SALINITY CONTROL AS A COMPONENT OF REGIONAL GROUND-WATER MANAGEMENT

Control of ground-water salinity is typically only one of multiple challenges facing regional water managers. Salinity mitigation strategies may have impacts on ground-water levels, flows, and water availability. Conversely, different water-supply strategies, addressing issues such as conjunctive use and water-emergency response, may have significant effects on salinity. This connection between salinity control and other aspects of regional ground-water management is illustrated with examples from the Los Angeles Basin. While there are several sources of salinity in the basin, the main regional water-quality issue is seawater intrusion from San Pedro and Santa Monica Bays. A simulation model of the regional ground-water system was used to evaluate alternative strategies for aquifer storage and recovery (ASR) in terms of their likely impacts on seawater intrusion. The ASR strategies have two phases. During the storage phase (average or wet periods), there is additional injection (at existing barrier wells or new inland wells) and in-lieu surface-water delivery to replace pumpage; during the recovery phase (dry periods), there is increased pumpage and reduced barrier injection. The likely extent and location of seawater intrusion that results from different strategies vary significantly, depending on the location, volume, and timing of injection, pumpage, and in-lieu deliveries. The model also was used to simulate the impacts of using ground water as a backup supply if surface-water delivery was disrupted as a result of an event such as an earthquake. Simulations indicate that short-term (two years or less) increases in pumpage during water emergencies could result in long-term increases in seawater intrusion.