Interactive Tritium-Helium groundwater age simulator

The atomic-bomb tests in the 1960ties released tritium into the atmoshere leading to a peak of ~ 6000 Tritium Units in rainwater. Some rainwater infiltrates into the ground and feeds the aquifers as groundwater recharge. The residence time of a water parcel in an aquifer after infiltration can be calculated from the ratio of the remaining Tritium and enriched Helium in a groundwater sample. The calulated age is an approximation only, as the hydrodynamic dispersion leads to bias, especially around the bomb-peak time.

The model interactively simulates the entry, transport and radioactive decay of tritium in groundwater, and the corresponding so-called Tritium-Helium groundwater age.

A web application of the model is available on our groundwater server:

Groundwater age simulator

Or it can be also downloaded as a Windows 10 executable, Linux executable, or as a python script from my cloud storage: https://cloudstorage.uni-oldenburg.de/s/ijZsFriii6nKGLW

The presented 2D-vertical cross-section model of an aquifer simulates the process in a very simplified manner. The model assumes a homogeneous aquifer with a constant groundwater recharge over space and time. It compares the Tritium - Helium age and the so called piston-flow age (which assumes no dispersion) in the aquifer, as well as the resulting mixing age in a groundwater sample, taken from a monitoring well of specific position and screen length.

The model is purely based on analytical solutions that describe the travel times and flow paths in an unconfined aquifer (Chesnaux and Allen, 2008; Greskowiak et al., 2013), as well as advective-dispersive-reactive transport (Kinzelbach, 1987) considering a time varying boundary condition based on the superposition principle (Wexler, 1992).

Literature:

Chesnaux, R. and Allen, D.M. (2008). Groundwater travel times for unconfined island aquifers bounded by freshwater or seawater. Hydrogeology Journal, 16: 437-445. https://doi.org/10.1007/s10040-007-0241-6.

Greskowiak, J., Röper, T., Post, V.E.A. (2013): Closed-Form Approximations for Two-Dimensional Groundwater Age Patterns in a Fresh Water Lens. Ground Water, 51(4), 629-634. https://doi.org/10.1111/j.1745-6584.2012.00996.x

Kinzelbach, W. (1987). Numerische Methoden zur Modellierung des Transports von Schadstoffen im Grundwasser, Habilitationsschrift, Universitaet Stuttgart.

Wexler (1992). Analytical solutions for one-, two-, and three-dimensional solute transport in ground-water systems with uniform flow Techniques of Water-Resources Investigations 03-B7, https://doi.org/10.3133/twri03B7.