Hydrochemical characterization of groundwater under agricultural land in arid environment: a case study of Al-Kharj, Saudi Arabia

This study focuses on chemical analysis of 180 different groundwater samples in Al-Kharj governorate, Saudi Arabia. The distribution of chemical constituents (major, minor, and trace elements) is determined and compared with drinking and irrigation water standards. The water quality index (WQI) is applied to investigate groundwaters suitability for drinking. The obtained results indicated that the concentrations of dissolved salts, soluble cations and anions, and nitrate, were above permissible limits set by drinking water standards, WHO, for most wells. The WQI concluded that 65.2 % of studied wells arc considered poor water "class (III)", 24.9 0 are very poor water "class (IV)", 6.1 % arc unsuitable water for drinking "class (V)", and only 3,9 % are good water for drinking or "class (II). Most groundwater is contaminated with nitrate with an average concentration of 14.7 mg L-1. The water evaluation for irrigation poses that 69.4 % of studied wells are classified as moderately saline; however, the remaining are classified as severe saline water. The US Salinity Laboratory's diagram reveals that majority of studied waters fall in class C4-S1, the area of very high salinity and low sodium hazards. Durov and Piper diagrams revealed that the majority of investigated waters are magnesium-calcium/sulfate chloride water type. The Gibbs's diagram revealed that the chemical weathering of rock-forming minerals and evaporation are influencing the groundwater quality. The hydrochemical modeling indicates that all water samples are undersaturated for halite and saturated for anhydrite and gypsum. The approach of this research could be applicable to similar situations worldwide.