Application of Hydro-geophysical Methods for Subsurface Stratigraphy and Aquifer Characterization in Sedimentary Terrian: A Case Study of Sabongida-Ora, Edo State, Nigeria

Abstract

Understanding subsurface geology is a premise to aquifer characterization. Five (5) Vertical Electrical Sounding (VES) and a 2D Wenner Electrical Resistivity Tomography (ERT) were carried out to image the subsurface for geologic (stratigraphic) characterization of the study area, in bid to delineating zone(s) characterized with high porosity and permeability as well as  saturated with sufficient groundwater for exploitation. The field equipment used was ABEM SAS1000 resistivity meter and accessories. The maximum spread obtained for half current separation distance (AB/2) for the VES (with six stations per decay) was 450.00m. The profile length of the ERT was 300m, with unit electrode spacing of 5m. Conventional field and computer assisted data interpretation techniques were observed with final interpreted model relative to altimeter elevation presented after data were subjected to processing to reduce noise effect. The interpreted models were corroborated with borehole data for parametric sampling. Findings showed existence of a perched water (aquifer) within a window depth of 15m to 35m (50ft - 120ft) followed by a claystone (clay unit) of about 100m to 130m (320ft to 400ft) and finally, deep seated confined aquiferous unit at depth of investigation beyond 240m (845ft) was captured.