Vulnerability assessment of hydrogeologic units in parts of Enugu North, Southeastern Nigeria, using integrated electrical resistivity methods

Abstract

Aim/objectives: This research is geared towards integrating Vertical Electrical Soundings (VES) and Electrical Resistivity Tomography (ERT) profiles constrained with geoelectric sections and borehole logs to assess the vulnerability of the aquifer units employing Aquifer Vulnerability Indexing (AVI) method. Method: The dataset used in this study comprises of fifty VES, five ERT profiles surveyed in parts of Enugu north in Enugu state, two geoelectric sections and three borehole logs. The computer and manual interpretation of VES resistivity data using WinResist software gave values of resistivity, depth and thickness of each geoelectric layer using half current electrode spacing of 1.0 to 450.0 m and maximum current electrode spacing of 900 m. 2D imaging data from the measured field resistance values were processed using RES2DINV×32 version 3.71.115 software. The geoelectrical sections show the variation of resistivities with depth along transcent lines. The geohydraulic parameters were also estimated. Finding: Interpreted VES data revealed five to six geoelectric layers and fundamental parameters generated were used to estimate the values of hydraulic conductivity (σ) and hydraulic resistance (C) of the covering layers ranging from 0.010 to 0.769 mday −1 and 40.47 to 8292.0 day −1 respectively. This research revealed high hydraulic conductivity in the western part implying good groundwater potential with moderate to high protective capacity while areas with low hydraulic conductivity correspond to areas with high resistivity indicating little or no pore space and total devoid of water. The hydraulic resistance quantifies groundwater vulnerability using AVI and reveals that the area of study is characterized by low to high AVI with moderate AVI dominanting. Originality and novelty: The estimated geohydraulic properties from resistivity data and their spatial spread are promising and could increase the depth of knowledge on groundwater vulnerability within and around the study area.

Evaluation of groundwater repositories in parts of Enugu, Eastern Nigeria via electrical resistivity technique

“…The study area lacks abundant surface water resources resulting to increase the demand for groundwater (Uguwanyi et al 2015;Ossai et al 2020). Insufficient knowledge of the aquifer nature of the subsurface materials limits groundwater development in the area which is important for borehole construction and in several cases has resulted in unproductive boreholes, extremely low yield, total failure of some boreholes in the area and risk of spending large sum of money in sinking boreholes that will eventually be unsuccessful.…”

“…Although, groundwater generally is naturally protected from contamination, it can be unsafe owing to the susceptibility of its protective layers (McDonald et al 2005). Substantial amount of money will be needed to clean up groundwater once it is contaminated, but most times it is not feasible to achieve clean up within a reasonable time frame (Talabi & Kayode, 2019;Ossai et al 2020) because replacing contaminated sources with potable sources like treated bottled water are costly and non-comparable to that of existing ground water resources (Abdalla 1990). Notwithstanding that pumping test method is good in evaluating aquifer characteristics; it is capital intensive and consumes much time.…”

“…Electrical resistivity method is one of the best tools in geophysical investigation used for site investigation toward the determination of overburden resistivity and thickness (Kearey and Brooks 1991). Many authors proved that in order to achieve long lasting boreholes and sustainable supply of water, electrical resistivity survey should be carried out so as to identify groundwater prospective potential and good protective capacity zones for groundwater exploitation (Ezeh et al 2012;Ugwuanyi et al 2015;Mallums et al 2019;Obiora and Ibuot, 2020;Ossai et al 2020;Ochuko et al 2021). The significance of using resistivity method in geological terrains to delineate subsurface geological structures, aquifer layers and types of aquifer, thickness and depth extent is successful because of the correlation that exists between electrical properties, geologic formations and fluid contents (Ossai et al 2020).…”

“…Many authors proved that in order to achieve long lasting boreholes and sustainable supply of water, electrical resistivity survey should be carried out so as to identify groundwater prospective potential and good protective capacity zones for groundwater exploitation (Ezeh et al 2012;Ugwuanyi et al 2015;Mallums et al 2019;Obiora and Ibuot, 2020;Ossai et al 2020;Ochuko et al 2021). The significance of using resistivity method in geological terrains to delineate subsurface geological structures, aquifer layers and types of aquifer, thickness and depth extent is successful because of the correlation that exists between electrical properties, geologic formations and fluid contents (Ossai et al 2020). In groundwater exploration, the vertical electrical sounding (VES) technique is commonly used due to its proneness to near surface lateral inhomogeneities and extraneous current (stray/telluric currents), greater probing depth, well developed and more diversified interpretation techniques, lesser time and its simplicity to determine the variation of the subsurface geomaterials.…”

Integrated resistivity study on the effect of dumpsite leachate on groundwater at Ezeani-Obimo, Nsukka, Enugu state Nigeria

“…The factors that control the quality of groundwater are discharge-recharge pattern, the nature of the host and associated rocks, and natural or artificial contaminations [2]. Groundwater is constantly under threat from pollution caused by the numerous human activities in the environment impinging into the hydrological cycle [3], [4]. Wastes are disposed of at dumpsites located away from the residential areas although the reverse is the case in most areas.…”