Hydrogeochemical and Geophysical Investigations of Groundwater in the Umuawulu-Isiagu Area, Southeastern Nigeria

Abstract

This study integrates hydrogeochemical and geophysical investigations to evaluate the groundwater quality, aquifer characteristics, and subsurface geology of Umuawulu-Nibo-Isiagu area in Awka South Local Government, southeastern Nigeria. A combination of physicochemical analysis and Vertical Electrical Sounding (VES) using the Schlumberger array was employed to characterize groundwater quality and delineate aquifer units. The hydrogeochemical results show that groundwater in the study area is generally fresh and dominated by the Ca-Mg-HCO₃ water type, as revealed by both Piper (1944) and Durov (1948) diagrams. These facies reflect carbonate weathering, silicate dissolution, and rock-water interactions as the dominant natural processes influencing groundwater chemistry in the area. The pH and electrical conductivity, major anion and cation values fall within World Health Organization (WHO, 2022) permissible limits, indicating suitability for domestic use. However, trace metal analyses revealed elevated concentrations of lead (Pb), mercury (Hg) and cadmium (Cd) in several samples, suggesting anthropogenic contamination from waste disposal, agricultural runoff, and metal corrosion. The geophysical survey revealed a multi-layered subsurface sequence consisting of lateritic sands, sandstone, and shaly units. Correlation of VES data from six stations shows that the Nanka Formation in the Umuawulu and Nibo areas is characterized by high resistivity, water saturated sandstone aquifers with good groundwater potential, while the Imo Formation in the Isiagu area comprises low resistivity wet and silty shales, acting as aquitards with limited productivity. The aquifer depths range between 65 m and 120 m, increasing southward and eastward with lithologic transitions from sand dominated to shale dominated strata. The integration of hydrogeochemical and geophysical data demonstrates that groundwater in the area is geogenically stable and recharged through the permeable Nanka sand, but is vulnerable to surface contamination from human activities. The study recommends periodic water quality monitoring, controlled waste management, and geophysically guided well siting to ensure sustainable groundwater development in the region.