Groundwater Resources

Community Development Agency

There are three primary groundwater basins in Marin County.  These basins are subject to the following programs:

California Statewide Groundwater Elevation Monitoring Program
In 2009, the State Legislature passed Senate Bill X7-6 established the California Statewide Groundwater Elevation Monitoring Program (CASGEM.) This was the first statewide program to collect data on groundwater elevations, facilitate collaboration between the State Department of Water Resources (DWR) and local monitoring entities, and to report this information to the public. The goal of this program is to track the long-term trends in elevations of California’s groundwater basins. Environmental Health Services (EHS) is the designated monitoring entity responsible for selecting wells and monitoring the elevations of Marin’s primary groundwater basins each year.

In 2011, EHS submitted the first Marin County Groundwater Elevation Monitoring Program to the DWR. This was updated in May 2019. The County has been monitoring wells in the Sand Point Area, Novato Valley and San Rafael Valley basins twice a year since October 2018.

Sustainable Groundwater Management Act
On September 16, 2014, Governor Jerry Brown signed into law the Sustainable Groundwater Management Act (SGMA). For the first time in its history, California has a framework for sustainable, groundwater management that will allow groundwater to be managed in a manner that can be maintained without causing undesirable results.

In his signing statement, the governor emphasized that “groundwater management in California is best accomplished locally.” As part of the legislation, SGMA established a process for local agencies to request that the DWR revise boundaries of the existing groundwater basins defined in DWR Bulletin 118.

On September 18, 2018, the Board of Supervisors approved an application to change the Sand Point Area Basin boundary to include that portion of the Wilson Grove Formation Highland that was in Marin County at that time (proposed GW Basin Boundary Notification). The formerly configured Wilson Grove Formation Highlands Basin extended from Dillon Beach to Forestville. Given the size of the basin and dramatically different water use in the Sonoma portion of the basin compared to Marin, the County requested a jurisdictional boundary modification. The DWR approved this application on March 28, 2019 (approved GW Basin Boundary Notification). The new northern boundary of the Sand Point Area Basin is the Marin County line. The remaining Wilson Grove Formation Highlands is now entirely within Sonoma County, where there are several sustainable groundwater agencies to assist in managing the basin groundwater practices.

If you have questions or need further information, please contact the EHS office at (415) 473-6907 Monday through Thursday from 8:00 AM to 4:00 PM, and Friday 8:00 AM to 12:00 Noon.