His group relies primarily on natural markers already present in the environment – such as inert gases, for example. “These are ideal tracers because they don’t react with other substances in the water or in the soil,” says Schilling. Schilling therefore considers it a privilege that his group is affiliated with Eawag’s Water Resources and Drinking Water Department, where inert gas measurement methods are being developed. “This gives us direct access to unique know-how and state-of-the-art measurement instruments.”
Motorways in the subsoil
Schilling says he is an environmental scientist by profession. It was only during his doctorate that he decided to devote himself fully to the topic of water in the subsoil. Since then the improvement and refinement of hydrogeological models has been the focus of his research interest. In the past, models were based on simple approaches and few measurements. “They were highly simplified,” says Schilling. But today it is increasingly important not only to know the water level, but also to correctly record and map other aspects such as flow velocities, temperatures and the quality of the groundwater.
Because it makes a big difference whether the water only moves slowly through fine-grained sand – or flows much faster through the coarse pores of pebbles and gravel. Gravel deposits are found in the so-called erosion channels of prehistoric rivers that meandered through the Swiss Plateau millions of years ago. Because the groundwater moves much faster in these underground channels, Schilling speaks of “motorways in the subsoil”.
The different flow velocities of groundwater are important, for example, in the designation of protection zones that must be established by law around drinking water wells. Where groundwater flows faster, it also covers a greater distance during the ten-day stay underground (on which, for example, the designation of protection zone S2 is based). Accordingly, such former erosion gullies should definitely be taken into consideration when designating protection zones, explains Schilling.