Evaluation of groundwater chemistry and its suitability for drinking and agricultural uses in the Lenjanat plain, central Iran

Abstract

Study of the 59 groundwater samples from Lenjanat area, central Iran, was carried out in order to assess their chemical compositions and suitability for drinking and agricultural purposes. Based on Gibbs’ diagram, weathering of rocks and evaporation were found to be the dominant processes in the ion concentration of the water samples. The saturation index calculated through geochemical modeling indicates a suitable chemical environment for anhydrite, aragonite, calcite, dolomite, fluorite, and gypsum dissolution in both wet and dry seasons. All samples have the SO₄ ²⁻ + HCO₃ ⁻ more than 5 meq/l indicating that in addition to calcite and dolomite, dissolution of gypsum is the probable process in this plain. Assessment of the concentration of Mg²⁺ + Ca²⁺ proportion to SO₄ ²⁻ + HCO₃ ⁻ demonstrates that the advanced direct and reverse ion exchange between groundwater and surrounding environment has occurred. The Chadha diagram indicates that the amount of earth-alkali parameters is more than alkali ones and by considering the high value of strong acids, the dominant hydrochemical facies in both wet and dry seasons are Ca²⁺–Mg²⁺–Cl⁻–SO₄ ²⁻. According to pollution index, in the selected time domain, all samples are in safe conditions. Calculation of entropy weighted water quality index for groundwater samples demonstrates that in the wet and dry seasons, over 57 and 42 % of the samples are in the range of “excellent” to “medium” quality, respectively. The values of SI, RSC, SSP, SAR, KR, PI, MAR, and CI show that 90 and 85 % of the samples in wet and dry seasons have the good quality for agricultural purposes.