Geo-electrical prognosis of aquifer protectivity, corrosivity, and vulnerability via index-based models within a major coastal milieu

Abstract

AbstractThis work was carried out to investigate the protective capacity, vulnerability, and corrosivity within a major coastal milieu in Southern Nigeria with the use of index-based geo-electrical modeling methods. Vertical electrical soundings were undertaken at twenty locations with the aid of Schlumberger array having a maximum electrode spacing of 400 m. The results indicated that the lithology comprised four subsurface layers having variable values of resistivity and thickness. The Dar-Zarrouk parameter, the Aquifer Vulnerability Index (AVI), and the GOD (Groundwater occurrence G, Overlying lithology O and Depth to aquifer D) models were employed to appraise measures of aquifer protectivity and vulnerability to contamination. The longitudinal conductance values ranged from 0.0071–1.95 mhos with a mean of 0.32 mhos, indicating moderate protectivity. AVI values ranged from 1.73–4.10 with a mean of 3.03, indicating moderate aquifer vulnerability. The GOD indices ranged from 0.35–0.63 with a mean of 0.49, indicating moderate aquifer vulnerability. Corrosivity was also computed based on topsoil resistivity values which ranged from 12.7 to 664.2 Ωm with a mean of 168.17 Ωm, indicating moderate corrosivity, and demonstrating the unsuitability of corrosive locations for laying underground pipes. All the index-based models gave similar interpretations, indicating moderate aquifer protectivity and susceptibility. These results were corroborated by 2D electrical resistivity tomography surveys conducted at four stations. This work has therefore delineated important aquifer geo-hydraulic properties with index-based geo-electrical modeling techniques. The results obtained are critical for effective aquifer management, conservation, and sustainability.