GSA presents 2024 groundwater annual report: pumping rose to ~16,210 acre‑feet; continued monitoring and actions planned

The Napa Valley Groundwater Sustainability Agency (GSA) presented its Water Year 2024 annual report to the Board of Supervisors on May 6, summarizing monitored conditions, modeled water budgets, sustainability metrics and planned implementation actions. The report said total groundwater extraction in the Napa Valley sub‑basin rose to roughly 16,210 acre‑feet for the year, with about 73% of pumping attributed to agricultural uses and roughly 18% to self‑supplied users (including domestic and on‑site uses).

Key findings: - Precipitation and context: Precipitation at the Napa State Hospital gauge was approximately 23 inches for water year 2024, a normal‑to‑below average year; staff cautioned that annual totals do not show seasonality and that 2024 featured a cool, wet spring followed by an unusually hot, dry summer that drove irrigation demand. - Groundwater and storage: Spring groundwater levels were higher than the historical lows recorded in 2020–2021, but modeled groundwater storage and a seven‑year average of pumping show an exceedance of the GSP—s sustainable yield metric (reduction in groundwater storage), continuing a multi‑year trend that the plan tracks as an undesirable result. - Interconnected surface water (ISW): Modeled stream depletion at two USGS gauging stations (Napa River at Oak Knoll and Pope Street) exceeded the GSP minimum thresholds in 2024 by modest amounts (about 20 acre‑feet at Oak Knoll and 100 acre‑feet at Pope Street); because the GSP defines “undesirable result” as three consecutive years of exceedance, these single‑year exceedances trigger the plan—s investigation and response requirements but do not in themselves constitute an undesirable result. - Localized wells: Two monitoring wells in the Northeast Napa Management Area recorded groundwater levels below their minimum thresholds in fall 2024; staff noted the area is geologically distinct (thin alluvium over volcanic rock, fault‑bounded) and responds differently than the rest of the valley floor. - Water quality and subsidence: Groundwater quality sampling recorded two monitoring wells with arsenic levels above threshold values; the team described these as areas to build a monitoring history rather than clear evidence of anthropogenic contamination. No subsidence concerns or seawater intrusion issues were identified outside the historically tide‑influenced areas.

Planned and ongoing actions: The report emphasized continued work to expand monitoring (DWR grant funding for five new stream gauges, four on tributaries), refine the Napa Valley Integrated Hydrologic Model (NVIHM), improve data collection (soil moisture and instrumentation pilots), implement a water‑certification partnership concept to incentivize voluntary reductions, coordinate with growers and the RCD on on‑farm recharge and conservation practices, and maintain outreach with the GSA Technical Advisory Group (TAG). Staff also noted potential for future targeted projects — including distributed recharge pilots and partnerships to anonymize grower metering data for basin‑scale analysis — and said the GSA would bring more detailed proposals and economic analyses to the board and technical committees later in 2025.

Board reaction and next steps: Supervisors emphasized the urgency of moving from voluntary measures to more robust basin‑wide approaches if metrics do not improve, requested clearer timelines and milestones, and asked staff to use the TAG and outreach channels to present options and economics for expanded recharge and demand‑reduction measures. No formal board action was required; the presentation was informational and the GSA will continue implementation and report progress to the board and TAG.