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River Islands Development at Lathrop January 2021 <br /> Final River Islands Potable Water Technical Report—Rev 3 #6520 <br /> For Phase I BPS PW storage tanks, the following assumptions were inputted into the model. <br /> • Secondary tank fill combination PSV <br /> The secondary tank fill combination PSV was assumed to be closed as the SSJID turnout#2 was <br /> modeled to be the primary source of water supply. Alarms were configured to indicate if the tanks <br /> were emptied during the analysis. <br /> • 2 x 1.5 MG and 1 x 1.6 MG Phase I BPS Potable Water Storage Tanks <br /> For the purposes of a steady state hydraulic analysis, all three Phase I BPS tanks are assumed to <br /> start full, with a water level elevation of 39 feet Oust below the invert elevation of the tank's inlet). <br /> 4.2.3.2 Phase I BPS Potable Water Booster Pump Station <br /> The Phase I BPS will have a combination of five vertical turbine pumps: three 2,000 GPM small booster <br /> pumps and two 4,000 GPM large booster pumps. The small booster pumps will be equipped with variable <br /> frequency drives (VFD) designed to maintain an operator adjustable distribution pressure. The large <br /> booster pumps are equipped with soft starters and are designed to be turned off and on during high demand <br /> windows. <br /> Due to the flat topography of the City's distribution system and to prevent excess cycling of the booster <br /> pumps, two 8-foot diameter, 8,000-gallon hydro-pneumatic tanks will provide pressurized storage for the <br /> distribution system. The tanks will be provided with a control panel to regulated the amount of compressed <br /> air needed to maintain the desired pressure range and volume. <br /> 4.2.3.2.1 Hydraulic Model Assumptions—Steady State Analysis <br /> According to the City Standards, the minimum and maximum distribution system pressure shall be 40 psi <br /> and 80 psi, respectively under all demand scenarios. The minimum system wide pressure required during <br /> fire flow events shall be 20 psi. The following control strategy was taken from the Phase I BPS basis of <br /> design report and inputted into the hydraulic model. <br /> • Total number of pumps <br /> The Phase I BPS was modeled at full buildout conditions with three small and two large booster <br /> pumps installed. <br /> • Phase I BPS small booster pumps <br /> All three small booster pumps were modeled to operate as lead pumps using their VFDs to maintain <br /> a distribution pressure of 67.5 psi. The small booster pump curves were taken from manufacturer <br /> shop drawings of the installed pumps as the site is currently under construction. <br /> • Phase I BPS large booster pumps <br /> The control strategy for the large booster pumps in the Phase I BPS basis of design report, stated <br /> the large booster pumps shall be operated as lag pumps to turn on when the distribution pressure <br /> drops below 52.5 psi and off at 65 psi. In order to model this control strategy appropriately, the <br /> large booster pumps were modeled as lag pumps and provided with VFDs to not exceed 65 psi. <br /> Without the inclusion of the VFDs, the large booster pumps would over pressurize the hydraulic <br /> model under steady state conditions. <br /> 23 <br />