Winning the Battle Against Seawater Intrusion with Recycled Water

In 2008, eighteen years after determining that the Talbert Seawater Barrier required expansion, the Orange County Water District flipped the switch on its Groundwater Replenishment 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 1975 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 purified recycled water treatment system and expanded barrier.  During the lengthy design and construction period, worsening seawater intrusion and increasing basin overdraft required OCWD to reduce groundwater production from the basin.  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 30 million gallons per day (mgd), with a seasonal operating range of 20 to 40 mgd.  With a 70-mgd capacity, the GWR System provides all the water the barrier requires, with the remainder conveyed to OCWD’s infiltration basins in Anaheim.  Four years after start-up, the expanded barrier has met all expectations in terms of capacity and groundwater elevation maintenance.  Declining salinity in monitoring wells indicates a reversal in seawater intrusion.  With success comes future challenges:  predictions of sea level rise from 1 to 5 feet by the end of the century may require additional approaches beyond injection.