Application of geographical information system to geoelectrical data for evaluation of the vulnerability of aquifers in parts of Bauchi, Northeastern Nigeria

Abstract

The poor quality and inconsistent nature of most surface water supply in arid and semi-arid regions of the world has increased the reliance on groundwater resources. However, the susceptibility of groundwater to anthropogenic pollution in most cities and rural communities in Nigeria has become a major source of concern. In this study, the protective capacity of the aquifers in parts of the Bauchi State, Northeastern, Nigeria, from surface contamination was investigated in light of the geoelectrical characteristics of the overburden materials for sustainable management of the resources. This study applied a geographical information system (GIS) technique to secondary geoelectrical parameters (Dar-Zarrouk) derived from 94 vertical electrical soundings (VES) to delineate aquifer vulnerability zones. Five different thematic maps (topsoil longitudinal unit conductance, total overburden longitudinal unit conductance, total transverse unit resistance, coefficient of anisotropy, and total overburden isopach) were developed. Suitable weights were assigned to the thematic maps based on their relative influence on the protection of groundwater systems in the area. Subsequently, the ranks of the subclasses of the themes were reclassified based on their respective suitability before the thematic maps were integrated using ArcGIS 10.3 software to generate the overall aquifer protective capacity map of the study area. To validate the map, water samples were collected from 40 wells and trace elements (e.g., Ni, Cu, Sb, Cr, and As) were analyzed. The study area was categorized into three aquifer vulnerability zones: moderate (32.4%), weak/fair (54.5%), and low/poor (13.1%). Moderate zones with limited portions of fair/weak zones were the predominant zones within the basement setting. This reflects the occurrence of clayey saprolitic units within the basement terrain ( 15,000 Ωm2). Over 60% of the basement settings are characterized by moderate aquifer protective capacity. On the other hand, the sedimentary zones due to weak and poor protective capacity zones are more vulnerable to pollution. The trace elemental analysis shows the predominance of As, Cu, and Sb in the sedimentary zones as compared to the basement setting which corroborates the aquifer protective capacity map produced.