Ten years of groundwater temperature monitoring at a residential neighborhood under intensive shallow geothermal energy use – insights and lessons learned

In 2013 we started a spatial and temporal high-resolution groundwater temperature monitoring campaign at a residential neighborhood under intensive shallow geothermal energy use in the western outskirts of the city of Cologne, Germany. The monitoring was conducted with the aim to identify effects of the intensive thermal use upon groundwater temperatures. Although individual systems sizes in the neighborhood are small, the installed 47 borehole heat exchanger systems sum up to a total borehole heat exchanger length of 11,009 m within a confined area of 0,12 km² to satisfy, together with three open systems, a total heat demand of 506 kW.

With almost ten years of groundwater temperature monitoring we created a valuable data set. Our results show a reduction of overall groundwater temperatures when comparing upstream and downstream groundwater temperatures during the first years of geothermal operation as an effect of the intensive use of shallow geothermal energy for heating and warm water provision. However, monitoring results depend on the measurement location in our study and it is known that urban subsurface and groundwater temperatures are influenced by several factors. In this contribution, the monitoring concept, results as well as pitfalls of the monitoring campaign are illustrated on our way to untangle urban groundwater temperature changes as a response to the intensive shallow geothermal energy use.