Applications in ground water

Earth (see Ballentine et al. 2002 and Ballentine and Bumard 2002 in this volume). 

Starting in the early 1950s, tritium ( H) from anthropogenic sources (mainly atmospheric nuclear weapon tests) was added to the atmosphere in significant amounts (Fig. 6). After oxidation to H HO, tritium participates in the global hydrological cycle. 

H- He dating has also been applied in fractured rock aquifers (Cook et al. 1996 Aeschbach-Hertig et al. 1998). Typical problems encountered in fractured systems are their extreme heterogeneity, double porosity causing differences between hydrodynamic and H- He age, and geochemical complications due to the presence of other He sources. 

From the begiiming, other environmental tracers such as chlorofluorocarbons (CFC-11, CFC-12), Kr, and more recently SFe have been used in parallel with H and He. Because of the different shape of their input functions, sources and sinks, the combination of these tracers provides better constraints on the ground-water flow regime than the use of a single method alone. In the following, two discussed in some more detail. 

and Kr were studied in a sandy, unconfined aquifer on the Delmarva Peninsula in the eastern USA by Ekwurzel et al. (1994). H and H+ He depth-profiles show peak-shaped curves that correspond to the time series of H concentration precipitation, smoothed by dispersion (Fig. 18a). The peak occuring at a depth of about 8m below the water table therefore most likely reflects the H peak in precipitation that occurred in 1963 (Fig. 6). The H- He ages show a linear increase with depth, reaching a maximum of about 32 years. The H- He ages are also supported by CFC-11, CFC-12, and Kr tracer data (Fig. 18b). The latter tracers are used here as dyes and their concentrations are converted into residence times by using the known history of the atmospheric concentrations and their solubility in water. From the vertical H- He age profile at well nest 4 at the Delmarva site, the vertical flow velocity can be 

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