Groundwater Monitoring

Overview

Given the importance of sustainable groundwater resources in Napa County, long-term, systematic monitoring programs are essential to provide data that allow for improved evaluation of water resources, conditions, and to facilitate effective water resources planning.

Groundwater data availability in Napa County varies widely among the subareas. The bulk of the historical and current groundwater level and quality data is located in the Napa Valley Floor Subareas. Recent efforts have expanded the geographic extent of data collection to other subareas.

In 2018, the Department of Water Resources resumed monitoring efforts at four wells that had been suspended in response to multiple, large wildfires that burned in many areas around Napa County in October 2017. The majority of these sites were privately owned wells volunteered by their owners and monitored by Napa County. Here is a video that highlights the importance of the program and the data collected.

 

In the principal aquifer system of the Napa Valley Subbasin, the volume of groundwater in storage decreased (a Dry year) relative to spring 2019 (a Wet year) based on an analysis of groundwater levels measured throughout the Subbasin. The volume of groundwater in storage decreased in 2020 by 24,707 acre-feet to result in a total storage volume of 196,651 acre-feet. From 1988 through 2020, the cumulative annual storage change is a net decrease of 8,945 acre-feet in the Subbasin.

Maps of saturated thickness and groundwater storage changes in the principal aquifer system show decreases in saturated thickness and groundwater storage throughout most of the Subbasin between spring 2019 and spring 2020. These decreases are consistent with the considerable lack of precipitation in water year 2020. Decreases in saturated thickness occurred in the vicinity of Rutherford.

Changes in saturated thickness in the alluvial deposits of the Napa Valley Subbasin, the primary aquifer, and changes groundwater storage volume changes were also evaluated for the period from spring 2007 to spring 2020, for comparison with the most recent year with a similar precipitation total. Saturated thickness and groundwater storage volumes were slightly less in spring 2020 compared to spring 2007. Groundwater storage volumes were generally 0 to 3 acre-feet per acre less in spring 2020 than in spring 2007. Saturated thickness in spring 2020 was generally 0 to 10 feet less than conditions measured in spring 2007.

Napa Valley Subbasin
Groundwater Storage Changes, Water Years 1988 - 2019
 

 

Napa Valley Subbasin
Groundwater use and Groundwater storage changes 1988 - 2019 

 

Napa Valley Subbasin Principal Aquifer Change in Groundwater Storage Spring 2017 to 2019

Napa Valley Subbasin Principal Aquifer Change in Groundwater Storage, Spring 2018 to 2019

 

Napa Valley Subbasin Principal Aquifer Change in Groundwater Storage Spring 2011 to 2019

Napa Valley Subbasin Principal Aquifer Change in Groundwater Storage, Spring 2011 to 2019

Napa Valley Subbasin Principal Aquifer Change in Saturated Thickness Spring 2018 to 2019

Napa Valley Subbasin Principal Aquifer Change in Saturated Thickness, Spring 2018 to 2019

 

Napa Valley Subbasin Principal Aquifer Change in Saturated Thickness Spring 2011 to 2019

Napa Valley Subbasin Principal Aquifer Change in Saturated Thickness, Spring 2011 to 2019

 

Interactive Map

Groundwater Subarea Maps