The Aquifer Storage and Recovery (ASR) project would store treated, high quality surface water in underground reservoirs, known as aquifers, during wet periods when Russian River water is plentiful. ASR is used to capture water when it’s available and send it underground (using new or existing wells). The stored water helps recover depleted aquifers and can help build up reserves to be used during droughts and emergencies.

Hydrologists refer to the Russian River watershed as ‘flashy’, meaning large storms known as atmospheric rivers, can turn normally mild creek and river flows into raging torrents in the space of hours. Lake Mendocino and Lake Sonoma were constructed to take the peaks off those high flows, store water and reduce downstream flooding. ASR represents a less costly and more environmentally friendly solution to our flashy system and can be used as part of a groundwater banking program.

In 2013, Sonoma Water, and local partners conducted a feasibility study for a regional groundwater banking program that would store surplus Russian River water produced at existing drinking water facilities in aquifers beneath the Santa Rosa Plain or in Sonoma Valley. Sonoma Water and the City of Sonoma piloted a successful, small-scale ASR project in 2018-2019.

Phase 1 of the Santa Rosa Plain Drought Resiliency Project would provide water to Sonoma Water customers by re-establishing the functionality of a groundwater production well in the Santa Rosa Plain. Sonoma Water owns three production wells within the Santa Rosa Plain. The wells were originally drilled in 1977 in response to the historic 1976-77 drought and their rehabilitation is a critical component of the regional drought and seismic emergency water shortage resiliency strategy.

In addition, the Phase 1 project will help drought-impacted farmers by providing supplemental water to the City of Petaluma (a Sonoma Water customer) for its water-hauling program. Phase 2 of the project will rehabilitate the two remaining wells and also add recharge (or ASR) capacity for at least one of the production wells. This would allow the well to work in ‘reverse’. Instead of pumping water out of the ground, the well would receive treated, high-quality drinking water when it’s plentiful. The water would be stored in underground reservoirs known as aquifers. This water would recharge the aquifer and would be available for use during future droughts and emergencies.

Through a policy known as ‘conjunctive use’, Sonoma Water increases its use of groundwater during droughts to offset declines in Russian River surface water. Secondly, during wet or normal water years, Sonoma Water reduces groundwater use to allow aquifers to recover. The production wells were last relied upon during the 2012-2015 drought years when they helped reduce Russian River water usage during those dry years. Increasing water conservation efforts during droughts is a third component of conjunctive use.

Sonoma Water’s production wells are deep (773 feet to 1,040 feet), and draw water from the deep aquifer, not the shallower aquifer. Monitoring from Sonoma Water’s network of 18 monitoring wells during the last drought period when the production wells were more consistently in use found that most home/private wells are connected to the shallower aquifer in the Santa Rosa Plain Basin and were not affected by the pumping. Similarly, creeks, streams, and the Laguna de Santa Rosa are connected to the shallower aquifer. Since groundwater-levels in the shallow aquifer system (which is connected to surface water sources like the Laguna de Santa Rosa) are not anticipated to be impacted by drought year pumping from these wells, streams and associated habitats are not expected to be affected. However, as part of planning and permitting ASR operations potential impacts to nearby well-users, creeks and water quality will be further assessed and monitored.

The Sonoma pilot project is the first ASR water supply approach to be tested in the North Bay region, and its success provides a blueprint for future permanent projects in the region. While the technology is new locally, ASR has been successfully applied to improve resiliency and sustainability of water resources in many other areas throughout the world by allowing stored water to be used in summer months or during droughts. ASR is a common water management strategy employed in California, the United States, and the world to increase water supply reliability.

For more information about the Santa Rosa Plain Drought Resiliency Project visit https://www.sonomawater.org/DroughtResiliency