chapter 4: temperature inside the landfill

2.3 Moisture Movement inside the Landfill
Moisture is essential for transporting of organic substrate to and waste products from the
micro-organisms. Water is also required for nutrient transport and heat transport. According to
Klink and Ham (1982), moisture content and movement are separate variables. They observed
that increase in methane production ranged from 25 to 50 percent when there was a moisture
flow through the waste as compared to waste having the same moisture content with no moisture
flow.
The models describing leachate flow inside a landfill assume that moisture moves
through the landfill as a vertical wetting front (Reinhart and Townsend, 1998). This assumption
leads to the conclusion that leachate exits from the landfill when moisture content is at field
capacity in the landfill and time of leachate generation could be easily determined based on the
depth of the landfill and the downward velocity of leachate front. Based on practical experience,
it has been found out that leachate has been generated well before the time predicted by these
models.
Several reasons may be responsible for this leachate arrival before the time includes
uneven distribution of moisture, channeling and stormwater runoff into leachate collection
system. Uneven distribution of moisture results from unsaturated flow which, in turn, is
exacerbated by the heterogeneity of solid waste. Particle size of waste ranges over many orders
of magnitude. Use of low permeable daily cover is another reason responsible for the uniform
distribution of moisture content. Furthermore, gas production blocks the pores through which
moisture travels (Reinhart and Townsend, 1998).
Channeling leads to faster velocities of moisture travel through interconnected pores.
Leachate exits from the landfill before the predicted time because of the formation of channels in
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