2025 Urban Water Management Plan

Section 7 2025 Urban Water Management Plan Water Supply Reliability Assessment City of Pleasanton Public Draft | May 2026 7-2 EKI Environment & Water, Inc. UWMP, the results are presented in DWR’s required tables, listing the supply availability and potential shortages under normal, single dry, and multi dry year periods from 2025 to 2050. 7.1 Constraints on Water Sources This section discusses the constraints on Pleasanton's potable water supply from Zone 7 and the recycled water supply that it produces. Strategies for managing the risks associated with each supply are also discussed. 7.1.1 Purchased Water Supply from Zone 7 One of the main limitations of Zone 7’s water system is the lack of interties. All of Zone 7’s imported water supplies are conveyed through the Delta and the SBA; Arroyo Valle water is also conveyed through the SBA. Zone 7 has been working closely with DWR, VW, and ACWD to improve the reliability of the SBA. Between 2003 and 2012, DWR made improvements to the SBA within Zone 7’s service area to increase capacity and improve reliability. The work included a new pump station (180 cubic feet per second (cfs)), inline reservoir (500 AF) and increased the canal carrying capacity to 380 cfs. As part of this project, Zone 7 had an emergency slide gate installed to maintain service in the event of a pipeline rupture downstream. Zone 7 will continue coordinating with DWR and South Bay Contractors to improve the reliability of the entire SBA system In addition, Zone 7 is pursuing the following projects to diversify its conveyance options: • Reliability Intertie – Zone 7 is also planning for the construction of a reliability intertie with another major water agency that would provide an alternative means of conveying water to Zone 7’s service area when the Delta and/or the SBA undergo an outage. For example, an intertie with EBMUD could convey treated water supply to the western portion of Zone 7’s service area. • Chain of Lakes Conveyance System – This project would allow for access to water stored in the COLs as an alternative local water supply; water would be accessible to the Del Valle Water Treatment Plant (WTP) via one of the SBA turnouts. 7.1.1.1 SWP Supplies Constraints on the SWP water supplies, including Delta conveyance, water quality, and SBA conveyance are discussed below. 7.1.1.1.1 Delta Conveyance Zone 7’s long-term contract with DWR for SWP supply provides Zone 7 access to Table A water, Article 56c carryover water, and Article 21 water. As a SWC, Zone 7 can use SWP facilities to convey water transfers or exchanges of SWP water (from another contractor) or from another water agency outside of the SWP system. SWP water moves through the Delta before it is conveyed by the California Aqueduct and the SBA to Zone 7's water facilities. The instability of the aging levees in the Delta (including their vulnerability to seismic events and climate change, further discussed in Section 7.1.5), regulatory uncertainty, water quality issues such as saltwater intrusion, and the impacts of climate change on water supply (such as reduced snowpack, altered runoff timing, and increased drought frequency), along with the declining health of the Delta ecosystem, all challenge the long-term reliability of the SWP and, more generally, the Delta’s water conveyance capability. These issues directly challenge the Tri-Valley’s long-term water supply reliability since a majority of Zone 7’s water supply is and will continue to be tied to the Delta and SWP system. Zone 7’s 2025 UWMP discusses additional current and future constraints on Delta conveyance, including