A Wet-season Geoelectrical Investigation for Groundwater Development at a Built-Up Property at the Western Bye-Pass, Minna, Nigeria

Abstract

In the desire to explore approaches that are not generally conventional, but ones that have good foundational basis, a wet-season geoelectrical investigation for groundwater development at a built-up property at the Western Bye-Pass, Minna, Nigeria, was planned and completed. The client had already commissioned a dry-season spell survey at the same built-up property, but the result was not known to the present survey crew beforehand. The result of the present endeavour would be essentially corroborative. The vertical electrical sounding (VES) mode of the resistivity type of geoelectrical survey employing the Schlumberger array was the preferred format for this exercise. The survey schedule was to do VES to a total depth of 100m, where possible, although that depth is well beyond the effective water-bearing subsurface environment and into the local bedrock proper. Nonetheless, the built-up nature of the neighbourhood of the survey locations precluded the 100m-target. In interpreting for possible locations of groundwater, two constraints are used, viz: the “ideal” log-log plot and the “Olasehinde Protocol:” such a log-log plot must have almost all plotted points alternately “rising-and-falling” along the curve and the Olasehinde Protocol states that resistivity values between 180Ωm and 250Ωm at the 20m to 25m depth mark is indicative of possible groundwater prospect. Only the third and last survey location approximates these impositions at the 20m - 30m depth mark with a smoothly-varying resistivity profile observed to the 40m depth mark, and its corresponding plot indicates a three-layer sequence. Based on the imposed constraints, the survey crew posits that the location of latitude 09°39′36.2′′and longitude 006°30′30.2′′ is the best prospect location identified from this survey. If drilling must be done at all, the survey crew recommended that this location should be drilled to a total-depth (TD) of 50m.