SV GSP Projects Archives - Sonoma County Groundwater Sustainability Agencies

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 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 Sonoma 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 for each of Sonoma County’s principal aquifers is considered a high priority data need to successfully implement the Sonoma 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 Sonoma Valley GSP is to create a system that monitors groundwater levels. This system is known as the Sonoma Valley Well Monitoring Network. Our network will help us understand how groundwater levels change over time and across different locations throughout the basin. Data collected will provide 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 will provide information from shallow and deep aquifer systems. The new wells range in depth from 110 feet to 465 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 to construct four deep multi-level monitoring wells that will be between 300 to 500 feet deep to evaluate groundwater levels and assess seawater intrusion. The wells will be instrumented with dataloggers to remotely collect water-level data on an hourly basis. 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 groundwater monitoring well project will expand on the existing monitoring networks, filling critical data gaps regarding groundwater levels and interconnected surface water as the region works to track progress toward continued sustainable use of our groundwater. 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 sea water intrusion and three deep multi-level monitoring wells were installed across the Sonoma Valley basin, filling critical data gaps regarding groundwater levels, saltwater intrusion, and interconnected surface water. 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 Sonoma Valley

Interconnected Surface Water & Groundwater Dependent Ecosystems in Sonoma 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 Sonoma 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 Sonoma 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 Sonoma Valley has 50 less acres of GDE than previously understood, with a total of 3,328 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 75% of GDEs Sonoma Valley are moderately healthy or very healthy, but 40% are showing declining trends from 2015-2024.

These studies greatly improved the GSA’s understanding of ISW and GDEs in Sonoma 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

Recycled Water Planning in Sonoma 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 Sonoma Valley. To support the development of a sustainable water supply portfolio for Sonoma County, the Sonoma Valley GSA is collaborating with the Sonoma Valley County Sanitation District to advance planning for additional recycled water opportunities.

During Water Year 2023, it is estimated that approximately 900 AFY of recycled water is delivered within the Subbasin for agricultural and landscape irrigation, significantly reducing the need for use of groundwater and other potable water supplies.

The Recycled Water Planning task will advance the planning and design of the Napa Road Recycled Water Pipeline project to 30% and complete CEQA for the project. The planning will support future expansion of the recycled water system, which is needed to offset and reduce groundwater demands in an area of the subbasin where chronic groundwater level declines and minimum threshold exceedances are occurring. The task will build on an ongoing assessment and survey of potential recycled water users in the area being funded by the GSA to help select the most optimal pipeline route for offsetting existing groundwater uses.

Water recycling is an efficient way to reuse and create a dependable water supply while reducing groundwater demand. 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.

Well Inventory and Groundwater Extraction Assessment in Sonoma Valley

The Sonoma Valley GSA conducted a Well Inventory and Groundwater Extraction assessment to obtain information on locations and volumes of groundwater extracted within the Subbasin. The completion of these assessments marks significant progress in filling data gaps to improve our understanding of the entire groundwater system.

Well Inventory

One important data gap for the Sonoma Valley basin is a thorough understanding of the number of wells, well locations, and well depths. Wells are the windows into our aquifer and the most direct way to gather information about the geology of the aquifer and to measure groundwater levels. Each well that is drilled has a respective “Well Completion Report.” The information in these reports describes the geology surrounding the well and the depth below the surface where water is first encountered. However, many of these reports pre-date computers, and may not have ever been digitized or geolocated.

Through a Well Inventory assessment conducted in 2024 to 2025, we found that Sonoma Valley has 2,355 wells, as seen in the photo above. These wells are subdivided by the intended use that was identified by the driller at the time of installation and includes 1,280 domestic wells, 36 industrial wells, 206 irrigation wells, 182 monitoring wells, 69 wells for other uses, 46 public supply wells, and 536 wells for unknown uses. By reviewing Well Completion Reports and adding the new information to our existing database, we improved our understanding about where groundwater extraction is occurring and historic groundwater levels, and identified wells that may be at risk to changes in groundwater levels.

This Well inventory represents an initial comprehensive compilation of well data. Additional refinement over time is recommended as additional data sources and tools become available, along with maintenance of the inventory to capture new well installations and destructions over time.

To learn more, read the full final report here.

Voluntary Flow-Metering Program

In addition to the location of groundwater extraction, it is critical for the GSA to understand how much groundwater is being extracted. Across the basin, the GSA relies on estimates of groundwater extraction at a parcel scale. The GSA’s Groundwater User Information Data Exchange (GUIDE) program allows groundwater users to provide corrections to these estimates which constantly improves the GSA’s understanding of groundwater extraction volumes. In addition, under the SGM Implementation grant funding, the GSA completed a voluntary flow-metering program for individual well owners to receive a free flow-meter (Flow Smart). This program provided flow-meters to 18 groundwater users in Sonoma Valley. Not only will these flow-meters provide valuable data to the GSA about groundwater extraction for various groundwater users, but it will also provide valuable information for well owners, such as well performance data, leak detection, etc. This groundwater use data, along with groundwater use data from the other Sonoma County GSAs will be used to improve groundwater use estimates across the basin.

To learn more, read the full final report here.

Small plant with black irrigation line planted in dirt

Water Use Efficiency Assessment & Pilot in Sonoma Valley

To achieve and maintain sustainable groundwater conditions within the Sonoma Valley subbasin we need to look at both water supply augmentation and demand reduction. One of the demand reduction programs the Sonoma Valley GSA is implementing through SGM grant funding is a Water Use Efficiency Assessment and Pilot Program.

The goal of this program is to reduce groundwater user demands through:

Completing a parcel-specific spatial analysis of crop and landscape types;
Assessing existing groundwater demand for agricultural, industrial, commercial, and rural residential users;
Performing targeted outreach to specific groundwater users; and
Identifying specific measures that could increase water use efficiency.

In 2024, the GSA conducted an assessment of groundwater demand in the basin to improve the understanding of existing groundwater uses. You can view the results of this assessment in the Technical Memo.

The results of this assessment were used to develop a water use efficiency pilot program unique to the Sonoma Valley basin that prioritizes actions to reduce water demands for private well users. In 2025 the Well Aware Pilot Program was launched in Sonoma Valley. The program included four elements designed to reach various groundwater well users across the three Sonoma County GSAs: Petaluma Valley, Santa Rosa Plain, and Sonoma Valley.

The Well Aware Pilot Program created the following:

Educational and Outreach Materials to encourage wise-water use
Well Aware Toolkit offering an interactive resource designed to guide groundwater use decisions
Consultations through local partners to provide site-specific water saving recommendations
Demonstration Site to highlight water saving and groundwater recharge practices in action

To find more information or access the list of water-efficient resources, visit Well Aware | Sonoma Valley Groundwater Sustainability Agency.

The results of the Pilot Program and recommendations for future program expansion are captured within the Sonoma County GSAs Water Use Efficiency 2025 Pilot Program Report.

Blue circle with the words 'Policy' as the title and a check board and check mark below the title.

Assessment of Potential Policy & Programs Options

Assessment of Policy & Program Options – Update (March 2026)
Groundwater policies provide a framework for local agencies to make informed decisions, implement projects, and achieve long-term sustainability. To support this effort, the Petaluma Valley Groundwater Sustainability Agency (GSA) has completed a Policy and Program Options Assessment in March 2026 (Assessment) to identify, prioritize, and further understand actions within the authority of the GSA and local land use agencies that support the Basin’s sustainability goal.

The Assessment was a collaborative effort between the GSA Board, local land use agencies, member agencies, and stakeholders to assess and develop policy and program options that may be appropriate for the GSA to consider implementing or recommending for adoption by partner agencies. In addition to Board and Advisory Committee discussions, the GSA conducted surveys of groundwater users in 2024 (open to all groundwater users) and 2025 (focused on agricultural users) to better understand community perspectives on potential policies and programs. Survey results highlighted strong interest in incentive-based approaches, support for voluntary metering, and the importance of clear communication, technical assistance, and cost-sharing opportunities. At the same time, respondents expressed concerns about potential regulatory impacts, costs, and equity across different types of groundwater users.

Stakeholder opinions were incorporated to evaluate a broad range of potential approaches that could supplement projects to increase water supply (such as recharge or recycled water projects which are also being pursued by the GSA) to help achieve and maintain sustainability. The result is a prioritized, adaptable, and “living” list of potential policies and programs that will periodically be updated as new information, groundwater conditions, stakeholder input, or future GSA Board priorities evolve.

The Assessment focused on policies and programs that exhibit the potential to achieve one or more of the following objectives:
1. Reduce groundwater demands
2. Fill data gaps
3. Align with existing policies and facilitate coordination with other agencies
4. Improve management of groundwater resources
5. Protect beneficial users

Based on technical evaluation and stakeholder input, the GSA grouped potential policies and programs into three general categories: 1) those to continue or initiate, 2) those to further evaluate, and 3) those to place on hold pending future need or additional information. Each policy or program evaluated in the Assessment includes information on the current status, future recommendations, and costs to implement that option.

Policies or programs to continue or initiate include activities that were conducted as pilot programs in 2024 and 2025 through funding provided to the GSA under the California Department of Water Resources’ Sustainable Groundwater Management Implementation Round 2 Grant, such as voluntary water use efficiency and flow-metering programs, and incentive and education programs. Other options such as alternative water sources, well permitting approaches, and mitigation strategies will continue to be evaluated. More complex actions like groundwater allocations or mandatory limits remain on hold unless future conditions warrant them.

Read the full assessment here to better understand the proposed policies and programs.