Assessement of Aquifer Vulnerabilty Near a Major Dumpsite in Goshen City, Nasarawa State, Nigeria Using Integrated Geophysical Methods

Abstract

This study utilized geophysical methods—including Vertical Electrical Sounding (VES), 2-D Electrical Resistivity Tomography (ERT), Self-Potential (SP), and Very Low Frequency-Electromagnetic (VLF-EM) to evaluate leachate migration into aquifer systems near a major dumpsite in Goshen City, Nasarawa State. The study area, located between latitudes 8°56'8.0874"N and 8°56'8.232"N and longitudes 7°40'52.1178"E and 7°40'35.241"E, comprises basement complex and sedimentary rock formations. Fifteen VES points, three 2-D ERT profiles, ten SP profiles, and ten VLF transverses were established at the dumpsite and a control site. Geophysical data were collected using an Ohmega Allied resistivity meter and a Gem VLF receiver. Data interpretation employed tools such as WINRESIST, RES2DINV, GRAPHER, SURFER and KHFFILT. These methods identified groundwater saturation zones and contamination pathways, including fractures and faults. Results identified five to six distinct layers, including Topsoil, clayey sand, weathered/fractured, and fresh bedrocks. Leachate infiltrated zones, with low resistivity values ranging from 1.6 to 35.3 Ω.m, were identified along twelve VES points, at an average depth of 15.8 m. Negative SP anomalies are attributed to leachate electro-kinetic reactions, while high positive VLF current-density in depths of 14 m are interpreted as electrical conducting paths. The percentage (80%) of the combined VES points indicating weak to poor aquifer protective capacity, suggests that the area is unsuitable for a dumpsite establishment. The study recommends continuous monitoring and the installation of geo-synthetic clay liners at the base of the dumpsite to safeguard groundwater resources from leachate infiltration.