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River Islands Development at Lathrop November 2020 Final Phase 2 Sewer Technical Report Rev 1 #6520 7.2 Sewer Collection Area A2 7.2.1 Sewer Collection Area Al —Land Uses,Average Dry Weather Flows, and Peak Wet Weather Flows Sewer Collection Area A2 is located in the southeast of the River Islands development and is the last collection area before sewage leaves the site. Area A2 will ultimately receive all 6 collection areas sewage and will pump the sewage directly to the Lathrop CTF through the installation of a 12 and 18-inch force mains. Collection Area A2 is comprised of development stages 1 B and 1A of Phase I, and encompasses approximately 975 acres composed of all land uses. Table 7-4 lists the ADWF that enter or are generated from area A2, and the corresponding PWWF entering PS-A2. Table 7-4: Sewer Collection Area A2 — Land Uses, ADWF, and PWWF Land Use Area A4 Sewer Flow Average Dry Total No of DU Factor Weather Flow Land Use or Acres GPD/du or ac) GPD) Low Density Residential (per DU) 1,512 200 302,400 Medium Density Residential (per DU) 114 180 20,520 High Density Residential (per DU) 668 170 113,560 Commercial (per acre) 202 590 119,422 Industrial (per acre) 0 355 0 Parks (per acre) 72 55 3,952 Schools/ Institutional (per acre) 1 34 1 245 8,355 Total Area A2 Average Dry Weather Flow 568,208 From Collection Area Al Average Dry Weather Flow 1,112,710 From Collection Areas 131+1132 Average Dry Weather Flow 1,333,801 Total Average Dry Weather Flow 3,014,719 Peaking Factor 2.05 Peak Wet Weather Flow' 6,180,211 Notes: 1. PWWF shown is based on the ADWF from areas C1+C2, 131+B2, Al and A2 conveyed to the PS-A2. 7.2.2 Sewer Collection Area A2— Pipe Capacity Under PWWF Figure 7-4 shows the PWWFs of all the pipes within Area A2. The PWWF for all of River Islands entering sewer lift station A2 is 6,180,211 GPD or 4,292 GPM. None of the pipes exceeded the maximum capacity (Depth/diameter ratio) requirement described in Section 4.1.1. 7.2.3 Sewer Collection Area A2 — Pipe Velocities Under PWWF Figure 7-5 shows the velocity of each pipe within Area Al under PWWFs. As discussed in Section 7.1.3, the northern trunk line along River Islands Parkway and Somerton Parkway can be expected to operate under low velocity conditions regularly. However, except for 1 pipe segment, none of the other sewer lines did not satisfy the City's minimum or maximum pipe velocities requirements. 32