| Title | Groundwater Circulation Wells for Geothermal Use: Preliminary Results of the Project Integralsonde Type II |
|---|---|
| Authors | Eva DINKEL, Burga BRAUN, Moritz MUHRBECK, Winfried REUL, Alexander MEEDER, Ulrich SZEWZYK, Traugott SCHEYTT |
| Year | 2018 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Groundwater circulation well, geothermal use, open loop, low-enthalpy, GWHP, groundwater quality, microbial community, pyrosequencing |
| Abstract | Groundwater heat pump (GWHP) systems are a widespread technique to provide buildings with heating and cooling. Most open loop shallow GWHPs are doublet systems which consist of two wells for extraction and reinjection of groundwater. Hence, there has to be enough space to set up such a system. Shallow groundwater circulation wells (GCW) are single-well open loop systems, which demand less space, but there are only very few installations so far. Our aim is to investigate the efficiency of those systems, their influence on groundwater chemistry and microbiology and evaluate their long-term productivity. These are the main research questions of our project Integralsonde type II (01LY1507B /BMBF, KMU-innovativ). GCWs for geothermal use and their impact on groundwater quality are investigated at several sites in the quaternary main aquifer (Saalian age) in the Berlin area. These open loop low-enthalpy shallow geothermal energy systems extract and inject groundwater in the same well via two filter screens at different depths. Groundwater is extracted at the lower filter screen and pumped to a GWHP where the thermal energy is utilized for cooling or heating of the building and then reinjected via the upper well screen. The temperature gradient between extracted and injected groundwater is around 3 K. Since the groundwater circulates in the same aquifer which is used for drinking water production, it is crucial to prevent any negative impact on aquifers. To reduce clogging, mineral precipitation and dissolution, or physical processes such as particle mobilization, degassing, and flocculation, it is decisive to prevent mixing of different redox zones. Especially the presence of high contents of ferrous iron and manganese are usually exclusion criteria for the installation of open groundwater systems. We monitored newly installed as well as running GCWs by sampling produced water from the well and nearby groundwater observation wells. Major anions and cations, especially ferrous iron, manganese and sulfate as redox sensitive parameters, as well as physicochemical parameters for redox zone determination were analyzed. To monitor microbiological community changes, we extracted DNA from groundwater samples to conduct quantitative real-time PCR with primers for iron-reducers, -oxidizers and sulfate-reducing bacteria. Our preliminary results show that redox zones in the vicinity of newly installed GCW remain stable if groundwater is pumped in intermittent intervals. Continuous pumping over weeks changes the bacterial community of the produced water. A groundwater circulation well could be viable option to avoid mixing of different redox zones giving the opportunity to use groundwater otherwise not suitable for geothermal use. |