Advances in Age Dating - chlorofluorocarbons
USGS scientists have developed a procedure to use chlorofluorocarbons (freon) as a tool for determining the age of ground water on the 0 to 50 year time scale. The 0 to 50 year time scale is particularly relevant to environmentally sensitive shallow ground-water systems; such water supplies which receive recent recharge are probably more vulnerable to contamination than older waters. Freon compounds have been released into the atmosphere in increasing amounts since about 1930 and thus can be used as a tracer of modern recharge. The validity of the chlorofluorocarbon dating method has been demonstrated by comparison to ages based on well-substantiated tritium data and to ground-water ages determined from nuclear dating techniques based on the radioactive decay of tritium and krypton-85. Ground water age-dating with chlorofluorocarbons was shown to greatly enhance the evaluation of subsurface flow and transport, the determination of rates of recharge to aquifers, and the evaluation of recharge mechanisms.
Busenberg, E., and Plummer, L.N., 1991, Chlorofluorocarbons (CCl3F and CCl2F3): Use as an age-dating tool and hydrologic tracer in shallow ground-water systems: in Mallard, G.E., and Aronson, D.A., eds., U.S. Geological Survey Toxic Substances Hydrology Program -- Proceedings of the technical meeting, Monterey, California, March 11-15, 1991: U.S. Geological Survey Water-Resources Investigations Report 91-4034, p. 542-547.
Busenberg, E., and Plummer, L. Niel, 1992, Use of chlorofluorocarbons (CCl3F and CCl2F2) as hydrologic tracers and age-dating tools: Example - The alluvium and terrace system of central Oklahoma. Water Resources Research, v. 28, 2257-2284.
Dunkle, S.A., Plummer, L.N., Busenberg, E., Phillips, P.J., Denver, J.M., Hamilton, P.A., Michel, R.L., and Coplen, T.B., 1993, Chlorofluorocarbons (CCl3F and CCl2F2) as dating tools and hydrologic tracers in shallow ground water of the Delmarva Peninsula, Atlantic Coastal Plain, USA: Water Resources Research, v.29, no. 12, p. 3837-3860.
For additional information and references, see the project description, Kinetics and Thermodynamics of Chemical Evolution in Ground-Water Systems Reston Chlorofluorocarbon Laboratory, or contact:
L. Niel Plummer
U.S. Geological Survey,
432 National Center,
12201 Sunrise Valley Drive,
Reston, VA 22092
Phone: 703- 648-5841