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HomeMy WebLinkAboutCT 13-03; ROBERTSON RANCH-RANCHO COSTERA; SEWER SYSTEM ANALYSIS FOR RANCHO COSTERA; 2015-04-28DEXTER WILSON ENGINEERING, INC. DEXTER S. WILSON, P.E. ANDREW M. OVEN, P.E. STEPHEN M. NIELSEN, P.E. NATALIE J. FRASCHETTI, P.E. April 28, 2015 936-003 Toll Brothers 725 W. Town & Country Rd., Suite 200 Orange, CA 92868 Attention: Peter Kim, P.E., Land Development Director Subject: Rancho Costera Sewer System Analysis Introduction - This letter-report summarizes our evaluation of the sewer system that will serve the western portion of the Robertson Ranch project (Rancho Costera). 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 and to be operated and maintained by the City of Carlsbad. 2234 FARADAY AVENUE • CARLSBAD, CA 92008 9 (760) 438-4422 • FAX (760) 438-0173 ,,.. Ar oe 404, dow /00 - / RANCHO COSTERA NO SCALE 0 Nb - ftsa / / - - - - / EL CAMINO REAL Wa At CD j 4W A 44 FIGURE 1 ALI LOCA liON MAP RANCHO COSTERA Peter Kim April 28, 2015 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 gpdJEDU Average Flow SF Residential Generation Factor = 220 gpd/unit MF Residential Generation Factor = 176 gpd/unit (per 2012 Sewer Master Plan) Peak Flow Factor = 2.5 x Average Day Demand Minimum Pipeline Velocity at Peak Flow = 2.0 ft.Is Maximum d/D, new12" and smaller pipes - 0.50 Maximum d/D, 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 153,865 gpd and the projected peak flow is 384,663 gpd (Peak Factor = 2.5). DEXTER WILSON ENGINEERING, INC. PAGE 3 Peter Kim April28, 2015 TABLE 1 RANCHO COSTERA PROJECTED SEWAGE FLOWS Maximum Planning Gross Generation Average Land Use Dwelling Area' Acres Factor Flow, gpd Units Community 1 1.87 -- 1,597 gpdlac 2,986 Facility 3 SF Residential -- 87 220 gpdlunit 19,140 5 SF Residential -- 36 220 gpdlunit 7,920 6 SF Residential -- 87 220 gpdlunit 19,140 7 MF Residential -- 96 176 gpdlunit 16,896 8 MF Residential -- 268 176 gpdlunit 47,168 9/10 SF Residential -- 75 220 gpdlunit 16,500 11 Commercial 15.1 --- 1,597 gpd/ac F24,115 TOTAL 649 153,865 'See Figure 3 for planning area locations Existing Sewer System There are several existing sewer lines in the vicinity of the Rancho Costera project. Figure 2 provides the location of existing facilities in the vicinity of the project. The North 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 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. DEXTER WILSON ENGINEERING, INC. PAGE 4 : I GATES" -GATESHEAD SEWER LIFT / STATION (TO BE ABANDONED) moo TION TO ABANDONED LIFT STA BE REMOVED BY DEVELOPER / I * / C1 / I - - / A - / RANCHO COSTERA Nb : :: I CD ry A5 CD - ELCAMINOREAL ( i NO SCALE (5 / I 1 -tl . L~j 1$IWA FIGURE 2 Aj / EXISTING SEWER - E XTER WL5QN ENGINEERN 'C FACILITIES RANCHO COSTERA Peter Kim April 28, 2015 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 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 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, labeled NAHT1B in the City's Sewer Master Plan. 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. DEXTER WILSON ENGINEERING, INC. PAGE 6 Peter Kim April 28, 2015 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 0.61. 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 dID 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. Recommendations Sewer service can be provided to the Rancho Costera 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 experience dID ratios of 0.36 to 0.61 during ultimate peak flows, including flow from 24 units along DEXTER WILSON ENGINEERING. INC. PAGE 7 Peter Kim April 28, 2015 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. M. C51070 Stephen M. Nielsen EXP.9130115 lilA d>'\. C I V t. SMN:ps DEXTER WILSON ENGINEERING, INC. PAGE 8 APPENDIX A HYDRAULIC ANALYSIS SEWER STUDY SUMMARY DATE: 4/27/2015 FOR: Rancho Costera Sewer System Analysis SHT I OF I JOB NUMBER: 936-003 BY: Dexter Wilson Engineering REFER TO PLAN SHEET: LINE FROM TO IN-LINE AVG. DRY AG PEAK FLOW (gpd PEAK FLOW (DESIGN FLOW) DESIGN FACTOR LINE SIZE (inches) SLOPE DEPTH K' (1) dn (feet) dn/D Ca for VELOCITY Remarks 24 22 13,420 13,420 2.500 33,550 0.034 0.052 8 8.05 0.005934 0.05333 0.08 0.0294 3.97 Part PA 5 (15 units) + Part PA 6 (46 units) 26 22 21,780 21,780 2.500 54,450 0.054 0.084 8 0.80 0.030550 0.11333 0.17 0.0885 2.14 PA 9 + PA 10 + 24 units (Gateshead Road) 22 28 37,535 59,315 2.500 148,288 58,960 0.148 0.059 0.229 0.091 8 8 0.50 2.95 0.105238 0.017227 0.21333 0.08667 0.32 0.13 0.2167 0.0600 2.38 3.42 MH 24 + PA 11 Part PA 8 (134 mf units) 34 32 23,584 23,584 2.500 30 28 32,780 32,780 2.500 81,950 0.082 0.127 8 1.01 0.040921 0.13333 0.20 0.1118 2.55 PA 3 + Part PA 5(21 units) + Part PA 6(41 units) 36 32 23,584 23,584 2.500 58,960 0.059 0.091 8 1.73 0.022495 0.10000 0.15 0.0739 2.78 Part PA 8 (134 mf units) 32 28 23,584 47,168 2.500 117,920 199,870 0.118 0.200 0.182 0.309 8 8 8.86 3.93 0.019880 0.050595 0.09333 0.14667 0.14 0.22 0.0668 0.1281 6.15 5.43 MH 34 MH 30 28 18 32,780 79,948 2.500 18 16 76,211 156,159 2.500 390,398 0.390 0.604 8 1.26 0.174532 0.28667 0.43 0.3229 4.21 MH 22 + PA (96 mf units) 16 14 0 156,159 2.500 390,398 398,798 0.390 0.399 0.604 0.617 8 8 1.00 1.40 0.195912 0.169138 0.30000 0.28000 0.45 0.42 0.3428 0.3130 4.44 3.96 Existing Trailer Park (21 units) 14 12 3,360 159,519 2.500 12 10 0 159,519 2.500 398,798 0.399 0.617 8 2.40 0.129182 0.24000 0.36 0.2546 5.45 10 8 1,830 161,349 2.500 403,373 403,373 403,373 403,373 0.403 0.403 0.403 0.403 0.624 0.624 0.624 0.624 8 8 8 8 2.00 0.80 0.80 0.40 0.143135 0.226316 0.226316 0.320059 0.25333 0.32667 0.32667 0.40667 0.38 0.49 0.49 0.61 0.2739 0.3827 0.3827 0.5020 5.13 3.67 3.67 2.80 Existing Commercial (15,000sf) 8 6 0 161,349 2.500 6 4 0 161,349 2.500 4 2 0 161,349 2.500 [Max dn/D I 0.61 1K' based on n= 0.011 2dn/D using K in Brater King Table 7-14 3 From Brater King Table 7-4 based on dnlD ERA DY VT/ON L(@201 0' Day Consultants, Inc. liON 2710 Laker Avenue West Civil Engineering ENGINEER OF WORK; Suite 100 Planning Carlsbad, California 92010 Processng - 760-931-7700 Surveying Fax: 760-931-6680 DATE: www.odaycannultonts.com GEORGE O'DAY RCE: 32014 G:\101307\Flydrology\Vesting TM\10076—DS—Proposed - 130403.dwg Apr 09, 2013 8:16am Xrefs: I007AMAP: 1007WTlAP; 1007AW01; 1007wstr 01I4TPCI-l; 1007a—preiim7; 98201P03—A; 1007autl7; 0114BGRD—REV; 1007csite; EXIST DRAINAGE - KELLY RCB; 1007wut1; 1007AS1TE 1007V—prelim3; 1007V—FIRE SEA GRAPHIC SCALE 200 0 100 200 400 1 INCH = 200 FEET ( ii ( ( I U A DOM I OF 0 X82-5 ANALYSIS A MN / (I 78"RCP - I 169.5 0 166.3 168 1622 165.4 I Tw 159.8 164.5 161.7 159.7 \RcP 169,5 1567 157.7 [( /3740SF/ 7b57428!r/ '15 7 1678 1484 / is R \\\ 1460151:00 146.1 4 159275861SFh15751570J 1538 7578 1498 78 7472 1477 1482 14,16 1486 7, 640 5F I/1 8"CP / I 2400 SF 870 146.1 1477 2I 120 /1 148.2 isfl/ irn 140.4 7,39.4 f IJ5.5 7350 I' 7435 1 980 SF 734 1430 1419 STREET © 1340 " IS RP 140.1 Z4 10 / EXIST DOUBLE 8'X4' ROB -77 EL CAMINO REAL / 24" RCP JO RCP Jo" RCP(2) I / / V \\ \\1 )6CP J6 RCP \ __ 1 fl EXIST CONCRETE--) [E / A CCESS ROAD 1O \ IV Jn 4/ © /J1 ITi 0/8 / /845/7 83.0 4 70.0 835 REC AREA I \\\\ - / _ PER C8 / PSTREAM DOMAIN OF H ANALYSIS LOCATION EXIST TRIPLE 10'X4' BOX CUL VERT PER DWG J90-9 LEGEND: cc—? PROPOSED GRADING PROPOSED DRAINAGE FACILITY ( POINT OF COMPLIANCE __ — STUDY REACHES (VARIOUS COLORS) EXTENSION OF POC OUTFALL TO CREEK FLOWLINE j I. •