OCWD weighs deeper basin overdraft to cut imported water costs, advances subsidence study

OCWD weighs deeper basin overdraft to cut imported water costs, advances subsidence studyThe Orange County Water District is exploring lowering its groundwater basin operating range to 700,000 acre-feet of overdraft, a move that could save millions annually but poses risks to production wells, seawater barriers, and land stability.

OCWD is evaluating expanding its basin operating range from a maximum of 500,000 acre-feet to 700,000 acre-feet of accumulated overdraft.

Operating at the 700,000 acre-foot level would nearly eliminate underflow to Los Angeles County, potentially saving $20 million to $30 million annually in imported water costs.

Model scenarios indicate the lower water levels could compromise up to 24 large-system production wells and overwhelm the Talbert Seawater Intrusion Barrier.

The committee approved a $97,693 amendment with GSI Environmental to conduct a Phase 2 land subsidence evaluation using 1D consolidation modeling.

The Orange County Water District (OCWD) is advancing evaluations to expand its groundwater basin operating range, a strategic shift that could yield substantial savings on imported replenishment water but requires careful management of infrastructure and environmental risks. During a May 13, 2026, Water Issues Committee meeting, staff presented findings on the potential impacts of increasing the basin's accumulated overdraft limit from the current 500,000 acre-feet (AF) to 700,000 AF. Modeling indicates that dropping to 700,000 AF would reduce groundwater underflow to neighboring Los Angeles County by 85%, or nearly 30,000 AF per year. According to the General Manager, avoiding the purchase of Metropolitan Water District (MWD) replenishment water to offset this underflow would save OCWD $20 million to $30 million annually. However, the deeper overdraft presents significant operational hurdles. Staff reported that at 700,000 AF, groundwater levels in the principal aquifer would drop by up to 70 feet in the Anaheim recharge area. This drawdown would leave 24 large-capacity production wells compromised, with water levels dropping to within 20 feet of pump intakes, and another 37 wells potentially compromised. Furthermore, the district's Talbert Barrier would be unable to control seawater intrusion at the 700,000 AF level, while intrusion at the Sunset Gap would double. A primary concern of the expanded operating range is the risk of inelastic (permanent) land subsidence. A Phase 1 assessment by GSI Environmental found that historical low water levels in the 1950s likely caused up to 1.5 feet of subsidence in some parts of the basin through 2010. To better predict future risks, the committee approved a $97,693 contract amendment for GSI Environmental to conduct a Phase 2 study. The consultant will process satellite radar (InSAR) data from 1992 to 2010 and utilize one-dimensional consolidation modeling. The goal is to establish critical head thresholds—specific groundwater elevations below which permanent subsidence is triggered—to determine how low and for how long groundwater levels can safely decline. The study is expected to take three to six months.