Geophysical Evaluation of the Impact of Solid Waste Dumpsite on the Groundwater in Ilokun, Ado-Ekiti, Southwestern Nigeria

Abstract

An investigation was carried out at the Ilokun dumpsite in Ado-Ekiti with the intention of converting it into a sanitary landfill. The goal was to determine the potential impact of the liquid waste draining from the dumpsite on the underground water sources. The study utilized the Vertical Electrical Sounding (VES) field technique, which measures the electrical resistivity, with the spacing between half-electrodes (AB/2) ranging from 1 to 65 meters. Three VES stations were set up for data collection, while a control VES point was established outside the dumpsite. The VES data were then quantitatively analyzed through methods such as partial curve matching and computer iteration. The dipole-dipole electrode configuration was also employed to carry out investigation on the dumpsite. The data acquired in this study was inverted using DIPRO software to generate 2-D resistivity structures. The geological layer below VES 1 was recognized as the aquiferous zone, although its remarkably low resistivity of 12 ohm-m was interpreted as an indication of pollution from a conductive contaminant plume. The geoelectric profile beneath VES 1 to 3 revealed the presence of five distinct layers, which are the topsoil, the lateritic sand, the weathered layer, the fresh basement, and the fractured basement. The resistivity and thickness of these layers vary within certain ranges: 61.8–933.6 ohm-m and 0.5–1.5m; 23.5–664.7 ohm-m and 0.6–2.7m; 12–177 ohm-m and 3 –16.9m; and 2356.6–4800.2 and 16.3-33m; and 34.7-146.4 ohm-m respectively. The fractured layer observed in the three VES points is considered the primary aquifer zone. However, the abnormally low resistivity values ranging from 34.7 to 146.4 ohm-m within the fractured layer beneath VES 1 and 3 are believed to be indicative of contamination caused by a conductive plume of pollutants originating from the dumpsite. The 2-D resistivity structures also confirm that the dumpsite is posing a serious threat to the surrounding formations and groundwater especially those located along the east-west direction of the dumpsite. The potential of leachate accumulation is relatively higher along the east-western axis.