Leachate migration, soil

Land disposal sites result in soil contamination through leachate migration. The composition of the substances produced depends principally on the type of wastes present and the decomposition in the landfill (aerobic or anaerobic). The adjacent soil can be contaminated by direct horizontal leaching of surface runoff vertical leaching and transfer of gases from decomposition by diffusion and convection. The disposal of... 

Several workers [ 1,29,66,67,104,146 -149] indicated that studying pollutants and/or SWM leachate migration profiles resulting from transport of pollutants with a test soil requires that replicate samples be subjected to leaching-column tests, where various pore volumes of the same solution are applied. 

Farquhar GJ, Sykes JF (1980) Landfill leachate migration in soil. Proc. of Leachate Management Seminar, University of Toronto, Toronto, p 157... 

Many of the waste constituents in the leachate are attenuated or retarded by the soil. For example, lead migrates very slowly through soil, whereas chloride and bromide ions migrate very quickly. With no retardation or attenuation, breakthroughs would occur at a c/cG of 0.5-1 pore volume of flow and below. With effective and total porosities being equal, a much delayed breakthrough of chemicals that have been absorbed or attenuated by the soil could be expected. 

The ability of mineralized soil to control the migration of aluminum was observed in another study. Acidic leachate from coal waste containing aluminum was percolated through soil containing varying amounts of calcium carbonate (Wangen and Jones 1984). Soluble aluminum was found to decrease dramatically as the pH of the percolating leachate increased and aluminum oxide precipitates formed at pH 6, no dissolved aluminum was measured. The authors concluded that alkalinized carbonaceous soils provide the best control material for acidic leachates from coal mineral wastes. 

Chose factors which directly influence the production, containment, attenuation or migration of leachate. These generally involve the groundwater system, the soil or rock permeability, and the structures within the overburden or rock that control either the direction of movement, rate of movement, or local concentration of fluids. In most cases, landfills or old dumps are located in unconsolidated soils or overburden but occasionally the character of the local bedrock is also significant. 

The landfill must have a double liner system that can prevent any migration of wastes out of the landfill to the adjacent soil, groundwater, or surface water. The liner system must include a leachate collection and removal system between the two liners. 

At that time dilute and disperse was still an accepted practice, most landfills were not lined and large volumes of degradable waste was placed in unlined pits in permeable soils (i.e. the worst conditions for landfill gas and leachate generation and migration). Co-disposal of hazardous waste with other types was also an accepted practice. Thus some domestic refuse sites from that period can include a wide range of hazardous materials. 

Wartth, M. a. 1987. Migration of leachate solution through a clay soil. PhD Thesis, McGill University, Canada. 

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