Using the Electrical Resistivity Method to Assess Groundwater Iron Concentration in Otuoke and Environs (Nigeria)

Abstract

The resolution of subsurface structures using the electrical method is often beclouded by uncertainty due to geophysical similarities in the behaviour of earth materials. Thus the integration of techniques aimed at constraining the level of uncertainty. This was archived in this study using a combination of electric method, geochemical analysis and in-situ borehole login samples. 8 vertical geoelectrical soundings, 8 groundwater samples and 1 borehole log were analyzed with the aim of lithostratigraphic mapping of shallow sediments to identify aquiferous formations and to infer the spectral variation of iron concentration levels. From the results, two layers were delineated; a clay topsoil with a maximum depth of 0.5 m to 1.3 m, resistivity range of 15.8 Ωm to 112 Ωm and a coarse sand aquiferous layer encountered at a depth of 1.7 to 3.5 m with a resistivity of 84.5 Ωm to 225 Ωm both separated by a transition zone of sandy-clay, which becomes fine sand with depth, identified on the geoelectric section with a resistivity range of 12.5 Ωm to 74.5 Ωm occurring at depth 0.5 m to 1.3 m with a maximum thickness of 2.2 m. High iron concentration levels were observed to correlate with low resistivity values and vis-vaser, which agrees with empirical facts, that the electrical conductivity of porous mediums at shallow depth is principally a function of pore fluid conductivity which by extension the concentration of conductive minerals in groundwater.