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2 Dobrzyński D.

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Geochemistry and age of groundwater in a hydrochemically diversified aquifer (Permo-Carboniferous, the Intra-Sudetic Synclinorium, SWPoland) derived from geochemical modelling and isotopic studies

Dobrzyński D.

Acta Geologica Polonica

2009

Vol. 59, no. 3

371-411

Comprehensive investigations of groundwater were performed in a sedimentary aquifer of Permo-Carboniferous, Intra-Sudetic Synclinorium, in SWPoland. The investigation included aqueous chemical and isotopic composition, chemistry of mineral phases, geochemical modelling, and tritium and radiocarbon groundwater dating. Chemical diversity in the groundwater system is created by the mixing of modern fresh water and older sulphate water with higher dissolved solids. The system is treated as a system of flows of two end-member water types. Geochemical modelling is used for: (1) explaining the origin of the chemistry of both water components, (2) quantifying the groundwater mixing, (3) correcting the radiocarbon age of the groundwater for the effects of chemical water-rock interactions, and (4) calculating reaction rates. Study of stable (C, S, O, H) and unstable ([^3H], [^14]C) isotopes allowed the inverse mass balance geochemical models to be verified and specified, and the groundwater to be dated. The chemistry of the modern, tritium-bearing, fresh water is a result of dissolution of limestones, dolomites and gypsum. The mean tritium-age of this water, based on the lumped-parameter approach, varies between 10 and 200 years. The sulphate mineral water owes its chemistry to the process of dedolomitization driven by gypsum dissolution. Its radiocarbon age is about 5.9 ka BP, i.e., during theMid-Holocene Climatic Optimum. Rates of chemical reactions responsible for the formation of sulphate type water are estimated to be: dissolution of gypsum (2.85 [mi]mol/L/year) and dolomite (0.21 [mi]mol/L/year), calcite precipitation (0.20 [mi]mol/L/year), organic matter decomposition (0.08 [mi]mol/L/year).

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

Dobrzyński D.

Acta Geologica Polonica

2007

Vol. 57, no. 1

97-112

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 Ca[^2+] (and Mg[^2+]) 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.