Hydrochemical identification of groundwater resources and their changes under the impacts of human activity in the Chah basin in western Iran.

Chemical properties and pollution of water resources were studied in the Chah basin that is located in the Hamadan province, western Iran. Water quality was characterized according to its major constituents and the geological features of the area. Chemical analysis results indicate that groundwaters show wide concentration ranges in major inorganic ions, reflecting complex hydrochemical processes. Groundwater in the studied area is, for the most part, weakly to moderately mineralized and dominated by the calcium (Ca(2+)) and bicarbonate (HCO3-) ions. Within the basin, three different hydrogeochemical facies have been identified: Ca-HCO(3), Ca-SO(4) and Mg-HCO(3). The predominant water type of groundwater samples is the Ca-HCO(3) facies in the recharge area and has a tendency toward Mg-HCO(3) and Ca-SO(4) facies along the direction of water flow. The samples were classified into four groups based on chloride (Cl(-)) and nitrate (NO3-) concentrations and the processes that control water chemistry has been discussed. The results explained the importance of cation exchange, mineral weathering, and anthropogenic activities on groundwater chemistry. It was indicated that cation exchange and Cl-salt inputs are the major process controlling the water chemistry of the low Cl(-) and high [NO3-] (group 2) and high Cl(-) and [NO3-] (group 4). Groundwaters low in NO3- and high in Cl(-) (group 3) and low in NO3- and Cl(-) (group 1) are mainly affected by cation exchange and mineral dissolution. Pollution of groundwaters appeared to be affected by the application of fertilizers, irrigation practice, and solubility of mineral phases and discharge of domestic sewage. Measuring and predicting the mass loading of pollutant to groundwater from specific agricultural systems seems to be useful aids in controlling pollutions in groundwater.