Vulnerability Assessment of Groundwater to Contamination Using Electrical Resistivity Method at the Open Dumpsite in Gosa, Abuja, Nigeria

Electrical resistivity method was used to investigate the open dumpsite at Gosa, Abuja in order to determine the vulnerability of the groundwater in the area as well as the surrounding environment to leachate contamination. A total of sixteen (16) vertical electrical sounding points with maximum current electrode of 100 m were investigated. The data were analyzed and used to establish the parameters required to fulfil the objectives of this research. A maximum of four geoelectric sections were identified in the area. They included sandy topsoil, clayey sand, weathered basement and fractured/fresh basement. Apparent resistivity values obtained for the four layers delineated were between 64.6 Ωm and 215.5 Ωm for the first layer; 19.0 Ωm and 295.6 Ωm for the second layer; 66.9 Ωm and 1003.7 Ωm for the third layer; and 438.0 Ωm and 1719.9 Ωm for the fourth layer. Furthermore, the ranges of the thickness of the layers were found to be 0.7 m and 12.9 m for the first layer; 1.3 m and 9.8 m for the second layer; and 1.6 m and 11.6 m for the third layer. The depths of water table in the area were estimated to range between 2.1 and 21.6 m. The parameters used in characterizing the aquifer protective capacity of the overburden units were layer thickness and their corresponding resistivity values. Accordingly, the total longitudinal layer conductance of the overburden of the area was generally found to be low, ranging between 0.014 mhos and 0.063 mhos, implying that the aquifer protective capacity of the area is poor. The 1D resistivity cross section for the three profiles investigated exposed the movement of contaminants toward the aquifer, further validating the fact that the aquifer is not protected. The low protective capacity of the area aided the conclusion that the water aquifer in the area was highly vulnerable to leachate contamination from the dumpsite.