Spatio-Temporal Assessment of Groundwater Quality in the Town of Moundou in South-Western Chad

Assessment of groundwater quality is becoming essential for effective resource management. In this study, we conducted a seasonal assessment of groundwater quality, hydrogeochemical processes, and statistical analyses in the city of Moundou. A total of 62 groundwater samples were taken in the 27 districts of the city, in August 2022 (rainy season) and May 2023 (dry season), respectively. From a geochemical point of view, the results highlighted two dominant geochemical facies in both the dry and wet seasons: the calcium-magnesium bicarbonate facies (Ca-Mg-HCO₃) and the sodium-potassium bicarbonate facies (Na-K-HCO₃). The multivariate analysis showed that the mineralisation of gypsum (CaSO4 · 2H2O), CaCl2 salts, silicates, carbonates and the decomposition of organic matter are the main processes affecting the quality of Moundou’s water. The physico-chemical results show that of the parameters monitored, only pH, iron and ammonium do not comply with the WHO standard, and almost 89% of the sites sampled are considered acceptable according to QWI values. Only the sites in the north-east of the city showed poor water quality during the rainy season. On the whole, this water is of better quality for irrigation.