Major ion chemistry of groundwaters in the Bahar area, Hamadan, western Iran

Hydrochemical investigations were carried out in Bahar area, Hamadan, western Iran, to assess the chemical composition of groundwater. The area falls in a semi-arid type of climate. In this area, groundwater has been exploited over the past century mainly for irrigation and water supply. A total of 135 representative groundwater samples were collected from different wells to monitor the water chemistry of various ions. Chemical analysis of the groundwater shows that the mean concentration of the cations is of the order Ca2+ > Mg2+ > Na+ > K+, while that for anions is SO42- > HCO3- > Cl- > NO3-. Statistical analyses indicate positive correlation between the following pairs of parameters Cl- and Mg2+ (r= 0.71), Cl- and Na+ (r= 0.76), HCO3- and Na+ (r= 0.56), SO42- and Mg2+ (r= 0.76), SO4 (2-) and Na+ (r= 0.69). Water presents a large spatial variability of the chemical facies (Ca-HCO3, Ca-SO4, Mg-HCO3, Mg-SO4, Na-HCO3) which is in relation to their interaction with the geological formations of the basin (carbonates, dolomite and various silicates) and evaporation. The hydrochemical types Ca-HCO3 and Ca-SO4 dominate the largest part of the studied area. The dissolution of halite, calcite, dolomite, and gypsum explains part of the contained Na+, Ca2+, Mg2+, Cl-, SO4 (2-) and HCO3-, but other processes, such as cation exchange and weathering of aluminosilicates also contribute to the water composition.