Groundwater age dating
H, half-life of 12.43 years (Unterweger and others, 1980)) has provided an excellent tracer of young waters.
Tritium input to ground water has occurred in a series of spikes following periods of atmospheric testing of nuclear devices that began in 1952 and reached a maximum in 1963-1964. Tritium measurements alone can be used to locate the depth of the mid-1960s bomb peak, but, because of radioactive decay, many samples may need to be collected and analyzed today to locate its position.
The CFC age of the young fraction is then computed by comparing air concentrations that would be in equilibrium with the CFC concentration in the young fraction with historical air concentrations (Busenberg and Plummer, 1992).
If the mixture contains multiple fractions of young water, the resulting age is regarded as a mean age of the young fraction(s) in the mixture.
Effects of mixing can be more significant when waters are sampled from relatively large intervals in aquifers. N., 1992, Use of chlorofluoromethanes (CCl) as hydrologic tracers and age-dating tools: Example - The alluvium and terrace system of central Oklahoma: Water Resources Research, v.
Mixing, if it occurs, may not be readily apparent if the concentration of a particular constituent (such as dissolved Cl He, there will almost always be compositional gradients, especially when ground water is sampled from relatively large intervals in aquifers.
Helium-3 confinement has also been shown to be a function of the vertical flow velocity (recharge rate) and dispersivity.
Schlosser and others (1989) calculated significant He, is of great value in hydrologic studies and can be used to determine ground-water velocities.
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).
G., 1993, Decrease in the growth rates of atmospheric chlorofluorocarbons 11 and 12: Nature, v.