Radiometric and electromagnetic investigations of the Olushosun dumpsite Lagos, Southwest, Nigeria

Abstract

The Olushosun dumpsite is one of the largest dumpsites in Nigeria, and variety of waste materials are often deposited on the dumpsite. Therefore, radiometric and electromagnetic (EM) investigation of the dumpsite was embarked upon to assess the radioactive status and the extent of leachate contamination. A well calibrated portable radiometric spectrometer nuclear radiation monitoring metre (Model BG0-Super-SPEC RS 230) and the Geonics EM 34 measuring instruments were used to achieve this objective. The mean activity concentration of 40K measured along all the profile lines ranged from 0.22% to 1.19% (68.86–372.47 Bq/kg), while that of 238U and 232Th ranged from 0.88 ppm to 2.02 ppm (10.87–24.95 Bq/kg) and from 4.87 ppm to 15.61 ppm (19.65–63.38 Bq/kg) respectively. The results of the radiation dose rate measurement showed that the overall mean absorbed dose rate measured in the study area were comparable to those reported around some cities in Nigeria. The radiation level along some points on the profile lines, even though high, did not exceed the safe limit of 70 μSvyr−1 as recommended by UNESCO on effect of Atomic Radiation. This implies that the inhabitants around this area are not exposed to radiological risk, and the dumpsite when reclaimed in future, could be used for the construction of buildings without any form of restrictions. However, continuous exposure to these radiations may have long term consequences on human health. Results from the EM data set along traverses on the dumpsite show that the subsurface is characterised by high conductivity (60–680 mS/m) up to a depth of 60 m. The high terrain conductivity signature here may be attributed to leached contaminats migrating into the subsurface and contaminating shallow aquifers. The descriptive statistical analysis of the measured EM data sets showed higher level of correlation among parameters measured along control lines outside of the dumpsite. Generally, correlation between the entire EM data on the dumpsite was poor, but reasonably better for the control data. This could be attributed to the heterogeneous properties of waste materials deposited on the dumpsite. Keywords: Electromagnetic, Resistivity, Contaminant, Horizontal dipole, Vertical dipole