Strategies for Controlling Seawater Intrusion

In previous studies, the areal extent of seawater intrusion in aquifers underlying the Oxnard Plain was overestimated because other sources of high-chloride water to wells were not recognized. Control of these other sources may require new solutions, such as the destruction of abandoned (unused) wells (Ventura County Public Works Agency, 1995). More accurate understanding of the areal extent of seawater intrusion also may allow increased pumping from the upper aquifer system, or the use of management solutions such as injection barriers, which had previously been rejected as impractical for control of the widespread seawater intrusion believed to exist in the upper aquifer system underlying the Oxnard Plain (Ventura County Public Works Agency, 1995).

Results of a recently completed U.S. Geological Survey simulation-optimization study of alternative water-resource management strategies (Reichard, 1995) showed that a significant reduction in pumping, particularly in the lower aquifer system, and a large quantity of additional water (either recharged to aquifers or used in place of ground-water pumping) would be required to control seawater intrusion. Numerous projects to reduce water demand and develop supplemental water sources through the expansion of existing ground-water recharge facilities, expansion of existing water-distribution facilities, use of reclaimed water, and injection of imported or reclaimed water into aquifers underlying the Oxnard Plain are planned by local water agencies and municipalities (Ventura County Public Works Agency, 1995). Information obtained from the U.S. Geological Survey RASA study of southern California coastal basins will aid in the development of those projects and aid in the effective management of the ground-water resources of the basin.