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 Conservation as a Napa Way of Life” and the implementation of water management strategies through reducing groundwater demand and increasing groundwater replenishment, even during non-drought years.
Napa County and the NCGSA recognize that future water conservation efforts must encompass all of the County’s communities, agricultural heritage, and ecosystems. Other California programs underway are also promoting climate resiliency related to healthy watersheds for all beneficial users; examples include:
• On January 30, 2024, Governor Gavin Newsom issued the Administration’s document, California Salmon Strategy for a Hotter, Drier Future: Restoring Aquatic Ecosystems in the Age of Climate Change, which “outlines a path to a healthier, thriving salmon population in California, but achieving this result will have broader benefits beyond salmon”, and promotes “working with local partners on locally driven solutions and coordinating on options for incentivizing the reduction of diversions and groundwater pumping;” and “working together, state agencies and partners will depending on available resources...by 2026, complete supply-demand assessment pilot projects in three watersheds to better manage water allocations and provide data for local water management decisions,” and “expand to at least 12 additional watersheds by 2029.”
• The State Water Resources Control Board (State Board) established the Supply and Demand Assessment Unit (SDA) in 2022 to develop water supply models and refine water demand data throughout California, and in April 2025 the State Board signed a Memorandum of Understanding with Napa County/NCGSA in support of data sharing and coordination of Napa River Watershed (one of the three pilot watersheds) modeling efforts. NCGSA technical consultants shared the Napa Valley Integrated Hydrologic Model with State Board staff. NCGSA staff and technical consultants, Napa County GSA Technical Advisory Group member Matt Kondolf, State Board staff and technical consultants met on August 15, 2025 for an update on the State Board’s watershed model development progress.
• Napa County together with the state and local partners prepared the SB 552-Drought Resilience Plan (Napa County, 2024) to aid the County in preparing for and identifying drought and water shortage risks and proposed short-term response actions and long-term mitigation strategies and actions, and the County also prepared the draft Napa County Regional Climate Action and Adaptation Plan (RCAAP, in progress). The State Drought Resilience Interagency Partners (DRIP) Collaborative has several goals for 2025 to increase resilience to droughts and water shortages, including reducing ecosystem impacts due to drought.
Climate change necessitates new strategies and innovation to build resilience. However, strategies require understanding the response of interconnected surface water and groundwater systems under highly variable and uncertain hydrologic conditions. Successful water resources management strategies require robust data.
1 Napa Valley Subbasin GSP Executive Summary <https://www.countyofnapa.org/DocumentCenter/View/23149/GSP_Executive-Summary?bidId=>
MEETING FOCUS
At this meeting, the NCGSA will receive a brief overview of GSP implementation actions, accomplishments to date, and a summary of numerous programs and management actions underway to support sustainable groundwater management (Attachments A and B). GSAs are required to evaluate the GSP at least every five years; for the Subbasin, the Periodic Evaluation is due January 31, 2027. Among other elements, the Periodic Evaluation “shall describe whether the Plan implementation, including implementation of projects and management actions, are meeting the sustainability goal in the basin” (GSP Regulations 356.4). If progress towards achieving the sustainability goal by at least 2042 is not occurring, then the NCGSA may require mandatory actions to ensure that progress is being made to achieve the sustainability goal.
The NCGSA will also receive information on multiple water conservation (WC) and groundwater pumping reduction (GPR) programs in progress, including data collection efforts, and how these programs further the goal of sustainable groundwater management through a cost-effective combination of demand management and groundwater replenishment. Importantly, the WC and the GPR Workplans show that there are numerous conservation opportunities, which if widely adopted by groundwater users, would be sufficient to achieve the Subbasin sustainability goal through programs that increase groundwater recharge and modestly reduce groundwater demand. The NCGSA will also receive information on plans to expand education and outreach and recommendations for additional sustainability measures.
OVERVIEW OF NAPA VALLEY SUBBASIN GSP IMPLEMENTATION PROGRESS
The GSP sets forth the Subbasin sustainability goal and provides a roadmap for implementation efforts. Following the NCGSA’s adoption of the GSP in January 2022, GSA staff and technical consultants developed several workplans regarding interconnected surface waters (ISW) and groundwater dependent ecosystems (GDEs), WC, stormwater resources, GPR, and outreach. Since early 2024, workplan implementation has included advancing technologies for water conservation, pumping reduction, potential utilization of surplus stormflows and/or surface water for managed aquifer recharge, measures for tracking and reporting groundwater use in the Subbasin, and assessments of ISW and GDEs within the Subbasin. The ISW and GDEs Workplan implementation began in 2024 and is ongoing with an update on monitoring results for the last two years (Attachment C). The WC and GPR Workplans also initiated implementation in 2024, which is ongoing with updates provided below and in the attached presentation.
Water Conservation and Groundwater Pumping Reduction Workplan Progress
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. 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 (e.g., mandatory metering and reporting) are also included as a backstop if the voluntary incentive-driven programs lack sufficient participation. GSP implementation also includes evaluation of on-farm practices to increase infiltration (recharge). The GPR includes multiple elements from outreach and education to incentive-driven conservation programs and groundwater recharge opportunities. These programs are currently being developed under multiple workstreams.
Recent program development for GPR implementation includes evaluating recharge opportunities and concepts for extending vineyard replanting or other agricultural water conservation. The recharge feasibility assessment study is an assessment of potential recharge opportunities, technical feasibility, and economic feasibility. An overview of the study progress, including review of developed scenarios will be presented to the NCGSA. The extended vineyard replant concept, and other agricultural water conservation, is a program concept that would offer incentives for voluntarily extending the idle period between when an old vineyard is removed and a new vineyard is (re)planted. Such programs could be targeted to areas near significant streams or other regions that provide the greatest groundwater benefits. An overview will be presented with updates on program development and an overview of the initial results of the preliminary geospatial analysis developed for both studies. Extending replanting and recharge opportunities provide groundwater benefits particularly for ISW and GDEs.
Napa Valley Integrated Hydrologic Model (NVIHM) Scenarios
NVIHM scenarios will be presented to illustrate the potential benefit of groundwater pumping reductions near significant streams in the Subbasin. The scenarios consider the effect of pumping reduction on reduced streamflow depletion. Groundwater pumping is modeled to reduce demand by about 10 percent of the historical baseline pumping for all agricultural, domestic, and small public water supply wells located within 500 feet and within 1500 feet of significant streams. The scenario results provide context for the benefits of pumping reductions.
Water Conservation Community Engagement and Education Plan
GSP implementation includes strong elements of outreach and education, and the NCGSA continues to provide opportunities for public engagement. This also works as a “behavioral nudge” to encourage water users to be more aware of resource use and take actions to conserve it. To engage stakeholders, the NCGSA updated the Communication and Engagement Plan (CEP Update; Stantec, 2024) to better align with implementation activities. Extensive stakeholder outreach has occurred and is ongoing to provide information about GSP implementation. In 2025, extensive outreach and engagement has occurred, especially with vineyard and winery organizations and entities administering existing certification programs, to support GPR program implementation.
The NCGSA will receive an update on ongoing outreach and education. Outreach and education has been expanded into a Water Conservation Community Engagement and Education Plan (WCCEEP; in progress), which presents an actionable strategic plan for countywide, all-sector stakeholder engagement, outreach, and education.
RECOMMENDATIONS
The WC and GPR Workplan programs are designed and expected to achieve the sustainability goal. The GSA staff and technical consultants recommend the NCGSA consider implementing additional measures and incentives to support scaling and effectiveness of these programs, and broader sustainability objectives in the Subbasin. These measures include: 1) actions already planned by the NCGSA related to the County’s 2023 Safety Element and 2) measures to inform groundwater use in the Subbasin to quantify the effect of water conservation programs and, importantly, assess the effect of programs in the vicinity of significant streams that are critical for ISW and GDEs.
Measure 1: Additional Water Conservation Measures
Additional water conservation measures are contained in the 2023 Safety Element, some of which include:
• Policy SAF-5.1: Develop a public water conservation campaign. Work with the Napa County Flood Control & Water Conservation District to develop a public education campaign to encourage water conservation during drought.
• Policy SAF-5.5: Update water conservation policies for landscaping. Amend or revise water conservation regulations for landscape design.
• Policy SAF-5.6: Adopt an outdoor watering conservation ordinance. Adopt a new water conservation ordinance for commercial and residential land uses limiting outdoor watering.
• Policy SAF-5.7: Invest in water use efficiency and conservation. Continue to invest in programs that help residential and non-residential customers save water and money by using the most efficient appliances and fixtures, fixing leaks, and practicing water-wise landscaping and indoor water consumption.
As a first step, NCGSA staff and technical consultants recommend the County update its Model Water Efficiency and Landscape Ordinance (MWELO) to reflect amendments to the California MWELO, align with the 2023 Safety Element policies, and coordinate with MWELO requirements adopted by local jurisdictions in Napa County.
The interconnection between surface water and groundwater is very sensitive to climate change uncertainties. Actual groundwater use in the vicinity of significant streams is currently simulated and has generally not been physically measured. Physical measurement would improve understanding of the Subbasin groundwater system. In addition, the WC and GPR program initiatives all require measurement to ensure that the programs are achieving expected groundwater savings. This is essential for ensuring that any incentives provide an appropriate return on investment, that programs are effective, and that programs are tailored to areas that provide the greatest benefits to groundwater sustainability.
Measure 2: Incentivize Measuring and Informing Groundwater Use
It is recommended that the NCGSA implement a program that incentivizes measuring and reporting groundwater use especially in areas near significant streams. Measuring and reporting by all types of groundwater users would be used to improve the understanding of groundwater use and assess opportunities for additional conservation and/or measure recharge or extended vineyard replant benefits to the local area and Subbasin. Early participation in such a program could be incentivized through means that include but are not limited to:
• A reduced or waived fee for participation in existing certification programs (e.g., Napa Green) that are selected through the upcoming Request for Qualifications process for the Pilot Water Certification Partnership Program;
• Waiver of some portion of the costs to administer the groundwater program which would otherwise be passed on to users in the groundwater fee under development;
• The County would facilitate program participation by developing a database tool for streamlining data collection, organization, and tracking groundwater conditions where participants can anonymously view their data;
• Cost-share or direct incentive payments for specific equipment (e.g. soil moisture meters), technologies (ET sensors), and reporting assistance;
• Other technical assistance.
FISCAL IMPACT
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Is there a Fiscal Impact? |
No |
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.