A wetland lot geoelectrical investigation for groundwater development at Bosso Estate, Minna, Central Nigeria

Abstract

In order to carry out a geoelectrical investigation for groundwater development at a wetland lot at the Bosso Estate, Minna, Central Nigeria, the target objective (i.e. client’s property) was visually reconnoitered; the extent, local geology, and preferred traverse directions of the area of survey were noted. The survey crew proposed a southwest-southeast profile to be the longitudinal traverse (LT) at 10m-separation between survey stations and 10m-separation between profile lines for the initial low-resistance reconnaissance scheme to a depth of 15m. Thence, detailed Vertical Electrical Sounding (VES) survey would be conducted for locations of “low-ohmic interest” to a depth of 70m. In essence, this exercise was treated as a blind geoelectrical prospecting by the team members because the client had exclusive possession of the result of an earlier, independent survey conducted for aquifer prospect at this lot. On-the-field inspection of the CST dataset revealed that the lowest resistance value of 2.1919Ω was obtained at “LT3-5” corresponding to the following geographic co-ordinate: 09039’15.8”, 006030’46.6”; an arbitrary field benchmark of <3Ω was selected for this fieldwork. The survey crew based their interpretation for aquifer prospect at the VES locations on an informal and fairly successful empirical rule to determine the likely presence of groundwater in the basement complex geological province, called the “Olasehinde Protocol.” Based on this standardization, the survey crew observed the prospect for groundwater yield is encouraging at location “LT3-5.” This location is actually circa 5-6m displaced from the position of the initial survey carried out two years before as verified by the client. The survey party recommends that a borehole be sunk at this location, down to an effective depth of 50m. Really, beyond the 20m depth mark, the resistivity varies smoothly down to the total depth (TD) surveyed.