Application of Integrated Geophysical Methods to Investigate Contaminants at a Landfill Site, Accra,Ghana.

Abstract

In the study electrical resistivity tomography (ERT), time-domain induced polarization (TDIP) and seismic refraction tomography (SRT) techniques were applied at an active unengineered municipal solid waste landfill site located at Pantang in the Ga East Municipality, Accra, Ghana. The environmental and public health hazards related with municipal solid waste disposal are rampant in developing countries like Ghana. The most common waste disposal system in Ghana is the open disposal of waste generated from industries, residents and commercial areas to un-engineered landfill sites. The consequences on the quality of livelihood and health risks as a result of this practice demand a comprehensive method to investigate and evaluate the impact of landfill sites on the environment. This study was aimed at mapping the conductive contaminant plume and level of contaminants migration within the subsurface, and also to determine the depth to bedrock of the landfill site. A total of five (5) survey lines were selected in conducting the electrical resistivity tomography and induced polarization methods. The dipole-dipole array was employed in investigating the extent of potential contaminant plumes beneath the subsurface. The analysis generated from the models revealed that the zones with possible leachate pollution have thicknesses ranging from 1 m to 4 m and a maximum depth of 15 m below the surface. In a complimentary effort, seismic refraction survey was conducted on two survey lines, to define shallow bedrock topography and the depth to bedrock of the landfill site. The seismic survey demonstrated that highly variable non-uniform subsurface conditions exist at the landfill site. The result proposes that, the Pantang landfill site has seismic velocities distribution ranging from; 72 ms-1 to 900 ms-1, which is interpreted as the overburden material, 1000 ms-1 to 6000 ms-1 for slightly weathered zone and velocities greater than 6000 ms-1 for competent rock material. The seismic refraction tomography helped to characterize geologic features within the waste dump and to assess the possible pathways for contaminant plumes. The outcome established by this research suggests for an evaluation of the waste management system policies in Ghana emphasizing on alleviation of the influence of municipal solid waste on the ecosystem.