DELINEATION OF SUBSURFACE LITHOLOGY AND AQUIFER STRUCTURES USING ELECTRICAL RESISTIVITY SURVEYS IN PARTS OF UKWUANI LOCAL GOVERNMENT AREA OF DELTA STATE

This study investigates aquifer structures and properties in Ukwuani Local Government Area, Nigeria, using Vertical Electrical Soundings (VES) with Schlumberger and Dipole- Dipole configurations. The Schlumberger were conducted at Obiaruku (VES 1–6), Obinomba (VES 7–12), Umutu (VES 13–15), and Umuaja (VES 16–18), employing an ABEM SAS 1000 Terrameter for data acquisition. Interpretation was done using WinResist for VES and Dipro Software to generate 2D resistivity images, vertical profiles and delineate subsurface formations and aquifer zones in the study area. Near-surface high resistivity values of 200 to 1000 ohm-m corresponding to compact topsoil, transiting to clayey sands and laterite layers with moderate resistivity, indicating varying clay content and moisture retention. Deeper layers in Umutu and Umuaja exhibit high-resistivity coarse sands, highlighting viable groundwater formations. In contrast, stations located in Obiaruku and Obinomba predominantly show medium-grain sand and clay layers. The Dipole-Dipole survey further delineated profiles showing unconsolidated, moisture-bearing topsoil transitioning to dense, low-permeability formations. The first two layers in Obiaruku with resistivity values of 116–145 ohm-m, suggest the presence of shallow aquifers, while deeper layers characterized by resistivity values of 581–930 ohm-m consist of gravels that serve as confining layers. This geophysical approach identified promising aquifer zones in upper layers and thick sand formations which are conducive to groundwater storage and flow. These findings provide valuable insights for sustainable groundwater exploration and management in Ukwuani Local Government Area.