Groundwater Quality Assessment in Kashan Pplain Using hydrogeochemistry analysis

Groundwater is the main source of water supply for different uses in the Kashan plain. Therefore, investigation and identification of natural and anthropogenic factors affecting its quality are of great importance. In this study, the groundwater quality of the Kashan plain was investigated based on hydrogeochemical analysis and water saturation index of different minerals. The chemical analysis results of groundwater quality parameters in 18 sampling points revealed that the dominant order of cations in the area is Na+> Ca2+> Mg2+> K+, while that of anions is Cl-> SO42-> HCO3-. The Chadha Plot made clear the predominance of Na-K-Cl-SO4 in 55% of the sampling points due to saline water upconing from deep layers and uncontrolled groundwater abstraction in the central part of the area, and chemical dissolution of clay-salty formations in the eastern part of the aquifer. In 38% of the samples, water type was Ca-Mg-Cl-SO4 and since gypsum is negligible in the study area, its origin can be the chemical fertilizers used for the agricultural activities in the region. According to the results of the saturation index, groundwater was saturated for calcite and dolomite minerals, and it was undersaturated for halite, gypsum, anhydride, and sylvite. The results of the combined diagrams of water quality analysis showed that ion exchange and chemical precipitation of calcite and dolomite, and halite dissolution are the major factors controlling groundwater quality in the study area. The ionic ratios did not show the effect of groundwater evaporation and dissolution of gypsum on the quality of water in the region. Carbonate dissolution was observed by reverse ion exchange in the limited part of the region.