A case for safe disposal of solid waste in Nigeria
Sir: Huge volume of waste is generated in most cities and towns in Nigeria as a result of rapid population growth and increased industrialisation. Exploration and exploitation of hydrocarbons and solid minerals also result in generation of waste. Despite the fact that most state governments have agencies that clear waste, heaps of wastes are not uncommon features in many of the nations’ cities.
Apart from the unhygienic odour that emanates from waste, waste also hampers free flow of water and may be dumped in river channels. This often results in flooding of flood plains.
Quite unknown to the public is the pollution of groundwater. Our studies over the years have confirmed that water in wells located on the down slope section of spaces between carriageways and even landfill sites are being negatively impacted. Chemical analyses of water samples from hand dug wells in the vicinity of illegal waste dumps and landfill sites have confirmed that quality of groundwater improves with distance from waste sources and depths of wells.
Solid waste can be disposed by use of incinerators, injection holes and landfills. Landfills are the commonest means of solid waste disposal. Before any site can be investigated for its suitability or otherwise, for a landfill, it has to satisfy some criteria: the site must be extensive with flat topography, it must be remote from major highways, rivers and habitable areas.
Integrated surface geophysical, hydrogeological and geotechnical investigations can help in generating subsurface model. The model will then be compared with standard model for a sanitary landfill.
Important features of a standard landfill are impervious seal at its base and appreciable vertical distance from the water table. Compaction at an appropriate level can reduce the permeability of the base while groundwater level can be lowered by use of state – of – the– art technique. If the proposed base of a landfill is not suitable, a suitable clayey soil has to be imported. Many lateritic soils have been found to possess geotechnical and hydraulic characteristics of a good landfill seal.
Environmental impact assessment of an active landfill has to be done in order to know the lateral extent of the influence of leachates from the waste. In other words, appropriate geophysical and geochemical methods must be utilised for the mapping of pollution plume. Such a map can be useful in isolating where wells should not be sunk.
In conclusion geoscientists must be made to be actively involved in environmental management in Nigeria. This is the practice in developed countries of the world.
• Prof. Gabriel Oladapo Adeyemi is the President of the Nigerian Association for Engineering Geology and the Environment.
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