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Home My WebLink AboutGPA 2017-0003; OAKMONT OF CARLSBAD; SEWER REPORT; 2018-02-01OAKMONT OF CARLSBAD CUP 2017-0008 SEWER REPORT TABLE OF CONTENTS Introduction ...................................................................................................................................... 2 Public System Impacts .................................................................................................................... 3 Onsite Pipe Sizing ............................................................................................................................ 3 Conclusion ....................................................................................................................................... 3 LIST OF APPENDICES APPENDIX A -SEWER EXHIBIT APPENDIX 8-SEWER GENERATION FACTORS APPENDIX C-ONSITE PIPE SIZING CALCULATIONS OAKMONT OF CARLSBAD CUP 2017-0008 SEWER REPORT Introduction The following is a Sewer Capacity Analysis Report for the Private Sewer System within the Oakmont of Carlsbad project (Lot 1 ), which is part of the Carlsbad Oaks North Master project. The private system has been designed using the Uniform Plumbing Code required for private system design. The UPC requires a minimum slope of 2.0% and sets maximum drainage fixture units for all pipe sizes. The sewer system within the Oakmont of Carlsbad site has been designed to meet these standards and specifications. Methodology As discussed with City of Carlsbad, Private Systems are not designed according to Public Sewer Design standards (City/County Standard) but using the aforementioned UPC. City design standards for public sewer systems use an alternative methodology for calculating discharge, minimum slopes velocity and capacity which will make the analysis flawed if methods/standards were to both be followed. The Oakmont of Carlsbad system follows UPC guidelines for pipe sizing and does not go below 2.0% slope as directed by City of Carlsbad in one of our initial meetings. Sewer Generation Below is a summary of sewer generation calculations that compare the existing land use at the site (industrial) to the currently proposed land use (residential, with no kitchen). SEWER GENERATION SUMMARY ZONE ACREAGE UNITS FACTOR REDUCTION FLOW ,j # gpd (E) INDUSTRIAL 277,913 800 gpd/10,000 sf 0.5 • 11,117 (P) RESIDENTIAL, NO KITCHEN 151 220 gpd/EDU 0.6 • 19,932 1 Reduction for 50% coverage 2 Reduction for no kitchen use within each unit The proposed sewer generation flow is considered conservative as Carlsbad bases their residential factor at a 220 gpd/EDU rate based on 2.76 residents per unit where Oakmont Senior Living facilities typically only have one resident per unit. In addition, the residents rarely, if at all, are able to use the kitchen facilities within their own unit. Even though the kitchen reduction factor is applied, the 220 gpd/EDU basis is considered an over-estimation of the actual generation within the Oakmont units. 2 OAKMONT OF CARLSBAD CUP 2017-0008 SEWER REPORT Public System Impacts Since the proposed Oakmont land use potentially generates more sewer flow than does the existing site land use, analysis of the City's municipal system is warranted. Proposed site flows of 19,932 gpd have been provided to the City to confirm the increase does not significantly impact the existing public system. Impacts will be assessed via computer model from outside City consultant and will be reported on when the data becomes available. Onsite Pipe Sizing For onsite pipe sizing, the DFU's stated on the provided sewer plan have been converted to CFS. Pipe sizing analysis using FlowMaster software has been performed each pipe segment of the onsite private sewer system. Per calculations included, the pipe size, minimum fixture units, minimum slope (2.0 %), and minimum velocities(> 2.0 fps) have been provided for the system utilizing the UPC design guidelines. Conclusion The sewer flows proposed at the Oakmont Senior Living facility are considered conservative in nature. Pending results of the City analysis for offsite public system impacts, the private sewer system described here is considered acceptable for construction. 3 spreadsheet for future development in LFMZ I was provided by City Staff. The spreadsheet, which includes parcel numbers, is more detailed than the Growth Database backup sheet and was used to locate future development in LFMZ I, which is primarily redevelopment in the downtown area. Once future development projections were finked to parcels, a map of future development was prepared and reviewed for accuracy. In the Growth Database, once building permits are issued the development is assigned to that calendar year and is no longer considered future development. Construction does not necessarily begin right after permits are issued, however, and it may take several years before developments are occupied and contributing sewer flows. This creates a lag berween "existing" and "future" development. Since future flows based on the Growth Database are added to the existing hydraulic model with 2009 wastewater flow data, development projects with recent building permits that have not yet been constructed or are not yet contributing wastewater flows need to be included. To identify these developments, projects in the Growth Database with building permits issued in the past three years were reviewed together with the most recent land use map, aerial photographs, and water use records. This investigation identified developments that were not contributing wastewater flows during the 2009 metering period and resulted in a significant increase in "future" development, primarily in some of the newer industrial parks, portions of Bressi Ranch, and in Robertson Ranch, where building permits have already been issued for the first phases. Several additional refinements were also made to the modified parcel-based growth database to account for future flows to the wastewater system. These included:- • Future recreation facilities in parks and a future high school in LFMZ 14 were added. • Residential properties that currently have septic systems were added on the assumption that they will ultimately connect to the sewer system. These parcels were identified by City Staff based on water and sewer billing records. • Residential units within the service areas of the La Golondrina and La Costa Meadows Ill Lift Stations were added to account for the additional flows that have been re-directed into Carlsbad with the construction of new gravity sewers and the recent removal of the lift stations. • Buildout projections for the proposed residential development known as Quarry Creek (LFMZ 25) were updated based on updated planning information provided by City Staff. • The residential categories were modified to separate high density development (apartment complexes, as noted in the growth database backup sheets) from all other residential development. This was done to more accurately project sewer flows, which are influenced more by the number of people per household than the lot size. Exhibit 2 in Appendix A illustrates the parcels with future development within the sewer service area. 5.3 FUTURE FLOW GENERATION FACTORS Flow generation factors are used, in conjunction with the modified Growth Database, to project ultimate wastewater flows. Unit flow generation rates were developed and presented in Chapter 3 of this report based on 2009 flow data. For planning purposes, more conservative unit flow factors are typically used. The City's established planning value for wastewater flow is 220 gpd/EDU. Flow factors typically used for design of sewer systems throughout San Diego County range between approximately 200 gpd/EDU in the Cities of Encinitas and Solana Beach, to 250 gpd/EDU in the City of Vista. The City City of Carlsbad SEWER MASTER PLAN 5-4 DUDEK April 2012 of San Diego Water & Sewer Design Guide r ecommends the use of 80 gallons per capita day (gpcd), which equates to 197 gpd/DU for the City of Carlsbad (based on 2.46 persons per household). Based on these comparisons and the calculated unit flow rate for current conditions, the previously established flow generation rate of 220 gpdfEDU is considered to be appropriately conservative for flow projections in this master plan update. A lower unit flow factor of 176 gpd (80 percent of 220 gpd/EDU) is applied to high-density residential units in excess of approximately 20 units per acre (apartment complexes). A non-residential land use flow factor of 800 gpd per I 0,000 square feet of building area is applied to commercial and industrial development projections in the Growth Database. The composite commercial/industrial unit factor was approved by City Staff for planning purposes, and is higher than the average unit flow calculated in the unit flow analysis documented in Section 3.7. It is noted that projections made using this factor are based on a mix of development types in-existing business/industrial parks and may not be representative of smaller areas with a single land use type. Flow projections for future schools. resort hotels, and t:he expansion of the Legoland Water Park are based on EDU conversions documented in the Carlsbad Municipal Code (Table 13.I0.020c). The unit flow factors established by City Staff to project ultimate wastewater flows in this Master Plan Update are summarized in Table 5-2. Table 5-2 Wastewater Unit Flow Factors Land U~e Category Unit Wastewater Flow Residential Low Density to Med-High Density 220 gpd/DU Residential High Density (Apartments) 176 gpd/DU Commercial/Industrial 800 gpd/ I 0,000 sq ft of building area High School 7.33 gpd/student Hotel 132 gpd/guest room Water Park (Legoland) 3,740 gpd/developed acre 5.4 PROJECTED ULTIMATE FLOWS Wastewater flow projections for future developments are made by applying the unit flow factors to the future build-out data in the modified Growth· Database. Future wastewater flows are projected to be approximately 2.1 mgd and are summarized in Table 5-3. The future flows are based on flow projections for future development, and also include unit counts for existing residences that currently have septic systems and areas in LFMZ 6 that previously were pumped to L WWD from the La Golondrina and La Costa Meadows Li~ Stations. It is noted that a minor wastewater service area boundary adjustment is assumed in the future to serve existing LWWD customers within the area of a proposed residential development: located on the west side of El Camino Real, just south of Poinsettia Lane. City of Carlsbad SEWER MASTER PLAN 5-5 DUDEK April 20 12 OAKMONT OF CARLSBAD SEWER DISCHARGE CONVERSION~ OFU'S TO CFS 10/13/17 SEGMENT DFU PIPE MAX CONVERT (SEE MAPS) COUNT SIZE CAPACITY TOGPM (IN) (DFU) {2 DFU:::: 1 GPM) 1 172 6 720 86 2 1032 8 2640 516 3 1262 8 2640 631 CONVERSION CONVERSION TO DISCHARGE % TO CF SECONDS (CFS) FULL (1 CF:::: 7.481 G) (1 MIN= GOS) 1/7.481 1/60 0.19 33.3 1/7.481 1/60 1.15 59.6 1/7.481 1/60 1.41 50.3 Worksheet for SEGMENT 1 Project Description Friction Method Manning Formula Solve For Normal Depth Input Data Roughness Coefficient 0.013 Channel Slope 0.02000 ft/fl Diameter 0.50 fl Discharge 0.19 fl'/s esults Normal Depth 0.17 fl Flow Area 0.06 ft2 Wetted Perimeter 0.62 ft Hydraulic Radius 0.09 fl Top Width 0.47 ft Critical Depth 0.22 ft Percent Full 33.3 % Critical Slope 0.00738 ft/fl Velocity 3.32 fUs Velocity Head 0.17 ft Specific Energy 0.34 ft Froude Number 1.68 Maximum Discharge 0.85 ft'/s Discharge Full 0.79 ft'/s Slope Full 0.00115 ft/ft Flow Type SuperCritical GV~ut Data Downstream Depth 0.00 fl Length 0.00 ft Number Of Steps 0 GVF Output Data Upstream Depth 0.00 ft Profile Description Profile Headloss 0.00 ft Average End Depth Over Rise 0.00 % Normal Depth Over Rise 33.29 % Downstream Velocity Infinity ft/s Bentley Systems, Inc. Haestad Methods SollditlleifMeifllaster VBi (SELECTseries 1) [08.11.01.03] 10/13/2017 4:02:43 PM 27 Siemens Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 Page 1 of 2 Worksheet for SEGMENT 2 GVF Output Data Upstream Velocity Infinity fUs Normal Depth 0.40 ft Critical Depth 0.51 ft Channel Slope 0.02000 fUft Critical Slope 0.01034 ft/ft Bentley Systems, Inc. Haestad Methods So8ditlhliftN<MasterV8I {SELECTseries 1) [08.11.01.03] 10/13/2017 4:04:37 PM 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 Page 2 of 2 Worksheet for SEGMENT 3 GVF Output Data Upstream Velocity Infinity ft/s Normal Depth 0.34 ft Critical Depth 0.56 ft Channel Slope 0.05200 ft/ft Critical Slope 0.01291 ft/ft Bentley Systems, Inc. Haestad Methods SoBltm/l!iftNNMasterVBi (SELECTseries 1) [08.11.01.03] 10/13/2017 4:08:37 PM 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 Page 2 of 2