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 many areas of Petaluma Valley, but in some areas groundwater levels have exhibited long-term declines.
Elevated levels of nitrate have been identified in groundwater within the western portions of the Petaluma Valley due to past land use practices.
A report from the California Department of Water Resources in 1982 found that saltwater intrusion from the tidally influenced portion of the Petaluma River affected shallow aquifers prior to 1962, but that there had been no further incursions after that time. They attributed the lack of further saltwater intrusion to substitution of groundwater with 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 a 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.