Rain as a groundwater tracer

• Applicants: Dr.-Ing. Diana Burghardt; Professor Dr. Peter Dietrich; Professor Dr. Rudolf Liedl
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 275519227

The objective of this project is the scientific validation of using native waters such as precipitation waters as groundwater tracers. It will be evaluated, whether it is possible to infiltrate collected precipitation waters (i.e. rain and melted snow) under controlled conditions into aquifers of interest and, after that, to detect these waters by analyzing the stable isotope signature and capturing the electrical conductivity. In addition, the usage of the temporary temperature change (associated with the water input) as a heat tracer will also be examined. In essence, the project is intended to establish the basis for the development of a non-toxic and environmentally friendly method to explore aquifers. The tracer concept is based on widely existing differences between groundwater and precipitation water (at most field locations), especially with respect to the stable isotope signatures of the water molecule elements, and the water's electrical conductivity. E.g. there are significant differences between even nearby regions or physical states. In many aquifers a conservative transport of both components can be expected, if the tracer water is well chosen. However, a step-by-step analysis of the transport behavior under realistic conditions is necessary to ensure a correct and field-site independent interpretation of tracer data. For a comprehensive assessment of the suitability of precipitation waters as groundwater tracers, these analyses have to be conducted both on small and large scale (under field conditions). This will be done in two consecutive projects.The focus of this first project is on the evaluation of possible interfering factors, which may influence the stability of the applied signals, on a relatively small scale (decimeters up to a few meters). The primarily laboratory-based experiments consist of one- and multi-dimensional flow experiments using different water-sediment combinations and also supporting batch experiments. Sedimentary and structural effects can influence the general flow behavior as well as the isotope and ion composition and will therefore be evaluated for their relevance. Chemical precipitation and solution reactions as well as density and viscosity-related effects due to the water and heat input will also be analyzed. The influence of effects which are caused by the input method itself, by time-location-dependent mixtures of the infiltrated water (e.g., with stagnant pore water or with other water) as well as by natural fluctuations have to be evaluated, too. In addition to the qualitative and quantitative evaluation of the influencing factors mentioned above, there will be a holistic assessment of the cumulative effect due to superposition. For this, the processes will be simulated using suitable models.

• DFG Programme: Research Grants
• International Connection: Australia
• Cooperation Partner: Professor Dr. Henning Prommer, Ph.D.