Another valley groundwater subbasin will likely escape state intervention

The Delta-Mendota subbasin, one of the largest in California, will likely avoid state enforcement.

Staff from the state Water Resources Control Board issued an  assessment March 2 that recommends the basin, which stretches over 765,000 acres across six counties, return to the oversight of the Department of Water Resources (DWR). 

The state Water Board will consider the recommendation at its April 7 board meeting. 

If the subbasin does not return to DWR, landowners face well metering and reporting requirements, registration fees of $300 per well and extraction fees of $20 per acre foot. 

In its assessment, Water Board staff determined that Delta-Mendota’s 2024 revised Groundwater Sustainability Plan made significant progress resolving deficiencies that sent the basin into the state’s intervention process in 2023 per the Sustainable Groundwater Management Act (SGMA). 

Some of the improvements include establishing a program to protect domestic wells, expanding monitoring of drinking water quality, evaluating impacts to interconnected surface waters and committing to resolve data gaps, and establishing groundwater extraction allocations specific to each groundwater sustainability agency (GSA) group. 

Delta-Mendota has 23 GSAs, divided into seven groups. Together, they submitted a single Groundwater Sustainability Plan (GSP). That’s a long way from their original approach of six separate GSPs, which the state said lacked coordination and did not adequately prevent lowered groundwater levels, land subsidence, degraded water quality or acknowledge the interconnectedness of surface waters. 

Delta-Mendota stretches along the central San Joaquin Valley’s west side and incorporates the cities of Los Banos, Newman, Gustine, Dos Palos, Mendota, Firebaugh and Patterson. Its primary water supply is surface water, though reliance on groundwater increases during droughts. 

The subbasin has an average overdraft of 140,000 acre-feet per year. 

If released from the threat of probation, Delta-Mendota will follow in the steps of the Chowchilla, Kaweah and Kern subbasins. The Tule and Tulare Lake subbasins remain on probation. Pleasant Valley subbasin in Fresno County was recommended for probation in 2025.