Guido Slangen1, Remco Vis1, Yvonne A'Campo1, Niels Hartog2, Gijsbert Cirkel2
Organisation(en): 1: Witteveen+Bos, The Netherlands; 2: KWR, The Netherlands

Leakage of geothermal wells poses a risk to the environment due to the high salt content and temperature of the geothermal brine. Effective monitoring is necessary to continuously prove that valuable groundwater is not impacted. This study gives a framework which can be used to set up effective groundwater monitoring around geothermal wells in a range of Dutch geohydrological conditions. The design was based on the requirements that were defined by a supervisory committee for three case locations. For each of these locations the end depth of monitoring system is the geohydrological base at the geothermal well location in order to protect groundwater recourses. The monitoring is continuous and aims to quickly detect the leakage, not the size of the impact of the leakage. Leakage can be detected by measuring vertical and temporal variations in temperature and conductivity in the groundwater. These variations can be measured by DTS (Distributed Temperature Sensing) and electromagnetic induction. The monitoring should take place in a separate well, within approximately 5 meters from the injection well. Materials such as PVC and GRE offer adequate resistance against high temperatures and salt content. The costs for building a monitoring system vary per location, but the largest determining factor is the drilling depth. We recommend to investigate the geohydrological situation in the Netherlands more extensively by means of drilling or seismic surveys in order to map the geohydrological base in more detail.