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River Islands Development at Lathrop January 2021 Final River Islands Potable Water Technical Report—Rev 3 #6520 River Islands' area of the distribution system as the City's distribution system operates as a single pressure zone, however, this operating scenario shall not be considered under normal operating conditions. At full buildout, Phase I BPS will consist of a 10,000 GPM firm pumping capacity pump station, 4.6 MG of storage through three separate tanks,secondary tank fill line, a free chlorine residual system and two 8,000- gallon hydro-pneumatic tanks on the pump station's discharge. The secondary tank fill line allows for the City's distribution system to back fill the storage tanks. Once completed, Phase I BPS will be owned, operated, and maintained by the City of Lathrop. 4.2.3.1 Phase I BPS Potable Water Storage Tanks As part of a steady-state analysis, all the potable water storage tanks were modeled as full (starting water level at each tank's high water level). It is recommended that prior to the start of the design of the proposed Phase II BPS and storage tank site that an extended state analysis be conducted to verify the storage tanks can be refilled during off-demand windows. This is because the Phase I and II PHD will exceed with maximum supply flow rate allocated from SSJID (see Section 5), which will result in a negative storage volume unless the tanks are filled during off-demand windows from the City's distribution system. The Phase I BPS storage tanks were originally designed to provide equalization, emergency, and fire storage for Phase I across three welded steel storage tanks. At final buildout, a total of 4.6 MG of PW storage will be provided through two 1.5 MG, and one 1.6 MG welded steel tanks. The two City of Lathrop PW distribution system connections allow River Islands to initially utilize the citywide fire storage of 0.72 MG, but over time, the River Islands storage tanks need to provide their share of fire storage which the maximum storage capacity is approximately 0.60 MG (see Section 3). The 1.5 MG storage tanks will be approximately 106-feet in diameter with a height of 30-feet and maximum surface water level of 27 feet(43 feet MSL as the tank FF elevation is 16 feet). The tanks are supplied with separate inlet and outlet lines with the inlet entering just below the maximum surface water elevation. The 1.6 MG tank will have the same design parameters as the 1.5 MG tank with the exception that the tank is approximately 108-feet in diameter. 4.2.3.1.1 Hydraulic Model Assumptions—Steady State Analysis As discussed in Section 4.2.2.2, one of the methods of filling the Phase I BPS storage tanks will be from the Site A SSJID transfer pumps and the 24-inch bypass pipeline respectively. The secondary method of filling the Phase I BPS tanks will be to utilize the connection to the City's distribution system to back feed/fill the tanks during off-peak windows. A combination back pressure sustaining and solenoid shut-off valve (PSV) will be installed to connect the distribution system and the tank's outlet line. Please note that the tank's outlet is not equipped with a check valve to allow for all three tanks to be backfilled and equalize. During operator adjustable windows the combination PSV will open allowing the distribution system to fill the tanks as long as a minimum back pressure is maintained. In other words, the combination back PSV will only be allowed to fill the tanks if a minimum distribution pressure is present, the booster pumps are off, and the tank has entered a fill cycle determined by the operators. 22