By John A. Izbicki
U.S. Geological Survey Fact Sheet 126-96
This report is a summary of isotopic studies of ground-water source, movement, and age in aquifers underlying the Santa Clara-Calleguas basin, Ventura County, California. It is part of a series summarizing the results of the U.S. Geological Survey's Southern California Regional Aquifer-System Analysis (RASA) study of a southern California coastal ground-water basin. The geologic setting and hydrologic processes described in this report are similar to those in other coastal basins in southern California.
Introduction
Understanding the contribution of recharge from different sources is important to the management of ground-water supply in coastal aquifers in California-especially where problems with water-supply or water-quality have developed as a result of ground-water pumping. In areas where water levels have changed greatly as a result of pumping and no longer reflect predevelopment conditions, an analysis of isotopic data can provide information about the source, movement, and age of ground water that is not readily obtained from a more traditional analysis of ground-water data. This information can be used to develop management strategies that incorporate the availability of natural and artificial recharge to control water-level declines and water-quality degradation.
In this study, the ratios of the stable isotopes of oxygen and hydrogen were used to determine the source and trace the movement of ground water in the Santa Clara-Calleguas basin, Ventura County, California. Tritium and carbon-14 data were used to estimate the age (time since recharge) of ground water.