Hydrogeophysical Characterisation of Aquifer Systems and Groundwater Quality in Gully Erosion-prone Communities of Orlu, South Eastern Nigeria

Abstract

This study characterised aquifer systems and evaluated groundwater quality in twelve gully erosion-prone communities of Orlu, Imo State, Nigeria, through integrated hydrogeophysical and hydrochemical methods. Twelve vertical electrical soundings using the Schlumberger configuration delineated aquifer geometry and provided hydrogeophysical parameters, while groundwater from twelve boreholes was analysed for physicochemical properties, major ions, and selected heavy metals. Aquifers occurred at depths of 28.9–49.2 m, with thicknesses of 33.5–56.3 m and resistivities of 624–931 Ωm. Transmissivity ranged from 281 to 681 m²/day, indicating moderate to high groundwater potential. Most physicochemical parameters satisfied drinking-water guidelines, although some samples were slightly acidic (pH 5.91–6.91). Iron (0.36–0.66 mg/L) and lead (0.010–0.019 mg/L) exceeded recommended limits at several locations. Calcium–bicarbonate facies predominated, indicating the influence of silicate weathering. Water Quality Index values ranged from 41.3 to 82.4; 41.7% of samples were classified as excellent and 58.3% as good. Heavy Metal Pollution Index values exceeded 100 at Ihioma, Ebenese, and Umuzike. Correlation, principal component, and cluster analyses indicated that groundwater chemistry was governed mainly by groundwater–rock interaction and mineral weathering, with localised trace-metal mobilisation associated with gully erosion. The aquifers are productive, but targeted monitoring and treatment are warranted in the affected communities. The integrated assessment provides a baseline for groundwater management in erosion-prone sedimentary environments.