Additional information needed for carbon dating

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. USGS scientists (Busenberg and Plummer, 1992) adapted analytical procedures developed by the oceanographic scientific community for ground-water studies and designed sampling equipment and procedures for collection and preservation of water samples in the field.Water samples for CFC analysis are now routinely collected from domestic, irrigation, monitoring, and municipal wells, and from springs. Nuclear Regulatory Commission-licensed USGS laboratory for analysis of CFC content by gas chromatography to a detection limit of about 0.3 picograms per kilogram (0.3 pg/kg) of water, which is equivalent to 0.3x10 Ground-water dating with CFC-11, CFC-12 and CFC-113 is possible because (1) their amounts in the atmosphere over the past 50 years have been reconstructed, (2) their solubilities in water are known, and (3) concentrations in air and young water are high enough that they can be measured.The detection of chlorofluorocarbons and tritium in ground water provides valuable information that can be used for dating and tracing young ground water—techniques that help water-resources managers develop management strategies for shallow ground-water systems.Young ground water in shallow ground-water systems Young ground water is typically found at depths from 0 to 100 feet in unconsolidated sediments and at depths up to 1000 feet in fractured-rock systems.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.

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Information about the age of ground water can be used to define recharge rates, refine hydrologic models of ground-water systems, predict contamination potential, and estimate the time needed to flush contaminants from ground-water systems.Chlorofluorocarbons are stable, synthetic organic compounds that were developed in the early 1930s as safe alternatives to ammonia and sulfur dioxide in refrigeration and have been used in a wide range of industrial and refrigerant applications. N., Busenberg, Eurybiades, Drenkard, Stefan, and Schlosser, Peter, 1996, Age-dating of shallow groundwater with chlorofluorocarbons, tritium/helium 3, and flow path analysis, southern New Jersey coastal plain: Water Resources Research, v. 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. 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. For this reason, the term “age” is normally qualified with the word “model” or “apparent,” that is, “model age” or “apparent age.” USGS scientists have investigated some of the most important factors that can affect CFC concentrations in ground water and the resulting age interpretations (Busenberg and Plummer, 1992; Plummer and others, 1993; Dunkle and others, 1993; Ekwurzel and others, 1994; Cook and others, 1995; Plummer and others 1998a, 1998b; Plummer and Busenberg, 1999).

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