Delineating Saline Water Zones in an Inland Brine Area Using Electrical Resistivity Indicators (Published)
This paper presents results of saline groundwater zone delineation using electrical resistivity sounding. The geologic setting of the study area, Awe Town is that of the Biddle Benue Trough, a structure filled with Cretaceous sediments that include Awe Formation. The town is a predominantly rural area plagued with saline groundwater resulting from brines associated with Awe Formation. As a result of this challenge, water supply scheme for the area was situated about 6km away from the main settlement making access to potable water difficult. The present study was prompted by the need to delineate the extent of groundwater contamination by the brines and in so doing identify aquifers close to the settlement for exploitation. Electrical resistivity method has been applied extensively in delineation of saline groundwater zones. Electrical resistivity surveys were done around the town with the sole aim of delineating the saline groundwater and fresh groundwater regions around the settlement. A total of 20 vertical electrical soundings were carried out using the Schlumberger configuration. Geophysical indicators (longitudinal conductance and transverse resistance (S and T respectively) as well as transverse resistivity (ρt) and longitudinal resistivity (ρl)) were used to assess saline water distribution in the aquifers of the study area. Of the four indicators, Longitudinal Unit Conductance and Transverse Unit Resistance clearly demarcated saline groundwater zones. Contour maps showing the distribution of these indicators aided in the identification of fresh groundwater, 1.2km from the main town. Analysis of borehole logs in the fresh groundwater region revealed fresh groundwater aquifers within Younger rocks i.e. Ezeaku and Keana Formations, which overlie the Awe Formation. Geologic setting of the study area is such that Awe Formation is exposed in the Old Town due to uplift and weathering, while younger rocks of Ezeaku and Keana Formations overlie Awe Formation in the New Town area. Aquifers in these formations have resistivity in the range of 150 to 300Ωm, with thicknesses ranging between 20m and 35m; these zones were interpreted to have high yield potential in terms of quality.
Keywords: Groundwater, Saline, electrical resistivity, inland brine