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River Islands Development at Lathrop January 2021 Final River Islands Potable Water Technical Report—Rev 3 #6520 According to the City's Master Plan, due to the relatively high cost of SCWSP water, the potential uncertainty of the reliability of the City's full SCWSP allocation(due to adopted revisions in the Water Quality Control Plan for the Bay-Delta Region), and to simplify operations of the City's Louise Avenue Water Treatment Facility(LAWTF),the City has historically relied upon its groundwater wells as the primary source of water to the distribution system. The operation of the City's potable water supply sources is beyond the scope of work of this report, as an extended state model situation with diurnal demand curves and specific operating parameters from the City's maintenance team would be required. However, to be described in Section 5, the full buildout MDD and PHDs are approximately 5,186 and 10,372 GPM respectively. If the City desired to utilize Turnout#2 as the primary source of water for River Islands, at a minimum, the Phase 2 SCWSP improvements would need to be constructed and the City would have to utilize off-peak windows to fill the River Islands storage tanks. According to SSJID, the 30-inch transmission main feeding Turnout #2 was designed to have a normal operating pressure of 35-40 PSI. For the purposes of providing a steady state model simulation,the SSJID connection feeding Turnout #2 was modeled as an elevated reservoir supplying a pressure of 40 psi. A flow control valve was added to the reservoir outlet to limit the SSJID supply to 8,023 GPM. Upon completion of the SSJID turnout #2, the pressure at the point of connection shall be verified at different flows rates and the hydraulic model shall be updated to verify the SSJID supply capacity. 4.2.2.1 SSJID Turnout#2/SSJID Potable Water Storage and Transfer Pump Station at River Islands (Site A) The Site A SSJID PW Storage and Pump Station will consist of the 24-inch SSJID Turnout#2, a 1.0 MG SSJID surge tank, SSJID transfer pump station, and a 24-inch bypass line. Site A will be owned, operated, and maintained by SSJID. The storage capacity of the 1.0 MG SSJID surge tank shall not be included as part of the City's PW storage capacity. Inflow from the 30-inch SSJID transmission mainline will be connected to the 24-inch SSJID turnout #2 structure located within Site A. Under normal operating conditions, a maximum flow of 8,023 gpm (with a pressure range of 35-40 psi) from the turnout structure will fill the 1.0 MG SSJID surge tank. The rate at which the tank is filled will be based on the current water level in the surge tank and controlled by an electric actuated, 12-inch sleeve valve. During high demands or maintenance periods, a 24-inch bypass line will be installed upstream of the 12-inch sleeve valve to bypass Site A and direct water to the Phase I BPS. A check valve will be installed downstream of the 24- inch motorized valve to prevent potential backflows from River Islands to SSJID. A 1.0 MG gravity surge tank shall be constructed at Site A, upstream of the Phase I BPS storage tanks to serve as interim storage during high demand windows. The bolted steel surge tank will be approximately 86 feet in diameter and 30-feet tall with a maximum surface water level of 27 feet(43 feet MSL as the tank finished floor (FF) elevation is 16 feet). The tank is supplied with separate inlet and outlet lines with the inlet entering just below the maximum surface water elevation. Three 25 horsepower (hp) constant speed transfer pumps (two on duty and one standby) will be installed to transfer potable water from the surge tank to the Phase I BPS storage tanks. Each pump will have a capacity of 2,000 gpm at 30 feet total dynamic head (TDH). The transfer pumps shall be vertical turbine pumps that have ON/OFF control based on the current water level in the tanks. 20