Geo-electrical Delineation and Geochemical Characteristics of Aquifer Systems in Kwa-Ibo River Watershed, Abia State, Nigeria

Abstract

Kwa-Ibo River watershed of Abia State, Nigeria cuts across four Local Government Areas in the State and lies geologically within the Benin Formation of Niger Delta Basin. Due to the prolific nature of Benin Formation aquifers, preliminary investigations for groundwater exploitation are seldom done but due to the recent borehole failures and the ever increasing population density of the area, a proper documentation of the hydro-geological conditions of the area is essential. This led to a geo-electrical investigation whereby thirteen Vertical Electrical Sounding (VES) data were acquired and the computer-aided Resist software method was used for further processing and interpretation. The interpretation of the VES data reveals the existence of three to seven geo-electric layers in the area and a variation in aquifer thicknesses with the least as 101m at VES Station 4 and the highest as 324m at VES Station 2. A comparison of some geo-electric sections generated from VES stations with some lithologs gave a good geological description of the study area. Water samples were taken from eleven boreholes for hydro-geochemical investigation which reveals the occurrence of two major groundwater types in the area with Calcium+Magnesium chloride bicarbonate [(Ca+Mg)-HCO3 + SO42-Cl] dominating in the entire area except in the North-western part where Sodium+Potassium chloride bicarbonate [(Na+K)-HCO3-Cl] dominates. Further analysis shows that the geochemical processes resulting from the major geologic controls are chloride dissolution, silicate weathering, carbonate weathering and ion exchange and by using Gibb’s Diagram the recharge occurs through precipitation while the local geology is the source of major ion concentrations in the samples.