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: Presentation on Napa Valley Subbasin Recharge Feasibility Analysis
RECOMMENDATION
title
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 development underway. In addition, the TAG will also receive an update on a vineyard replant modeling scenario that assesses the potential benefit over a 30-year period associated with extending the timeframe for vineyard replants in Napa Valley. The results of a preliminary modeling approach to assess recharge opportunities will also be presented. This is intended to spur discussion and 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 the voluntary incentive-driven programs are insufficient.
An overview of current vineyard replants and idle land was presented to the TAG in December 2025. Current wine industry market conditions have prompted shifts in planting and replanting in the Subbasin following the 2024 harvest, which may influence the adoption of an extended vineyard replant program and potential recharge sites. An analysis was developed to review current winegrape market conditions impacting growers’ decisions and document vineyards that have come out of production in 2025.
Napa Valley Subbasin Groundwater Sustainability Plan (GSP) implementation includes GSP Project #1: Managed Aquifer Recharge. Preliminary efforts have been implemented to evaluate on-farm practices to increase infiltration (recharge) and prepare a recharge feasibility study.
During the March meeting, the TAG will receive additional updates on the status of the preliminary phases of the Recharge Feasibility Analysis. Components of the recharge feasibility analysis include economic, technical, and financial investigations. NCGSA and its consultant team have been refining datasets and developing groundwater model data and inputs to evaluate the four recharge scenarios. Data development includes additional field-level information on vineyard characteristics, water use, and the age distribution of vineyards across a 40-year period considering typical replanting practices.
A presentation on modeling results will include (1) an evaluation of replanting management strategies on groundwater pumping, (2) an evaluation of recharge suitability to better identify locations in the Subbasin where recharge may optimize the enhancement of low flows, and (3) a description of next steps regarding recharge scenario modeling and project implementation. NCGSA staff and consultants have continued to discuss recharge with growers and potential partners to inform the analysis.
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. Presentation on Groundwater Pumping Reduction Workplan Update and Recharge Feasibility Study (Duncan MacEwan, ERA; and Nick Watterson, LSCE).