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: Update on Implementation of the Water Conservation, Groundwater Pumping Reduction and Interconnected Surface Water/Groundwater Dependent Ecosystems Workplans
RECOMMENDATION
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Receive an update on Napa Valley Subbasin Groundwater Sustainability Plan (GSP) implementation progress.
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Procedure
Staff introduces.
Questions and answers with the TAG.
Public comments.
BACKGROUND AND DISCUSSION
Overview of GSP implementation Progress
The GSP sets forth the Napa Valley 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 and groundwater dependent ecosystems (GDEs), water conservation, stormwater resources, groundwater pumping reduction, and outreach. Since early 2024, workplan implementation has included implementing advanced technologies for water conservation, pumping reduction, potential utilization of surplus stormflows for managed aquifer recharge, measures for tracking and reporting groundwater use in the Subbasin, and assessments of GDEs within the Subbasin.
GSAs are required to evaluate their GSPs at least every five years; for the Napa Valley 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
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. Bill Dodd (Emeritus Senator District 3) in a June 2025 California Water Data Consortium Roundtable welcome speech about improving water management, including public access to high-quality water and ecosystem data, commented, “…with the escalating impacts of climate change, more extreme climatic events, and the risks and opportunities associated with artificial intelligence and other technological drivers, the need to modernize California’s water data systems is more urgent now than ever.”
The TAG will receive a presentation that includes: 1) update on several other Water Conservation and Groundwater Pumping Reduction program elements; 2) update on the Interconnected Surface Water and Groundwater Dependent Ecosystems Workplan implementation focused on monitoring results from 2025 and work related to the California Environmental Flows Framework; and 3) an update on the NCGSA Water Certification Partnership process; The TAG will also receive a brief overview of GSP accomplishments and a summary of numerous voluntary management actions underway to support sustainable groundwater management (Attachments A and B).
Water Conservation and Groundwater Pumping Reduction Workplans and Implementation
The 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. 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 if the voluntary incentive-driven programs are insufficient. Napa Valley Subbasin 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. At this meeting, the TAG will receive an update on the development and implementation of GPR programs. This will include an overview of the GPR programs and summary of the timeline for developing key program elements: 1) water conservation certification program, 2) domestic conservation program concepts, 3) water measurement pilot, and 4) water conservation education and outreach.
The TAG will also have an opportunity to review progress toward other GPR implementation elements, including a recharge feasibility study and the extended vineyard replant concept (similar to the concept of vineyard “mothballing” described by Napa Valley Grapegrowers). Preliminary work will be presented. The recharge feasibility study is an assessment of potential recharge opportunities, technical feasibility, and economic feasibility. An overview of the study progress, including review of developed scenarios and considerations will be presented to the TAG with an opportunity to offer feedback. The extended vineyard replant concept would offer incentives for extending the fallow/idle period between when an old vineyard is removed and a new vineyard is (re)planted. 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 interconnected surface water 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 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 reduction. At a future TAG meeting, NVIHM scenarios will illustrate the potential benefits of recharge and the extended replant concept.
Interconnected Surface Water and GDE Workplan Implementation
Climate change, including drought effects and hotter/drier conditions, have resulted in increased pumping in response to those conditions. The Subbasin was significantly affected by persistent drought conditions during Water Years (WY) 2020, 2021, and 2022; groundwater levels exceeded Minimum Thresholds , and Undesirable Results occurred for two sustainability indicators – interconnected surface water and reduction in groundwater storage (key requirements of the Sustainable Groundwater Management Act and sustainable management criteria (SMC) for the Napa Valley Subbasin are summarized in the GSP Executive Summary ). In WY 2024, one 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 Napa Valley Subbasin GSP definition for an Undesirable Result for the SMC for reduction of groundwater storage is for a period of seven years). As described previously, the Subbasin responds relatively quickly to changed hydrologic conditions; slight differences in groundwater levels affect stream flow. This highlights the importance of Water Conservation as a Napa Way of Life and water management strategies that help mitigate climate change effects by reducing groundwater demand and increasing groundwater replenishment even during wetter years.
Napa County and the NCGSA recognize that future water resiliency must encompass all 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 (NVIHM) with State Board staff. The NCGSA staff, GSA technical consultants, TAG member Matt Kondolf, State Board staff, and State Board technical consultants met on August 15 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.
As part of the implementation of the Interconnected Surface Water (ISW) and Groundwater Dependent Ecosystems (GDEs) Workplan: Napa Valley Subbasin (2024), the technical team is using the California Environmental Flows Framework (CEFF) to characterize aquatic and terrestrial GDEs and assess instream flows in the Subbasin. The goal is to complete the science-based sections of CEFF (Sections A and B) by late 2025/early 2026 to inform updates for the GSP Periodic Evaluation. The CEFF evaluation includes monitoring to better understand special-status species and GDEs’ distribution and associated aquatic habitat and water quality, including stream temperature and dissolved oxygen, at the extensive study sites. Most high-quality aquatic and riparian habitats in the Napa River Watershed generally occur upstream of the Subbasin, but the degree to which the Subbasin is used by aquatic species to maintain their populations and provide resiliency to disturbance in the upper watershed is unknown.
The CEFF process involves identifying overarching ecological management goals, including streamflow goals to maintain ecosystem health. These goals are a function of the species and lifestages present, their ecological needs, the physical system (e.g., water year type, temperature, water year trends), and the degree to which the ecological functional needs are being met or can be met in the future (i.e., whether flows would be sufficient given the constraints of the physical system). Some ecological management goals are similar throughout the Subbasin while other goals vary depending on the species using the site and their ecological needs. Flow constraints under variable conditions, including climate extremes and ISW conditions with and without groundwater pumping, will be characterized and assessed using the NVIHM. Ecological management goals will be refined based on evaluation of the literature for the Napa River and similar watersheds and the 2024 and 2025 ISW and GDEs’ monitoring results for the Subbasin. Stream reach-specific objectives will be developed as the NVIHM update is completed later in 2025. A comprehensive summary of GDEs monitoring conducted in 2024 is provided in the Technical Memorandum, Napa Valley Subbasin Interconnected Surface Water and Groundwater Dependent Ecosystems Monitoring, 2024 (Stillwater Sciences, Napa Resource Conservation District, and Luhdorff and Scalmanini Consulting Engineers; 2025). This Technical Memorandum is in the Napa County Groundwater Sustainability, Annual Report - Water Year 2024 (March 2025) in Appendix K.
The outcome of CEFF will be groundwater and associated flow recommendations to support the ecological management goals. The flow recommendations will likely vary by site and may differ from the requirements of other beneficial users of water in the Subbasin. The flow recommendations from CEFF will be used to inform future refinement of ISW sustainable management criteria.
2025 Monitoring
The climate in 2025 differed from 2024. WY 2024 was a below average water year at the Napa State Hospital rain gage with a very hot period in June. Precipitation at the State Hospital was slightly lower in 2025 than 2024, but Summer 2025 was much cooler, with maximum average temperature about 10 degrees Fahrenheit lower than 2024 in June and July. Through mid-August, the maximum average temperature was about the same in 2025 as 2024. While precipitation was slightly different between 2024 and 2025 at the Napa State Hospital, rainfall in the northern portion of the watershed was much higher in 2025 relative to 2024, in part due to a very large November rainstorm concentrated in the northern half of the watershed.
The 2025 ISW and GDEs monitoring occurred at all six sites outlined in the ISW and GDEs Workplan, including:
• Napa River at Calistoga
• Napa River at St. Helena
• Napa River at Yountville
• Napa River at Oak Knoll
• Sulphur Creek
• Bale Slough
Due to challenges involved with site access, this was the first year of surveys at the Napa River at Oak Knoll and Bale Slough sites, and the second year of surveys at the other sites.
Surveys conducted in 2025 at each of the sites included:
• Flow connectivity studies;
• Continuous water quality measurements for temperature and dissolved oxygen;
• Fish surveys (May and June);
• Special-status plant surveys (April);
• Visual encounter surveys and environmental DNA surveys for northwestern pond turtle and foothill yellow-legged frog (one in May and one in July); and
• Audio recording of bird usage at all sites except Bale Slough
Fish habitat was mapped at the Napa River at Oak Knoll and Bale Slough in June 2025 to supplement habitat surveys at the four other sites in 2024. Surveys for California freshwater shrimp in the Calistoga Reach of the Napa River and groundwater-dependent vegetation community health and composition will occur in early October and September, respectively, and the flow connectivity data will be processed in October following the end of the water year.
Juvenile steelhead were observed in large numbers at the Sulphur Creek site, and smaller numbers occurred at the Napa River at St. Helena site. Surprisingly, juvenile Chinook salmon were observed at every site, with over 2500 individuals noted at the Napa River at Calistoga site. Foothill yellow-legged frog eggs, tadpoles, and adults were observed at the Sulphur Creek site, and repeated surveys revealed that they metamorphosed to subadult frogs capable of leaving the stream prior to the creek going dry. An environmental DNA sample at Oak Knoll found evidence of foothill yellow-legged frogs at that site. A subsequent survey found that foothill yellow-legged frog DNA was likely from Dry Creek, just upstream of the site. Northwestern Pond Turtles were detected by eDNA at the Napa River at St. Helena site. None of the 15 special-status plants that were identified in the Workplan as likely or possibly associated with groundwater were observed at any of the study sites. Sound recorders deployed in Spring 2025 at all the sites except Bale Slough identified 62 bird species.
The groundwater and flow connectivity data from 2025 are still being processed; however, wet conditions generally persisted for longer in 2025 relative to 2024, and stream temperature and dissolved oxygen were more suitable for rearing steelhead juveniles in 2025.
Ecological Management Goals
Based on the 2024 and preliminary 2025 monitoring results, previous observations, and relevant literature, preliminary ecological goals for all sites include:
• Maintain upstream and downstream fish passage for adult and juvenile steelhead and Chinook salmon.
• Support spring and early summer habitat for juvenile Chinook salmon.
• Maintain groundwater levels within the rooting zone of mapped GDEs (generally 10 to 30 ft for willows and oaks, respectively).
• Support the current distribution and populations of special status species and natural communities to maintain ecosystem diversity.
Site-Specific Ecological Management Goals
• Napa River at Calistoga: maintain isolated pools to support California Freshwater Shrimp habitat steelhead rearing if water temperatures are sufficient (i.e., wet years with cool summer temperatures).
• Sulphur Creek, Napa River at St. Helena, and Dry Creek: maintain flowing conditions (generally in the late spring/early summer depending on temperature) to support emergence of foothill yellow-legged frogs as well as support Northwestern Pond Turtle.
• Sulphur Creek: maintain flowing conditions (generally in the late spring/early summer depending on temperature) to support emergence of foothill yellow-legged frogs and growth of juvenile steelhead.
• Napa River at Yountville and Napa River at St. Helena: support habitat for Northwestern Pond Turtle and perhaps juvenile steelhead.
• Sulphur Creek and Napa River at Calistoga: sustain habitat conditions to promote juvenile steelhead and Chinook salmon rearing sufficient to promote successful migration to cooler water with dependable flow later in the dry season.
Continuing uncertainties related to fish habitat in the Napa Subbasin include:
1) the degree to which streams in the Subbasin provide rearing habitat for steelhead and Chinook salmon,
2) the spatial variability of available habitat from year-to-year, and
3) the degree to which juveniles rearing in streams in the Subbasin are able migrate to more suitable habitat as habitat conditions decline.
The preliminary goals listed above are based on two years of data; these goals will be refined based on the results of subsequent surveys coupled with results of the updated NVIHM. The science-based portions of CEFF will be completed in late 2025/early 2026 but may be refined based on future data collection. The CEFF analysis will be included as an appendix to the 2027 Periodic Evaluation. As new monitoring results are obtained, adaptive management principles will be applied to adjust ecological management goals and flow recommendations as appropriate.
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. To engage stakeholders, the NCGSA updated the Communication and Engagement Plan (CEP Update; Stantec, 2024) to better align with implementation activities. Extensive stakeholder outreach occurred in WY 2024 and is ongoing to provide information about GSP implementation. In WY 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 TAG 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), which presents an actionable strategic plan for countywide, all-sector stakeholder engagement, outreach, and education.
Questions for TAG Discussion
Staff and the technical team invite any questions from the TAG and request TAG members’ input and feedback on two (2) questions below:
1. What other considerations should be included in the development of recharge scenarios for the recharge feasibility study? How can they be improved?
• Additional context: The current recharge scenarios developed offer three different potential projects to enhance water capture and groundwater storage in the Subbasin. Understanding the range of factors that may impact the feasibility and efficacy of each proposed scenario can improve the resulting program design and implementation.
2. What else might strengthen the geospatial analyses for potential recharge and/or replant programs, especially when determining ideal recharge and replant sites?
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. Summary of Napa Valley Subbasin GSP Implementation Efforts including Projects and Management Actions (as of August 22, 2025)
B. Powerpoint Presentation, GSP Implementation: Progress Since 2022 and Work Underway, September 11, 2025