ASGP (2017), vol. 87: 183–197

HYDROGEOLOGICAL SETTINGS AND ORIGIN OF GROUNDWATER COMPOSITION IN THE SOUTHERN PART OF THE GORCE MTS, KOWANIEC MAŁY CATCHMENT

Joanna ŻACZEK & Adam POROWSKI

Institute of Geological Sciences, Polish Academy of Sciences (ING PAN), Twarda 51/55, 00-818 Warsaw, Poland; e-mails: zaczekjoanna (at) wp.pl, adamp (at) twarda.pan.pl

Żaczek, J. & Porowski, A., 2017. Hydrogeological settings and origin of groundwater composition in the southern part of the Gorce Mts, Kowaniec Mały catchment. Annales Societatis Geologorum Poloniae, 87: 183–197.

Abstract: The Gorce Mts of southern Poland occur in a, natural upland area that is viewed as valuable and is protected. It has an inadequate and irregular network of long-term monitoring points at the national level with regard to groundwater quality and vulnerability to contamination. The paper discusses the results of an investigation of groundwater in the Kowaniec Mały drainage basin, in the southern part of the Gorce Massif. It provides new hydrogeochemical data that shed light on the origin and evolution of groundwater chemistry in this region. On the basis of a hydrogeological survey of 33 natural springs, trends in the spatial and temporal variation of the physicochemical properties of the groundwater are presented. Three hydrochemical types of water were distinguished, namely HCO3-Ca, HCO3-Ca-Mg and HCO3-SO4-Ca. The detailed analysis of ionic ratios shows that the dissolution of carbonates (mainly calcite) and aluminosilicates (mainly albite) played a fundamental role in the formation of the chemical composition of the groundwater in the study area. These processes are responsible for the presence of the dominant ions, such as HCO3- and Ca2+, as well as SiO2 and in part Na+ and K+. Chloride–sodium mineralization is connected first of all with recharge by rain water and the direct dissolution of halite, contained in the aquifer rocks or formed during the evaporation of the water. The most probable sources of dissolved SO42- are the atmospheric sulphates contained in recharge meteoric waters in the case of springs located at higher altitudes and the reduced inorganic sulphur compounds dispersed in fine-grained sedimentary rocks, mostly as pyrite, which undergoes oxidation during rock weathering. Ion exchange processes involving clay minerals also were present and affected mainly the concentrations of Na+ + K+ and Ca2+.