The objective of this study was to investigate the impact of anthropogenic and natural sources of contamination on the groundwater quality of the upper unconfined aquifer system of the Chad Basin around Maiduguri. This has been determined by obtaining a total of 20 groundwater samples over a 4 months period in 2 different sites (Moduganari and Gwange) in Maiduguri. Groundwater samples were analysed for pH, EC, TDS, major cations (Na+, Ca+2, K+, and Mg+2), major anions (Cl-, SO4-2, PO4-2, NO3 -, CO3- and HCO3-). Results obtained showed that the water in site 1 is alkaline (pH 6.61 to 7.57), while that of site 2 ranged from slightly acidic to alkaline (pH 6.2 to 7.31). Concentration of all the cations and anions in both sites vary significantly (p<0.05) across all the samples. Sodium, calcium, potassium, and magnesium as well as carbonate and bicarbonate concentrations in the groundwater samples analysed is as a result of natural processes such as ion-exchange processes, silicate weathering and calcium carbonate dissolution. Nitrate, chloride, sulphate and phosphate indicate the impact of above ground anthropogenic activities on the groundwater. Water quality results for both sites showed that concentration of major ions significantly fall below the WHO standard limit. In total, 75% of the water samples is Calcium-Bicarbonate (Ca-HCO3) type, while the remaining 25% are of sodium-bicarbonate (Na-HCO3) type.
Key words: Groundwater quality, Maiduguri, contamination, major ions.
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