APPLICATION OF ELECTRICAL RESISTIVITY METHOD FOR THE EVALUATION OF GROUNDWATER POTENTIAL IN EKPOMA AND ITS ENVIRONS

Abstract

The problem of acute water shortage resulting from failed or nonproductive boreholes in the study area particularly the University town of Ekpoma has persisted over the years. Attempts to solve the problem have remained futile. However, a nearby community of Irrua, despite not being far from Ekpoma, is not facing the problem as many boreholes located in the area are functioning. Consequently, attempt is made in this study to holistically evaluate the groundwater potential of the area and also to account for the reasons why Ekpoma is experiencing groundwater scarcity whereas a nearby community of Irrua is always having water. To achieve the objectives of the study, thirty six (36) Vertical Electrical Soundings (VES) using Schlumberger Electrode Array Configuration were carried out across the study area with maximum electrode separation (AB/2) of between 5m-550m. Five geo–electrical layers were delineated and these were: Top soil, Clayey Sandstone, Sand, Consolidated sandstone and Unconsolidated Sandstone. The Unconsolidated sandstone layer constituted the aquifer units in the area depth to which ranges between 93 m and 258 m and resistivity values which ranges from 219.9- 781.4m which are found within the Bende–Ameki formation. It was established from this study that there is a very good indication/evidence of saturation of the aquifer delineated in the Bende–Ameki Formation around Irrua with highly porous and permeable materials overlying it thus explaining the highly productive wells and boreholes in the region. On the contrary, the aquifers delineated in and around areas of Ekpoma community are characterized by relatively high resistive values suggestive of less saturation and are equally overlain by less porous and permeable materials and this accounts for the reason why Ekpoma (located within Bende-Ameki and Ogwashi Asaba Formations in the central part of the study area is having perennial groundwater shortage). The shallow aquifer units in the study area are found to be relatively thin with most of them having thickness less than 30 m, making them less sustainable for long term groundwater abstraction, resulting in the failed boreholes in most parts of Ekpoma community. The study concludes that the groundwater prospects of Ekpoma and its environs is low and deep boreholes reaching a minimum depth of about 150 m should be sited because it is sustainable due to its considerable thickness to cater for the inhabitants of Ekpoma community and its environ.