Electro-sequence valorization of specific enablers of Aquifer vulnerability and contamination: a case of index-based model approach for ascertaining the threats to quality groundwater in sedimentary beds

Abstract

Evidently, sedimentary basins have a large potential for groundwater. However, the main issue has been the aquifer system's susceptibility to contamination coming from both anthropogenic and natural sources. This research was designed with the intention of valorizing the unique enablers of aquifer vulnerability and the ensuing pollution of economical and accessible aquifers using an index-based technique. On the basis of this obsession, this research was carried out to appraise the quality of the groundwater depository systems in the mapped area, which was chosen to be near a newly established university. The study used geo-electrical technology to evaluate the lithological sequence of the hydrogeological units and their first and second-order geo-electric properties, as well as the significant geochemical constituents of groundwater. The outcomes of using vertical electrical soundings with geo-electrical technology showed that the hydrogeological units are composed of sequences of sands prograding from finer to medium and medium to gravelly sands, minimally laced within sandy clay, according to the results of geo-electrical technology using vertical electrical soundings (VES). Layers 2 and 3 were accessible by the twenty VES (V1-V20), which gained access to designated economic and prospective aquifer systems. The ranges of resistivities for layers 1 to 4 gave 21.0 - 2872.3 (mean: 729.1 ), 26.3 – 3576.5 (mean: 746.3 ), 58.0-3588.8 (mean: 840.5 ) and 30.6 -921.7 (mean: 281.7 ) correspondingly. In respective order, layers 1 to 3 with defined depths and thicknesses ranged from 0.8 -40.0 m (7.5 m), 0.8 -83.6 m (69.1 m) and 55.0 -245.4 m (106.4 m) and 0.8 -40.0 m (7.5 m), 2.9 – 40.0 (61.7 m) and 26.7 -212.1 m (80.0 m). The aquifer systems considered have resistivity values ranging from 26.3 -3576.5 and mean value of 832.97 The five vulnerability models deployed showed very high spatial variability and moderate negative and positive correlations construed to be due to subjectivity in the weight-rate assignment. The coefficients of variation (CV) from sensitivity analysis (SA) indicated a relatively elevated contribution to the variation of the vulnerability index due to topography (9.7%) and the impact of the vadose zone (4.3%), which are marginally higher than the 1.6% displayed by other parameters. The groundwater displayed WHO’s disallowed concentrations of heavy ions, and the SA indicated that CV for the groundwater geochemical contamination is highest in cadmium ions (140.9%) followed by manganese ions (132%) and copper ions (88. 2%) across the wells. The moderate contribution distributions across the wells are nickel ions (48.8 %), lead ions (41.6%), chromium ions (39.8%) and iron ions (35.0%). All the realized geophysical and geochemical indices affirm that the groundwater is vulnerable and contaminated, and therefore, proper monitoring and management of resources is required.