2025 Urban Water Management Plan

Section 7 2025 Urban Water Management Plan Water Supply Reliability Assessment City of Pleasanton Public Draft | May 2026 7-4 EKI Environment & Water, Inc. the Delta may be restricted, reducing the amount of water supply available during certain times of the year. Salinity intrusion can be a problem during dry years, when there is insufficient freshwater to repel salinity. Sea level rise due to climate change is also expected to increase salinity in the Delta. Finally, levee breaks due to earthquakes and other factors would result in significant saltwater intrusion from the Bay as water floods affected islands that are below sea level in the Delta. • Algal blooms: In addition to T&O and the threat of algal toxins, algal blooms can significantly degrade filter performance through clogging. Filter clogging reduces plant production capacities and could require supplemental groundwater use. As noted above, Zone 7 has state-of-the-art ozonation facilities at the DVWTP and PPWTP. Ozonation improves treatment of T&O, TOC/DOC, turbidity, and algal blooms and significantly increases the surface water system’s reliability. In 2008, the SBA contractors (Valley Water, ACWD, and Zone 7) developed the SBA Watershed Protection Program to protect water quality once the water from the Delta reaches the SBA. The primary objectives of the SBA Watershed Protection Program include developing a Watershed Management Program for the SBA system, including Lake Del Valle and Bethany Reservoir, and protecting local drinking water and water resources from identified contaminant sources (e.g., septic tanks) for urban, agricultural, recreational, and environmental uses. Additional information on Water Quality Control Plan for the San Francisco Bay/Sacramento-San Joaquin Delta Estuary (Bay-Delta Plan) is included in the Zone 7 2025 UWMP. 7.1.1.1.3 SBA Conveyance A limitation of Zone 7’s water supply system is its dependence on the SBA. 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 continuously worked with DWR, Valley Water, 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 building a new pump station (180 cfs) and Dyer reservoir (500 AF) and increasing the canal carrying capacity to 350 cfs. As part of this project, DWR installed an emergency slide gate to maintain service to Zone 7 in the event of a pipeline rupture downstream. Zone 7 will continue coordinating with DWR and the other SBA contractors to improve reliability of the entire SBA system. A recent possible threat to Zone 7’s primary water supply emerged in 2024 when DWR discovered Golden Mussels in the Delta. Since then, these organisms have proliferated throughout the SWP system as far away as southern California. This species, which is more resilient than the previously discovered Zebra Mussel, has the potential to clog water systems by settling and growing in pipes, valves, pumps, gates, canals or any other surface suitable for settling. Individual specimens have been found in the SBA, but colonies have not yet been confirmed. DWR, in collaboration with DFW, is developing a Golden Mussel management plan including chemical injection, UV radiation and physical removal at critical facilities. Experts have stated that it is unlikely that this invasive species can be fully eradicated, but measures can be taken to minimize their impact. Zone 7 is carefully monitoring the situation and is taking precautions to avoid disruption to its water supply. Zone 7 is also obtaining guidance from DFW on developing a Golden Mussel control plan. In addition, Zone 7 is pursuing the COLCS project to reduce its reliance on the SBA. This project would allow for access to water stored in the COLs as an alternative local water supply and storage source; water would be pumped to DVWTP for use.