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Home My WebLink AboutEast MU Sewer System Analysis for 2.25.19 DEXTER WILSON ENGINEERING, INC. WATER ● WASTEWATER ● RECYCLED WATER CONSULTING ENGINEERS 2234 FARADAY AVENUE ● CARLSBAD, CA ● (760) 438-4422 SEWER SYSTEM ANALYSIS FOR THE OTAY RANCH PLANNING AREA 12 EAST RESIDENTIAL SITE CITY OF CHULA VISTA February 25, 2019 SEWER SYSTEM ANALYSIS FOR THE OTAY RANCH PLANNING AREA 12 EAST RESIDENTIAL SITE CITY OF CHULA VISTA February 25, 2019 Prepared by: Dexter Wilson Engineering, Inc. 2234 Faraday Avenue Carlsbad, CA 92008 760-438-4422 Job No. 605-837 DEXTER WILSON ENGINEERING, INC. February 25, 2019 Baldwin & Sons 610 W. Ash Street, Suite 1500 San Diego, CA 92101 Attention: Nick Lee, Vice President DEXTER S. WILSON , P.E . ANDREW M. OVEN, P.E. STEPHEN M. NIELSEN, P.E. NATALIE J. FRASCHETTI, P.E. STEVEN J. HENDERSON, P.E. 605-837 Subject: Sewer System Analysis for the Otay Ranch Planning Area 12 East Residential Site Project PROJECT DESCRIPTION The Otay Ranch Planning Area 12 East Residential Site project is located in the City of Chula Vista. The project is located in the northwest portion of Otay Ranch Planning Area 12. The project is located along the east side of Town Center Drive, along the south side of Olympic Parkway. Figure 1 provides a location map for the project site. The approximately 10.4 acre site is currently undeveloped. The project proposes to develop 578 multi-family residential dwelling units in two buildings. Building "A" proposes 237 units as well as 15,000 square feet of retail commercial space. Building "B" proposes 341 units. The project site has elevations that range from 617 feet to 636 feet. The purpose of this report is to present an analysis of the private onsite sewer system that will provide service to the project and to evaluate the impact of the project on the public sewer system in the area. 2234 FARADAY AVENUE • CARLSBAD , CA 92008 • (760) 438-4422 • FAX (760) 438-0173 CONSULTING ENG I NEERS (760) 438-4422 FIGURE 1 VICINllY MAP PLANNING AREA 12 EAST RESIDENTIAL Nick Lee February 25, 2019 PRIVATE SEWER SYSTEM ANALYSIS Sewer System Overview All onsite sewer lines for the project site will be private sewer lines. The project will have two connections to the 8-inch public sewer line in Town Center Drive. One connection will be made to an existing stub. The backbone 8-inch private sewer lines that convey flow from the building sewer laterals were designed to the City of Chula Vista Engineering Department public standards. Figure 2 provides the proposed sewer system for the project. Design Criteria The criteria for evaluating sewer line sizing is provided as follows: Private Sewer Lines Designed to Engineering Department Standards. According to the Sewer Design Criteria provided in the City of Chula Vista Subdivision Manual, Section 3-300, the minimum size for sewer mains is 8-inch diameter. The minimum required velocity is 2.0 feet per second (fps). Where a velocity of 2.0 fps cannot be achieved, a minimum pipe slope of 1.0 percent is recommended. Additionally, while conveying peak flow, pipes should not flow more than half full. A Manning's Equation "n" value of 0.012 was used for the calculations. Estimated Sewage Flows The project consists of 578 multi-family residential units and retail commercial space. The City of Chula Vista 2014 Wastewater Master Plan indicates that the sewage generation factor for multi-family residential units is 182 gpd/DU and for commercial space is 80 gpd per 1,000 square feet. DEXTER WILSON ENGINEERING, INC. PAGE3 Nick Lee February 25, 2019 Peak flow was determined by using the peaking factor curve CVD-SW0l found on the City of Chula Vista Development Services website. The peaking factor is based on the total estimated population for the project. Equivalent population was determined based on a factor of 80 gpd/capita. Using the peaking factor curve gives a peaking factor of 2.42. Table 1 provides a summary of the total estimated sewage flow from the PA 12 East Residential project. TABLE 1 ESTIMATED SEWAGE FLOW Proposed Sewage Average Development Quantity Generation Sewage Factor Flow, gpd Multi-family 578 units 182 gpd/unit 105,196 Commercial 15,000 sf 80 gpd/1,000 1,200 sf Total 106,396 Equivalent Population 1,330 Peak Factor 2.42 Peak Flow 257,478 Analysis of Private Sewer Designed to Engineering Department Standards Hydraulic calculations were performed for the 8-inch backbone private sewer lines designed according to the Engineering Department public standards. The calculations are presented in Appendix A and verify that the recommended pipe sizes are adequate . The lines that convey flow from the project will flow less than 50 percent full by depth during peak flows as required by the City Engineering Department Standards. DEXTER WILSON ENGINEERING, INC. PAGE4 Nick Lee February 25, 2019 PUBLIC SEWER SYSTEM ANALYSIS Flows from the project will connect to an existing 8-inch public sewer line in Town Center Drive. This line conveys flow north to the Poggi Canyon Interceptor in Olympic Parkway. Capacity in the Poggi Interceptor was analyzed as part of the SPA Amendment for the project and, as a result, this study is focused on evaluating capacity in the 8-inch line in Town Center Drive. The 8-inch sewer line in Town Center Drive was constructed at a slope of 2.0 percent. This sewer was stubbed out to serve the Planning Area 12 East Residential site. Appendix B provides the calculation for this existing sewer line with the addition of project flows and confirms that it has capacity to serve the project. Sewer System Conclusion and Recommendations The following recommendations and conclusions are presented based on the sewer system analysis for the Planning Area 12 East Residential project. 1. All onsite sewer lines will be private sewer lines. The onsite backbone 8-inch sewer lines are designed to the City of Chula Vista Engineering Department Public Standards. 2. Flows from the project will be connected to an existing 8-inch public line in Town Center Drive at two locations. One connection will be made to an existing stub. 3. The existing 8-inch public sewer line in Town Center Drive was confirmed to have adequate capacity to serve the project. DEXTER WILSON ENGINEERING, INC. PAGES Nick Lee February 25, 2019 Thank you for the opportunity to assist you with the sewer system planning for this project. If you have any questions regarding the information presented in this report, please do not hesitate to call. Dexter Wilson Engineering, Inc. Stephen M. Nielsen, P.E. SMN:pjs Attachments DEXTER WILSON ENGINEERING, INC. PAGE6 ~ N I BUILDING A CONNECT TO EXISTIN SEWER STUB ~------I I ----8,)t ~ ... ,e,£> ~ £,>J\\J)\\, ~ ----- ::::--- ---=::::::..____ _ -------------1:EGEN~R ~ECT BOUNDARY - - - -EXISTl~G PUBLIC SEWER -----PROPo l D PRIVATE SEWER \ XTER WILSON ENGINEERING , INC . DE CO N S U L TI NG ENG IN EE R S (7 60) 4 38-44 22 --....... ---I ---l 1-- FIGURE 2 PROPOSED SEWER SYSTEM PLANNING AREA 12 EAST RESIDENTIAL APPENDIX A HYDRAULIC ANALYSIS OF PRIVATE SEWER LINE PA -12 East Residential Site Backbone Sewer Line 8-lnch Private Sewer Line Calculations 8" Sewer Line Capacity at 0.5% Slope Utu11 = (0.463/n)*(D)813 *(S)112 Where Utull = full pipe capacity, cfs n = Manning's coefficient= 0.012 D = Pipe diameter, ft. S = Pipe slope, ft/ft So Utull = (0.463/0.012)*(8/12)813 *(0.005)112 Utull = 0.925 cfs = 0.60 mgd Peak Flow URes = 341 units x 182 gpd/unit = 62,062 gpd (worst case = all of Building B) Total Oavg = 62,062 gpd Peak Factor= 2.50 (lpk = 155,155 gpd (lpk = 0.155 mgd Determine d/O Qpk/Otull = 0.155/0.60 = 0.26 Per attached graph, d/D = 0.35 < 0.50 OK M PROFESSIONAL ENGINEERING REGISTRATION PROGRAM P.O. Box 91 i, San Carlos, CA 94070 Figure 5.20 Circular Channel Ratios Page: 5-27 Experiments have shown that n varies slightly with depth. This figure gives velocity and flow rate ratios for varying n (solid line) and constant n (broken line) assumptions .. ---------,,. , --~ / .__ / ' ........ 1,,,. ---"~ ... , .... ' .... I ', ... ,~ -~ .... ~ ' ..... ' "' ........ " "' . \ ' ~ I\ "- \ , " \ ~ r,.._ \ \ \ . '"' \ \ \ ·-' \ \ \ \ \ \ ' ~ \ \ \ \ ' \ \ \ \ }. I/ I\ ., e "' ~ u .. 'c , C: -----:--....---__.... L---...-----I . --- ' ' .' . \ ' ' ' \, \ \ :,. ' ... u 0 ' oi J( > '· N \ \ ' "". \ \ ' "' ~ \ \ ' \ ' \ ' \ \ \ i\ \ \ \ \ \ \. '"' \ \ ' \ \ "- .. \ \ \ \ \ \ \ ' ' ·, ~ .. \ \ ' \ . ' ~ \ \ \ \ I\ \ \ \ ' ' \ \ \ \ \ I' \ ' \ \ \ -i'---...., \ "'~ \ ' ..... ', -......:: ~ _1 ---' ... ... 0. ... ~ I!! Lq 0 0. O"! 0 co c:i ,... c:i (0 ci SI; 0 l.rl , I'? ,..,. . • 0 N 0 -0 -0 Ratio of Flow Depth to Diameter (d/D} :, 0 g -c C "' .E. ~ ~ APPENDIXB HYDRAULIC ANALYSIS OF PUBLIC SEWER LINE PA -12 East Residential Site Town Center Drive 8-lnch Public Sewer Line Calculations 8" Sewer Line Capacity at 2 .0% Slope Otull = {0.463/n)*{D)813 *{S)112 Where Otu11 = full pipe capacity, cfs n = Manning's coefficient= 0.012 D = Pipe diameter, ft. S = Pipe slope, ft/ft So Otull = {0.463/0.012)*{8/12)813 *{0.02)112 Otull = 1.85 cfs = 1.20 mgd Peak Flow 0Res = 578 units x 182 gpd/unit = 105,196 gpd Ocom = 15,000 SF x 0.08 gpd/SF = 1,200 gpd Total Oavg = 106,396 gpd Peak Factor= 2.42 Qpk = 257,478 gpd Qpk = 0.257 mgd Determine d/D Qpk/Otull = 0.257 /1.20 = 0.21 Per attached graph, d/D = 0.31 < 0.50 OK M 3 ... C .-]: ,- PROFESSIONAL ENGINEERING REGISTRATION PROGRAM P.O. Box 91 i, San Carlos, CA 94070 Figure 5,20 Circular Channel Ratios Page: 5-27 Experiments have shown that n varies slightly with depth. This figure gives velocity and flow rate ratios for varying n (solid line) and constant n (broken line) assumptions .. ------.... --,,.. -,-.. .......... _ .,,. ,,, I ' ..... 1,,, --.... .... ',. ..... ,, .... I ' V -' ~ ~ ... .... ' "" . --........ "' I'\ ' '\ \. "" I'\ ·. :-.... \ .. " \. r"-. " \ \ . '~ r,, \ \ \ .. ' \ \ \ \ \ \ ~ \ \ \ \ \ \ \. \ \ \ )- ll I\ ., C, ... .. .i:; (J .. ~ / " " .'' \ ' ' ' V, ' ' > ' ... u 0 ' j ,( '· N ' "'· "" ~ \ \ \ ' \ ' \ \ ' I\ \ \ \ \ \ '\ ~..,. \ \ \ \ \ ' \ \ \ \ \ ' \ \ \ T \ \ i\ \ .. \ \ \ \ \ \ I\ \ \ ' \ \ \ \' \ I- \ ... ... q ... "": tq Lt? 3 0 g -0 C: .. "5 > } rJ \ \ N • ·c "' \ \ \ ' \ C: ~ " -~ \ ------' ·, ...... ---~ " "\ --' ---..... "' .,...,.-------' ~ \~ __.,.. I ----i 0 . ' .. 00 ci .... ci tq Lt? '<I; -~ 0 0 0 M O .. ci Ratio of Flow Depth to Diameter (d/D-1 O