Largest Water Rights Adjudication in California

The Antelope Valley groundwater adjudication is the largest groundwater rights dispute in California. The 16-year-old class action involved competing water rights claims by multiple parties and stakeholders—from individual property owners, agricultural interests, public water suppliers and the United States government.

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GEOSCIENCE was retained by attorneys for Los Angeles County to update and refine the USGS Antelope Valley Groundwater Model as part of the adjudication process. The USGS model incorrectly identified and simulated several key components of the water balance for the basin, resulting in a much lower calculation of safe yield. The GEOSCIENCE model was calibrated to the court-accepted safe yield value using updated values for groundwater pumping and evaluating the contribution of mountain front runoff, which was essential for an accurate water balance for the basin. The refined model calibration run showed the overall water level and land subsidence residual statistics for the calibration period. Dr. Dennis Williams also served as and expert witness in the court proceedings.

The calibrated model was used as along with other evidence to craft a settlement of the longstanding dispute, which was recently approved by the court.