USE OF CHLOROFLUOROCARBONS (CCL3F AND CCL2F2) AS HYDROLOGIC TRACERS AND AGE-DATING TOOLS - THE ALLUVIUM AND TERRACE SYSTEM OF CENTRAL OKLAHOMA

The use of chlorofluorocarbons (CFCs) as an age-dating tool and tracer in shallow groundwaters has been investigated. New methodology for field sampling and preserving groundwaters containing parts per trillion concentrations of the CFCs, F-11 and F-12, is presented. Samples are analyzed by purge-and-trap gas chromatography with an electron capture detector. Physical and chemical processes that can alter natural concentrations (air-water equilibrium) of CFCs were investigated to assess dating uncertainties. CFC model recharge ages appear to be defined within 2 years under optimum conditions. The method was applied to central Oklahoma to demonstrate the usefulness of CFCs as (1) an age-dating tool of shallow groundwaters, (2) a tracer of sewage effluent in surface and shallow groundwaters, and (3) a tracer of shallow groundwater. Results of dating indicate two primary recharge periods in central Oklahoma over the past 45 years that correspond to the wet periods 1945-1960 and 1967-1975.