Chemical diversity of groundwater in the Carboniferous–Permian aquifer in the Unisław Śląski – Sokołowsko area (the Sudetes, Poland); a geochemical modelling approach

Abstract

Groundwater in the Carboniferous–Permian sedimentary aquifer in the vicinity of Unisław Śląski–Sokołowsko (Intra-Sudetic Basin, the Sudetes, SW Poland) manifests spatial chemical diversity. The water chemistry varies from fresh calcium-magnesium-bicarbonate groundwater at the recharge area to calciumsodium-sulphate mineral water downwards the basin. Geochemical mass balance modelling confirms that the main chemistry features of the sulphate mineral water are controlled by dedolomitization and calcium common-ion effects. Congruent dissolution of gypsum promotes incongruent dissolution of dolomite with calcite precipitation. Cation exchange between Ca2+ (and Mg2+) solutes and Na+ (and K+) also takes place. The sulphate mineral water shows elevated concentrations of numerous trace elements. Iron, zinc and manganese originate from dissolution of carbonates (dolomite and/or siderite) and/or sulphides. The hydrogeological system studied should be considered as a series of individual flow systems. The results of preliminary geochemical modelling corroborate the role of mixing in the formation of the spatial pattern of the aqueous chemistry in the system. The main factor that controls groundwater chemistry is the mixing of two components: modern (tritium-bearing) fresh water and older (pre-bomb Holocene) sulphate mineral water.