Project Concept
The pilot project used in-lieu groundwater banking to store groundwater in the ESJ Subbasin. EBMUD provided NSJWCD with up to 1,000 acre-feet of EBMUD surface water from the Mokelumne River. Participating landowners used the EBMUD surface water supply for irrigation instead (in-lieu) of pumping groundwater from the ESJ Subbasin, thereby allowing groundwater to be banked for future use. Under the DREAM groundwater export permit issued by San Joaquin County in 2017, EBMUD could draw up to half of the banked groundwater, minus five percent for losses annually, to use as supplemental supply. The other half remained in the ESJ Subbasin to help replenish groundwater levels in the region.
Recharge Operations
EBMUD released the entire 1,000 acre-feet of Mokelumne River water available to NSJWCD as part of the pilot project in 2018, 2019, and 2023. About 283 acre-feet (AF) of the water released was diverted by NSJWCD and used for irrigation. The remaining 413 AF was diverted and recharged into the basin through infiltration.
Extraction Operations
An existing irrigation well operated by NSJWCD was used to extract the banked groundwater for this project. The additional facilities required to convey groundwater nearly three miles from this well and into EBMUD’s Mokelumne Aqueducts were constructed in 2022. Groundwater extraction took place for approximately two weeks in February 2023 to test the facilities that brought San Joaquin County groundwater into EBMUD’s raw water system for the first time. About 40 AF of groundwater was incorporated with EBMUD’s Mokelumne water supply.
Additional groundwater extraction was conducted from January through April in 2024. Approximately 223 AF of water was extracted and incorporated with EBMUD’s Mokelumne water supply.
Groundwater Monitoring
To ensure protection of the ESJ Subbasin, environment, and community water supply during groundwater extraction:
- NSJWCD monitored water pumped from the extraction well and made sure it matched the planned amount.
- San Joaquin County (SJC) observed groundwater levels at nearby wells to ensure they stayed above protective minimum levels, called thresholds.
- EBMUD tracked how much water was delivered into the Mokelumne Aqueduct system.
- Pumping operations were overseen by a Monitoring Committee comprised of representatives from San Joaquin County, NSJWCD, and the EWA. If groundwater levels fell below thresholds, the Monitoring Committee could reduce or stop extraction and decide the best course of action based on a review of monitoring data.
During the 2023 and 2024 groundwater extraction periods, no negative impacts to groundwater levels and the ESJ Subbasin were observed.
Water Quality Monitoring
Prior to delivering water to customers throughout the East Bay, EBMUD treats raw water to levels that meet or exceed standards for safe drinking water. For the DREAM Project, EBMUD blended groundwater into our raw water source and maintained the same high standards of treatment and testing. Prior to incorporating the groundwater into EBMUD's raw water source, EBMUD analyzed the DREAM Project groundwater source for over 400 constituents over a period of one year. Much like EBMUD’s current drinking water sources, these constituents are less than the maximum contaminant levels set by the EPA.
The DREAM pilot project will be used to evaluate the possibility of pursuing a larger groundwater banking project in San Joaquin County with the goal of improving EBMUD’s long-term water supply reliability, while also benefitting the ESJ Subbasinin.
Successes and Lessons Learned
The pilot project demonstrated successful implementation of a groundwater banking and extraction project in the ESJ Subbasin. EBMUD was able to supply water to NSJWCD for recharge and the banked water was returned without negatively impacting the ESJ Subbasin. In addition, a total of 462 AF remains in the ESJ Subbasin to help replenish groundwater in the region.
The pilot project was also an effective way to gather lessons learned for a larger groundwater banking project in San Joaquin County. The following lessons will be incorporated during the development of the larger groundwater banking project:
- Increase groundwater banking opportunities through increasing areas for irrigation with surface water instead of groundwater and through use of facilities such as recharge basins. Recharge basins are designed specifically for the purpose of holding water to allow time for it to seep into the groundwater basin.
- Invest in new banking, extraction, and monitoring facilities for efficient and effective operations.
- Address monitoring and operations coordination challenges.
- Continue to develop partnerships and build trust to support regional groundwater banking.
Reliable Future Water
With the goal of improving EBMUD’s long-term water supply reliability, while also benefitting the ESJ Subbasin, EBMUD is in the process of working with San Joaquin County agencies, including NSJWCD and Stockton East Water District, to develop a concept for a larger groundwater banking project in San Joaquin County.
Contact Information
Grace Su, Senior Civil Engineer
Email: Grace Su
Phone: 510-287-7013
Other Sources of Information
Additional details about the DREAM Project can be found on San Joaquin County’s DREAM webpage.