Aquifer Characterization and Groundwater Potential Assessment of the Sedimentary Basin of Ondo State

Abstract

The sedimentary basin of Ondo State, underlain by the Coastal Alluvium, Coastal Plain Sands, Imo Shale Group, Upper Coal Measures and Nkporo Shale, was investigated using integrated electrical resistivity and borehole lithologic logs with a view to characterizing the aquifer and assessing the groundwater potential. One hundred and four Vertical Electrical Soundings (VES) were quantitatively interpreted using the partial curve matching technique and computer assisted 1-D forward modeling. Fourteen (14) borehole lithologic logs were used to generate columnar sections from which aquifer units were delineated. Geoelectric sections were generated from the VES interpretation results, constrained by borehole lithological logs, for aquifer identification and geoelectric parameter determination. Depths to top and thicknesses of the aquifer units within each geologic unit were determined. Four aquifer units were identified within the Coastal Alluvium/Coastal Plain Sands. The depths to top/thicknesses of the aquifer units were 5–23 m (7–26 m); 7–80 m (6–67 m); 63-188 m (20-143) and 245–261 m (61–117 m) respectively. Within the Upper Coal Measures, two aquifer units were identified. The depths to the top/thicknesses of the aquifer units were 9.8 m (1.7 m) and 23 m (5.3 m) respectively. The Nkporo Shale had depth to top and thickness of the only identified aquifer unit as 10 m and 16 m respectively. The study concluded that the groundwater potential of the Coastal Alluvium and Coastal Plain Sands was high while the groundwater potential of the Imo Shale Group, the Upper Coal Measures and Nkporo Shale was adjudged low.