About the lab
We study groundwater flow and transport mechanisms on multiple scales, especially heat transport, coupled mechanical deformation and environmental impacts. This is motivated by the thrill of exploring the enormous diversity of the geo-environment hidden beneath our feet from the depth of a few centimeters to kilometers. Our work seeks to expand our understanding of fluctuations in the subsurface as a consequence of urbanization, geothermal energy use and climate change. To achieve this, we link multiple disciplines such as hydrogeology, geophysics, rock mechanics, computational, energy and environmental science. Among our means are new field, laboratory and model-based investigation techniques. The focus of our research is also reflected in our leading role in undergraduate and graduate te
Featured research (12)
Built-up areas are known to heavily impact the thermal regime of the shallow subsurface. In many cities, the answer to densification is to increase the height and depth of buildings, which leads to a steady growth in the number of underground car parks. These underground car parks are heated by waste heat from car engines and are typically several degrees warmer than the surrounding subsurface, which makes them a heat source for ambient subsurface and groundwater. Thus, the objective of this study is to investigate the thermal impact of 31 underground car parks in six cities and to upscale the thermal impact that underground car parks have on the subsurface in Berlin, Germany. Underground car parks have daily, weekly, and seasonal temperature patterns that respond to air circulation and traffic frequency, resulting in net heat fluxes of 0.3 to 15.5 W/m2 at the measured sites. For the studied underground car parks in Berlin, the emitted annual thermal energy is about 0.65 PJ. Recycling this waste heat with geothermal heat pumps would provide a sustainable alternative for green energy and counteract the urban heat island by cooling of the shallow subsurface.
In this study, we infer the structural and hydraulic properties of the highly fractured zone at the Grimsel Test Site in Switzerland using a stochastic inversion method. The fractured rock is modeled directly as a discrete fracture network (DFN) within an impermeable rock matrix. Cross-hole transient pressure signals recorded from constant-rate injection tests at different intervals provide the basis for the (herein presented) first field application of the inversion. The experimental setup is realized by a multi-packer system. The geological mapping of the structures intercepted by boreholes as well as data from previous studies that were undertaken as part of the In Situ Stimulation and Circulation (ISC) experiments facilitate the setup of the site-dependent conceptual and forward model. The inversion results show that two preferential flow paths between the two boreholes can be distinguished: one is dominated by fractures with large hydraulic apertures, whereas the other path consists mainly of fractures with a smaller aperture. The probability of fractures linking both flow paths increases the closer we get to the second injection borehole. These results are in accordance with the findings of other studies conducted at the site during the ISC measurement campaign and add new insights into the highly fractured zone at this prominent study site.
Precise information about the spatial distribution of hydraulic conductivity (K) in an aquifer is essential for the reliable modeling of groundwater flow and transport processes. In this study, we present results of a new inversion procedure for induced polarization (IP) data that incorporates petrophysical relations between electrical and hydraulic parameters, and therefore allows for the direct computation of K. This novel approach was successfully implemented for the Bolstern aquifer analog by performing synthetic IP experiments with a combined surface and cross-borehole setup. From these data, the distribution of K was retrieved with high accuracy and resolution, showing a similar quality compared to images achieved by hydraulic tomography. To further improve the quantitative estimates of K, we use synthetic pumping test data to inform two novel calibration strategies for the IP inversion results. Both calibrations are especially helpful for correcting a possible bias of the IP inversion, e.g., due to resolution limitations and/or to bias in the underlying petrophysical relations. The simulation of tracer experiments on the retrieved tomograms highlights the accuracy of the inversion results, as well as the significant role of the proposed calibrations.
Anthropogenic warming of the atmosphere is one if not the most pressing challenge we face in the 21st century. While our state of knowledge on human drivers of atmospheric warming is advancing rapidly, little so can be said if we turn our view toward the Earth’s interior. Intensifying land use and atmospheric climate change condition the changing thermal state of the subsurface at different scales and intensities. Temperature is proven to be a driving factor for the quality of our largest freshwater resource: groundwater. But there is only insufficient knowledge on which sources of heat exist underground, how they relate in their intensity of subsurface warming, and which consequences this warming implies on associated environments, ecosystems and resources. In this review, we propose a differentiated classification based on (1) the geometry of the heat source, (2) the scale at which the subsurface is heated, (3) the process that generates the heat, and (4) the intention of heat release. Furthermore, we discuss the intensities of subsurface warming, the density of induced heat fluxes, as well as their abundance, and draw implications for depending processes and ecosystems in the subsurface and the potential of recycling this waste heat with geothermal installations.