Investigation of Leachate Plume and Groundwater Pollution using Geophysical and Physio-chemical Methods in an Open Dumpsite at Idugosa, Federal Capital Territory (FCT), Abuja, Nigeria

Abstract

A geophysical study has been carried out using the electrical resistivity method, Very LowFrequency Electromagnetic (VLF-EM) and physiochemical analysis to investigate the effects of groundwater contamination in the vicinity of an open dumpsite at Idugosa. A Vertical Electrical sounding was carried out at 100 m away from the dumpsite and the results revealed an H-type curve with 3- layers, with a low resistivity value of 90.0 Ωm, thickness of 9.8 m and depth of 11.3 m at the weathered basement. The control VES revealed 5 –layers of HK-type curve. The resistivity of the weathered and fractured basement ranged from 241.8 Ωm to 2908.4 Ωm with a thickness range of 3.5 m to 13.6 m and a depth range of 5.6 m to 19.1 m. Results of the horizontal profiling using Wenner profiling revealed a low resistivity value of 1.6 Ωm to 3.8 Ωm at a depth of 15 m to 30 m, concentrated at stations 20 to 100. The bottom of the western part showed that the leachate plume had infiltrated and contaminated the groundwater in the zone. The VLF-EM with the three profiles revealed high current density values on the KarousHjelt filter plot at distances of 20 m to 38 m for profile 1, 25 m to 50 m and 75 m to 95 m for profile 2, revealing the presence of contaminants which is mainly from decayed organic matter from waste bodies and heavy metals from the dumpsite. Profile 3 which is further away from profile 1 revealed that the contamination is reduced as we move further away from the dumpsite at about 10 m to 20 m, 50 m to 60 m and 90 m respectively. The physio-chemical analysis results showed a pH range of 6.73 – 7.17 which is within the World Health Organization (WHO) standard (6.5 - 8.5). The Electrical Conductivity (EC) value of the Idugosa dumpsite was found to be 804.9 μS/cm, which is above the WHO standard for EC values, which should not exceed 400 μS/cm. This high value can be attributed to the infiltration of the leachate plume from the dumpsite. The EC for Idugosa control which is 188.0 μS/cm is within the WHO limit for groundwater, thus its safe for consumption.