ABSTRACT

Geo-electrical resistivity techniques are increasingly being applied in addressing a wide range of hydrological, environmental, and geotechnical problems. This is due to their effectiveness in near-surface characterization. Seven (7) vertical electrical soundings (VES) was integrated with 2-D geo-electrical resistivity in three locations and three traverses to characterize the near-surface and subsurface and also delineate the underlying aquifer properties in the sedimentary terrain. The geophysical survey was conducted as part of preliminary studies to evaluate the possibility of groundwater resource contamination in Ogba-Iyo, Ijoko, South-western Nigeria. The Vertical electrical sounding (VES) and two-dimensional (2-D), direct-current ERT methods employed identified resistivities less than 10 ohm-meters, deep in the subsurface, along the 7 VES points and the 2-D resistivity profile lines within the site. Data with resistivity values of below 10 ohm-meters were considered to be anomalies and were interpreted as possible areas of salt contamination/intrusion. Data from the resistivity lines indicate deeper subsurface salt contamination. The two 2-D profile lines located towards the north of the study area, yielded data indicating no salt contamination at a depth of 16m-25m, while the saltwater contamination occurs at a depth greater than 30m. Data from resistivity profile line 1, trending South-East/North-West across the site, identified an area of possible salt contamination at the subsurface, approximately 35 in depth. Resistivity line 2, trending south to north across the study area also indicated an area of possible salt contamination at the subsurface, approximately 25 in depth.