Basin Conditions

View the Groundwater Conditions Fact Sheet for an in-depth look at groundwater conditions in the basin. Check this page regularly for more information.

Groundwater Levels

Groundwater information in Petaluma is currently very limited. A study underway by the U.S. Geological Survey (USGS) will provide detailed, up-to-date data. However, the available groundwater elevation data suggest that groundwater elevations are relatively stable in the southern to central areas of Petaluma Valley, but in some areas of the northwest basin, groundwater levels have exhibited long-term declines.


Groundwater Quality

Elevated levels of nitrate have been identified in groundwater within the western portions of the Petaluma Valley due to past land use practices.

Saltwater intrusion from the tidally influenced portion of the Petaluma River was found to affect shallow aquifers prior to 1962, but a 1982 report found that salt water intrusion has not occurred groundwater was largely substituted for surface water. However, the risk of saltwater intrusion due to changes in land use and pumping patterns that have occurred since 1982 is unknown.


Groundwater Sources and Usage

The 46,000-acre Petaluma Valley groundwater basin is located within the larger 93,440-acre Petaluma Valley watershed. The City of Petaluma currently relies on local groundwater to supplement imported water supplies. Other groundwater users within the Petaluma Valley include rural residents, agriculture, mutual water companies, and commercial users. Estimates of total groundwater use in Petaluma Valley, along with the water budget, are not available, but will be developed as part of the onoing USGS study.


Petaluma Valley USGS Study

In 2014, the Sonoma County Water Agency and City of Petaluma partnered with the U.S. Geological Survey to conduct a groundwater study of the Petaluma Valley. The study is nearing completion and is anticipated to be released in 2018. The study will analyze current groundwater levels and water quality. Information provided in the study will serve as a foundation for the Groundwater Sustainability Plan (GSP) that is required by the Sustainable Groundwater Management Act.