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The accuracy of the determined age depends in part on how perfectly the CFCs are transported with the water.

Chemical processes, such as microbial degradation and sorption during transit, can also affect the concentration of CFCs and other compounds used in dating.

CFCs also can be used to trace seepage from rivers into ground-water systems, provide diagnostic tools for detection and early warning of leakage from landfills and septic tanks, and to assess susceptibility of water-supply wells to contamination from near-surface sources.

During the past 50 years, human activities have released an array of chemical and isotopic substances to the atmosphere.

Because of the effect of these factors on CFC concentration, collection of additional data is often needed to determine the apparent age of ground water.

For example, measurements of concentrations of dissolved gases, such as dissolved oxygen, help to define the potential for microbial degradation.

Measurements of dissolved methane are useful in recognizing environments where all three CFCs can be degraded.

Production of CFC-12 (dichlorodifluoromethane, CF). CFC-11 and CFC-12 were used as coolants in air conditioning and refrigeration, blowing agents in foams, insulation, and packing materials, propellants in aerosol cans, and as solvents. The recharge temperature of 10C was determined from analysis of dissolved nitrogen and argon in the water sample. and Busenberg Eurybiades, 1999, Chlorofluorocarbons in P. Herczeg, eds., Environmental Tracers in Subsurface Hydrology: Kluwer Academic Press, in press. L., 1998a, Flow of river water into a karstic limestone aquifer, 1. Dating the young fraction in groundwater mixtures in the Upper Floridan aquifer near Valdosta, Georgia: Applied Geochemistry, v. Other chemical dating tools Tritium (half-life 12.4 years) provides another useful tracer of young ground water. Tracing the young fraction in groundwater mixtures in the Upper Floridan aquifer near Valdosta, Georgia: Applied Geochemistry, v. Sampling for tracers The feasibility of using CFCs as tracers of recent recharge and indicators of ground-water age was first recognized in the 1970s (see Plummer and Busenberg, 1997 and references therein).CFCs have been increasingly used in oceanic studies since the late 1970s as tracers of oceanic circulation, ventilation, and mixing processes.

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