Geothermal energy is a crucial component contributing to the development of local thermal energy systems as a carbon-neutral and reliable energy source. Insights into its availability derive from knowledge of geology, hydrogeology and the thermal regime of the subsurface. This expertise helps to locate and monitor geothermal installations as well as observe diverse aspects of natural and man-made thermal effects. Temperature measurements were performed in hydrogeological boreholes in south-western Poland using two methods, i.e., manual temperature logging and optical fibre distributed temperature sensing (OF DTS). It was assumed the water column in each borehole was under thermodynamic equilibrium with the local geothermal gradient of the subsurface, meaning rocks and aquifers. Most of the acquired results show typical patterns, with the upper part of the log depending on altitude, weather and climate as well as on seasonal temperature changes. For deeper parts, the temperature normally increases depending on the local geothermal gradient. The temperature logs for some boreholes located in urban agglomerations showed anthropogenic influence caused by the presence of infrastructure, the urban heat island effect, post-mining activities, etc. The presented research methods are suitable for applications connected with studies crucial to selecting the locations of geothermal installations and to optimize their technical parameters. The observations also help to identify zones of intensified groundwater flow, groundwater inrush into wells, fractured and fissured zones and many others.

Evaluation and statistical interpretation of low-temperature geothermal energy potential for selected locations in Poland

The Sudetes, like the other parts of the Bohemian Massif, are rich in medicinal waters, though the wealth of these resources have still not yet been sufficiently identified nor analysed. The Sudetes are characterised by extensive fractured and fractured-porous aquifers, significant depth of water infiltration and coexistence of fresh, medicinal and thermal waters. These often mix with ordinary groundwater under various geological and hydrogeological conditions, which results in complex groundwater chemistry. In this study, we analyse selected occurrences of potentially medicinal waters, i.e. radon, carbonic and acidulous ones among eight currently unused prospective areas and reassess their hydrogeological and hydrogeochemical properties. Physicochemical parameters of water were measured in situ in winter 2023 and 12 new samples were taken for laboratory analysis. The results were compared to historical hydrogeological and hydrochemical datasets from between 1968 and 2022. They help to understand the conditions of occurrence of potentially medicinal waters in the Polish Sudetes, and to some extent in the proximal parts of the Bohemian Massif showing similar geological and hydrogeological settings, including the hard-rock crystalline massif environment and the Bohemian Cretaceous Basin.