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River Islands Development at Lathrop November 2020 Final Phase 2 Sewer Technical Report Rev 1 #6520 5. River Islands Sewer Collection System Model 5.1 GIS Sewer Collection System Model ArcGIS, a geographic information system (GIS) software, was used to conduct a steady state analysis of the River Islands sewer collection system under ADWF and PWWF. A steady state analysis determines the operating performance of the sewer collection system at a specific point in time under steady state conditions (flows and hydraulic grades remain constant over time). The results of the steady-state analysis helped validate the following performance criteria of the River Islands sewer collection system. • Pipe capacities per the City Standards • Average Dry Weather Flows in each pipe • Peak Wet Weather Flow peaking factors in each pipe • Peak Wet Weather Flows in each pipe • Required firm pumping capacity for each sewer lift station. • Pipe Velocities under Peak Wet Weather Flows 5.2 GIS Sewer Collection System Model Basis and Assumptions The GIS model was created from a combination of as built drawings, issued for construction improvement plans, or preliminary sanitary sewer utility exhibits. The AutoCad drawings were imported into GIS to provide the following parameters of the model. • Location, slope, pipe size and length of the sewer lines • Location and inlet and outlet pipe invert elevations of the sanitary sewer manholes • Parcel size, land use, and corresponding sewer lines based on the location of the sewer laterals. As required by the City's Standards, the following baseline assumptions were used in the steady state analysis. • Pipe capacities and velocities for each pipe were determined utilizing a manning's coefficient(n)of 0.013 • Pipe capacities were determined at the maximum allowable flow depth listed in the City's Standards (see Table 4-1) • Peaking factors were determined based on each pipe segments ADWF. In other words, the peaking factors were higher at lower ADWF typically seen at the start of the collection system based on the City's Standard Detail S-1 (see Appendix D). 5.2.1 Areas Without Finalized Improvement Plans Assumptions In locations where improvement plans or as built drawings were not available, the following was assumed in order to conduct a steady state analysis. • The location of all sewer lines was assumed to match the preliminary sanitary sewer exhibits provided by Odell Engineering. o For Phase II, the location of the main trunk lines was provided by Odell Engineering. The location of the smaller lateral sewer lines was assumed in order to reasonably provide service to each applicable parcel. Sizes shown are based on the minimum requirements listed in the City's Standards. • The location of manholes was assumed to be at all pipe junctions or major turns. • The slope is assumed to remain constant in each individual pipe segment(between manholes) • The slope of each pipe is assumed to be minimum allowable slope listed in the City Standards (see Table 4-3) 17