TO: Board of Supervisors
FROM: Brian D. Bordona - Director of Planning, Building & Environmental Services
REPORT BY: Patrick Ryan - Assistant Director of Planning, Building & Environmental Services
SUBJECT: 2026 Water Availability Analysis & Supporting Technical Report
RECOMMENDATION
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Receive a presentation on the 2026 Water Availability Analysis guidelines and Supporting Technical Report; provide feedback and/or direction to staff. (No Fiscal Impact)
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BACKGROUND
The Water Availability Analysis document was originally developed in 1991 to fulfill the County’s obligations under the California Environmental Quality Act (CEQA) (Public Resources Code 21000-21177) and the CEQA Guidelines (California Code of Regulations, Title 14, Division 6, Chapter 3, Sections 15000-15387). Initially, this process was introduced to address drought conditions and declining groundwater levels. For over 30 years, the Water Availability Analysis (WAA) has been used to determine the potential impacts of groundwater extraction on existing groundwater conditions and nearby non-project wells. The WAA also supports groundwater policies in the Napa County General Plan. CEQA requires an environmental analysis of all discretionary permits submitted for review. Under the 2015 WAA, analyses pertaining to potential impacts on surface water and groundwater interaction have also been required.
The Napa County Board of Supervisors (BOS) is committed to preserving groundwater for agricultural and rural residential uses. Through responsible management, conservation, and ongoing stewardship, the County’s groundwater and interconnected surface water resources can be sustained for future generations.
The WAA process has improved understanding of groundwater use countywide and increased awareness of efficient water use and measures to protect these resources. The WAA recognizes each landowner’s correlative right to access and use groundwater beneath their property, provided that use does not significantly impact other users or public trust resources.
The WAA provides the information and supporting documentation necessary for the Planning, Building and Environmental Services (PBES) Department to evaluate whether a proposed groundwater use, or a change in the location or intensity of groundwater extraction, may significantly affect groundwater resources or reasonable and beneficial uses within the affected area. By promoting responsible groundwater use and preventing wasteful or harmful practices, the WAA is intended to help sustain sufficient groundwater and interconnected surface water for beneficial uses and users, both now and in the future.
In 2026, the WAA has been updated to address many important groundwater and interconnected surface water management considerations that have occurred since the adoption of the 2015 WAA. Under the public trust doctrine (the Doctrine), Napa County has an affirmative duty to consider and give due regard to trust resources and protect public trust uses whenever feasible. The Doctrine applies only to extractions of groundwater that are interconnected to navigable surface water bodies and associated non-navigable tributaries. The County BOS, which also serves as the Napa County Groundwater Sustainability Agency (NCGSA) Board of Directors, recognizes Napa Valley Subbasin sustainability as a critical requirement and is committed to coordination between the County’s permitting process and consistency with the Napa Valley Subbasin Groundwater Sustainability Plan (GSP). The Napa Valley Subbasin GSP was submitted to the California Department of Water Resources (DWR) in January 2022; DWR approved the GSP on January 26, 2023. In February 2022, the County BOS approved an effort to update the County’s Groundwater Ordinance; the 2026 Water Availability Analysis Guidance (2026 WAA) and Water Availability Analysis: Supporting Technical Documentation (Technical Report) provide a key framework for the planned Ordinance updates.
Concurrently with Napa Valley Subbasin GSP implementation and public trust considerations, the State of California and most counties, including Napa County, addressed a drought emergency, including the Governor’s Executive Orders (EOs; N-7-022 and subsequently N-3-23 and N-3-24) to tackle worsening drought conditions. The March 28, 2022, Governor’s EO and other factors-initiated revisions to the County’s well permitting requirements (Napa County BOS meeting June 7, 2022). Although the Governor’s EOs were among the factors that led to changes to the County’s well permitting process, County policies that support building climate resilience, integrated regional water management, and drought mitigation and preparedness are among the County’s highest priorities, which are supported by continued consideration of appropriate well permitting requirements, regardless of the EOs.
The 2026 WAA includes updated water use criteria; new protective well sitting and construction standards; water conservation measures for domestic, agricultural, commercial, and community water systems; and monitoring and reporting to reduce streamflow depletion and support interconnected surface water and groundwater sustainability. The Technical Report includes detailed technical analyses and rationale for the updates to the 2026 WAA.
2026 WAA
The 2026 WAA is for proposed groundwater uses that are new, change the place of use, change the groundwater source for existing use(s), and/or increase the intensity of groundwater use on a parcel through an existing, improved, or new water supply system. The 2026 WAA (Appendix A) includes a comprehensive checklist of the information required of all applicants for new or replacement wells, or changes to the location or intensity of groundwater use. Any additional technical studies that may be required by the WAA, such as analysis of mutual well interference and/or potential streamflow depletion, must be included with the application.
The 2026 WAA includes the delineation of three existing groundwater areas (and one additional area within the Napa Valley Subbasin) within which specific requirements apply:
• Napa Valley Floor: this is the portion of the Napa Valley Subbasin defined by DWR, excluding the overlapping Northeast Napa Management Area (NENMA) and the portion of the Subbasin extending into the Milliken-Sarco-Tulucay (MST) area.
• NENMA: this area is located entirely within the Napa Valley Subbasin; this is a new WAA area with special groundwater use requirements. In 2017, the NENMA was first designated as a Subbasin management area to better manage groundwater in a complex hydrogeologic setting unique from the rest of the Subbasin.
• Groundwater Deficient Area: this is the MST area, including the portion of the Napa Valley Subbasin extending into the MST.
• All Other Areas: these areas include all locations in the County located outside the Napa Valley Subbasin and the MST area.
The 2026 WAA makes several significant changes and improvements to Napa County’s groundwater use and screening criteria, as outlined below.
Screening Criteria
Tier 1:Groundwater Use
The Tier 1 screening and groundwater use criteria have changed for the Napa Valley Subbasin, including the NENMA identified and delineated as part of the GSP. The water use criteria for the MST also apply to the portion of the Subbasin extending into the MST. The groundwater use criteria for domestic wells in All Other Areas (i.e., areas not located in the Subbasin and the MST) have also changed. These areas are depicted in Figures 1-1a and 1-1b of the attached 2026 WAA.
o The Napa Valley Floor area has a water use criterion of 0.5 acre-feet per acre per year, which is a reduction from the 1.0 acre-feet per year criterion contained in the 2015 WAA. Regarding the NENMA, with its inclusion in the GSP and the assigned 0.3 acre-feet per year criterion, that threshold is now being carried over into the 2026 WAA. The previous criterion for the NENMA was 1.0 acre-feet per acre per year.
o Outside the Napa Valley Subbasin, the MST area maintains a water use criterion of 0.3 acre-feet per acre per year for domestic use with a cap of 0.6 acre-feet per year. The 2026 WAA maintains the requirement for existing agricultural, commercial and industrial wells to stay within the existing volume of use or the 0.3 acre-foot per acre per year threshold, whichever is greater.
o Groundwater use criteria for areas outside the Napa Valley Subbasin include a new streamlined methodology for estimating recharge.
The updated water use criteria apply to proposed groundwater use on a parcel through an existing, improved, or new water supply system. The WAA criteria will also be used to ensure that a changed place and/or intensity of groundwater extraction does not exacerbate groundwater conditions, including effects on interconnected surface water. Monitoring and reporting requirements are improved to ensure a consistent standard is applied uniformly countywide.
Tier 2:Well and Spring Interference
The Tier 2 of the 2026 WAA evaluates whether proposed groundwater extraction could cause unacceptable interference with nearby wells or springs by assessing the potential effects of pumping on surrounding groundwater users and resources. The 2026 WAA clarifies the methodology for conducting the Tier 2 analysis.
Tier 3:Surface Water and Groundwater Interaction
The most significant changes in the 2026 WAA pertain to the Tier 3 screening criteria, well siting, and groundwater use for new and replacement wells and existing wells located within 1,500 feet of significant streams. A significant stream is a County-identified stream that supports aquatic habitat or has a Strahler stream order greater than one and is used by the WAA to screen for potential groundwater-surface water interaction.
o Protective Well Siting and Construction Standards:
In addition to the well siting and analysis of potential streamflow depletion requirements in the 2015 WAA, the 2026 WAA requires applicants with new wells or replacement wells located in the vicinity of significant streams to implement new protective standards to reduce the potential for streamflow depletion. The 2026 WAA Tier 3 protective standards and required analyses are detailed in the 2026 WAA Tables 2-3, 2-4, and 2-5. New wells within 1,500 feet of a significant stream must meet the applicable water use criterion and the protective standards (e.g., seal depth, water conservation, metering, and reporting). For example, the protective standards for new wells located within 500 feet of significant streams include well seal depths of 150 feet or greater, metering groundwater use, and reporting.
New or replacement wells or existing wells within 1,500 feet of a significant stream and that do not meet the protective standards are required to describe planned operations (including operational changes) to clearly demonstrate and ensure potential impacts related to streamflow depletion have been adequately addressed. Within the Napa River Watershed, when existing groundwater uses are already occurring, and these uses exceed the water use criterion, additional analyses will be required to demonstrate that the proposed use includes public trust considerations during project design and future operations will decrease stream depletion.
o Water Conservation Measures for Domestic, Agricultural, Commercial, and Community Water Systems:
Water conservation measures are essential to increase water use efficiency, including surface water and groundwater, and reduce water use as much as possible. The 2026 WAA and the Technical Report describe Best Management Practices (BMPs) related to GSP implementation of the Water Conservation and Groundwater Pumping Reduction Workplans (2024) to reduce groundwater use, especially to reduce stream depletion.
The 2026 WAA (Appendix G) also includes Water Conservation Declaration Forms for applicants to complete as applicable. Completion of the form involves information provided by the project applicant (typically the property owner), including contact information, project location and details, and a summary of conservation measures demonstrating a reasonable effort to achieve water conservation consistent with the 2026 WAA. The conservation measures (BMPs) include Existing Measures (e.g., any conservation efforts currently underway on the property) and Planned Measures (e.g., additional conservation efforts associated with existing measures and/or planned efforts to implement one or more new water conservation measures on the property and anticipated implementation dates). The information provided by the applicant at the time of the application does not mean that the applicant must implement all measures indicated at the time of application in perpetuity. It is anticipated that groundwater users will adaptively manage their groundwater use to contribute to the County's goal of Making Water Conservation a Napa Way of Life.
o Adaptive Management:
The Napa Valley Subbasin GSP's sustainability goal specifies (among other aspects) that the NCGSA will implement sustainable management criteria and an adaptive management approach supported by the best available information and best available science, resulting in the absence of undesirable results within 20 years from GSP adoption. The GSP (Section 11) describes an adaptive management approach to address dynamic climatic factors and identify actions needed to achieve the sustainability goal. Similarly, the 2026 WAA recognizes that future WAA updates may be necessary to ensure water supply availability and resiliency, including consideration of public trust resources.
As described in Technical Report (Section 2.8.4), future updates to the water use criteria would rely upon the key foundations of the analyses described in the Technical Report, including the most current estimate of the DWR-approved sustainable yield and current land use data. Other factors that may need to be considered in the future include significant changes to sources of supply used by the municipalities and other entities that currently rely on surface water to meet water demands. These changes and other updates, as needed to remain consistent with the GSP and other considerations, will be incorporated in future WAA updates. Climate, land use, and other factors affecting changes to water use criteria are dynamic. While there is no prescribed WAA update schedule, GSP sustainable management criteria, the persistence of undesirable results for sustainability indicators, and/or hydrologic conditions (e.g., hotter, drier conditions) together with increased surface water, groundwater, and groundwater dependent ecosystems monitoring and reporting in response to GSP and/or 2026 WAA implementation will inform necessary WAA updates.
In the future, significant changes to sources of supply used by the municipalities and other entities that currently rely on surface water to meet demands, and other new data may result in an updated estimate of the sustainable yield. If the sustainable yield is different than the presently established DWR-approved sustainable yield (2022 GSP), then the water use criteria may be updated based on a new DWR-approved sustainable yield. Future updates to the water use criteria would rely upon the methodology described in the Technical Report.
2026 WAA PUBLIC OUTREACH EFFORTS
A public notice posted and distributed by the County on March 27, 2026, announced the opportunity for public review and comment on the Public Draft 2026 WAA documents through May 26. Essential elements of the Public Draft 2026 WAA documents were presented to the Napa County Technical Advisory Group (TAG) on April 9 and the Napa County Planning Commission on May 6. The County’s PBES staff met with stakeholders and remained available to answer questions and receive comments prior to the submission deadline.
Napa County’s PBES received comments at the public meetings and via email at Groundwater@countyofnapa.org. Many commenters provided comments on similar topics. To facilitate responses to all comments, PBES has prepared a Global Response document and an accompanying comment-response matrix (see attached). The 2026 WAA documents have been revised to clarify content and address comments. The Global Response document includes detailed responses to the following topics:
1. Sustainable Yield
2. Tier 1 Recharge Analysis Options: Slope - 30 Percent
3. Tier 3 Protective Standard: 150 Feet Well Seal Depth
4. Domestic Well Definition and Water Use
5. Public Trust and Significant Streams
6. Tier 3 - the “Project Design and Operation Plan” that demonstrates Public Trust and Stream Depletion Considerations
7. GIS layers available to permittees to aid completion of application
8. Adaptive Management
9. Best Management Practices (BMPs)
The comment and response matrix includes the locations in the 2026 WAA document where clarifications and revisions have occurred in response to comments (see attached). Some key revisions include:
1. Domestic Well Definition and Water Use. Definitions for domestic use and domestic well have been added to the 2026 WAA (Section 2.1). Comments received also led to other considerations related to individual residences that rely on self-supplied water from a private water supply well; these residences typically have larger parcels than urban area residential parcels. Accordingly, a two-tiered approach was developed for residential parcels that are 1) smaller than two acres and 2) larger than two acres, including:
• Residential Parcel <2 acres - 1 acre-foot per year allotment and submit Water Use Declaration Form.
• Residential Parcel <2 acres with existing Municipal connection - 0.5 acre-feet per acre per year based on parcel size. Submit Water Use Declaration form reflecting the amount. For example, a 0.75-acre parcel could extract up to 0.38 acre-feet per year.
• Residential Parcel >2 acres - 0.5 acre-feet per acre per year based on parcel size. Submit Water Use Declaration form and Water Demand Analysis (see 2026 WAA, Appendix A Checklist) substantiating total domestic demand. For example, an 8-acre parcel could receive up to 4 acre-feet per year for beneficial domestic use if substantiated by including a Water Demand Analysis.
2. Tier 3 and Well Seal Depth Requirements. The Technical Report (Appendix B) analyses have been reviewed with consideration of the concerns expressed regarding the 150 feet depth-specific well seal, and the County has determined that some flexibility to the seal depth could occur for new or replacement wells located further than 500 feet from significant streams, including:
• Wells Located 500 to 1,000 feet from Significant Streams: Well seals shall extend 125 feet or deeper.
• Wells located 1,000 to 1,500 feet from significant streams: Well seals shall extend 100 feet deep or deeper.
The revised well seal depths are incorporated in the Final 2026 WAA in Tables 2-3, 2-4, and 2-5.
3. Recharge Analysis Information. Comments received pertaining to the Tier 1 recharge analysis included questions about the development of the recharge percentage based on the U.S. Geological Survey Basin Characterization Model (BCM). The 2026 WAA (Appendix B, Attachment B-1) includes a technical memorandum pertaining to the update and use of the BCM to develop the recharge percentages for the WAA Tier 1 streamlined recharge analysis.
4. 2026 WAA Appendix A Checklist. The Public Draft 2026 WAA (Appendix A) contained a placeholder for inclusion of an Application Checklist following public review and comments on the 2026 Public Draft WAA documents. The Final 2026 WAA includes a detailed checklist and templates for tabular information. The checklist identifies the information required for applications involving new or replacement wells, or changes to the location or intensity of groundwater use, under the 2026 WAA.
5. Monitoring and Reporting Requirements. Water resources management requires tracking groundwater conditions at the local to countywide scales. The County conducts groundwater level monitoring (and other types of monitoring) as described in Napa County’s Groundwater Sustainability Annual Reports and for evaluating water budget components for the Napa Valley Subbasin. To ensure water resources reliability and sustainability (Tier 1), protect against well and spring interference (Tier 2), protect significant streams and consider public trust interests (Tier 3), unless expressly exempted, permit applicants shall be required to implement groundwater extraction monitoring and submit periodic groundwater reporting. In consideration of comments on monitoring and reporting consistency and compliance, the 2026 WAA (Section 4) has been updated with clarifying edits for purposes of ensuring a consistent standard is applied uniformly countywide.
Completion of the 2026 Water Availability Analysis (WAA) represents an important milestone in the County’s ongoing efforts to ensure a resilient and sustainable water future. As the Board considers the 2026 WAA, Technical Report, and supporting documents, the WAA provides both an updated framework for evaluating groundwater use and a foundation for continued adaptive management consistent with the goals of the Groundwater Sustainability Plan (GSP).
Recognizing that groundwater conditions and our understanding of groundwater resources will continue to evolve, the BOS may also elect to direct staff to evaluate additional, balanced protections for discretionary projects that could further or accelerate achievement of the GSP’s sustainability goals. These could include additional conservation measures, groundwater use limitations, or other management strategies that build upon the protections established through the 2026 WAA. Staff is prepared to evaluate these options at the Board’s direction and return with recommendations for future consideration.
After staff have reviewed and incorporated any feedback from this Board, staff will return with a future agenda item to formally request the BOS adopt the 2026 WAA and supporting documents.
Requested Action:
Receive a presentation on the 2026 Water Availability Analysis guidelines and Supporting Technical Report; provide feedback and/or direction to staff.
FISCAL IMPACT
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Is there a Fiscal Impact? |
No |
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Is it Mandatory or Discretionary? |
Discretionary |
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Discretionary Justification: |
This is a presentation on amendments to the Napa County’s Water Availability Analysis |
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.