Solano Subbasin

Monitoring to Maintain Sustainability in the Solano Subbasin Factsheet

The Solano Subbasin of the Sacramento Valley Groundwater Basin occurs over the eastern half of Solano County in the southern Sacramento Valley, a portion of the larger Central or Great Valley geologic province of California. It has been reported on by federal, state and local entities, including the U.S. Geological Survey (USGS), United States Bureau of Reclamation, DWR and various hydrogeologic consulting firms as contracted by local municipalities for local investigations.

The Solano Subbasin includes the southernmost portion of the Sacramento Valley Groundwater Basin and extends into the northern portion of the Sacramento-San Joaquin Delta. The Solano Subbasin boundaries are defined by Putah Creek on the north, the Sacramento River on the East (from Sacramento to Walnut Grove), the North Mokelumne River on the southeast (from Walnut Grove to the San Joaquin River), the San Joaquin River on the South (from the North Mokelumne River to the Sacramento River), the Lower Members of the Great Valley Group on the Northwest, and the Suisun-Fairfield Valley Basin on the Southwest. The Solano Subbasin underlies the Cities of Vacaville, Dixon and Rio Vista, and is pumped extensively for local agricultural and municipal uses.

The state has designated the Solano Subbasin as medium-priority, and thus subject to SGMA. The Solano Subbasin is contained mostly within Solano County, but portions are also within Sacramento and Yolo Counties. It underlies the Cities of Dixon, Rio Vista, and Vacaville, and is pumped regularly for local agricultural and municipal uses. 

Am I in the Subbasin?
Link to Poster Sized Map with Roads
(PDF 3.7MB)

 

Click on Map for Poster Sized Version with Roads
(JPG 20 MB)

Click on Map for Poster Sized Version with Roads
(JPG 20MB)

 

If you are not located in the Solano Subbasin, you may be in one of the neighboring subbasins. The References page has links to our neighboring subbasins: South American Subbasin, Tracy Subbasin, and the Yolo Subbasin.

 

Geology and Groundwater Resources

The Solano Subbasin includes the southernmost portion of the Sacramento Valley Groundwater Basin and extends into the northern portion of the Sacramento-San Joaquin Delta. The Solano Subbasin boundaries are defined by Putah Creek on the north, the Sacramento River on the East (from Sacramento to Walnut Grove), the North Mokelumne River on the southeast (from Walnut Grove to the San Joaquin River), the San Joaquin River on the South (from the North Mokelumne River to the Sacramento River), the Lower Members of the Great Valley Group on the Northwest, and the Suisun-Fairfield Valley Basin on the Southwest. The Solano Subbasin underlies the Cities of Vacaville, Dixon and Rio Vista, and is pumped extensively for local agricultural and municipal uses.

The Solano Subbasin of the Sacramento Valley Groundwater Basin occurs over the eastern half of Solano County in the southern Sacramento Valley, a portion of the larger Central or Great Valley geologic province of California. It has been reported on by federal, state and local entities, including the U.S. Geological Survey (USGS), United States Bureau of Reclamation, DWR and various hydrogeologic consulting firms as contracted by local municipalities for local investigations.

The Sacramento Valley has had tectonically subsiding sedimentary deposits through most of Cenozoic time. Within these sedimentary deposits, fresh groundwater extends to an elevation of -3,000 feet mean sea level (msl) along the axis of the basin. The freshwater aquifer system in the Solano Subbasin, includes a relatively thin alluvial aquifer underlain by the pre-Holocene Tehama formation. The Tehama formation has been differentiated into three segments, including upper, middle and basal zones. Each of these is characterized by patterns of lithology that reflect the processes that influenced their formation. The majority of current municipal groundwater production in the northern Solano Subbasin, including that of the City of Vacaville and Rural North Vacaville Water District, occurs from the basal zone of the Tehama formation. The middle and upper zones of the Tehama formation as well as the overlying alluvial aquifer are utilized on a more distributed basis by individual agricultural and domestic wells, outside of the municipal service areas. It is not currently understood the degree of confinement in the Alluvium and the upper zones of the Tehama, and this will continue to be investigated with further monitoring. The basal zone of the Tehama formation is a confined aquifer system and pumping from this zone results in rapid groundwater level responses.

Recharge of the alluvium comes from direct percolation of rainfall and return flows of applied water by agricultural and municipal users. Recharge of the Tehama Formation is believed to occur in the northwestern area of the County where the formation outcrops. A portion of the recharge to the basal Tehama may be due to leakage from the overlying Quaternary alluvium and upper zones of the Tehama Formation in the outcrop areas. Due to the limited groundwater level record, the ability of recharge from this area to replenish the larger regional basal zone in a timely manner is uncertain.

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Solano Subbasin Data Gaps Map

We need your groundwater data! We are looking for voluntary data on groundwater conditions in certain areas within the subbasin-can you help us? This information will give us a better understanding of overall groundwater conditions in the Solano Subbasin. This map shows the areas where we have some data gaps. All personal information will be redacted.

Am I in the Solano Subbasin?

Clicking on the link above will take you to the Solano Subbasin page where you can access a detailed map of the Solano Subbasin and GSA Boundaries.

 

 

 

News

Open House: Solano Subbasin Groundwater Sustainability Plan

Press Release-March 18, 2019

  • April 2, 2019-Dixon Community Center
  • April 4, 2019-Rio Vista High School
  • April 10, 2019-Vacaville Ulatis Center

October 11, 2018 Solano Groundwater Sustainability Plan Presentation to Solano GSA Board of Directors

* February 2017: GSA Prospective Board Workshop

 

Contact

Solano Groundwater Sustainability Agency

810 Vaca Valley Parkway, Vacaville, CA 95688

Tel: 707.451.6090 Fax: 707.451.6099