Determination of Leachate Plume Migrations from Selected Cemeteries in Benin-City Metropolis using Integrated Physicochemical and Geophysical Methods

Abstract

Environmental geo-forensics which involves an integrated suite of geochemical and geophysical  techniques was used to detect and evaluate contaminant plume migrations from three cemeteries (names of the cemeteries are; First, second and third cemeteries, all in Benin City) within Benin-City metropolis, South-South Nigeria. The study aimed at determining the risks to groundwater and soil by assessing the rate of leachate plume migrations on the study area. The Very Low Frequency-Electromagnetic (VLF-EM) surveys revealed locations of conductive bodies. The Electrical Resistivity Imaging (ERI) surveys showed patterns and resistivity values indicating the presence of leachate plumes around second and third cemeteries, and no presence of leachate around first cemetery. Soil samples from shallow depths within the vicinities of the cemeteries revealed pollution which had probably migrated from the study area. The surface and subsurface soil investigations showed pure laterites which is impervious to fluid flow. Generally, many depressions were identified within the study area, although migration rate is low because it is controlled mainly by the subsurface geology. A time lapse study showed contaminant migration rates of 41.6 cm/month and 51.7 cm/month in the horizontal directions in the second and third cemeteries respectively and 19.2 cm/month in the vertical directions for both (second and third) cemeteries. Also, the arrival time of migrating plumes in laterite layer under was estimated to be 4 years. This investigation demonstrates the suitability of environmental and criminal geo-forensics for identification and evaluation of electrically conductive contaminant plumes, and also to monitor the plume as it travels within the subsurface.