Hydrogeochemistry and Related Processes Controlling the Formation of the Chemical Composition of Thermal Water in Podhale Trough, Poland

Abstract

The most promising Polish region in terms of its geothermal resource potential is the Podhale Trough in the Inner West Carpathians, where the thermal water occurs in the Eocene-Mesozoic strata. The origin and conditions of formation of the chemical composition of the thermal water are different in a regional scale due to the impact of infiltrating water on the chemical compounds present in nearby thermal intakes, chemical processes responsible for the concentration of major elements and residence time. The article presents the regional conceptual model in regard to the factors controlling the chemistry of thermal water from Podhale Trough and the conditions of its exchange. It was allowed by performing the hydrogeochemical characteristics of studied water and analyzing its changes according to flow direction from HCO3-Ca-Mg type to SO4-Cl-Na-Ca and SO4-Ca-Mg types. The hydrogeochemical modelling was also made allowing identification of the impact of reservoir rocks on the formation of the chemical composition. For confirmation of the theories formulated and for more accurate interpretation of the results obtained from hydrogeochemical modelling, hydrochemical indices were calculated, i.e., rHCO3−/rCl−, rNa+/rCl−, rCa2+/rMg2+, rCa2+/(rCa2+ + rSO42−) and rNa+/(rNa+ + rCl−). The results revealed the most important processes evolving the chemistry of thermal water are progressive freshening of the thermal water reservoir, which in the past was filled with salty water, dissolution of gypsum, and ongoing dolomitization. Conducted research presents the important factors that in the case of increased exploitation of thermal water in the Podhale Trough, may influence the quality of thermal water in terms of its physical and chemical parameters.