TO: Technical Advisory Group for the Napa County Groundwater Sustainability Agency
FROM: Brian D. Bordona, Director of Planning, Building and Environmental Services
REPORT BY: Jamison Crosby, Natural Resources Conservation Manager
SUBJECT: Napa Valley Subbasin: GPR Implementation and GSP Project #1: Managed Aquifer Recharge
RECOMMENDATION
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Technical Advisory Group (TAG) members will receive a presentation on Project 1 of GSP Implementation: Managed Aquifer Recharge, including an update on the feasibility study underway. The TAG will also receive an update on current vineyard fallowing in Napa Valley. This is intended to spur discussion, questions, and provide feedback to staff and participants.
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Procedure
Staff introduces.
Questions and answers with the TAG.
Public comments.
BACKGROUND AND DISCUSSION
The Napa County Groundwater Sustainability Agency (NCGSA) is implementing the Water Conservation (WC) and Groundwater Pumping Reduction (GPR) Workplans (March 2024). The WC Workplan identified a suite of water conservation practices and the GPR Workplan developed an implementation plan to achieve measurable groundwater pumping reductions and overall water savings in the Napa Valley Subbasin (Subbasin). GPR implementation includes a voluntary, incentive-driven program for growers and other water users/industries in the Subbasin to adopt and expand water conservation practices. Mandatory measures are also included if voluntary incentive-driven programs are insufficient.
An overview of current vineyard replants and idle land will be presented to the TAG. Current wine industry market conditions have prompted shifts in planting and replanting in the Subbasin following the 2024 and 2025 harvests, which may influence the adoption of an extended vineyard replant program and potential recharge sites (see below). An analysis was performed of current winegrape market conditions impacting growers’ decisions and to document vineyards that have come out of production in 2025.
Napa Valley Subbasin Groundwater Sustainability Plan (GSP) implementation also includes GSP Project #1: Managed Aquifer Recharge. Preliminary work has been done to evaluate on-farm practices to increase infiltration (recharge) and prepare a recharge feasibility study. The TAG will receive an update on the planned content of the recharge feasibility study, current vineyard removals in the Subbasin, and the development of recharge-related modeling scenarios.
The recharge feasibility study is a preliminary assessment of potential recharge opportunities, including technical and economic considerations associated with each opportunity. Since the last meeting, the technical team has defined and updated potential project scenarios to reflect new opportunities uncovered through outreach and discussion. This process has also clarified the characteristics of locations suitable for recharge, refined the data required to develop these scenarios, and informed potential groundwater modeling. The current analysis includes preliminary parcel screening used to identify potential sites for each scenario.
Questions for TAG Discussion
Different data sources and information are being used to develop these projects and analyses.
• Do TAG members have any questions, insights, or considerations to improve and refine the development of this work?
ENVIRONMENTAL IMPACT
ENVIRONMENTAL DETERMINATION: The proposed action is not a project as defined by 14 California Code of Regulations 15378 (State CEQA Guidelines) and therefore CEQA is not applicable.
SUPPORTING DOCUMENTS
A. ERA Economics and LSCE PowerPoint Presentation: GPR Implementation and GSP Project #1: Recharge Feasibility Scenario Development, December 2025