Two voluntary groundwater data programs set in motion by the Sonoma Valley GSA have yielded their first set of results thanks to the participation of our community members across the basin!
Groundwater Level Monitoring Program
Level Up! is a voluntary well monitoring program aimed at filling groundwater-level data gaps and enabling well users to gain a better understanding of their water resources. Community participants have supported this program during three seasonal monitoring events so far: Fall 2024, Spring 2025, and Fall 2025. The result is an important insight for groundwater managers into the seasonal variability of groundwater levels through wet years and dry years.
Level Up! targeted geographic areas where groundwater level information was not already available to groundwater managers (data gap areas, shown in teal above). Our team reached out to well owners in those data gap areas via bilingual mailers, social media, newsletters, and outreach events. Volunteers were enthusiastic about learning how to take technical measurements and provide meaningful information that will impact the future of groundwater sustainability in the subbasin.
The results are highly valuable groundwater level data in areas where this information was previously limited. The data can now be used by groundwater managers to inform decision making and is also publicly available on our Data Dashboard for anyone interested in exploring local groundwater conditions.
More information about the results of the Level Up! Program are available in the technical report. Interested in participating in the Level Up! Program? Learn more and sign up here!
Seawater Intrusion Monitoring Program
The Sustainable Groundwater Management Act (SGMA) identifies seawater intrusion as a critical indicator of groundwater sustainability in coastal basins.
What makes seawater intrusion a groundwater sustainability indicator? In coastal basins, like Sonoma Valley, freshwater and seawater exist side by side. When sufficient fresh groundwater flows toward the bay, it keeps the sea water from moving inland. But, when groundwater levels decline due to pumping, the change in pressure gradient draws seawater inland, increasing salinity and potentially affecting water quality in wells.
According to a 2015 USGS study, the story gets even more interesting in the Sonoma Valley Basin. When researchers investigated high chloride concentrations near the Eastside Fault, they found that the salinity wasn’t coming from seawater intrusion alone. Instead, the water also contained elevated levels of naturally occurring tracer minerals associated with deep, thermal, connate water, sometimes referred to as “fossil water.”
Monitoring salinity along the Baylands allows us to understand how salinity levels may shift over time and to prepare for potential impacts on the quality of groundwater used for drinking and irrigation. That’s where the Voluntary Seawater Intrusion Monitoring Program comes in. In 2025, the GSA identified willing landowners along the Baylands to collect groundwater samples from their wells and analyze the results to establish baseline salinity conditions. The results demonstrate that salinity along the eastern edge of the Baylands is linked to connate waters associated with the Eastside Fault, consistent with USGS findings from 2015. They also show that chloride and salinity levels remain consistent with historical patterns, indicating that seawater intrusion from groundwater pumping is unlikely to be occurring.
Other areas with elevated salinity continue to be largely confined to wells within the tidal Baylands, confirming that while brackish conditions are naturally present near the Bay, they are not advancing inland into areas where groundwater is used for drinking and irrigation.
More information about the results of the Seawater Intrusion Monitoring Program is available in the technical report.
Conclusion
Thanks to the volunteer participants, data collected in these programs now help us better understand groundwater basin conditions and help plan proactively to protect water quality and sustainability for years to come.