PV GSP Projects Archives - Sonoma County Groundwater Sustainability Agencies

Voluntary Groundwater Level and Seawater Intrusion Monitoring in Petaluma Valley

Two voluntary groundwater data programs set in motion by the Petaluma Valley GSA have yielded their first set of results thanks to the participation of our community members across Petaluma Valley 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 puzzle piece for groundwater managers that improves their understanding of 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 Petaluma Valley basin.

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 Petaluma 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.

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, took groundwater quality samples of their wells, and analyzed the results to establish baseline salinity conditions. The initial results show that chloride and salinity levels remain consistent with historical patterns and indicate that seawater intrusion due to groundwater pumping is likely not occurring. Elevated salinity continues 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.

Aquifer storage and recovery projects underway

aquifer storage and recovery projects As California continues to face increasingly unpredictable weather patterns, water agencies across the state are seeking smarter, more resilient ways to manage our most precious resource. Here in Sonoma County, one innovative solution is gaining momentum: aquifer storage and recovery (ASR).

What is aquifer storage and recovery?

Aquifer storage and recovery, commonly known as ASR — or sometimes referred to as groundwater banking — is a forward-thinking water management approach that

Here’s how it works: During rainy seasons, high-quality drinking water from the Russian River is delivered through Sonoma Water’s aqueduct system and injected into deep underground aquifers through specially designed ASR wells. This water can then be safely stored for months or even years and pumped back up when it’s needed most — whether during a summer drought, multi-year dry conditions, or a natural disaster.

Unlike traditional reservoirs, which store water aboveground, ASR taps into natural underground storage — making it an environmentally sound and cost-effective alternative.

Why ASR Matters in Sonoma County

Water reliability is more important than ever. Droughts, climate change, and the threat of natural disasters all place strain on our water systems. ASR offers a smart, sustainable strategy to meet those challenges head-on. Here are just a few of the benefits:

Improved water security: ASR allows us to save surplus water when it’s plentiful and access it when it’s scarce — especially important during hot, dry summers.
Cost-effective infrastructure: It reduces the need for major new construction projects like dams or surface reservoirs.
Efficient use of existing systems: ASR integrates with existing infrastructure, offering phased testing and lower implementation costs.
Boosts groundwater levels: ASR can help stabilize and even improve groundwater conditions in areas facing long-term declines.
Supports local ecosystems: By reducing the need to draw from rivers and lakes in dry seasons, ASR helps protect important surface water habitats, like those in the Russian River watershed.

Compared to aboveground storage, ASR has a smaller environmental footprint and makes better use of the infrastructure we already have.

ASR in action: proven success in Sonoma County

Sonoma County has been exploring ASR for over a decade, and early results have been promising.

In 2013, a regional Groundwater Banking Feasibility Study was completed. This study looked at water availability, aquifer conditions, and technical methods for storing and recovering water. It showed that Russian River water — with its excellent quality and low mineral content — is ideal for long-term underground storage.
In 2018, Sonoma Water partnered with the City of Sonoma to conduct the region’s first ASR pilot project, injecting and successfully recovering 3.5 million gallons of potable water. The project not only boosted local water reliability, but also helped raise groundwater levels — with no negative impacts to nearby wells.

What’s next for ASR?

Sonoma County isn’t stopping with a single pilot. Building on the groundwork from the 2013 feasibility study, we’re now moving forward with updated planning and regional coordination — supported by funding from the California Department of Water Resources’ Sustainable Groundwater Management (SGMA) Implementation Grant in partnerships with local partners.

This effort has expanded with recently completed and in progress ASR planning and projects across all three groundwater basins in collaboration with Valley of the Moon Water District in the Sonoma Valley Subbasin, the city of Petaluma in the Petaluma Valley Basin, and with Sonoma Water, the town of Windsor and city of Santa Rosa in the Santa Rosa Plain Subbasin. These projects will help incorporate new data and insights into existing models and strategies and help advance toward goals outlined in our local Groundwater Sustainability Plans.

What is Interconnected Surface Water? What do we know about it in our GSA basins?

Did you know that in some places, our groundwater aquifers are directly connected to surface water and influence groundwater resources and ecosystem health in these areas? This interconnected surface water is characterized by surface water bodies (e.g. streams, rivers, and lakes) interacting with aquifers in all types of landscapes, and the biological health of plants and animals in those places is dependent on this flow of water. The interaction takes place in three basic ways: surface-water bodies gain water from inflow of groundwater through their bed, they lose water to groundwater by outflow through the bed, or they do both, gaining in some areas and losing in other areas. Many variables contribute to these outcomes, including climate conditions, elevation, and directional flow of water and groundwater pumping.

This year, with funding from the state grant, the GSAs are working to better understand interconnected surface water in our basins via collaboration with a work group of experts including scientists from state and local agencies and organizations like the Laguna de Santa Rosa Foundation, Sonoma County RCD and Gold Ridge RCD, Sonoma Ecology Center and the California Department of Fish and Wildlife. The group will assess the location, quantity and timing of depletion of surface water, hoping to better determine if the depletion of surface water is causing a significant impact to groundwater levels, and determine the impact of groundwater pumping on habitats associated with interconnected surface water. Field work will commence in Summer 2025 with many data collection activities such as monitoring and measuring flow rates and water temperature, oxygen and moisture levels in streams and a survey of other environmental health and habitat conditions.

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Curious to know more about this topic, in depth? Read Depletions of Interconnected Surface Water, and Introduction from the California Dept. of Water Resources Sustainable Groundwater Management Office.

photo of road construction in City of Petaluma with sign indicating the work includes recycled water extension

Urban Recycled Water System Expansion – Maria Drive Extension/Loop project

Update – Fall 2024

The City of Petaluma has completed the Urban Recycled Water System Expansion – Maria Drive Extension/Loop project which involved the installation of approximately 6,000 feet of 12-inch recycled water pipeline which was paired with the complete reconstruction of the existing two-lane road, including the addition of new curb ramps, signalized crosswalks, and traffic-calming elements. The recycled water expansion project will lead to 41 acre-feet per year of potable water offset, increasing water resiliency for the City and protecting local groundwater supply.

This work represents the first phase of the larger Urban Recycled Water System Expansion. By coordinating the installation of the recycled water pipeline with the road reconstruction, the City has efficiently leveraged resources and minimized disruption to residents. The 12-inch recycled water pipeline installed along Maria Drive is a key element of the broader expansion project, which aims to extend recycled water service throughout Petaluma. This phase lays the groundwork for future connections and extensions, setting the stage for increased water conservation and sustainable resource management across the city.

Here’s where the GSA fits into the picture: The original base bid scope connected the recycled water line to the existing line at Rainier Avenue and brought it to Lucchesi Park. However, after construction commenced, the Petaluma Valley GSA was awarded State Sustainable Groundwater Management Implementation grant funding, prompting the opportunity for the GSA to collaborate the city and help advance both groundwater sustainability goals and the City’s own recycled water delivery goals. The Petaluma Valley GSA’s additional investment helped the project reach further, extending the recycled water line along the remaining stretch of Maria Drive to South McDowell Boulevard, representing a proactive step to offset groundwater use in the basin. By working in collaboration with the City’s project already in motion, the opportunity was an efficient use of public funds, too.

This recycled water project is just one of many activities that the Petaluma Valley GSA Groundwater Sustainability Plan undertakes, with a goal to provide practical alternatives that offset the need to pump groundwater.

The City of Petaluma operates a disinfected tertiary recycled wastewater system serving large agricultural, vineyard, and golf course customers, as well as providing recycled water for landscape and turf irrigation at parks, schools, open spaces, commercial/industrial facilities, and the airport. The City of Petaluma is currently working on an updated Recycled Water Master Plan as part of their Integrated Water Master Planning effort, planned for completion in early 2025. Over the next year, with funding from the Sustainable Groundwater Management Implementation grant, the City will continue to work on the recycled water pipeline expansion, with additional construction planned in 2025.

Update – March 2026

The City of Petaluma has completed the Urban Recycled Water System Expansion – Ranier Drive project, Phase 2 of the Urban Recycled Water System Expansion, funded in part with the GSA’s California Department of Water Resources Sustainable Groundwater Management Implementation grant. This project installed approximately 1,900 feet of 12-inch recycled water pipeline under Rainier Drive from Maria Drive to North McDowell Street, expanding off of the Phase 1 installation. Construction occurred in Fall 2025, and was paired with replacing the water main pipe, repaving the street, and adding traffic calming upgrades.

Currently, the City offsets approximately 2-3 percent of total demand for potable water in the urban system with recycled water. The Maria Drive Extension and the Ranier Drive project will expand the number of recycled water customers in the urban system and provide an alternate water supply for parks, schools, and other irrigation customers. Not only will this help build the City’s water supply resiliency by providing assurance and access to water especially during water supply shortages due to climate change and other natural disasters such as earthquakes and fires, but it will also reduce groundwater extraction which the City uses to supplement their Russian River water during dry years.

For more information about planning for future recycled water projects, check out the Recycled Water Planning page.

Photo of a construction site and well rig with the Santa Rosa GSA sign posted on a chain link fence in the foreground

Monitoring Well Design & Installation in Petaluma Valley

A big challenge with managing groundwater is that it’s invisible to the human eye. Unlike surface water in lakes and rivers, we can’t actually see groundwater levels rise and fall. That’s why monitoring wells are so important: These wells are drilled for the sole purpose of “showing” us what’s happening in local aquifers.

Filling data gaps in the monitoring network is considered a high priority data need to successfully implement the Petaluma Valley Groundwater Sustainability Plan (GSP). You can think of the GSP as our road map that defines projects, actions and a schedule to use, protect and sustain our groundwater resources. One of the key projects within the Petaluma Valley GSP is to create a system that monitors groundwater levels. This system is known as the Petaluma Valley Well Monitoring Network. Our network helps us understand how groundwater levels change over time and across different locations throughout the basin. Data collected provides information from shallow and deep aquifer systems, and will help track seasonal and annual fluctuations in groundwater levels.

Since the GSA was formed, the agency has been expanding the monitoring well network through GSA owned wells, partner agency wells, and voluntary private wells. However, data gaps still exist in several portions of the basin.

Update – Fall 2022

In 2022, with funding from the California Department of Water Resources Proposition 68 grant, three new multilevel groundwater monitoring wells (GMWs) were constructed by the GSA. These GMWs expand on the existing monitoring network, filling critical data gaps regarding groundwater levels, saltwater intrusion, and interconnected surface water, as the GSA works to track progress toward achieving the Groundwater Sustainability Plan goal of sustainable groundwater management by 2040.

Data collected provides information from shallow and deep aquifer systems. The new wells range in depth from 103 feet to 505 feet below ground surface. The GMWs will help track seasonal fluctuations in groundwater levels and quantify annual changes in water budget components. The monitoring wells have been instrumented with dataloggers to remotely collect water-level and temperature data on an hourly basis.

Read the full report on the new monitoring wells here.

Update – August 2024

In 2023, the GSA was awarded grant funding through a California Department of Water Resources Sustainable Groundwater Management Implementation grant to construct three shallow monitoring wells that will be around 50 feet deep to evaluate interconnected surface water and groundwater interactions, and four deep multi-level monitoring wells that will be between 300 to 500 feet deep to evaluate groundwater levels and assess seawater intrusion. The GSA’s will upload this data to DWR’s SGMA Portal where it can be viewed by the public. “The geologic information obtained during the drilling process has been very helpful in improving the 3-D models of the basin, and the wells will continue to provide valuable high-resolution data to the GSAs and stakeholders over at least the next 20 years” explains Mitch Buttress, hydrogeologist with Sonoma Water.

The wells will be constructed in 2025.

Update – March 2026

In February 2026, the GSA finished construction of the last of our grant-funded monitoring wells. Since 2024, three shallow and five deep multi-level monitoring wells were installed across the Petaluma Valley basin, filling critical data gaps regarding groundwater levels, saltwater intrusion, and interconnected surface water. The GSA was able to install one additional monitoring well with funds from the City of Petaluma through a partnership project to assess the feasibility of Aquifer Storage and Recovery – read more about that project here. The monitoring wells have been instrumented with dataloggers to remotely collect water-level and temperature data on an hourly basis.

Read the full report on the new monitoring wells here.

Photo of blue sky and green rolling hills with a small helicopter in the air completing an AEM survey

Aquifer System Hydrogeologic Characterization in Petaluma Valley

Interconnected Surface Water & Groundwater Dependent Ecosystems in Petaluma Valley

Have you ever wondered what goes on beneath a river? Rivers, lakes and streams – all different types of “surface water” are often interconnected to the underlying groundwater aquifer. This system is known as Interconnected Surface Water (ISW) – and it supports a special type of habitat known as Groundwater Dependent Ecosystems (GDEs). What a mouthful, right? These ecosystems support plant and animal species that live in and along waterways and wetlands where groundwater provides critical water, especially where surface water can be seasonally scarce. Many rare and endangered species in California rely on these types of ecosystems. The Petaluma Valley GSA has identified data gaps in our understanding of how surface water conditions and water use activities affect GDE’s.

Using grant funds from the Department of Water Resources (DWR), in 2024 and 2025 the GSA conducted ISW and GDE studies to strategically fill these data gaps and better understand how we can manage our groundwater resources to avoid significant depletion of surface water and maintain the vitality of groundwater dependent ecosystems.

To evaluate ISW, the GSA conducted seepage runs, compared stream flow measurements with groundwater levels, and piloted temperature sensors as a proxy measurement where groundwater data is unavailable. The ISW analysis indicates varying degrees of surface water interconnection throughout the basin. This study’s findings will help the GSA further refine the ISW sustainable management criteria and help comply with DWR guidance.

The GDE analysis focused on reassessing GDE acreage and health in Petaluma Valley. The GSA had initially estimated GDE acreage when developing the Groundwater Sustainability Plan (GSP), by comparing the Sonoma Vegetation Digital Elevation Model (DEM) with 2015 groundwater levels. This analysis was updated using groundwater levels from 2023. The updated GDE analysis estimated that Petaluma Valley has 325 more acres of GDE than previously understood, with a total of 1,552 acres of freshwater marsh, oak woodland, riparian forest, wetlands, and vegetation dependent on groundwater. To estimate the health of these areas, the study compared their normalized difference vegetation indexes (NDVI). NDVI is essentially how green vegetation is, which is an indicator of health or stress. Results showed that 55% of GDEs Petaluma Valley are moderately healthy or very healthy, but 30% are showing declining trends from 2015-2024.

These studies greatly improved the GSA’s understanding of ISW and GDEs in Petaluma Valley. These results alone do not provide enough information to make policy decisions or establish protective metrics, but give further direction to fill remaining data gaps. Through these collaborative efforts and focused scientific studies, we are working towards long-term sustainability and health of our groundwater ecosystem.

To learn more, read the final report here.

Cartoon of two wells - 1 well that shows water being both pumped into the aquifer and 1 well being pumped out from the aquifer

ASR Planning

Stormwater Recharge Planning

Sonoma County’s weather is characterized by rainy winters, followed by long, dry summers. During large winter storms, creeks and streams are often overwhelmed and can cause flooding in local communities. In contrast, dry summers—and increasingly frequent droughts— can place strain on both surface water and groundwater supplies. This Mediterranean pattern is becoming increasingly pronounced as our climate changes, but it also provides an opportunity.

Across California, water managers are rethinking how we handle stormwater. Instead of viewing it solely as a flood risk, we are beginning to see stormwater as a valuable resource that can help replenish our groundwater basins and improve long-term water reliability. By slowing, spreading, and sinking stormwater into the ground through recharge basins, open spaces, and natural waterways, we can use high-flow events to increase groundwater levels within the aquifer, enhance baseflows to interconnected surface water, and help support sensitive beneficial users.

With SGMA Implementation grant funds, the Petaluma Valley GSA has taken steps to build on stormwater recharge projects identified in the Southern Sonoma County Stormwater Resources Plan and further planning toward broader implementation of Stormwater Capture and Recharge projects.

In 2024 and 2025, the GSA and a consultant team led by Bachand & Associates began planning for three pilot projects on sites yet to be determined:

Stream Restoration to Reconnect Streams to Shallow Groundwater: Pilot will construct beaver dam analogs (essentially human made beaver dams) in a stream to slow flows and widen stream area, increase stream to aquifer connectivity, and reduce losses from shallow aquifer to surface water.
Upland Vineyard Cover Cropping and Compost Applications to Increase Groundwater Storage: Pilot will study best management practices for vineyards to increase groundwater storage, such as using a crop cover mix that will have elevated groundwater benefits and high-rate compost application.
Upland Swales on Contours to Increase Groundwater Storage on Upland Pasture and Rangeland: Pilot will construct swales (shallow depressions) on slopes in pastures to slow water as it travels downhill.

Stormwater recharge is an integrated and voluntary resource management strategy that takes collaboration with landowners, farmers, scientists, and water managers to create a successful project. The pilot projects are designed to answer practical questions such as: How quickly does water soak into the ground, and what factors — like soil type and cover crops — affect that rate? The pilots hope to lay the groundwork for future projects by figuring out what it takes to run programs like these, from working with willing landowners to managing the day-to-day logistics.

Staff will use what they’ve learned from these pilots to estimate the costs and potential benefits of expanding on-farm and other stormwater recharge to a larger scale. This is an important step toward building a more resilient local water supply.

Read more about the pilot plans and ongoing efforts here.

purpole signs that says Irrigated with Recycled Water

Recycled Water Planning in Petaluma Valley

Freshwater availability has become increasingly limited in recent years due to climate events, environmental needs, increasing population and economic demands. This has forced us to think outside of the box and to consider ways we can safely reuse water that has not been traditionally used for drinking.

Enter into the picture Recycled Water – which is water that has been used and then treated to remove impurities to be reused for various purposes, including agricultural and turf irrigation, industrial processes, and environmental restoration.

Recycled water has been and will continue to be an important source of irrigation water to offset the use of local groundwater and other potable water supplies in the Petaluma Valley. To support increased demand, the City of Petaluma completed Phase 1 and Phase 2 of the Urban Recycled Water System Expansion by installing 7,900 feet of 12 inch recycled water pipeline. Read more about that project here. To continue to support the development of a sustainable water supply portfolio for Sonoma County, the Petaluma Valley GSA is collaborating with the City of Petaluma to perform an assessment of additional recycled water opportunities.

The Feasibility Study shows that Petaluma will need 5,223 acre-feet of recycled water a year by 2045. To be able to meet this demand, it is likely that increased storage and pipeline expansion will be needed. The study analyzed various urban and agricultural expansion alternatives, which if implemented would expand the City of Petaluma’s recycled water distribution system by 16.5 miles. This extension would potentially offset between 10-30 acre-feet and 175 acre-feet of groundwater pumping per year in urban areas and in agricultural areas, respectively. The study also compared the cost of different expansion projects with how many customers would be served. To learn more specifics about the details of this study, read the full report here.

As water demands increase and ecosystems continue to experience stress of human impacts and a changing climate, water recycling will play an essential role in our water supply resilience. While the Feasibility Study and recycled water planning have made great strides towards increasing the City’s recycled water supply, the coordination is far from over. The GSA and the City of Petaluma will continue to share information about changes to groundwater use and the expansion of recycled water, prioritize recycled water access to agricultural groundwater users, and look for grant opportunities that are mutually beneficial.