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CFCs provide excellent tracers and dating tools of young water (1940 to present time scale).

CFC-11, CFC-12 and CFC-113 concentrations in water can be determined to a detection limit of about 0.3 picograms per kg of water (pg/kg-1) using purge and trap, gas chromatographic techniques with electron-capture detector (GC-ECD; Bullister, 1984; Bullister and Weiss, 1988; Busenberg and Plummer, 1992).

The protocol was strengthened in 1990, requiring industrial countries to phase out CFCs completely by the year 2000, and developing countries to do so by 2010. Sixth ed., p.527, Smithsonian Institution Press, Washington, D.

Groundwater dating with CFC-11, CFC-12 and CFC-113 is possible because (1) the atmospheric mixing ratios of these compounds are known and/or have been reconstructed from 1940 to the present, (2) the Henry's law solubilities in water are known, and (3) concentrations in air and young water are relatively high and can be measured. (1996) Sulfur hexafluoride - A powerful new atmospheric tracer.

The samples are then transported to the NRC-licensed laboratory for analysis. (1971) Atmospheric fluorine compounds as indicators of air movements.

In field sampling, a closed path is established between the well or pump through refrigeration-grade copper tubing in order to flush and cap a 125ml glass bottle with an aluminum foil lined cap.

The feasibility of using CFCs as tracers of recent recharge and indicators of groundwater age was first recognized in the 1970s (Thompson et al., 1974; Schultz et al., 1976; Randall and Schultz, 1976; Thompson, 1976; Hayes and Thompson, 1977; Randall et al., 1977; Thompson and Hayes, 1979; Schultz, 1979). (1974) conducted tracer tests by injecting fluorescein dye, and later a solution containing 100 mg kg-1 of CFC-11 into an aquifer of poorly sorted sand and gravel.

The fluorescein dye was not recovered whereas the CFC-11 arrived at a nearby monitoring well within the expected travel time.

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The Henry's law solubilities of CFC-11, CFC-12 and CFC-113 were measured to high precision (Warner and Weiss, 1985; Bu and Warner, 1995), and purge and trap GC-ECD analytical procedures improved (Bullister and Weiss, 1988).