Hydrochemistry and Stable Isotopes Characteristics of Groundwater in an Urban Aquifer, Southwest of Iran

The effect of different recharge sources on the chemical evolution of an urban aquifer, Behbahan plain, southwest of Iran, has been studied using hydrogeochemistry and stable isotopes (18O and 2H). Groundwater samples were collected from 40 water wells in June 2017 and April 2018 as the dry and wet periods, respectively. The water samples were analyzed for the determination of major ions, nitrate, fluoride, and bromide for both periods and stable isotopes concentrations only for the dry period. The hydrochemical maps was investigated to determine anomalous groundwater zones associated with urban sources of groundwater pollution. Characteristic bivariate composition diagrams and cluster analysis (CA) method were employed to identify the hydrochemical processes and to evaluate the recharge sources. Two major water types Ca-SO4 and Ca(Na)-SO4(Cl) were present in the Behbahan groundwater plain. The dominant hydrogeochemaical processes in the aquifer were the dissolution of gypsum and somewhat halite, dedolomitization, scant normal and reverse cation exchange, and mixing. The main sources of the nitrate pollution of groundwater were leaching of organic manure applied to cultivated areas as well as wastewater of Behbahan City. Five distinct recharge sources were recognized for the Behbahan aquifers based on the characteristics of 2H and 18O isotopes.