Environmental Engineering Reference
In-Depth Information
•
pH (Relatively neutral conditions, pH of 6.7 to 7.2, promote decomposition)
•
Alkalinity and volatile acids (alkalinity greater than 2,000 mg/l as calcium
carbonate and volatile acids less than 3,000 mg/L as acetic acid promote
decomposition)
•
Temperature (temperature between 86
◦
F and 131
◦
F promote decomposi-
tion)
Table 7.4 presents the typical composition of landfill gas (Vesilind et al. 2002).
Landfill gases can move upward or downward in a landfill, depending on their
density. For unvented landfills, the extent of this lateral movement varies with
the characteristics of the cover material and the surrounding soil.
The gas management strategies may include the following options:
•
Controlled passive venting
•
Uncontrolled release
•
Controlled collection, purification, and use
5.3.3 Surface Water Drainage System
Surface water management is needed to ensure that rainwater runoff does not
drain into the waste from surrounding areas.
These objectives should be achieved by the following steps:
1.
Intercept rainwater running off slopes above and outside the landfill area.
2.
Collect and/or manage the rain falling on active tipping areas and channel
to leachate collection drain and leachate collection sumps.
3.
Divert the rainfall onto areas that have been completed and direct it to a
settling pond to remove suspended silt, prior to discharge.
5.4
Operation
A landfill is developed in phases. A landfill phase is a subsection of a landfill;
it consists of daily cells, lifts, daily cover, intermediate cover, liner and leachate
collection facility, gas control facility, and final cover over the subarea. Landfill
cells are developed from the base to the final/intermediate cover and capped.
Ta b l e 7 . 4
Composition of Landfill Gas
Constituent
Percentage by Volume
Methane
45-60
Carbon dioxide
40-60
Nitrogen
2-5
Oxygen
0.1-1.0
Ammonia
0.1-1.0
Hydrogen
0-0.2
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