Groundwater quality assessment for drinking and agricultural purposes under arid climate in N’Djamena, Chad (Central Africa)

The present study was carried out in the N’Djamena and Hadjer-Lamis localities (Lac Chad basin). The main objective was to examine the groundwater quality for domestic and agricultural purposes, using hydro-chemical modeling, Water Quality Index and Geographical Information System Technics. Thus, 66 groundwater samples were collected from 22 boreholes for physicochemical and biological analysis. The analytical parameters considered were: pH, electrical conductivity, Ca²⁺, Mg²⁺, Na⁺, K⁺, NH₄⁺, HCO₃⁻, NO₃⁻, F⁻, SO₄²⁻, Fecal Coliform, Total Coliform, Escherichia Coli, Fecal enterococci and Mesophyll Aerobic Flora. The results revealed that groundwater of the studied zone presents a neutrality (6.40 ≤ pH ≤ 7.57), very weakly to weakly mineralized (92 ≤ electrical conductivity ≤ 590 µS/cm) with only one water type (Ca–Mg–HCO₃), characteristic of the homogenous quaternary aquifer, the most used. The decreasing order of magnitude of the cations is as: Ca²⁺˃Mg²⁺˃Na⁺˃K⁺, while that of anions is HCO₃⁻˃Cl⁻˃SO₄²⁻˃NO₃⁻. The Water Quality Index varied from 188.41 to 866.89, corresponding to poor (9.09%), very poor (18%) and unsuitable (72%) for drinking. The poor quality is linked to the presence of bacteriological species. It should therefore be noted that groundwater in N’Djamena and Hadjer-Lamis can be used to irrigate crops, but it should be purified before being used for drinking purposes. In general, this study provides an overview of the aquifers characteristic in the Lake Chad Basin, and calls on local and administrative authorities and development partners to effectively cooperate in the permanent monitoring and preservation of the quality of this water. This would undoubtedly guarantee their sustainable and efficient management.