Groundwater Basics


Groundwater is water located below ground where the voids or pore spaces between sediment grains or rocks are fully saturated. Groundwater originates from a variety of sources, including precipitation, irrigation, infiltration from surface waters, and injection wells to name a few. Groundwater can flow from one part of the subsurface to another; it can also leave the subsurface as outflow to streams or other surface waters, spring flow, evaporation, and discharges from wells. In a sense, all groundwater starts as some form of surface water. The two types of water, surface water and groundwater, are inherently connected.

Groundwater is part of the hydrologic cycle

Depending on location, slope, geology, soil type and vegetation, the ground can receive and retain groundwater similar to the way a sponge soaks up water. The percolation process that moves water from the surface to the subsurface is often a relatively slow process that occurs over several years to over a millennium in some cases. 


Napa County Groundwater Monitoring Plan

Groundwater and surface water are highly important natural resources in Napa County. The Napa County Groundwater Monitoring Plan was put in place in order to address groundwater-related challenges within the County. The Napa County Groundwater Monitoring Plan is a living document that will be updated based upon the data collected. Its purpose is to formalize and augment current groundwater monitoring efforts (levels and quality) to better understand the groundwater resources of Napa County. The plan will aid in making the County eligible for public funds administered by the California Department of Water Resources (DWR), and will regularly evaluate trends to identify changes in levels and/or quality and factors related to those changes that warrant further examination to ensure sustainable water resources.


Voluntary Groundwater Monitoring

The Voluntary Groundwater Level Monitoring Program measures groundwater elevation twice per year (Spring and Fall). These measurements improve the understanding of groundwater for the landowner and the County. A comprehensive network of privately owned volunteer wells, along with publicly owned wells, provide a greater understanding of Napa County aquifers. The program will be strengthened by expanding the voluntary well network to areas where data is lacking or nonexistent.  

2017 Groundwater Level Monitoring Sites

2018 Groundwater Level Monitoring Sites
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To learn more about groundwater monitoring occuring in Napa County visit the Groundwater Monitoring page. On this page you can read a brief summary of current monitoring results and trends. You can also use the interactive map below to get more details about groundwater in various parts of Napa County.