Logo courtesy of the City of Gridley

GRIDLEY, CA (MPG) – Groundwater supplies across the Butte Subbasin have remained stable despite two dry years that increased pumping demands, according to findings approved Oct. 5 by the Gridley City Council.

The evaluation covers 2021 through 2025 and found no significant problems threatening groundwater sustainability. City Administrator Elisa Arteaga said the findings indicate water levels showed little change, groundwater storage showed signs of recovery by 2025, and monitoring found no significant land subsidence, or sinking of the ground.

Groundwater officials said the findings reflect how the region manages its water supplies. During wetter years, agriculture relies heavily on surface water from the Feather River, Sacramento River and Butte Creek. When those supplies decline, groundwater helps make up the difference, they said.

The review also examined water quality, including nitrate contamination documented southeast of Gridley.

Of 107 wells monitored between 2000 and 2025, two recorded maximum nitrate concentrations at or above the drinking water standard of 10 milligrams per liter during that 25-year period. One was southeast of Gridley, while the other was near Angel Slough in northwestern Butte County, officials said.

Nitrate monitoring continues through existing agricultural water quality programs. The evaluation determined that additional nitrate monitoring by the groundwater sustainability agencies was unnecessary at this time.

Gridley officials also raised questions about land subsidence and how a potential data center development might obtain water. The evaluation found no significant sinking of the ground, while city officials said water sources for future development would depend on the project's location and the development review process.

The evaluation is part of California's Sustainable Groundwater Management Act, which requires local agencies to develop and implement long-term plans to prevent groundwater depletion.

Eleven agencies participate in managing the Butte Subbasin. Their original groundwater sustainability plan was submitted to the state in 2022 and approved by the California Department of Water Resources in 2023.

According to groundwater officials, the latest assessment also addresses improvements requested by state regulators, including better monitoring of groundwater levels, potential impacts on wells and connections between groundwater and surface water.

Although the review found existing management practices remain effective, participating agencies will continue expanding monitoring efforts and gathering information to better understand changing groundwater conditions.

Gridley's participation carries an annual financial obligation. The council approved a supplemental appropriation of $12,791 for its 2026-27 contribution to the Butte County Groundwater Sustainability Agency because the adopted city budget lacked sufficient funding for the payment.

City officials said the money supports regional groundwater monitoring, reporting, planning and implementation of the sustainability program.

Once the participating agencies complete their approvals, the five-year evaluation will be submitted to the California Department of Water Resources. The final report is due in January 2027.