Porous aquifers contain structural heterogeneities like different sediment layers or lenses. Of special importance are low permeable areas containing immobile water not actively contributing to transport. Solutes diffuse from high permeable areas into immobile water regions and can be stored there for a long time in comparison to residence times of mobile water. An often observed effect caused by the storage function of immobile water regions is a contaminant rebound after site remediation. In cases where the concentration gradient turns around solutes diffuse back from immobile water regions into mobile water regions resulting in a continuous release over a long time eventually exceeding thresholds at downstream located observation wells. Heterogeneity and the percentage of immobile water are often unidentified in natural aquifers. Hence, the mathematical prediction of solute transport taking regions with immobile water into account remains challenging. New methods are needed to determine the amount of immobile water in an unknown system (1) to calculate the storage capacity of immobile water regions for pollutants and (2) to evaluate the risk of a contamination rebound after site remediation.

The objective of the thesis is (1) to conduct multi tracer experiments in a well-defined 2D aquifer (Dirac injection) at different flow rates, (2) to model experimental data to quantify the amount of immobile water in the system using the Single Fissure Dispersion Model and (3) to directly and indirectly validate the applied model.

The work will include the performance of multi tracer tests with bromide and deuterium. Experimental data will be modelled using the Single Fissure Dispersion Model.

Christine Stumpp und Bastian Knorr

The master student’s office is in Munich (Helmholtz Zentrum München, Institute of Groundwater Ecology).

Christine Stumpp christine.stumpp@helmholtz-muenchen.de Tel. +49 89 3187 4165

2-D aquifer experiments, multi tracer tests, modelling

English

Levy, M., Berkowitz, B., 2003. Measurement and analysis of non-Fickian dispersion in heterogeneous porous media. J. Contam. Hydrol., 64(3–4): 203-226.

Knorr, B., Maloszewski, P., Krämer, F., and Stumpp, C. (accepted) Diffusive mass exchange of non-reactive substances in dual-porosity porous systems – a column experiment under saturated conditions. Hydrological Processes, doi: 10.1002/hyp.10620