Conceptual hydrogeological model of the City of Munich, Germany, as a basis for geothermal groundwater utilisation

The Munich Gravel Plain has been studied under various aspects, but there has been no detailed hydrogeological underground model of the entire city area. As a result of the urban heat-island effect, groundwater temperatures reach 18 A degrees C and locally exceed 20 A degrees C. This aquifer is therefore suitable for systematic and large-scale near-surface geothermal energy exploitation. The goal of this study was to establish the first detailed hydrogeological model of the city of Munich, as a basis for estimating the geothermal potential. A database of more than 20,000 drill holes was available, of which 730 were selected, interpreted and processed. As a result, 26 east-west cross sections were constructed, showing the geometry and structure of the aquifer and the position of the unconfined water table during low, average and high-water conditions. Based on these profiles and basic hydraulic considerations, a groundwater flow rate of about 3 m(3)/s was established. Results of this study indicate a high potential for thermal groundwater use and corresponding reductions of heating oil consumption and CO2 emissions. At the same time, thermal rehabilitation of the overheated urban groundwater could be achieved. The quantification of this geothermal potential and the space-time optimisation of thermal groundwater use for heating and cooling require a detailed analysis of groundwater temperatures and numerical groundwater flow and heat transport modelling.