Impacts of deep groundwater monitoring wells on the management of deep geothermal Pre-Neogene aquifers in the Mura-Zala Basin, Northeastern Slovenia

Abstract

Management of deep geothermal resources in Slovenia is very complex because of the depth of the geothermal aquifers. In this study we have developed a conceptual model for the management of deep geothermal aquifers in Northeastern Slovenia, which has turned out to be much more complex. Evolution of the problems that occurred when developing a conceptual model are based on previous and newly collected data of geothermal waters of Pre-Neogene aquifers in Mura-Zala Basin. Isotope and chemical compositions of groundwater revealed that mixing of deep groundwater in the Pre-Neogene aquifers occurs in exploitation wells at Veržej and Petišovci.According to the history of explotation well construction it is difficult to identify the real cause of mixing of groundwater and of pressure lowering with increasing depth inside wells. Monitoring of groundwater wells in the Mura-Zala Basin based only on exploitation and not monitoring the wells may lead to misleading results. Groundwater mixing is thought to be due either to inadequate construction of exploitation wells in the past, which were and still are used for monitoring or to changed hydrodynamic conditions resulting from uncontrolled exploitation of groundwater without reinjection rate. In this respect, new construction of multilayer monitoring wells in the future is needed, which could lead to more reliable monitoring results, better control of better control of groundwater resources and the hydrogeological system of the Pre-Neogene aquifers.