2025 Urban Water Management Plan

Section 7 2025 Urban Water Management Plan Water Supply Reliability Assessment City of Pleasanton Public Draft | May 2026 7-6 EKI Environment & Water, Inc. Zone 7 will continue to coordinate closely with DWR, other SWCs, Semitropic, and Cawelo to ensure the future reliability of the banked water supplies. Zone 7 will also continue to pursue new non-local groundwater banking opportunities. Additionally, some of Semitropic’s wells are contaminated with arsenic and trichloropropane. This is currently being managed through treatment before the affected groundwater is pumped into the California Aqueduct. The DWR Facilitation Group established arsenic criteria for this “pump-in” to mitigate any impacts to the downstream SWCs. Semitropic and the banking partners have developed a coordination process for discussing arsenic treatment. While the presence of arsenic in the Semitropic groundwater bank may increase the cost of this water storage option, it is not likely to affect overall reliability levels. 7.1.1.6 Water Exchanges and Transfers Transfer water can be used to supplement Zone 7’s existing water supplies. Advantages of water transfers include: 1) they can be pursued as needed in any given year and 2) they do not require new infrastructure. Annual water transfers are subject to water market conditions. Generally, water transfers are less expensive in wet years when extra water is available and more expensive in dry years when extra water is scarce. One strategy Zone 7 could utilize is purchasing more water during wet years at a lower cost to store for later use in dry years. Zone 7 continues to pursue and evaluate water transfer opportunities in the Bay Area and statewide. 7.1.2 Groundwater Section 6.2 details the issues affecting Zone 7’s use of the Main Basin, specifically water quality management and prevention of overdraft. Zone 7 is actively implementing its SNMP. Basin salt levels are being addressed primarily through groundwater pumping and demineralization using the MGDP in the Mocho Wellfield. Simultaneously, the Basin is being recharged with water containing low salt concentrations. The facility allows for the export of concentrated minerals or salts from the Main Basin while improving the water quality of treated water. The MGDP is expected to be offline from 2026 to 2028 while a new PFAS treatment facility is constructed at the Mocho Wellfield. Zone 7 will continue its Basin management under the SNMP while the facility is down. PFAS have been detected above the EPA’s proposed MCLs and the Response and Notification Levels established by DDW in several of Zone 7’s wellfields. Zone 7 is managing PFAS under its PFAS management strategy by monitoring contaminant levels, blending and treating groundwater, and diversifying groundwater resources. Zone 7 is planning a dedicated Mocho PFAS Treatment Plant at the existing Mocho Well 3 facility. This facility, which will be Zone 7’s third PFAS treatment project following the Stoneridge and COLs PFAS plants, will use ion exchange technology to remove PFAS from Mocho Wellfield groundwater and restore production reliability. Planning, environmental review, and funding efforts are underway, with design anticipated in 2026 and construction expected to follow. Zone 7 continues to meet water quality standards and is currently meeting the PFAS MCLs ahead of the EPA’s deadline. While Zone 7 has several groundwater wells with naturally occurring hexavalent chromium (Cr(VI)) concentrations, the levels have been below the current MCL, 50 micrograms per liter (μg/L) MCL. On October 1, 2024, the SWRCB reduced the Cr(VI) MCL to 10 μg/L, effective October 1, 2026. Zone 7 has detected Cr(VI) at levels near the upcoming 10 μg/L MCL at several wells and continues to monitor groundwater for Cr(VI) and research treatment options if necessary for elevated concentrations. Zone 7 is currently delivering treated groundwater with Cr(VI) concentrations below the upcoming 10 μg/L MCL.