Hydro-Chemical and Bacteriological Assessment of Groundwater in the City of Djara and Surrounding Areas (Kanem-Chad)

Abstract

This study aims to assess the hydrochemical processes and the physicochemical and bacteriological quality of groundwater in the city of Djara and its surrounding areas. Hydrochemical analysis, performed using Piper diagrams, revealed that 94.11% of the samples exhibited a sodium sulfate (Na-SO4) facies and 5.89% a sodium bicarbonate (Na-HCO3) facies. Additional analytical tools, including Gibbs diagrams, Gaillardet plots, and binary diagrams, indicate that groundwater chemistry is primarily controlled by interactions with aquifer materials, particularly silicate weathering and cation-exchange processes. The results show that the groundwater has a moderate level of mineralization. Iron concentrations range from 0.1 to 4.55 mg/L, with more than half of the samples exceeding the WHO guideline limit for drinking water (0.30 mg/L). The affected boreholes, distributed throughout the study area, represent 58.22% of the analyzed samples. This elevated iron content is likely linked to drilling equipment, especially metallic pipes, which can release iron into the groundwater and result in concentrations above the WHO limit (<0.3 mg/L). The analysis of sodium content (%Na) in groundwater shows high sodium concentrations, placing the water in the categories of "excellent," "acceptable to doubtful," and "doubtful" for irrigation. High concentrations can affect stomatal function, water uptake, and photosynthesis in plants. The evaluation based on the Sodium Adsorption Ratio (SAR) and Electrical Conductivity (EC) shows that the samples belong to the C1-S1, C2-S1, C3-S1, and C3-S2 classes, indicating a high risk of salinity and an alkalinity risk ranging from low to high. This suggests the adoption of specific management practices, such as selecting salt-tolerant crops to ensure sustainable irrigation. Bacteriological analyses revealed that 100% of the samples tested positive for total coliforms and aerobic flora, while the presence of Escherichia coli (E. coli) and fecal enterococci varied. In accordance with drinking water quality standards, this groundwater is unsuitable for human consumption, as the detected bacterial levels exceed the WHO requirements, which stipulate the absence of bacteria in 100 mL of drinking water.