Thermal tracer testing in a sedimentary aquifer: field experiment (Lauswiesen, Germany) and numerical simulation

Abstract

An active and short-duration thermal tracer test (TTT) was conducted in a shallow sedimentary aquifer at the Lauswiesen test site, near Tübingen, Germany. By injecting 16 m3 of warm water at 22°C, a thermal anomaly was created, which propagated along the local groundwater flow direction. This was comprehensively monitored in five observation wells at a few meters distance. The purpose of this well-controlled experiment was to determine the practicability of such a TTT and its suitability to examine hydraulic characteristics of heterogeneous aquifers. The results showed that the thermal peak arrival times in the observation wells were consistent with previous observations from alternative field testing such as direct-push injection logging (DPIL). Combined analysis of depth-dependent temperatures and peak arrival times, and comparison with a numerical heat transport model, offers valuable insights into the natural flow field and spatial distribution of hydraulic conductivities. The study was able to identify vertical flow focusing and bypassing, which are attributed to preferential flow paths common in such sedimentary sand and gravel aquifers. These findings are fundamental for further development of experimental designs of active and short-duration TTTs and provide a basis for a more quantitative analysis of advective and conductive transport processes.