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River Islands Development at Lathrop January 2021 FINAL River Islands Non-Potable Water Technical Report Rev 2 #6520 4.2.3.1 RI NPW Distribution System Hydraulic Model Assumptions -Sources of Non-Potable Water 4.2.3.1.1 Primary Sources of Non-Potable Water—City of Lathrop's RW Distribution System The primary source of water for the River Islands NPW distribution system will be Title 22 RW from the City's RW distribution system. River Islands will extend the City's RW distribution system to the wet well of the existing Main and the proposed Phase II NPW PS to provide RW based on the level in each wet well. As the irrigation pumps draw from the wet well, the electric actuated, recycled water fill line will be opened allowing the City's RW distribution system to fill the PS wet well through an equalized, air-gap manhole. After the irrigation demand window ends, the recycled water fill line will continue to fill each wet well until a predetermined level and shut off. For the purposes of determining the performance of the NPW Distribution System under PMIDs, the recycled water supply for each station was not modeled. Instead, each pump station was modeled with a finished floor elevation of 13 feet and wet well water level of 5 feet, which is equal to the minimum wet well water level (Main Pump Station Control Strategy Specification Section 17500). River Islands will be working with the City of Lathrop to model and confirm that the existing City RW pipelines will provide adequate capacity to the RI NPW pump stations. 4.2.3.1.2 Secondary Sources of Non-Potable Water During high irrigation demand windows, the irrigation pump skids have the potential to draw down the level in the wet well faster than the supply of recycled water. As the level decreases, a level differential between each station's lake recirculation and irrigation wet wells will occur,causing the check valve on the equalizing line to open (see Figure 4-1). This will allow for lake water to fill the irrigation wet well to be used as a secondary supply of water for NPW irrigation demands. Each irrigation wet well will is/will be installed with a Total Dissolved Solids (TDS) probe continuously monitoring the TDS of the wet well. If the TDS in the wet well exceeds an acceptable threshold, each stations has/will have a potable water fill line allowing potable water to be used for irrigation and diluting the irrigation wet well. For the purposes of determining the performance of the NPW Distribution System under PMIDs and steady- state conditions (snap-shot in time), the secondary sources of NPW were not included in the NPW distribution model. 4.2.3.2 RI NPW Distribution System Hydraulic Model Assumptions - Existing Main Pump Station The Main PS is equipped with five irrigation booster pumps providing a firm pumping capacity of 2,400 GPM as shown in Table 3-3. The pressure sustaining pump, jockey pump, and the lead irrigation pump (Irrigation Pump #1 in Table 3-3) are all designed to operate as lead pumps maintaining a constant distribution pressure of 80 psi through a variable frequency drive (VFD). The lag irrigation pump (Irrigation Pump#2 in Table 3-3), is designed to operate when a large pressure drop is detected and will turn on and off at operator adjustable low and high set points. In order to model this control strategy appropriately, the lag irrigation pump as modeled with a VFD to not exceed 80 psi. Without the inclusion of the VFDs in the model, the lag booster pump would over pressurize the hydraulic model under steady state conditions leading to misleading model results. 4.2.3.3 RI NPW Distribution System Hydraulic Model Assumptions —Proposed Phase II Non- Potable Water Pump Station The future Phase II NPW PS was modeled with two 3,775 GPM NPW irrigation pump skids,with each skid equipped with five pumps as depicted in Table 3-4. The hydraulic model assumptions for the proposed Phase II NPW PS are similar to the existing Main Pump Station including modeling the lag pumps with VFDs to prevent over-pressurizing the model under steady state conditions. 19