Hydrogeophysical Delineation and Hydrogeochemical Characterization of the Aquifer Systems in Umuahia-South Area, Southern Nigeria

Abstract

In Umuahia-South Local Government Area of Abia State Nigeria, some cases of boreholes failure and groundwater discolouration have been observed. An investigation in order to determine the hydrogeological conditions of the area was carried out using geoelectrical, drill-hole and hydrogeochemical data. Using the Schlumberger electrode configuration, ten vertical electrical sounding data were acquired and the computer-aided Resist software method was used for further processing and interpretation. The interpretation of the VES data obtained from the study area shows that the vicinity of VES station 1 is likely to record failure in borehole exploration. A high variation in aquifer thicknesses is observed with the least as 27m at VES Station 5, and the highest 226m at VES Station 3. A new approach was used in the estimation of aquifer hydraulic parameters such as hydraulic conductivity and transmissivity. Some geoelectric sections generated from VES stations were compared with some lithologs which gave a good geological description of the study area; thereby revealing a multi-aquifer hydrogeologic system. Water samples were taken from ten boreholes for hydrogeochemical investigation which reveals the occurrence of same geochemical process; but slightly varying water quality which is associated to the multi-aquifer status of the area. The discolouration of water observed in some boreholes owes its origin from the silty-sand aquiferous units with slightly high iron content. A further analysis of the samples when plotted on Gibb's Diagram reveals that recharge occurs through precipitation, but the local geology of the area is the source of major ion concentrations in the samples.