CHLOROFLUOROCARBONS (CCL3F AND CCL2F2) AS DATING TOOLS AND HYDROLOGIC TRACERS IN SHALLOW GROUNDWATER OF THE DELMARVA PENINSULA, ATLANTIC COASTAL-PLAIN, UNITED-STATES

Concentrations of the chlorofluorocarbons (CFCs) CFC-11 and CFC-12 were determined in groundwater from coastal plain sediments of the Delmarva Peninsula. CFC-modeled ages were calculated independently for CFC-11 and CFC-12, and agreed to within 2-3 years in the majority of the waters. Recharge temperatures, determined from dissolved nitrogen and argon concentrations, varied from 9 +/- 2-degrees-C over most of the peninsula to 14 +/- 2-degrees-C at the southernmost tip of the peninsula in Virginia. The CFC-modeled ages were examined in relation to the known hydrogeologic environment, both on regional scales and in more intensively sampled local scale networks. The CFC-modeled recharge years and measured tritium concentrations were used to reconstruct a tritium input function that was compared to the modeled tritiUM plus He-3 distribution. Most of the present distribution of tritium in Delmarva groundwater is consistent with low dispersivities. The results of the study strongly support the use of CFCs for dating shallow, aerobic groundwater.