HYDROCHEMICAL CHARACTERIZATION OF GROUNDWATER IN THE CONTINENTAL TERMINAL AQUIFER OF MOUNDOU AND ITS SURROUNDINGS (SOUTHWEST CHAD)

Our study aims to characterize the physicochemical and bacteriological parameters of the groundwater of the city of Moundou and its surroundings. These waters of this locality, contained in formations of the continental Terminal, are made up exclusively of sand and sandstone. Two campaigns carried out in December 2023 and March 2024 made it possible to collect sixty (60) samples. Forty (40) samples were used for physicochemical analyses (iron, zinc) and twenty (20) for bacteriological analyses (fecal and total coliforms, total aerobic mesophilic flora, Escherichia coli and total germs). The results of the physicochemical parameters indicate that these waters are acidic (average pH value between 6.3-6.94), and that their mineralization has an origin resulting from both natural and anthropogenic factors. The maximum values of potassium (93.09 mg/l in low water and 56.28 mg/l in high water) and silica (54.92 mg/l and 43.97 mg/l respectively in low and high water) are mostly higher than the WHO standard (2017). The maximum nitrate content is 44.19 mg/l (low water) and 39.09 mg/l (high water). That of nitrite and phosphate are respectively 2.39 and 2.73 mg/l in low water on the one hand, and 2.89 and 2.016 mg/l in high water on the other. The evolution of the concentrations of pollutants (nitrate, nitrite and phosphate) suggests an anthropogenic involvement in the degradation of groundwater although the nitrate content in all the waters analyzed is in accordance with the WHO standard (2017) for water intended for human consumption. These levels, although in accordance with the WHO standard (2017), suggest an anthropogenic implication because they sometimes exceed the natural contribution. The groundwater in the study area is dominated by the calcium and magnesium bicarbonate facies, followed by the calcium and magnesium chloride and sulfate facies. The GWQI values vary from 19.37 to 78.48, indicating that these waters are excellent and of good physicochemical quality for human consumption, although the mineralization results from anthropogenic action. However, the bacteriological study shows that the waters of the surface and deep aquifers are of poor quality and imperatively require filtration and disinfection before any consumption.