TO: Napa County Board of Supervisors
FROM: Brian D. Bordona, Director of Planning, Building and Environmental Services
REPORT BY: Jamison Crosby, Natural Resources Conservation Manager
SUBJECT: Approval of Amendment No. 2 to Agreement 200194B with the City of Napa
RECOMMENDATION
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Approve and authorize Amendment No. 2 to Agreement 200194B with the City of Napa to extend the term through June 30, 2026 and increase the County’s share from $200,000 to $250,000 for joint water quality monitoring of the Lake Hennessey and Milliken Reservoir watersheds. (Fiscal Impact: $250,000 Expense; General Fund; Budgeted; Discretionary).
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BACKGROUND
The City and County have a shared interest in gathering additional data to further our understanding of how land use changes in the Hennessey and Milliken watersheds might impact the drinking water in these reservoirs. The City of Napa owns Lake Hennessey Reservoir and the Milliken Reservoir which serve as municipal drinking water supplies for the citizens of Napa and over 2,000 customers in unincorporated Napa County.
The Hennessey watershed drainage area is composed of approximately 34,000 acres reaching as far north as Angwin. Of this total area, the City owns just 2,822 acres. The Milliken watershed drainage area is composed of 6,200 acres of which the City owns nearly 2,200 acres. Both watersheds are located in the unincorporated area of the County; thus, the County approves zoning and land use laws, and processes land use permits for private development, on these important lands.
On June 20, 2017, the County and City entered into a Memorandum of Understanding (MOU) regarding a study of the watersheds that would be cost shared equally. On September 26, 2017, the Napa City Council and County Board of Supervisors approved a professional services agreement with Systech to develop a calibrated watershed analysis risk management framework (WARMF) model simulating hydrology and water quality, develop a water quality sampling and analysis plan, and provide a tool which the City and County can use for watershed management on an ongoing basis. The WARMF model combines the physical characteristics of the watershed (topography, land use, soils, vegetation, stream locations etc.) with historical weather data (rainfall, wind etc.), known hydrology (stream flow and depth, lake elevations, diversions etc.) and available water quality data (total dissolved solids, pesticides, nitrogen, phosphorous, sulfates, dissolved oxygen, etc.) collected over time at various sampling points in the watersheds. The model was calibrated by comparing model simulations with known past events to verify accuracy. If the model accurately represents known events, it can be relied upon to predict future events.
On March 19, 2019, staff presented a report that documents the inputs to the model, how the model works, and recommended Water Quality Monitoring and Analysis Plan. On November 19, 2019, the County and City entered into a MOU to gather the samples and perform analyses during the winter rainy seasons 2019/20 through 2021-2022.
City and County staff have identified sites, and field-verified logistics to gather water samples from the main tributaries that feed the drinking water reservoirs. The sampling sites are accessible and repeatable to ensure consistency of data. Samples are gathered approximately monthly (generally late October through late May) depending on the rain year when tributaries are flowing due to rainfall runoff. Historical rainfall data shows that most reservoir recharge occurs during a handful of large storms during winter months. As stated in 2019, it is recognized that it takes 5-10 years of data to establish baseline water quality data and start to recognize trends. There are currently 21 established sites in the Hennessey watershed and 6 in the Milliken watershed. Samples are gathered throughout the rainy season representative of first flush, large runoff events, and average winter flows. The first two drought years 2019-2020 and 2020-2021 resulted in limited sampling opportunities with just 2 and 4 sampling events respectively. 2021-2022 was the first rain year that had runoff sufficient for 8 sampling events to take place from October through May.
The County authorized Amendment No. 1 to the agreement in November 2022. Sampling has occurred annually between 2019 and 2025. This Amendment No. 2 would continue the water quality sampling under the existing sampling schedule through June 2026.
Work will be managed jointly by the City and County and 50% of the cost will reimbursed by the County. To continue to further our understanding of runoff water quality in watersheds that contribute to municipal drinking water supplies, staff recommends the Chair approve and sign Amendment No. 2 to Agreement 200194B, a MOU with City of Napa for continued water quality monitoring of the Lake Hennessey and Milliken Reservoir watersheds.
Requested Action:
Approve and authorize Amendment No. 2 to Agreement 200194B with the City of Napa increasing the County portion from $200,000 to $250,000 and extending the term to June 30, 2026.
FISCAL & STRATEGIC PLAN IMPACT
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Is there a Fiscal Impact? |
Yes |
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Is it currently budgeted? |
Yes |
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Where is it budgeted? |
Natural Resources Division, Org 1704000 |
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Is it Mandatory or Discretionary? |
Discretionary |
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Discretionary Justification: |
Approval of Amendment No. 2 will allow the continued sampling and analysis of water collected from the watershed areas contributing to Lake Hennessey and Milliken Reservoirs. |
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Is the general fund affected? |
Yes |
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Future fiscal impact: |
Appropriations have been included in the approved Fiscal Year 2025-26 budget. |
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Consequences if not approved: |
The watersheds surrounding Lake Hennessey and Milliken Reservoirs will not be sampled and additional information about the water quality in the reservoirs will be absent. |
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.