Detection of groundwater level and heavy metal contamination: A case study of Olubunku dumpsite and environs, Ede North, Southwestern Nigeria

Abstract

This research presents the result of the application of the PQWT Electromagnetic Groundwater Detector and analysis of heavy metal contamination around an open dumpsite in Olubunku, Ede North, Southwestern Nigeria, which has been in operation for the past fifty years. A PQWT-300S 300 m was used to acquire 8 profiles at the site. The quantitative analysis of heavy metals was conducted for seven available well water samples and five surface soil samples. The water and soil samples (digested) were read on BuckScientific Atomic Absorption Spectrophotometer model 210/211 vap to determine the concentration of Pb,Cd,Cr, Co, and Ni in the samples. As and Hg in the samples were read colorimetrically using a Niesa Spectrophotometer. From the PQWT results, profiles 1,4,5,6,7, and 8 indicate a shallow level of groundwater at a depth of around 30m, which is prone to contamination as most water in the study area is obtained from hand dug wells less than 20m deep. Profile 2 and 3 show contacts that indicate a boundary between fresh basement and well fractured basement, which serves as the water-bearing rock. The HPI scale indicates a high presence of Cd, Hg, Pb, As, and Co in all the samples, which is above the maximum allowable concentration for water. The low scale of Ni and Cr indicates the water is free from Ni and Cr contamination. In the soil, the Igeo scale of Co, Ni, Cd, Pb, and Hg are higher than the maximum allowable concentration, while As and Cr are very low and therefore pose no threat. Chromium is generally low in both the soil and water samples analyzed, while Co, Cd, Hg, and Pb are high above the prescribed scale in both soil and water samples.The groundwater depth in the study area is predominantly at a shallow level of around 30m. The high conductivity of the top shallow level is suspected to be due to contamination by leachates from the dumpsite. The soil and groundwater in and around the investigated dumpsite may be polluted. The study has indicated the vulnerability of the unconfined shallow aquifer underlying the predominantly clayey sand and the effectiveness of PQWT EM in delineating groundwater zones in the basement complex.