2025 Urban Water Management Plan

Section 6 2025 Urban Water Management Plan Water Supply Characterization City of Pleasanton Public Draft | May 2026 6-13 EKI Environment & Water, Inc. Figure 6-4 Main Basin Groundwater Storage Zone 7 is continuing to study the Basin and develop new tools (including an improved groundwater model completed in 2025 and a Decision Support Tool completed in 2026) to better understand the levels of groundwater extraction possible under various conditions and contributing factors, such as groundwater connectivity, spatial distribution in the Main Basin, and others. These efforts strengthen Zone 7’s ability to sustainably manage the Basin and maintain a resilient long-term water supply portfolio. Section 7.1.2 presents additional information related to groundwater supply reliability. 6.2.3.4 Groundwater Quality Monitoring and Protection Zone 7 chloraminates groundwater supply to match the disinfectant residual in the transmission system. In terms of groundwater supply, several constituents of concern have been identified throughout the Basin. Zone 7 is actively implementing both monitoring and management programs to protect water quality in the Basin and ensure that Zone 7 continues to provide safe and reliable drinking water, as discussed in the following subsections and in Section 7.1.2. 6.2.3.4.1 Salinity and Nutrient Management Zone 7 is actively implementing its Salt and Nutrient Management Plan (SNMP). Basin salt levels are being addressed primarily through groundwater pumping and demineralization using the Mocho Groundwater Demineralization Plant (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. 6.2.3.4.2 PFAS Management In November 2022, Pleasanton ceased production in all three of its active municipal wells due to PFAS detections. Following the shutdown, in 2023, Pleasanton and Zone 7 agreed to collaborate on the Joint Groundwater Wells project. The project involves the design and installation (i.e., drilling and equipping) of new municipal production wells within the Bernal Subbasin, which is believed to be outside the existing PFAS plume based on Zone 7 testing and groundwater modeling.