Evaluation of groundwater quality in the Takelsa basin (Northeastern Tunisia) for irrigation and drinking suitability using water quality index

Abstract

Abstract Groundwater serves as a vital freshwater resource in various regions worldwide. However, the combination of climate change, population growth, intensive agricultural and industrial practices, as well as the proliferation of drilled water wells, has resulted in declining water table levels and deterioration in physico-chemical water quality. This study aims to investigate the hydrogeochemical parameters (concentration of major ions: magnesium (Mg), calcium (Ca), potassium (K), sodium (Na), bicarbonate (HCO3), nitrate (NO3), sulfate (SO4), and chloride (Cl)), pH, Total Dissolved Solids (TDS), and electric conductivity (EC)) to discern the main geochemical processes and origin of groundwater salinity. The findings from the analysis of groundwater samples indicate the prevalence of Na-Cl and Cl-SO4-Ca facies. The mineralization of water is influenced by the dissolution of evaporites (halite, anhydrite, and gypsum), anthropogenic activities (nitrate contamination), and ion exchange processes. Moreover, the Water Quality Index (WQI) calculated from the percentage of sodium (%Na) and the Sodium Adsorption Ratio (SAR) demonstrates that the groundwater in the Takelsa basin is suitable for irrigation purposes but unsuitable for drinking. Furthermore, detailed geological mapping of the Takelsa basin, along with comprehensive field lithostratigraphic cross-sections, has enabled the following outcomes: 1) determination of a new basin structure; 2) identification of various water reservoirs within the Saouaf formation; and 3) characterization of aquifer geometry and features.