Various leachate control and collection system designs are in use.
Typically, a barrier of low-permeability soil or a flexible membrane line
is placed at the bottom of the site before initial placement of wastes to
contain leachate that may percolate from above. The landfill bottom is
prepared to accommodate the barrier, and is sloped to direct leachate to
or more central collection sumps where it can be stored for subsequent
onsite treatment or handling or be discharged to a sewer. Generally,
leachate from solid waste is first channeled through a granular media (an
often times perforated plastic collection pipes) placed atop the barrier
liner layer. Figure 18 illustrates one design for a leachate collection
system configuration.
Soil liners are usually constructed of clayey soils. These soils can
often be obtained onsite, but imported clay minerals such as bentonite ca
also be used singularly or mixed with onsite soils if onsite soils are no
suitable. If such soils are not available locally, the import by truck m
be very expensive.
Flexible membrane liners can also be used in lieu of clay barriers.
However, the long-term (>20-year) life of flexible membrane liners is not
proven in a landfill environment, so a combination of clay and membrane
liners are common. Manufacturers of synthetic polymeric liners (e.g., PV
and chlorinated polyethylene) claim service lives from 15 to 30 years.
However, a landfill may generate leachate for a significantly longer peri
Table 21 presents a list of various materials used for landfill liners.
Collected leachate may be treated by one or more of the methods shown
in Table 22.
Depending on the leachate characteristics, volume, and local
regulations, it may be technically and economically practical to discharg
untreated, collected leachate to an existing sewerage system for subseque
treatment along with municipal wastewater. The acceptability of disposin
of leachate in this manner must be confirmed with local regulatory agenci
If direct discharge to a sewerage system is not practical, onsite
treatment or truck haul to a wastewater treatment plant or a hazardous wa
facility are options.
7.4.5.2 Landfill Gas. Landfill gas (LFG) is produced by decomposition o
the organic matter in solid waste. Immediately after solid waste is in
place, and for several months thereafter decomposition occurs aerobically
The principal byproducts of aerobic decomposition are carbon dioxide gas
water. Once the free oxygen in the solid waste is depleted the
decomposition process becomes anaerobic, and the principal byproducts are
methane and carbon dioxide gases. Hydrogen sulfide, hydrogen, and some
volatile organic gases are also sometimes generated. This methane-rich
mixture of gases is called landfill gas.
The volume and composition of landfill gas produced depends on variou
factors, including the quantity and characteristics of solid waste
deposited, the age of the landfill, and the amount of moisture present.
p gas is generated over an extended period. Landfill gas has been detect
in landfills 75 years after site closure.
5.10-82
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