Abstract

Onicha Olona, Atuma Iga and Akwukwu-Igbo have experienced severe hardship in getting reliable boreholes over many years due to their high topography. They are transition towns as it is from here that marked variations in subsurface structures and topography commence. Although the entry point at onicha Olona which is tied to Issele Uku is a flat land by contouring, the western end of the town has evidence of intermittently occurring deep valleys. It is important to study and ascertain the formation strata and groundwater occurrence in these towns. Hence, this study was made in Onicha Olona, Atuma Iga and Akwukwu-Igbo Delta State Nigeria. Seven vertical electrical sounding (VES) stations were sounded using Schlumberger configuration. The apparent resistivity values obtained in the field were plotted against half current electrode spacings. Interpretations of data were done qualitatively and quantitatively from which seven to eight layers with complex curve types of HAK, HAH, HK, QHK, QKHK, HKHKQ and QHKHA were mapped. Parches of springs from faults in the weathered rocks within the valleys at depths of about 30 m and low yield aquifers at depths of 125 m and beyond are delineated in Onicha Olona. Akwukwu-Igbo and Atuma Iga have sustainable aquifers at depths of 85 to 105 m due to topographic variation.

Key words: Formation strata, Schlumberger, apparent resistivity, aquifer, topographic variation.