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Section 7 2025 Urban Water Management Plan Water Supply Reliability Assessment City of Pleasanton Public Draft | May 2026 7-5 EKI Environment & Water, Inc. 7.1.1.2 Groundwater Refer to Section 7.1.2 for constraints on groundwater supplied by Zone 7 and the City. 7.1.1.3 Arroyo Valle and Lake Del Valle ACWD and Zone 7 both have water rights to divert water from the Arroyo Valle. This water is captured and stored in Lake Del Valle, which is owned and operated by DWR. DWR utilizes Lake Del Valle for flood control, water supply, and recreation. Typically, DWR lowers the lake elevation after Labor Day, allowing Zone 7 and ACWD to put runoff from the Arroyo Valle to beneficial use. In the summer months, lake elevations are raised for recreational purposes. Historically, access to Zone 7’s stored water in Lake Del Valle has not been problematic, unless there is an outage on the Del Valle Branch pipeline. Zone 7 closely coordinates use of Arroyo Valle water with both ACWD and DWR. Water collected from the local watershed is protected under the SBA Watershed Protection Program Plan. In general, the water quality of Arroyo Valle runoff is good and does not affect the reliability of this water supply; however, as noted above, T&O can also affect supplies from Lake Del Valle. Zone 7 treats T&O using ozonation, although a switch to groundwater supplies is sometimes necessary under excessive levels of T&O compounds. Algal blooms in the lake can also reduce production capacities, though adding ozonation at DVWTP and PPWTP has significantly reduced the impact. 7.1.1.4 Local Storage Constraints for Zone 7’s existing local storage options, the Main Basin and Lake Del Valle, are discussed in Sections 7.1.2 and 7.1.1.3, respectively. The COLCS project, once constructed, will increase Zone 7’s local storage. Currently, Zone 7 is planning to construct the project using the two lakes that are available, Lake I and Cope Lake. These lakes will provide additional local storage in the near term. However, the transfer dates for the remaining lakes are uncertain, as the timing of gravel mining operations and reclamation is not yet known, and a full transition may extend through 2060. Zone 7 continues to work closely with mining companies and quarry operators to coordinate planning efforts. Through this project, Zone 7 can enhance its use of the available lakes during the interim period before all lakes are transferred to Zone 7’s ownership. 7.1.1.5 Non-Local Storage Access to banked water in Semitropic and Cawelo, which are both downstream of Zone 7, requires exchange(s) with other SWCs located south of Kern County (e.g., Metropolitan Water District of Southern California). There must be sufficient water flowing through the Delta and California Aqueduct system to facilitate these exchanges, which could be challenging during a drought. Furthermore, the banked water must be conveyed through the Delta, rendering this supply susceptible to the Delta disruptions described in Section 7.1.1.1.1. During the 2020-2022 drought, access to banked water became uncertain because of the historically low Table A allocation (leading to minimal amounts of water moving through the SWP) and the potential cessation of pumping in the Delta to control salinity intrusion. DWR was able to manage salinity so that Delta pumping could continue, and with coordination among stakeholders including Zone 7, DWR prioritized the delivery of banked water to Zone 7 and other SBA contractors. Ultimately, despite severe drought conditions in 2021 and 2022 and historic low 5% SWP allocation, Zone 7 was able to successfully recover 20,000 AF from both groundwater banks. Between 2020 and 2022, Zone 7 recovered approximately 21,000 AF from non-local storage.