TO: Technical Advisory Group (TAG) 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: Comment letter regarding the State Water Resources Control Board’s Water Supply and Demand Assessment for the Napa River Watershed
RECOMMENDATION
title
Review draft final comment letter from the TAG expressing concerns related to the State Water Resources Control Board’s (State Water Board) Supply and Demand Assessment Unit and Paradigm Environmental, Inc. project to model water supply and demand in the Napa River Watershed.
The TAG will be asked to: 1. Authorize and approve TAG Chair, Albert Filipelli, to sign the letter and 2. Recommend the NCGSA Board of Directors authorize and approve staff to send the letter on the TAG’s behalf following the NCGSA’s meeting on December 3, 2024.
body
Procedure
Staff introduces.
Questions and answers with the TAG.
Public comments.
Vote
BACKGROUND AND DISCUSSION
The Technical Advisory Group received a presentation from the State Water Board and their consultants, Paradigm Environmental, Inc., on a project called “Modeling Water Supply and Demand in the Napa River Watershed” on September 12, 2024. The State Water Board is responsible for allocating surface water through California’s water rights priority system. The presentation provided an overview of the modeling effort proposed in the Napa River Watershed, which is to develop a water supply (hydrologic) model that assesses surface water availability where low flows and drought conditions may threaten water supplies, impair critical habitat, and/or create uncertainty for water users. The State Water Board’s stated objective is to better allocate surface water through California’s water rights priority system during critical drought periods to maintain water supplies in the Napa River critical for habitat and species. Please see the link (in the Supporting Documents) for the staff report from the September 12, 2024 TAG meeting, which includes an explanation of the model, the data needs, and the State Water Board’s presentation providing an overview of the modeling.
The TAG posed questions and expressed several concerns regarding the proposed modeling effort to the State Water Board and its consultants. Namely, the TAG expressed concern about the State Water Board’s model, which (1) presents an overly simplified approach to groundwater and surface water interactions in Napa Valley, which have been well studied and incorporated into local efforts to model groundwater, (2) the impact surface water curtailments could have leading to further groundwater pumping by irrigators in lieu of surface water diversions, as well as (3) concerns about the lack of integration of the State Water Board’s model with the existing Napa Valley Integrated Hydrologic Model (NVIHM), which was built and is actively used to model groundwater and surface water in the Napa River Watershed by the NCGSA.
The TAG remains concerned that utilizing a separate surface water model that does not accurately utilize and incorporate existing groundwater data and knowledge about surface water and groundwater interactions will lead to conflicting results and discrepancies. These discrepancies could lead to difficulties in communicating differences between model results to stakeholders within the Napa Valley and could undermine efforts by the NCGSA to work with stakeholders on implementing five workplans which have been prepared and adopted by the GSA. The workplans include:
• Napa County Water Conservation Workplan: A Guide for Vineyards, Wineries and Other Water Users
• Groundwater Pumping Reduction Workplan: Napa Valley Subbasin
• Interconnected Surface Water and Groundwater Dependent Ecosystems (GDEs) Workplan: Napa Valley Subbasin
• Stormwater Resource Plan
• Communication and Engagement Plan.
The TAG will be asked to: 1. Authorize and approve TAG Chair, Albert Filipelli, to sign the letter and 2. Recommend the NCGSA Board of Directors authorize and approve staff to send the letter on the TAG’s behalf following the NCGSA’s meeting on December 3, 2024.
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. Comment letter from the Technical Advisory Group to State Water Board on their modeling effort
B. Link to September 12, 2024 TAG Staff Report: <https://napa.legistar.com/LegislationDetail.aspx?ID=6855998&GUID=D525C9FA-DA46-49BB-B3A8-20DC18222696&Options=&Search=&FullText=1>