 4 *_ / i• _j c*4* N Ai ~NA 4 4 7 / / 411 1 1 O~ . . ., , a .. FIGURE 2 EXISTING SEWER oN FACILITIES Erik Pfahler December 20, 2011 The second alternative considered was to construct a sewer pipe line across El Camino Real to connect into the sewer lines in Eucalyptus Lane or Crestview Drive. A review of the 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 construct a sewer line westerly in El Camino Real to convey the wastewater to the existing 8" sewer that the remainder of the project will connect to, except Planning Area 1. 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 and the 21 trailer park units on the south side of El Camino Real, the maximum depth-to-diameter (dID) ratio in this section of line during peak flows is 0.60. While new 8- inch sewer lines are to be designed for a maximum dID ratio of 0.5, it is reasonable to allow an existing gravity sewer to flow at a dfD 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. The project will be required to replace approximately 320 feet of 8-inch sewer (from MH1 to MH2 on Drawing 222-4) to eliminate the existing drop manhole. Re commendations Sewer service can be provided to the Robertson Ranch West property Planning Areas 2 through 11 by the City of Carlsbad. All onsite sewer lines are recommended as 8-inch with connections to the existing 8" 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 DEXTER WILSON ENGINEERING, INC. PAGE 7 I I I I I F I I I I I lii F I I I I I I Erik Pfahler December 20, 2011 experience dID ratios of 0.36 to 0.60 during ultimate peak flows, including flow from 24 units along Gateshead Road to the north of the project and 21 units from the trailer park on the south side of El Camino Real. Planning Area 1 will connect to the existing 10-inch sewer line on the north side of El Camino Real. At the time of this report, Planning Area 1 is shown as a mass graded pad and the exact location of the connection to the existing 10- inch line is unknown. If you have any questions on the information contained herein, please let us know. Dexter Wilson Engineering, Inc. Stephen M. Nielsen SMN:ps DEXTER WILSON ENGINEERING, INC. PAGE 8 I I I I I I I I I I I I I I I I I I I EL CAMINO REAL — — — — PROJECT TO REPLACE APPROX. 320' OF 8" SEWER LINE TO ELIMINATE EXISTING DROP MANHOLE. - EXISTING & SEWER CONNECT TO EXISTING SEWER / / I I, I Ii Ii I I I I I I I I I I I I I I I 4c. LEGEND — — EXISTING GRAVITY SEWER NOTE: ALL PROPOSED GRAVITY SEWER PROPOSED GRAVITY SEWER LINES ARE RECOMMENDED AS 8-INCH. SCALE: 1" = 400' FIGURE 3 PROPOSED SEWER SYSTEM U U APPENDIX A U HYDRAULIC ANALYSIS 11 I I I I I I I I I I n L ET L I SEWER STUDY SUMMARY DATE: 12/16/2011 FOR: Robertson Ranch West Sewer Study JOB NUMBER 936-001 BY: Dexter Wilson Engineering LINE FROM TO IN-LINE FLOW (gpd) AVG. DRY WEATHER FLOW (gpd) PEAKING FACTOR PEAK WET WEATHER FLOW (DESIGN FLOW) LINE SIZE (inches) DESIGN SLOPE (%) DEPTH K' (I) dn (feet) dn/D2 Ca for Velocity (3) C.F.S. VELOCITY (f.p.s.) Remarks M.G.D. 34 1 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 19,580 31,020 2.50 0.08 0.12 8 4.00 0.019458 0.09333 0.14 0.07 4.04168 PA 30 16 34,800 65,820 2.50 0.16 0.25 8 4.00 0.041287 0.13333 0.20 0.11 5.12405 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) 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 PA 10 20 18 31,020 53,460 2.50 0.13 0.21 8 1.90 0.048656 0.14667 0.22 0.13 3.63226 Part PA 6 (37 units) + 1/2 PA 8 18 16 22,350 75,810 2.50 0.19 0.29 8 1.00 0.095107 0.20667 0.31 0.21 3.18137 PAll 16 14 75,500 151,310 2.50 0.38 0.59 8 1.00 0.189824 0.30000 0.45 0.34 3.87334 1/2 PA 7 + flow from MH 30 14 12 3,360 154,670 2.50 0.39 0.60 8 1.40 0.163993 0.27333 0.41 0.30 4.43991 Existing Trailer Park (21 units) 12 10 0 154,670 2.50 0.39 0.60 8 2.40 0.125252 0.24000 0.36 0.25 5.34198 10 8 1,830 156,500 2.50 0.39 0.61 8 2.00 0.138830 0.25333 0.38 0.27 5.04484 Existing Commercial (15,000 SF) 8 6 0 156,500 2.50 0.39 0.61 8 0.80 0.219509 0.32000 0.48 0.37 3.64200 6 4 0 156,500 2.50 0.39 0.61 8 0.80 0.219509 0.32000 0.48 0.37 3.64200 4 2 0 156,500 2.50 0.39 0.61 8 0.40 0.310433 0.40000 0.60 0.49 2.76851 1K' based on n = 0.011 2 dnlD using K' in Brater King Table 7-14 3 From Brater King Table 7-4 based on dn/D / J/f, AbANL)UNL.D Ur BEjkEMbVED BY SAFPROXIMA 'p Z:ÔCoNNEC \TEXIS11NG 1C co 04 ------------ - - 1411 CONNECT TO EXISTING SEWER cv /CDg / j LEGEND - EXISTING GRAViTY SEWER —-I-- PROPOSED GRAVITY SEWER EXISTING 8" SEWER NOTE: ALL PROPOSED GRAVITY SEWER LINES ARE RECOMMENDED AS 8—INCH. SCALE: 1" = 400' / EXHIBIT A / NODE AND PIPE DIAGRAM