Hydrogeochemical characteristics and source identification of salinity in groundwater resources in an arid plain, northeast of Iran: implication for drinking and irrigation purposes

Groundwater salinization is a worldwide problem where groundwater is the principal source of water. A combination of geochemical and statistical approaches was used to investigate the mechanisms governing the groundwater chemistry and origin of salts in the Neyshabour aquifer (north-eastern Iran). The mean values of Mg2+ (61.4 mg/L), Na+ (553.2 mg/L), Cl- (800.4 mg/L), SO4 2- (428.7 mg/L), EC (3404 μS/cm), TH (525.0 mg/L) and TDS (2212.8 mg/L) in 55 groundwater samples taken from deep wells were higher than WHO and ISIRI guideline values. Geochemical and multivariate statistical analysis suggested that: i) the dissolved solids in the water samples are controlled mainly by geology, and ii) Na-Cl and Na-HCO3 type waters are dominant in the area. Besides the water-rock reactions (e.g., evaporites dissolution), groundwater salinity in Neyshabour aquifer has been intensified by irrigation return flows and groundwater level decline. The chemical weathering of mafic and ultramafic rocks in ophiolitic rocks is responsible for Mg enrichment in the majority of samples. Water quality index (WQI) and different indices calculated for the groundwater samples indicated that the most of them have poor water quality for drinking and agricultural uses especially in the southern, central and western parts of the plain.