Hammadou ABDOU¹, Moustapha DINAR IBRAHIM¹*, Abdelhamid MAHAMAT ISSA², Mahamat Nour ABDELHAKH SAFI², Charles LAOKOURA³
¹Department of Geology, Faculty of Sciences and Technics, Adam Barka University of Abéché, Abéché, Chad
²Department of Chemistry, Faculty of Sciences and Technics, Adam Barka University of Abéché, Abéché, Chad
³Laboratoire de Géosciences et Développement Durable, Département des Sciences de la Terre, Université de Maroua, Cameroon
*Correspondence: Moustapha Dinar Ibrahim (moustaphadinard@gmail.com, +235 66 001394)
Abstract:
Groundwater is a vital source of drinking water in arid sub‑Saharan Africa, but its quality is threatened by both natural mineralization and anthropogenic contamination. This study assesses the hydrogeochemical and microbiological quality of groundwater in unserved urban neighborhoods of Abéché, Chad, where residents depend on shallow wells and boreholes. Sixteen samples collected in dry and wet seasons 2023 were analyzed for physicochemical and bacteriological parameters. Results show slightly basic pH (6.3-7.7), variable electrical conductivity (61-2900 μS/cm), and total dissolved solids (55-2030 mg/L), with dominant Ca-Mg-HCO₃ facies reflecting carbonate and silicate weathering. Principal component analysis (PCA) indicates that water-rock interactions (42.3% of variance) are the primary mineralization driver, followed by anthropogenic inputs (21.4% from NO₃⁻ and Cl⁻). Seasonal differences (higher EC in dry season, p < 0.01) highlight evaporation effects. Bacteriological analysis reveals 81% of samples exceed WHO limits for total coliforms (up to 1.6×10⁴ CFU/100 mL) and 38% for Escherichia coli (up to 4.32×10³ CFU/100 mL), indicating fecal pollution from nearby latrines and runoff. The chemical Water Quality Index (WQI) classifies 81% as chemically suitable, but integration of bacteriological data reduces fully safe water to 19%. Irrigation indices classify most samples as C2S1 (medium salinity, low sodium hazard), posing moderate risks for salt‑sensitive crops. Geochemical modeling (saturation indices) confirms calcite near equilibrium and gypsum undersaturation, supporting geogenic control. Findings underscore chemical acceptability but severe microbiological vulnerability, urging sanitation improvements, well protection, and low‑cost disinfection. This work provides a transparent, data‑based foundation for sustainable water management in data‑scarce arid regions, aligning with SDG 6.
Keywords: groundwater quality, hydrogeochemistry, microbiological contamination, Chad
