Groundwater Program


Public WorksFlood Control and Water Resources

Napa Bridge

NEWSpecial Study Examines Localized Northeast Napa Groundwater Trends - On Tuesday, October 24th at 11:00am the Napa County Board of Supervisors will receive a presentation and report on a Special Study of groundwater level trends in a small portion of the Napa Valley Groundwater Subbasin located northeast of the City of Napa and west of the Milliken, Sarco, Tulocay (MST) creek drainages. Links to the presentation and Special Study report are available HERE.

The importance of Groundwater

Groundwater is a vital source of water supply in Napa County. Residents, businesses and agriculturists rely on groundwater, as do fish, wildlife and natural habitats. It is essential to:

  • Preserve the quality and availability of all local and imported water supplies
  • Sustain groundwater supplies to meet future needs and availability during drought conditions
  • Anticipate and avoid potential environmental effects due to the overuse of groundwater
  • Anticipate and take steps to avoid potential losses in long-term groundwater availability and quality.

Everyone in Napa County has a stake in protecting the County's groundwater resources. Without sustainable groundwater resources, the character of the County would be significantly different in terms of its economy, communities, and ecology.

What is being done

To address these challenges, long-term, systematic monitoring is essential to provide data allowing for improved evaluations of water resource conditions and trends. Napa County has embarked on a countywide Groundwater Monitoring Program to develop a sound understanding of groundwater conditions through groundwater monitoring and data management. The program has delineated the entire county into 17 subareas based on geographic, geologic, and districts. These subareas provide a basis for the presentation of data and related reports. Overall, the Groundwater Monitoring Program will provide a foundation for future coordinated, integrated water resources planning and sharing of key water resources information.

Over the past 6 years, Napa County has developed a more focused understanding of the geology that controls the occurrence and availability of groundwater and doubled the number and distribution of wells that it monitors. The County has constructed additional dedicated monitoring facilities in key locations designed specifically to provide data on the interactions between groundwater and surface water. Added groundwater quality monitoring is currently underway and also planned for the upcoming 2016-17 monitoring cycle. 

What's known about Groundwater

Napa County and other public agencies have been monitoring local groundwater resources since the mid 1900s. 

Based on recent studies and bi-annual monitoring of groundwater levels in over 100 volunteered wells (map), level trends in the Napa Valley Sub-basins of the Napa-Sonoma Valley Groundwater Basin are stable in the majority of wells with long-term records. Although some wells show a response to drought conditions, levels in recent drought years are generally higher than those during the 1976 to 1977 drought. Elsewhere in the County long-term groundwater level records are more limited, with the exception of the Milliken-Sarco-Tulucay (MST) Subarea. Groundwater level declines observed in the MST Subarea as early as the 1960s and 1970s have stabilized since about 2008. The observation that groundwater level responses differ within the MST Subarea and even within the north, central, and southern sections of this subarea indicate that localized conditions, whether geologic or anthropogenic in nature, might be the primary influence on conditions in the subarea.

While there is limited long-term groundwater quality data (map), overall quality appears to be good except in select areas in the most northern and southern parts of Napa County. Areas near Calistoga exhibit geothermal influences and the southern lowlands of the County exhibit elevated levels of naturally occurring dissolved solids and chlorides, likely due to their proximity to San Pablo Bay.

You can find details about groundwater in your local area by visiting the Watershed Information and Conservation Council (WICC) website

 Groundwater Sustainability Planning

The 2014 Sustainable Groundwater Management Act (SGMA) provides a framework for sustainable management of groundwater resources by local authorities. The act provides a timeline – 20 years – to implement actions that achieve long-term groundwater sustainability. It protects existing surface water and groundwater rights and does not impact current drought response measures. The California Department of Water Resources (DWR) is in charge of the SGMA Program and has developed guidelines for local agencies to follow. DWR has also prepared a SGMA brochure to explain the requirements under the Act. Napa County is currently working towards meeting the requirements of the SGMA. A good summary of the SGMA can be found on the Association of CA Water Agencies website.

The County and its groundwater consultant have completed work to meet the requirements of SGMA, which was in the form of a Basin Analysis Report (one of the Alternatives to a Groundwater Sustainability Plan defined in the Act). This report, Napa Valley Groundwater Sustainability - Basin Analysis Report for the Napa Valley Subbasin, provides an extensive analysis of the basin and demonstrates it has operated within its sustainable yield and that it is being managed consistent with the goal of SGMA and DWR regulations.

For medium and high priority groundwater basins/subbasins, a Basin Analysis Report or other Alternative must be submitted to DWR by January 1, 2017. The Napa Valley Subbasin (map) is the only basin in Napa County with a medium priority ranking by DWR that is subject to SGMA at this time.

A Basin Analysis Report for the Napa Valley Subbasin was presented to the Board of Supervisors at a Special Meeting on December 13, 2016. At that meeting, the Board approved the report and its submittal to DWR. The Report was submitted to DWR on December 16, 2016. DWR is currently reviewing the Basin Analysis Report, with their comments and recommendations expected by early 2018. See DWR's SGMA Portal for Alternatives and Reporting for additional information and updates. A hard-copy of the report is available for review at the Napa County Flood Control and Water Conservation District office, 804 First St., Napa, (707) 259-8600. An electronic copy of the report is available below.  

Final Basin Analysis Report Documents Submitted to DWR

Draft Bain Analysis Report Document List:

Refer back to this webpage often to learn what Napa County is doing to comply with the SGMA and ensure the sustainability of local groundwater resources.

Groundwater Program Contact Information

Patrick Lowe
Natural Resources Conservation Program Manager
(707) 259-5937  

Groundwater Email List

Signup on the Napa County Groundwater Email List to receive updates and informational emails regarding the County's Voluntary Groundwater Monitoring Program, annual monitoring updates, and groundwater sustainability planning related to the SGMA.

Sign up HERE

Do-It-Yourself (DIY) Groundwater Level Monitoring

Napa County is offering assessments, training and tools to residents to help them monitor the level of groundwater in their well. This is a new program to allows residents to learn how water depth in their well changes over the course of the year and help them to better understand how the groundwater reservoir beneath their land responds to winter recharge and use over the dry months. Measurements are best taken in the spring and fall over multiple years to see trends in recharge. You can learn more about the DIY Groundwater Monitoring Program by viewing this short video and downloading the program flier.

"Well Owners Guide, A guide for private well owners in Napa County" is a new guide intended to make private well ownership a little easier, by alerting well owners of potential sources of contamination and the need for periodic water quality testing, by introducing the basics of proper well construction, destruction and maintenance, and informs well owners of their responsibilities in Napa County.