Our GOVERNMENT

Joint Groundwater Supply Project

Background

The City of Pleasanton (City) has historically relied on local groundwater wells to supply up to 3,500 acre-feet per year of water (known as the City’s groundwater production quota or GPQ), representing approximately 20 to 30 percent of the City’s total water supply needs. The City’s remaining water supply was purchased from the Zone 7 Water Agency (Zone 7). Zone 7 is a water wholesaler that procures and treats water from the California Department of Water Resources (DWR) and produces water from its joint groundwater wells to sell to Tri-Valley water retailers for distribution to its customers.

In 2022, PFAS (per- and polyfluoroalkyl substances) were detected above regulatory requirements in portions of the Livermore-Amador Valley Groundwater Basin. This detection impacted some of Zone 7’s joint groundwater wells (see Zone 7 PFAS Information for details) and resulted in all of the City’s groundwater wells becoming non-operational (see Pleasanton Water for details). As a result, the City began importing 100% of its water supply from Zone 7. 

In October 2022, the City launched a Water Supply Alternatives Study to assess multiple strategies, including rehabilitating the City’s existing wells with PFAS treatment, developing new groundwater wells, and continuing to rely entirely on purchased water from Zone 7. The study identified the development of new groundwater wells as the most economical and reliable long-term path forward.

On October 17, 2023, the City Council approved proceeding with planning for new groundwater wells within the Bernal subbasin (which is believed to be outside the known PFAS footprint based on Zone 7 testing and groundwater modeling) to restore a reliable, long-term local groundwater supply. On June 18, 2024, the City Council approved an agreement with Zone 7 to evaluate the feasibility of jointly constructing and operating these new groundwater wells, known as the Joint Groundwater Wells Project. 

Project Overview

The Project includes the following proposed elements:

  • Construction of new groundwater wells in the Bernal subbasin with the goal of increasing Zone 7’s groundwater production capacity and drought resiliency for the overall Tri-Valley region, recovering the City’s GPQ, and producing a diversified water supply that meets and exceeds all State and federal water quality standards.
  • Connection of the new groundwater wells to Zone 7’s water supply system and upgrade of the existing Zone 7 Hopyard Treatment Facility to treat the water.
  • Delivery of the City’s GPQ via the Zone 7 water supply system (as opposed to the current configuration of direct delivery from dedicated City wells).

Zone 7 will serve as the lead agency in the evaluation, permitting, design, construction, operation, and maintenance of the project. The City will support Zone 7 by providing necessary land rights and paying its fair share of costs.

The Project will be implemented in the following phases:

  • Phase I – Feasibility: This phase assessed the Project’s feasibility and was completed in late 2025. The feasibility study found that a joint groundwater wells project in the Bernal Subbasin is technically feasible and identified Pleasanton Tennis and Community Park and Hansen Park as feasible locations for new groundwater wells.  
  • Phase II – Design and Construction: This phase includes the design and construction of improvements in accordance with Phase I recommendations. The target completion date for this phase is early to mid-2029.
  • Phase III – Operation and Maintenance: This phase would start after completion of Phase II, and when required permits to operate are in place.

Project Status

Phase 1 has been completed, finding that a joint groundwater wells project in the Bernal Subbasin is technically feasible and identifying Pleasanton Tennis and Community Park and Hansen Park as the best locations for new groundwater wells. On April 21, 2026, the City Council approved proceeding with the implementation of the Joint Groundwater Supply Project in partnership with the Zone 7 Water Agency.

The next step will be to finalize a draft agreement with Zone 7 regarding the design, construction, and operation of the new facilities, and to bring it back to the City Council for further consideration and approval.

Phase I-Feasibility Activities

Phase I-Feasibility activities were completed in December 2025, and the Project is advancing toward Phase II – Design and Construction activities. Activities completed as part of Phase 1 included: 

  • Well Siting Evaluation: A well-siting analysis completed in June 2024 identified Del Prado Park, Pleasanton Tennis and Community Park, and Hansen Park as the top locations for potential groundwater facilities. Benefits of these locations included City ownership, which simplifies implementation; proximity to Zone 7’s Hopyard Treatment Facility for cost efficiency; sufficient space for construction and operation; and the likelihood of being outside the known PFAS footprint.
  • Test Well Construction: Test wells were successfully constructed at Del Prado Park in January 2025, Tennis and Community Park in March 2025, and Hansen Park in May 2025. The test wells were used to collect information on water yield and quality for analysis during the feasibility study discussed above.
  • Feasibility Study: A feasibility study completed in December 2025  evaluated factors including water yield and quality, groundwater basin sustainability, project costs, and implementation requirements. The completed study found that a joint groundwater well project in the Bernal Subbasin is technically feasible and identified Pleasanton Tennis and Community Park and Hansen Park as feasible locations for new groundwater wells. 
  • Cost-Benefit Analysis: Following completion of the feasibility study, the City conducted a cost-benefit analysis comparing a joint project with a City-only project. The evaluation considered factors including project costs, long-term water supply reliability, operational flexibility, groundwater sustainability, and community impacts. The analysis found that annualized costs for the joint project were lower than those of the alternatives and that capital costs were consistent with the assumptions in the City’s 2025 Water Rate Study. Based on the analysis, the City Council approved moving forward with the implementation of the joint project with Zone 7 on April 21, 2026. 

Water Project FAQs

The City of Pleasanton and Zone 7 Water Agency are advancing a joint groundwater wells project to develop new groundwater wells in the Bernal Subbasin. The project is intended to restore the City’s groundwater production capacity lost due to PFAS impacts at existing City wells and support long-term water supply reliability and drought resilience for Pleasanton and the Tri-Valley region.

All of the City’s existing groundwater wells are currently out of operation due to PFAS impacts. New wells are needed to replace the lost water supply and support a more reliable, cost-effective, and drought-resilient long-term water supply for Pleasanton residents.

Groundwater wells are vertical shafts drilled into the ground to access underground water sources, known as aquifers. Wells are typically created by drilling a hole into the ground and installing a pipe (casing) with screens to allow water in while keeping soil and debris out. Most modern wells use electric pumps to bring water to the surface.

Through the Joint Groundwater Supply Project, new wells are being developed to replace existing wells affected by PFAS, helping to ensure a continued supply of safe drinking water for Pleasanton residents.

PFAS (Per- and Polyfluoroalkyl Substances) are a large group of synthetic chemicals designed to resist heat, water, and oil. PFAS are used in a wide range of industrial and consumer products, including firefighting foams, stain- and water-resistant clothing, carpets, cleaning products, non-stick cookware, and food packaging.

PFAS have been found in air, soil, and water around the world, and are persistent in the environment. They can accumulate in the human body over time and are toxic at relatively low concentrations. Scientific studies have shown that exposure to some PFAS in the environment may be linked to harmful health effects in humans and animals. Although certain PFAS are no longer manufactured in the U.S., these chemicals are still produced internationally and imported into the U.S. in consumer goods.

For additional information about PFAS, see the Pleasanton Water webpage.

The project is separated into three phases:

  • Phase I – Feasibility: Evaluation of the feasibility of the joint project was completed in late 2025.
  • Phase II – Design and Construction: This phase includes the design and construction of improvements in accordance with Phase I recommendations. The target completion date for this phase is early to mid-2029.
  • Phase III – Operation and Maintenance: This phase would start after completion of Phase II, and when required permits to operate are in place.

Three City-owned park sites were evaluated during Phase I feasibility activities:

  • Pleasanton Tennis and Community Park (5801 Valley Ave.)
  • Del Prado Park (5196 Golden Rd.)
  • Hansen Park (5697 Black Ave.)

Based on the completed feasibility study, Pleasanton Tennis and Community Park and Hansen Park were identified as feasible locations for new groundwater wells.

The three sites were selected for the following reasons:

  • City-owned, allowing for easier implementation
  • Close proximity to Zone 7’s Hopyard Treatment Facility for cost efficiency
  • Sufficient space for construction and operation
  • Likelihood of being outside of the known PFAS groundwater footprint

The City of Pleasanton is committed to keeping the community updated throughout the project. 

This webpage will contain the project background, the latest updates, and information about relevant community outreach events. Residents can also sign up for the Pleasanton Pipeline e-newsletter, participate in upcoming community meetings, and monitor the City’s social media pages to stay informed on the project.

To provide input, contact the Public Works Department via our contact form or (925) 931-5500.

Additional Information

Project-related information is provided below:

  • On April 21, 2026, the City Council approved moving forward with the Joint Groundwater WellsProject in partnership with Zone 7 following completion of the joint feasibility study. View the Press Release. 
  • In December 2025, the City and Zone 7 completed a joint feasibility study. The study found that a joint groundwater project is viable and identified Tennis Park and Hansen Park as feasible locations for new wells.
  • On June 18, 2024, the City Council approved an agreement to partner with the Zone 7 Water Agency on Phase I (Feasibility) of constructing new wells as part of a Joint Groundwater Wells Project.
  • On May 7, 2024, the City Council approved the execution of a $19 million water revenue bond to assist in financing improvements to the City’s water system, including Phase I of the Joint Groundwater Wells Project.
  • View the October 17, 2023, City Council Water Supply Alternative Agenda Report

Should you have any questions or comments regarding the Project, please contact the Public Works Department at (925) 931-5500.