Large-Scale Aquifer Replenishment and Seawater Intrusion Control Using Recycled Water in Southern California

Abstract

In 2008, eighteen years after determining that its Talbert Seawater Barrier required expansion, the Orange County Water District started up the world’s largest indirect potable reuse facility, the Groundwater Replenishment System (GWR System). The GWR System provides a reliable potable-quality water supply to the Talbert Barrier, which consists of 109 multi-depth injection wells. The Talbert Barrier began operation in 1976 with the completion of Water Factory 21, the first project in California permitted to inject recycled water into a potable-supply aquifer. By 1990, as groundwater pumping increased, it was evident that the barrier’s original injection wells were incapable of maintaining protective groundwater elevations to prevent seawater intrusion. Ten years of technical planning and public outreach culminated in the decision to demolish the undersized Water Factory 21 and build a state-of-the-art advanced recycled water treatment system and expanded barrier. Barrier expansion entailed construction of over 20 new injection wells in key areas where seawater intrusion was observed. Flow modeling indicated that average barrier injection needed to be doubled to 80 m³/min (30 mgal/day). Based on seasonal groundwater pumping patterns, model simulations indicated that the barrier should inject up to 107 m³/min (40 mgal/day) in the summer/fall months and one-half that rate in winter/spring months to maintain a protective hydraulic barrier. With a capacity of 187 m³/min (70 mgd), the GWR System provides all of the high-quality water that the barrier requires, with the remainder conveyed to OCWD’s infiltration basins in the city of Anaheim. Five years after start-up, the expanded seawater barrier has met all expectations in terms of capacity and groundwater elevation maintenance using a reliable locally-produced water supply.