TAGRA 2025

This study evaluates groundwater vulnerability and contamination in Osubi and surrounding communities, Delta State, Nigeria, using an integrated geophysical, hydrogeological, and geochemical approach. The investigation combined 1D, 2D, and 3D electrical resistivity surveys (21 Wenner–Schlumberger profiles and 38 VES), ten MASW seismic traverses, hydrogeological data from fifty hand-dug wells, and laboratory analysis of eleven water and fifteen soil samples. Geoelectrical parameters—including longitudinal conductance, transverse resistance (TR), longitudinal (PL) and transverse resistivity (PT), coefficient of anisotropy (COA), hydraulic conductivity, and transmissivity—were analyzed to assess aquifer integrity and protective capacity. Longitudinal conductance (9.6×10⁻⁵–0.159mhos) indicates predominantly poor to moderate overburden protection, suggesting vulnerability to downward contaminant migration. TR, PL, and PT values reveal largely coarse-grained, resistive lithologies consistent with permeable, hydraulically active aquifer systems. COA (0.12–2.00) reflects a mix of homogeneous sands and heterogeneous sand–clay sequences driven by natural depositional variability. Hydraulic conductivity (0.122–3.481m/day) and transmissivity (0.43–67.18m²/day) further confirm moderate to high groundwater potential, particularly around VES 17–20. Localized low-resistivity zones (<50Ωm) at VES 19, 20, 22, 24, and 35 suggest possible shallow contamination. Inverted 2-D and 3-D resistivity models (RMS error 7.29%) show subsurface resistivities generally above the contamination threshold (<40–50Ωm), indicating an overall uncontaminated groundwater system. MASW results delineate a three-layered sequence comprising a loose topsoil, a semi-compacted transition zone, and a deeper saturated aquifer, with limited confining layers that enhance vertical infiltration and aquifer vulnerability. Geochemical indices indicate low to moderate pollution, with notable hotspots near PTI Skills, WOJ-30, and Government Land. PCA and correlation analyses attribute metal enrichment primarily to anthropogenic activities including vehicle emissions, industrial effluents, waste disposal, and agriculture. While groundwater metal concentrations mostly remain within acceptable limits, health-risk assessments highlight greater susceptibility in children, particularly from Pb-, Cd-, and Cr-exposure. Overall, integrated results underscore vulnerable but largely uncontaminated groundwater system requiring continuous monitoring and targeted mitigation.