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For dating studies of waters from crystalline rocks, or even for waters from alluvial aquifers associated with crystalline bedrock, it is best to sample several old (tritium-free) waters to aid in defining RHe remained in the ground water at Liedern/ Bocholt.

Calculations based on the "Vogel" model (Vogel 1967), as applied to shallow, homogeneous sand aquifers of isotropic hydraulic conductivity, showed that the shape of the bomb pulse will be detectable in tritiogenic H data because of radioactive decay and advection/dispersion (Schlosser and others 1989).

Determination of the H in the water sample (Schlosser et al., 1988, 1989).

Locating the position of the mid-1960s bomb peak is difficult due to the required high density of vertical sampling and, therefore, is often an impractical means of obtaining ground-water age information. Ekwurzel, B., Schlosser, P., Smethie, Jr., Plummer, L. L., Weppernig, R., and, Stute, M., 1994, Dating of shallow groundwater: Comparison of the transient tracers Kr: Water Resources Research, v.

In some mixtures, the CFC age of the young fraction could be determined from the ratio of two CFCs in the water sample, and mixing fractions based on the ratio of observed to expected CFC concentrations in the water sample (see Plummer and others, 2000). C., 1993, Age dating ground water by use of chlorofluorocarbons (CCl), and distribution of chlorofluorocarbons in the unsaturated zone, Snake River Plain aquifer, Idaho National Engineering Laboratory, Idaho: U. Geological Survey Water-Resources Investigations Report 93-4054, 47p.

If mixing of young and old water occurs, the CFC concentration in the ground-water sample must be divided by the fraction of young water in the mixture before age of the young fraction can be estimated.

The age of the young fraction(s) in ground-water mixtures can be particularly useful when assessing the susceptibility of ground-water resources to contamination from anthropogenic sources.

There are fundamental differences between dating the young fraction in ground-water mixtures with CFCs and with H can be almost entirely attributed to the young fraction. J., and Top, Z., 1976, Determination of tritium by mass spectrometric measurement of He: International Journal of Applied Radiation and Isotopes, v.

Comments The dating ground