Evaluation of Groundwater Supply Alternatives Within Bernal Subbasin

EVALUATION OF GROUNDWATER SUPPLY ALTERNATIVES WITHIN BERNAL SUBBASIN APRIL 2026 / FINAL / CAROLLO CITY OF PLEASANTON 1 SECTION 1 INTRODUCTION 1.1 Purpose The purpose of this study is to evaluate water supply projects that would allow the City of Pleasanton (City) to recover and utilize its 3,500 acre-feet per year (AFY) of Groundwater Production Quota (GPQ). In 2022, the City fully shutdown use of Wells 5, 6, and 8 due to the detection of per- and polyfluoroalkyl substances (PFAS). To offset the loss of its GPQ in the interim, the City has increased its purchases of treated water from the Zone 7 Water Agency (Zone 7) at wholesale rates. Long-term, the City’s goal is to determine the most reliable and cost-effective alternative for recovering and utilizing its GPQ. This study evaluates three alternatives for recovering and utilizing its GPQ based on established criteria, weighted scoring, and a cost evaluation (capital and life cycle) to identify the preferred alternative. In addition to water supply changes, all alternatives require specific improvements to the City’s distribution system to convey water to customers. 1.2 Introduction The City retained Carollo Engineers (Carollo) to evaluate three water supply alternatives intended to restore the use of the City’s GPQ of 3,500 AFY in January 2026. The three potential groundwater supply alternatives defined by the City are:  Alternative 1 – Continuing to Offset its GPQ with Increased Wholesale Purchases from Zone 7 (Baseline Project).  Alternative 2 – New Joint Groundwater Project between City and Zone 7 (Joint Project).  Alternative 3 – New City Groundwater Project (City Only Project). Each alternative represents a distinct approach to developing and delivering the City’s GPQ, including differences in ownership structure, cost sharing, infrastructure improvements, and operational responsibilities. Distribution system improvements associated with each alternative were identified by Akel Engineering Group, Inc. (Akel) in November 2025 during a hydraulic analysis of the City’s water system. The hydraulic modeling evaluated each groundwater supply configuration and determined the system upgrades necessary to deliver the full GPQ under both annual and maximum day demand conditions now and into the future. This study defines and evaluates the unique components of each alternative using established evaluation criteria and a weighted scoring methodology. The alternatives are further assessed through a life-cycle cost analysis and a cost-benefit framework to recommend a preferred alternative. 1.3 Background Zone 7 supplies treated water to multiple agencies in the Tri-Valley, including the City. The City has historically met their potable water demands by purchasing treated water from Zone 7 and utilizing its GPQ through operation of City-owned groundwater wells (Wells 5, 6, and 8). The City’s GPQ historically represents approximately 20 to 30 percent of the City’s total water supply needs. In 2022, the City fully