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Calibration and Reliability in Groundwater Modelling: From Uncertainty to Decision Making (Proceedings of ModelCARE’2005, The Hague, The Netherlands, June 2005). IAHS Publ. 304, 2006. pp.38–45.

Simulating environmental tracer transport in unsaturated-saturated porous media

G. A. ONNIS¹, R. ALTHAUS², S. KLUMP³, H. J. W. M. HENDRICKS FRANSSEN¹, F. STAUFFER¹& W. KINZELBACH¹

1 Institut of Hydromechanics and Water Resources Management, ETH-Hönggerberg, CH-8093 Zürich, Switzerland

onnis@ihw.baug.ethz.ch

2 Climate and Environmental Physics Division,University of Bern, CH-3012 Bern, Switzerland

3 Department of Water Resources and Drinking Water, EAWAG, CH-8600 Dübendorf, Switzerland

Abstract Environmental tracers have been released to the atmosphere by human activities since the early 1950s. They provide a powerful tool for investigations of subsurface dynamics, in particular for the determination of groundwater residence times. When considering deep groundwater tables (>10 m below surface), the unsaturated zone transport of these tracers becomes a key issue for the correct evaluation of the groundwater age. Delays of more than 10 years can occur in crossing the vadose zone. In the present work we investigate the subsurface dynamics of four different environmental tracers, ³H, ³He, ⁸⁵Kr and SF₆, with particular emphasis on the tracer transport in the unsaturated zone. The method developed is applied to the Baltenswil aquifer (Switzerland).

Keywords environmental tracers; groundwater; groundwater age dating; transport; unsaturated zone