Napa groundwater update: staff seeks voluntary measurement, pilots and incentives after modeling shows limits to small-scale cuts

NAPA, Calif. — County staff and technical consultants presented an annual update Sept. 23 on implementation of the Napa Valley Subbasin Groundwater Sustainability Plan, reporting added monitoring and outreach and asking the board to support more incentives and measurement to preserve groundwater and summer stream flows.

Lede and key point: The county reported new monitoring wells, a state-funded stream-gauge installation program and an expanded ecological-monitoring effort at six intensive sites. Consultants’ modeling showed a 10 percent reduction in groundwater pumping focused near the Napa River’s tributaries produces measurable benefits, but under the drier conditions after 2015 the subbasin could need larger reductions — as much as about 24 percent in the model scenarios — or a combination of reductions and supply augmentation to meet the plan’s sustainability goal.

Why it matters: Napa’s aquifer is shallow and closely connected to surface flows that support fish and other species. The Groundwater Sustainability Plan implementation is intended to keep the county in local control of groundwater management under the state Sustainable Groundwater Management Act (SGMA) and to avoid state intervention.

What staff and consultants said Jamieson Crosby (Natural Resources Conservation Manager) introduced the update and said the county has installed 16 monitoring wells in 2023 and two additional wells in Calistoga in 2025 and has a grant from the Department of Water Resources to refurbish or install five stream gauges.

Vicky Kretzinger Graebert (Ludorf & Scalmanini, senior principal) and Duncan McEwen (ERA Economics) summarized model results and work-plan implementation. McEwen said the county can likely deliver a significant portion of the groundwater-pumping reduction target using incentive-driven measures but that implementation should be coupled with better measurement and pilot projects to confirm outcomes.

Duncan McEwen, ERA Economics: “If you stack up a pilot certification partnership, domestic conservation, benchmarking and expanded outreach, and targeted recharge, the estimates show conservative potential to reach a 10 percent reduction; scaling the mix could achieve more.”

Model results and targets Consultants used the valley-scale model developed for the GSP to test a suite of scenarios that focused reductions near “significant streams” (buffers of 500 to 1,500 feet). The study noted the GSP’s sustainable-yield figure (15,000 acre-feet on average, derived during plan development) and compared it with more recent pumping: 17,700 acre-feet per year on average from 2015–2024.

Model highlights: - A 10 percent pumping reduction concentrated within a 500-foot buffer around significant streams reduced modeled exceedances of the GSP’s minimum thresholds in many years; it produced a meaningful improvement in modeled stream depletion during June–October, when streams are most stressed. - Because pumping rose in 2015–2024, the modeling shows that in a sequence of drier years the county might need reductions larger than 10 percent in some scenarios (consultants cited a modeled need near 24 percent in order to meet the plan’s stated sustainability goal across a recent-period scenario).

Recommendations and pilots Staff proposed a multi-pronged approach: continuing to expand monitoring; launching a pilot “water certification partnership” that would partner with vineyard certification programs (Napa Green and others) to obtain anonymized water-use data in exchange for incentives; pilot a simple QR-code meter reporting tool (the “TAP H2O” pilot already under way in the Milliken-Sarco-Tulocay area); and pursue technical and economic work on targeted recharge, including “in-lieu” and replanting/repurposing programs.

Jamieson Crosby (Natural Resources Conservation Manager): “We are recommending incentives to measure and report — the ability to measure is the most important missing piece to make sure voluntary programs deliver real water reductions.”

Public comment and reaction Public speakers included Lester Hardy, who urged faster mandatory data collection, and representatives of local conservation and business groups. Chris Malan (executive director, Institute for Conservation Advocacy Research and Education) said voluntary approaches involving incentives are high-risk unless measurement and reporting are substantially expanded.

Board direction and next steps Supervisors asked staff to expand outreach, consider appealing to appellation and industry groups for data-sharing, and return with refined pilot program details and financing options. Staff said the Department of Water Resources has engaged county model assets for watershed-level assessments and the state is coordinating with the county on integrated modeling.

Provenance (transcript evidence) The groundwater update and the modeling discussion begin at the board agenda item for the Groundwater Sustainability Agency (presentation introduced around 19:49:54 in the meeting file) and continued through consultant presentations and public comment.