SANITARY LANDFILL OPERATIONS - Environmentally Conscious Materials Handling - page 206

5.3.1 Leachate Collection System
Leachate is generated due to infiltration of water into the landfill and water gen-
erated during decomposition of the waste materials. Leachate quality depends on
waste composition, age of fill and stage of decomposition, temperature, moisture,
and available oxygen. The concentration of COD in the leachate fluctuates signif-
icantly during the first three years after wastes are deposited and then decreases
to relatively low values. Leachate control within a landfill involves prevention of
migration of leachate from the fill area and landfill base to the subsoil, as well as
collection and removal of the leachate from the landfill. Liner systems comprise
a combination of leachate drainage and collection layer(s) and barrier layer(s).
A liner system may consist of a combination of low-permeability materials such
as natural clays, amended soils, and flexible geomembranes. Figure 7.4 presents
the components of leachate collection systems.
Types of liner systems used at sanitary landfills include the following:
• Single liner system . This is a single primary barrier under the leachate
collection system with an appropriate separation/protection layer.
• Single composite liner system . A composite liner is composed of two barri-
ers, made of different materials, placed in intimate contact with each other
to provide a beneficial combined effect of both the barriers. Usually, a
flexible geomembrane is placed over a clay or amended soil barrier.
• Double liner system . A double liner system consists of two single liners
placed one over the top of the other. This type of system offers double
safety and is often used beneath industrial waste landfills. It allows the
monitoring of any seepage that may escape the primary barrier layer.
The leachate collection system typically consists of a drainage layer, a per-
forated pipe collector system, sump collection area, and a removal system. The
disposal and treatment options for the leachate collected include following:
1. Discharge to sewer lines
2. Recirculation

Municipal solid waste

Filter sand

Protective layer

Drainage gravel

Leachate collection pipe

Primary liner

Figure 7.4 Components of leachate collection systems (adopted from Vesilind et al. 2002)