Integrated geophysical characterization of municipal solid waste disposal sites in the Kumasi Metropolis
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Date
2015-11-16
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Abstract
Full wave spectral time-domain induced polarization, magnetic susceptibility and ground
base magnetic datasets were acquired to map and characterize both engineered (Dompoase
Landfill) and unengineered (Ohwim and Kwame Nkrumah University of Science and
Technology municipal solid waste disposal sites) located in the Kumasi Metropolis. These
geophysical datasets were selectively applied and integrated to help in full characterization of
the waste disposal sites in terms of waste thickness, pollution plume mapping and the
geological model development of the sites. In addition, a total of six boreholes were drilled
around the sites to help in correlating the observed geophysical signatures with the waste
thickness and the lithostratigraphic sequence in order to help in interpretation and
characterization of the sites. The study was carried out with the aim of determining the risk
posed by the waste deposit to the quality of soil and the groundwater system which is now
becoming the main means of potable water supply in the metropolis due to the erratic supply
supply and the inability of the Ghana Water Company (GWC) to supply water especially to
new developing settlements in the metropolis. The intrinsic Cole-Cole IP parameters such as
chargeability, resistivity and relaxation time as well as the normalized chargeability
distributions, together with the magnetic results, aided in a full characterization of the wastes
(vertical and lateral distribution), associated pollution plumes and for developing the
geological model of the sites. The KNUST site was characterized using Cole-Cole parameters
namely resistivity and chargeability as well as normalised chargeability and magnetic
datasets. In particular, a clear contrast in resistivity and polarization effect between the
saprolite layer and the granite bedrock, the main lithological units of the area aided in the
development of a geological model of the site. Furthermore, it was found that the KNUST
waste deposit is characterized by a low-chargeability and low-resistivity signature, and that
the low-resistivity area spreads out from the waste deposit into the permeable saprolite layer,
indicating the presence of a leachate plume which was mapped to be in the range of 5 to 30 m
thick. A mapped fracture zone within the granitic bedrock linked to the pollution plume with
the potential of aiding in leachate percolation of groundwater by serving as a conduit for
infiltration of the leachate was also mapped. Similarly, the Ohwim Waste Disposal Site was
mapped with the magnetic, magnetic susceptibility and full wave spectral time-domain
induced polarization. These methods helped in determining the waste thickness and the extent
of the pollution plume as well as the geological model of the site. The waste recorded high
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magnetic anomaly, low resistivity and high normalized chargeability. The geological model
of the site was developed by using the strong chargeability signature it produced.
Furthermore, the Dompoase Landfill survey which was planned mainly to determine and
monitor possible pollution plume around the waste, produced some intriguing result. The
magnetic and the magnetic susceptibility results aided in the full mapping of the lateral extent
of the waste as well as the channel of the released effluent from the treatment sewage pond,
showing the high ferromagnetic iron content of the leachate. The strong IP effect in terms of
chargeability and normalized chargeability as well as the low resistivity signature associated
with the plume helped in mapping the plume around the catchment area of the waste. The
controlled nature of the waste disposal at the Dompoase landfill makes it a possible resource
for the production of natural gas. The research provides a cost effective means of monitoring
and characterizing municipal solid waste site in the Kumasi Metropolis. It provides a full
outline of the solid waste disposal sites investigated and also provides the information needed
for assessing the future impact of the waste on the water quality in the area, and the need for
designing risk-mitigation actions in these sites. The impact of waste disposal sites on the
quality of the environment as shown by this work calls for a review of national policy in the
waste site management with focus on reduction of the impact of the waste on the ecosystem.
Description
A thesis submitted to the Department of Physics, Kwame Nkrumah University of Science
and Technology in partial fulfilment of the requirements for the award of the degree of Doctor of Philosophy (Geophysics), 2015