What is Known About Groundwater

What is Known About Groundwater

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

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 2019, groundwater level data was available for 109 sites throughout the county, including 13 of the 17 groundwater subareas and 61 sites within the Napa Valley Subbasin. 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.

Precipitation was above average for the 12-month water year that ended in September 2019, based on records from the long-term rain gauge at the Napa State Hospital. The precipitation total for water year 2019 was 33.29 inches, while the average water year total from 1920 to 2015 was 24.86 inches. The most recent water year with a similar precipitation total was 2011.

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