Abstract
As leachate has been a source of groundwater contamination worldwide, this paper examines the phenomenon of leachate migration on different gradations of compacted laterite soil used as sanitary landfill liners. Three different soil gradations (30%, 40% and 50% with respect to fines content) used in this study were compacted in circular acrylic columns to provide a clear visualization of leachate migration into the soils. Digital image technique was used in capturing photos at successive time intervals to monitor the leachate migration. The captured digital images were fed into Matlab and converted into hue-saturation-intensity (HSI) format. Surfer software then read the HSI and generated 2D contour plots. The results of the experiments showed that the leachate moves downward faster in the soil gradation with the least fines content. Hydraulic conductivity values decrease with increase in time duration and equally with increase in fines content. The hydraulic conductivities of the leachate for 30%, 40% and 50% fines were 3.64×10-9m/s, 2.40×10-9m/s, and 1.24×10-9m/s respectively. This reveals that for tropical laterite soils, gradation containing 50% fines content provides better hydraulic conductivity. The use of noninvasive digital image technique can enable designers/engineers to monitor and visualize the leachate migration in compacted soils in waste containment application systems.
Highlights
Groundwater is one of the major sources of water supply for domestic and industrial purposes
The effect of laterite soil gradations on leachate migration and the subsequent determination of their hydraulic conductivities using digital image techniques (DITs) provide an innovative means of visualizing contaminant transportation in compacted soil liners
Contour plots (2D) of HSI intensity value provide details and useful information in order to understand the characteristic of leachate migration behavior
Summary
Groundwater is one of the major sources of water supply for domestic and industrial purposes. One of them is contamination by leachate through landfills because landfills are the final destinations of the majority of waste generated in most urban areas. A liquid that permeated through waste, and contains heavy minerals and suspended materials is defined as landfill leachate [3]. Leachate is generated either from external water or from within the waste mass. Leachate generated from urban solid waste contains heavy metals. These heavy metals leach out from the soil and enter the underlying aquifer, which affects the livelihood of the surrounding community [4,5]. To prevent leachate contamination through landfill, hydraulic barriers known as liners and covers are constructed. Leakage of leachate through hydraulic barriers can be one of the main pollution hazards to groundwater. Soil materials used as hydraulic barriers must have the following attributes which make them suitable in sanitary landfills:
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