Geology, Geophysics and Hydrogeochemistry of Nanka and Its Environs, Southeastern Nigeria, for Sustainable Groundwater Resource Management

Abstract

This research work, presents an integrated geological, geophysical, and hydrogeochemical investigation of groundwater occurrence and quality in Nanka and its environs, located in Orumba North Local Government Area of Anambra State, Southeastern Nigeria. Increasing pressure on available water resources due to population growth and rural development necessitated a comprehensive evaluation of groundwater potential in the area. The study integrates geological field mapping, Vertical Electrical Sounding (VES), and laboratory-based water quality analyses to characterize aquifer geometry, lithology, and hydrochemical suitability. Geological mapping reveals that the area is predominantly underlain by the Eocene Nanka Formation, consisting of poorly consolidated, friable, medium to coarse-grained sands interbedded with shale and claystone units. These lithologies exert strong control on groundwater occurrence, storage, and vulnerability to erosion. Five VES stations were occupied using the Schlumberger array configuration to delineate subsurface stratigraphy and aquifer characteristics. The interpreted geoelectric sections show multilayered subsurface conditions comprising topsoil, dry sand, clayey sand, water-saturated sand, and shale. Aquifer units were identified at depths ranging approximately from 46 m to 146 m, with resistivity values between 289 Ωm and 3940 Ωm, indicating predominantly unconfined sandy aquifers of moderate to high transmissivity. Hydrochemical analysis of groundwater and surface water samples shows that while most physicochemical parameters fall within acceptable limits, certain trace metals such as iron (1.0020-1.2803 ppm), copper (0.143-0.243 ppm), and nickel (0.034-0.045 ppm) exceed recommended standards in some locations. The study confirms that groundwater potential in the area is significant but requires quality monitoring and treatment before domestic consumption. The integrated approach adopted in this work demonstrates its effectiveness in reducing uncertainty in groundwater evaluation and supports sustainable resource management in erosion-prone sedimentary terrains.