Solano Subbasin’s Local Plan

Our Groundwater Sustainability Plan covers what is called the Solano Subbasin. It is a small part of the very large Sacramento and San Joaquin Valley groundwater basin. This large basin was divided into smaller subbasins to help capture local conditions and variations. The Solano Subbasin includes the communities of Dixon, Rio Vista, Isleton, Elmira, Sherman Island, and portions of Vacaville, the Montezuma Hills, and Walnut Grove.

Are you in the Solano Subbasin?

Learn More About the Solano Subbasin

Solano Subbasin Community Mapping

Solano Snapshot

Learn More About Groundwater Users in the Subbasin

The Solano Subbasin covers 424,832 acres in eastern Solano County and portions of Yolo and Sacramento Counties. The Subbasin has an estimated population of 120,000 people (Department of Water Resources, 2019) and about 50,000 residents rely on groundwater for their drinking water, in addition to agriculture and industrial water users. 

There are also municipalities that rely on groundwater. The cities of Dixon (population 19,610) and Rio Vista (population 7,360) supply all of their water from multiple industrial wells and nearly 1/3 of Vacaville’s (population 92,428) water supply comes from underground sources. (U.S. Census Bureau, 2010 Census).

The Solano Subbasin includes a dense quantity of shallow wells (~1400) which can be used for drinking water, home kitchens, and small-scale or tenant farming (Drought and Water Shortage Risk Explorer for Self-Supplied Communities, Department of Water Resources, 2020). The Subbasin also boasts numerous recreational sites, including campgrounds and marinas, that rely on groundwater for their drinking water.

The Subbasin includes a large portion of Solano county, so naturally agricultural production is a large user of groundwater, with approximately 170,000 acres of irrigated lands, 24% of which rely on groundwater (Department of Water Resources, 2019).

Tribes use groundwater for cultural practices, subsistence fishing, and sanitation, among other uses. The Yocha Dehe Wintun Nation is a neighboring federally recognized tribe located just north of the Solano Subbasin. Their ancestral land includes modern-day Solano County, and although they do not fall within the Subbasin boundaries, water management in Solano could impact their ability to supply farming, business, and residents.

One user that isn’t as obvious are all of the groundwater-dependent ecosystems in the area. In the Solano Subbasin, there are 75 species of birds, 143 species of plants, and 7 different species of fish that rely on ecosystems sustained by groundwater.

There are about 50 small community water systems that rely on groundwater for drinking water and supply. Some may have only 1-2 water service connections, like schools and churches, that supply drinking water to the community; others, like mobile home parks, marinas, or resorts, may have up to 200 water service connections that supply drinking water. Some of these small systems are not able to connect to larger public water systems, which could make them more at-risk to drought conditions and water quality issues.

Many water users within the Solano Subbasin are fortunate to have multiple sources of water (like Lake Berryessa and the Solano Project) that reduce pressure on groundwater. Even with our relative wealth of water sources, however, there are places in the Subbasin where we see signs of concern such as availability and quality of groundwater for both household and farm use. The process of developing the GSP will help us understand local groundwater conditions and plan for basin-wide sustainability.

Rated Medium Priority under SGMA

The California Department of Water Resources (DWR) determined that the Solano Subbasin is subject to the Sustainable Groundwater Management Act as a medium priority subbasin. This rating is not about current groundwater conditions in the Subbasin, which are generally good, but rather about future pressures we may experience, including population and economic growth, vulnerability to climate change, and the overall importance of groundwater for both drinking water and agriculture.

Solano & SGMA

A major portion of the plan development includes strengthening our understanding of how the Solano groundwater basin works, including how much water is stored within the basin, how much water comes into the basin each year through recharge, how much is used or leaves the basin through evaporation and leakages into neighboring basins. This “hydrogeology” allows us to assess the reliability of our groundwater resources and the baseline conditions. Once that is better understood, we can then make management decisions to ensure that groundwater conditions remain reliable in the future.

GSP development will occur in 2020 and 2021.

Our Groundwater Sustainability Plan

As required by law, the GSP will include these sections:

  • A description of our local groundwater basin (also called the plan area), including an assessment of current and future groundwater conditions, and a ‘water budget’ that helps us understand how much water is coming into and being used in our basin.
  • Sustainability goals and criteria to avoid ‘undesirable’ results such as widespread patterns of wells drying up, saltwater intrusion, or land sinking (subsidence). These sustainability goals and criteria will outline failure points (referred to as ‘minimum thresholds’), when we need to take action to protect groundwater based on indicators like water quality or water quantity (‘sustainability indicators’). This will ensure that beneficial uses and users such as farms, household wells, cities and fish, birds, rivers, and wetlands are protected from negative changes in groundwater conditions.
  • Descriptions of the projects, programs and actions we will take to achieve these sustainability goals. Our challenge is to come up with effective and innovative ways to keep our groundwater supply reliable and accessible (in the law these ideas are called “projects and management actions”).  These ideas will either help refill the basin (called recharge) or reduce the demand on groundwater (with tools like groundwater trading markets and water-saving technologies and programs).
  • A monitoring plan that will measure progress over time.

The GSP will be a living, evolving document and will be reviewed again, every 5 years after adoption. The plan is designed to serve the subbasin over the long-term.

Our Groundwater Managers

In the Solano Subbasin, several eligible public agencies formed GSAs including the reclamation districts, the Solano GSA (which is a partnership of eleven agencies), Solano Irrigation District, the County of Sacramento, Northern Delta GSA , and the City of Vacaville. Five Groundwater Sustainability Agencies have joined together as the “Solano Collaborative” to jointly develop one Groundwater Sustainability Plan (GSP) for the entire Subbasin. To guide that process, they have created a Memorandum of Understanding (MOU), outlining their agreements on their shared terms of governance and implementation of the GSP formation process.

Is developing
Groundwater Sustainability Plan (GSP) for the entire Solano Subbasin.

Our Timeline


The Groundwater Sustainability Plan for the Solano Subbasin must be submitted to the California Department of Resources for review by January 31, 2022.

January 2022
January 2022

The Groundwater Sustainability Plan for the Solano Subbasin must be sumbitted by January 31, 2022

January 2022

Every 5 years, the Solano Collaborative will review monitoring data and assess if the Solano Subbasin is on track to meet sustainability goals.


5-Year Effectiveness Evaluation


5-Year Effectiveness Evaluation

5-Year Effectiveness Evaluation


Achieve Groundwater Sustainability in the Solano Subbasin

Per the Sustainable Groundwater Management Act, the Solano Subbasin must meet it's sustainability goals by 2042.

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