Carbon-14 Ages Related to Occurrence of Salt Water

Under native conditions Hilton Head Island, SC, the original regional flow path was northeastward (generally from the south end to the north end of the island). At the south end, the fresh water (less than 35 mg per 1 chloride content) is older than 22,000 yr. In the central and higher part of the island, the age of the fresh water ranges from about 2,000 yr to 12,000 yr. This age range is interpreted to mean that with a lowering of regional head, owing to heavy pumping in the Savannah, GA, area, regional flow has reversed, and recharge is being induced into the aquifer in this area. In the central part of the island, the deeper contaminated zone (chloride content about 1,500 mg per 1) has an age of about 26,000 yr B.P. In the northern part of the area, water of the same chloride content has an age of about 7,000 yr B.P. In this study, therefore, radiocarbon concentrations show: (1) the effects of reversal of flow; (2) the area of resultant recharge; (3) the area of modern ocean-water encroachment; and (4) the area of contamination by saline formation water.