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River Islands Development at Lathrop November 2020 Final Phase 2 Sewer Technical Report Rev 1 #6520 6. River Islands Sewer Collection System Model — Preliminary Phase 2 Results 6.1 Overview The Phase II sewer collection system is proposed to be subdivided into 4 separate collections areas designated areas C1, C2, B1, and B2. Each collection area will be equipped with sewer laterals designed to convey sewage from each point of connection to the larger trunk lines located in the major streets. The function of the larger trunk lines will be to convey the collected sewage to each area's lift station, located at the lowest (end)of the collection system. As shown in Appendix B, the preliminary alignment of the main trunk lines still has sufficient cover to allow for slopes greater than the City's minimum requirements should future modeling scenarios determine low sewer velocities should occur. It is recommended that the sewer model be updated as sewer improvement plans are developed to verify the future sewer infrastructure will meet the City's requirements. 6.2 Sewer Collection Area C1 6.2.1 Sewer Collection Area C1 —Land Uses,Average Dry Weather Flows,and Peak Wet Weather Flows Sewer Collection Area C1 is proposed to be located in the western portion of Phase II and will be bounded by Paradise Cut levee in the south, the Old River distributary in the west and collection areas C2 and B1 in the north and east. Area C1 will encompass approximately 283 acres of low and medium density residential units as well as parks and school land uses. Table 6-1 lists the proposed number of dwelling units or acreage of each land use in collection area C1, the corresponding land use sewer flow factor, and the ADWF in gallons per day. The total PWWF generated from sewer collection area C1 and conveyed to the proposed sewer lift station C1 (LS-C1) is approximately 593,236 GPD with a peaking factor of 2.85 as shown in Table 6-1. As discussed in Section 5.2, only the location of the main trunk lines was provided by Odell Engineering. The location of the all the Phase II lateral lines conveying flows from each parcel to the main trunk lines was assumed in order to reasonably provide service to each applicable parcel. Figure 6-1 shows the PWWFs of each pipe if the sewer lines were designed as shown. Figure 6-1 also shows the minimum pipe sizes required by the City Standards to convey that segments PWWF. Please note that smaller pipe sizes may be used if the slope is increased. Upon completion of the Phase II improvement plans, the sewer model will be updated accordingly and also run for pipe velocities. 19