Prior to the late 1980s, however, there were no reliable means of dating ground water recharged during this time scale and, until recently, none of those methods were considered practical for use in establishing regional patterns.In the early 1990s, USGS scientists (Busenberg and Plummer, 1992) developed a method to date ground water on the basis of chlorofluorocarbon (CFC) content of the water that is practical, cost-effective, and applicable to most shallow ground-water systems.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).
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.
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.
CFC-113 has been used primarily by the electronics industry in semiconductor chip manufacturing, in vapor degreasing and cold immersion cleaning of microelectronic components, and surface cleaning.