Tritium 3he dating of shallow groundwater
These tests which were mainly performed in the early 1960s, led to an increase of tritium in precipitation over the continents of the northern hemisphere from roughly 5 TU to levels of the order of 1000 TU.
One TU (Tritium Unit) means a tritium to hydrogen ratio of 10.
Michel, “Flow of River Water into a Karstic Limestone Aquifer. Dating the Young Fraction in Groundwater Mixtures in the Upper Floridan Aquifer near Valdosta, Georgia,” Applied Geochemistry, Vol.
Bosch, “Helium as a Semi-Quantitative Tool for Groundwater Dating in the Range of 104 to 108 Years,” In: Isotopes of Noble Gases as Tracers in Environmental Studies, International Atomic Energy Agency, Vienna, 1992, pp.
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.
The concentrations of tritium, helium isotopes and neon have been measured in groundwater samples from a shallow and deep groundwater system recharged by bank infiltration from the Oder River in northeastern Berlin, Germany. El-Gamal, "Tritium/Helium-3 Dating of River Infiltration: An Example from the Oderbruch Area, Berlin, Germany," Journal of Water Resource and Protection, Vol.
Munnich, “Tritium/3He-Dating of Shallow Groundwater,” Earth and Planetary Science Letters, Vol.
The correspondence between the 3H/3He and CFC ages indicates that dispersion has had a minimal effect on the tracer-based ages of water in this aquifer.After oxidation to HTO, it takes part in the natural water cycle.Before the full potential of natural tritium as a tracer for water movement in natural systems could be explored its distribution was masked by addition of large amounts of so-called ‘bomb tritium’ produced during the surface tests of nuclear weapons.Water samples for age dating were collected from three sets of nested observation wells (10 wells) with 1.5-m-long screens located near groundwater divides.Three steady state finite difference groundwater flow models were calibrated by adjusting horizontal and vertical hydraulic conductivities to match measured heads and head differences (range, 0.002-0.23 m) among the nested wells, with a uniform recharge rate of 0.46 m per year and porosities of 0.35 (sand) and 0.45 (silt) that were assumed constant for all model simulations and travel time calculations.