Evaluation of Groundwater Supply Alternatives Within Bernal Subbasin

EVALUATION OF GROUNDWATER SUPPLY ALTERNATIVES WITHIN BERNAL SUBBASIN APRIL 2026 / FINAL / CAROLLO CITY OF PLEASANTON 2 shutdown use of Wells 5, 6, and 8 due to the detection of PFAS. As an interim solution, the City has increased its water purchases from Zone 7 to offset the loss of its GPQ. Extension of this interim solution into the long-term is Alternative 1 in this study. In parallel to the interim purchase of water from Zone 7, the City developed the basis of design for the PFAS Treatment and Wells Rehabilitation Project in August 2021. This project would return wells to service, extend their useful life, and implement a centralized PFAS treatment facility. This project evaluated rehabilitating Well 8, constructing new Wells 9 and 10 (near the locations of Well 5 and Well 6), and constructing a centralized PFAS treatment facility. The project was advanced to the 50 percent design level and then put on hold in October 2022. While the project was on hold, the City reviewed other potential projects under the Water Supply Alternatives Study, which was completed in November 2023. The Water Supply Alternatives Study identified implementation of new groundwater supply wells outside the PFAS detection plume and in the Bernal Subbasin as the preferred option to restore its GPQ. Concurrently, Zone 7 recognized the opportunity for a joint project that could both support the City’s GPQ and enhance Zone 7’s overall drought resiliency and supply reliability for the region. With recognition of potential regional benefits, the City and Zone 7 elected to evaluate the feasibility of the New Joint Groundwater Project between City and Zone 7 in August 2024, and Luhdorff & Scalmanini Consulting Engineers (LSCE) was hired as the lead consultant with technical/engineering support from Carollo. LSCE and Carollo completed the technical feasibility evaluation of the Joint Project in December 2025. This joint project with Zone 7 is Alternative 2 in this study. The City hired Carollo in January 2026 to also determine the feasibility of the City implementing its own groundwater supply wells at similar locations to that of the Joint Project. The City Only Project is Alternative 3 in this study. Carollo was then tasked with evaluating the three water supply alternatives to determine the preferred alternative. 1.4 Project Goals The City’s goals for this project are:  Recover use of the City’s GPQ of 3,500 AFY.  Reduce overall water supply and distribution costs.  Improve water supply reliability, management of water quality, and ability to meet regulations. SECTION 2 ALTERNATIVE 1 – BASELINE PROJECT 2.1 Project Overview Alternative 1 assumes the City will continue to offset its GPQ with increased purchases from Zone 7 at the wholesale rate as a long-term solution. This alternative does not include the construction of any new groundwater supply facilities by the City but does require the construction of new distribution improvements as described in Section 2.2 to reliably receive water from Zone 7’s transmission system and convey to existing and future customers. Figure 1 shows the required City distribution system improvements identified by Akel’s Hydraulic Analysis Results Package No. 1 (Revised) dated November 2025.