Due to uncertainties in the reliability of regional future water supplies (both surface water and groundwater), Sonoma Water, City of Sonoma, and other local partners, including the cities of Rohnert Park and Cotati, Valley of the Moon Water District, and the Town of Windsor (study participants) have conducted a feasibility study for a regional groundwater banking program (Groundwater Banking Feasibility Study) to investigate the viability of enhancing the conjunctive management of surface water and groundwater resources (GEI, 2013). Conceptually, the groundwater banking program would involve the diversion and transmission of surplus Russian River water produced at existing drinking water production facilities during wet weather conditions (i.e., the winter and spring seasons) for storage in aquifers beneath the Santa Rosa Plain and/or Sonoma Valley. The stored water would then be available for subsequent recovery and use during dry weather conditions (i.e., the summer and fall seasons) or emergency situations. The Groundwater Banking Feasibility Study provided an evaluation of the regional needs and benefits, source water availability and quality, regional hydrogeologic conditions, and alternatives for groundwater banking.
Based on the findings from the study, pilot studies to further assess the technical feasibility of Aquifer Storage and Recovery (ASR) as a method for groundwater banking were recommended and currently are being pursued in Sonoma Valley, as described below.
Aquifer Storage and Recovery Project
In 2018, Sonoma Water and the City of Sonoma conducted a pilot project for water supply technology known as Aquifer Storage and Recovery (ASR). The project stored treated, high quality surface water in an underground reservoir, known as an aquifer, during a wet period when surface water supplies were plentiful. During the pilot project, the water was injected, stored and then pumped out in three cycles. The purpose of the project was to see if the stored water helped increase local groundwater levels and to determine if the injected water changed the quality of the groundwater. The results of the pilot test were promising, showing that groundwater levels increased and that water quality remained good.
The Sonoma project is the first ASR water supply approach 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.
Background information on ASR and the Sonoma Pilot Study: