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Tritium age dating

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

As with any environmental tracer, age applies to the date of introduction of the chemical substance into the water, and not to the water itself.

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

If the tritium delivery as a function of time can be reconstructed, this penetration process can be used for quantitative studies of water movement through identification of the bomb peak in certain ground water bodies.

However, there are natural limits to this method because tritium decay and dispersion make it increasingly difficult to identify the bomb peak in groundwater.

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.

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.

Significant differences between the apparent tritium/ is mainly determined by the ratio of advection to dispersion in water parcels moving away from the water table.

H), and other chemical and isotopic substances in ground water, can be used to trace the flow of young water (water recharged within the past 50 years) and to determine the time elapsed since recharge.

Whereas the addition of bomb tritium to the environment practically eliminated the use of natural tritium as a tracer, it offered a new tool, i.e., the use of the bomb tritium peak (Fig.

1) as a ‘dye’ that is delivered to natural water systems from the atmosphere on local to global scales.

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.