TO: Napa County Groundwater Sustainability Agency (NCGSA)
FROM: Brian D. Bordona - Director of Planning, Building and Environmental Services
REPORT BY: Jamison Crosby - Natural Resources Conservation Manager
SUBJECT: Groundwater Sustainability Plan (GSP) Implementation Update
RECOMMENDATION
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Provide Napa County Groundwater Sustainability Agency with an update and receive feedback on Napa Valley Subbasin Groundwater Sustainability Plan (GSP) implementation progress since 2022, including: 1) Water Conservation and Groundwater Pumping Reduction program elements, 2) NCGSA Pilot Water Certification Partnership process, and 3) provide recommendations to the NCGSA to support GSP implementation activities. (No Fiscal Impact)
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BACKGROUND
Climate change, including drought effects and hotter/drier conditions, have resulted in increased pumping in response to those conditions. As a result, the Napa Valley Subbasin (Subbasin) was significantly affected during Water Years (WY) 2020, 2021, and 2022. During that period, Undesirable Results occurred for two sustainability indicators: 1) interconnected surface water and 2) reduction in groundwater storage. Requirements of the Sustainable Groundwater Management Act and sustainable management criteria (SMC) for the Subbasin are summarized in the GSP Executive Summary1. In WY 2024, an Undesirable Result occurred for reduction in groundwater storage.
While significant groundwater replenishment occurred in WYs 2023 and 2024, the reduction in groundwater storage emphasizes the importance of achieving sustainability by maintaining balanced conditions over a period representative of long-term conditions (the GSP definition for an Undesirable Result for reduction of groundwater storage is for a period of seven years). The Subbasin responds relatively quickly to changes in hydrologic conditions. However, even slight differences in groundwater levels can affect stream flows. This dynamic reiterates the importance of "Water Con...
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