From July 1978 to January 1980, water levels declined more than 100 feet in the southern part of the Santa Barbara ground-water basin. The water-level declines are the result of increases in municipal pumping since July 1978. The increase in municipal pumping was part of a basin-testing program to determine the usable quantity of ground water in storage. The pumping, centered in the city less than 1 mile from the coast, has caused water-level declines in the main water-bearing zones to altitudes below sea level. Consequently, the ground-water basin is threatened with saltwater intrusion if the present pumpage is maintained or increased.
Data indicate that saltwater intrusion has degraded the quality of water yielded from six coastal wells. Chloride concentrations in the most recent samples from coastal wells ranged from about 250 to 3,800 milligrams per liter. Four of the wells yielded water with chloride concentrations in excess of 1,000 milligrams per liter.
Previous investigators believed that saltwater intrusion was limited to the shallow part of the aquifer directly adjacent to the coast. The possibility of saltwater intrusion into the deeper water-bearing deposits in the aquifer was thought to be remote because an offshore fault truncates these deeper deposits against consolidated rocks on the seaward side of the fault. Results of this study indicate, however, that ocean water has intruded into the deeper water-bearing deposits to a much greater extent than in the shallow part of the aquifer. Apparently the offshore fault is not an effective barrier to saltwater intrusion.
