Electrical Resistivity Investigation of Aquifer Vulnerability to Surface Contaminants in Yenagoa Metropolis, Bayelsa State, Nigeria

Vertical electrical sounding, 2-D tomography survey and Dar-zarrouk parameters were used for the investigation of the aquifer subsurface layers, the protective capacity of the overburden layers and the vulnerability of the aquifer to surface contaminants in the area. Eleven (11) vertical electrical sounding (VES) were deployed using a maximum electrode separation, AB/2 of 200metres for the study. The VES data were interpreted using the IP12WIN software to delineate the aquifer into 4-5 geo-electric layers of silty-clay, clay, clayey-sand, fine-sand to coarse–sand. The aquifers zones were mainly of medium to coarse sand with average resistivity values of 1,800Ωm and average thickness of 10.3m. The average depth of the aquifer zone is 40m across the area. Dar-zarrouk parameters were employed to determine the protective capacity of the overburden layers and the vulnerability of the aquifer to surface contaminants. From the vulnerability ratings, the study area was classified mainly into high vulnerability and extremely high vulnerability zones. The 2-D tomography survey reveal zones of high resistivity and low resistivity values in the study area. The zone of high resistivity ranges from 460- 955Ωm and is refers as the noncontaminant zone. While the low resistivity zone range between 41 - 101Ωm and is refers as the contaminant zone. The result showed that the contaminant zone (leachate) is found at the depth of 7m. This means that the aquifer zone which is at the depth of 40m has not been affected.