Vertical Electrical Sounding for Aquifer Characterization around the Lower Orashi River Sub-Basin Southeastern Nigeria

The different aquifer units within the Lower Orashi River Sub-Basin Southeastern Nigeria were delineated using the Vertical Electrical Sounding (VES) technique. Twenty two (22) VES soundings were carried out using the ABEM SAS 4000 Terrameter. The data generated were analyzed using the Zohdy software which outputted modeled curves in terms of depth and resistivity. Six profiles were taken in the Northeast–Southwest and Northwest–Southeast directions to cover the entire area of study. Four to six geo-electric layers comprising the top soil, clayey sand, dry sandstone, saturated sandstone, shaley sand and sandy shale were delineated with the later usually occurring as the last layer. The third and fourth layers underlying dry sandstone form the aquiferous unit. This unit was found to have an average resistivity value range of 10.7 – 6060Ωm and an average thickness of 32m. It was observed that most of the aquifer units within the area are unconfined with static water level varying between 10.6 to 62.8m. Some of the aquifer units are shallow with static water level less than 40m while others are deeper with static water level occurring at over 60m below the surface. It was advised that care ought to be taken in drilling and casing at shallow aquiferous areas to maintain proper sanitary condition so as to reduce the risk of groundwater contamination.