Evaluation of Groundwater Supply Alternatives Within Bernal Subbasin

REGIONAL GROUNDWATER FACILITIES PROJECT FEASIBILITY STUDY 1 Zone 7 Water Agency December, 2025 1. INTRODUCTION Zone 7 and the City commissioned this Study to evaluate the development of new groundwater production wells in the Bernal Subbasin of the Livermore Valley Groundwater Basin. Zone 7 is the regional water wholesaler and designated Groundwater Sustainability Agency (GSA) for the Basin, responsible for long-term supply reliability, groundwater management, and regulatory compliance. Zone 7 supplies treated and untreated water to multiple retail agencies in the Tri-Valley, which include the Cities of Pleasanton and Livermore, Dublin San Ramon Services District, and California Water Service Company. Zone 7 serves more than 280,000 residents and businesses across a service area of approximately 425 square miles in Alameda and Contra Costa Counties through surface water treatment plants, groundwater wells, and over 40 miles of transmission pipelines. Pleasanton’s potable water demand has historically been met by a combination of Zone 7 treated water purchases and a City groundwater production quota (GPQ) of 3,500 acre-feet per year (AFY). 1.1. Background Zone 7 supplies treated drinking water to multiple agencies in the Tri-Valley, including the City. The City’s potable water demands have historically been met by a mix of Zone 7 treated water purchases and City owned groundwater wells (Wells 5, 6, and 8). In 2020, PFAS was detected in these wells and near after were removed from service, increasing the City’s reliance to 100% Zone 7 supplies at the more expensive wholesale rate. To address this immediate loss, the City advanced the PFAS Treatment and Wells Rehabilitation Project (2020–2022), which reached the 50-percent design stage and included well rehabilitation, construction of new wells, and a centralized PFAS treatment facility. In late 2022, the City put the project on hold pending completion of a broader Water Supply Alternatives Study before committing to long-term treatment (Brown and Caldwell, 2024). That study, completed in 2023, identified a project involving construction of two new City wells west of the PFAS footprint as the preferred alternative. While the City was prepared to pursue this independently, Zone 7 and the City recognized that a coordinated regional project could provide broader benefits, including drought resilience, reduced reliance on imported supplies, and cost efficiencies. Zone 7 and the City initiated this Feasibility Study (Study) for the Regional Groundwater Facilities Project as part of Phase I, which includes the exploratory test well program and evaluation of up to three new municipal supply wells in the Bernal Subbasin. The purpose of Phase I is to identify a preferred project alternative capable of providing a minimum of 7,000 AFY of groundwater under drought conditions, of which 3,500 AFY will be allocated to meet the City’s GPQ. LSCE was retained as lead consultant, with Carollo Engineers supporting conceptual project design and cost estimating and associated Phase I design tasks. If Zone 7 and the City decide to proceed with the identified project alternative, the project will then be advanced into Phase II which consists of detailed design of production wells, pipelines, and required HCF upgrades, followed by construction and implementation. Because PFAS, TDS, and other regulated constituents occur in the Bernal Subbasin, the Study included test well drilling, aquifer testing, and water quality sampling to characterize production capacity and assess long-term water quality risks. Any new groundwater supplies developed as part of this project will be integrated into Zone 7’s HCF, which uses chloramines for disinfection prior to being combined with separate treated surface water sources in the distribution system. Delivery of the City's GPQ would be via the Zone 7 water supply system (as opposed to the City current configuration of direct delivery from dedicated City wells). Separate from this Study, the City is evaluating needed improvements to their distribution system to receive the water in this fashion. An overall project site map is shown in Figure 1.