HAZARDOUS WASTE TREATMENT - Environmentally Conscious Materials Handling - page 190

Gas monitoring probes

Groundwater
monitoring well

Protective
cover soil

6'' Top soil

Liner

Clay
or liner
Separation
berm

Gas collection
trench (typ.)
Groundwater
monitoring well

Leachate
collection pipe

Leachate
collection
Groundwater flow

3' Compacted
clay liner

Water table

Figure 6.3 Schematic of a hazardous waste landfill with drums

irrigation water into the landfill. A schematic of a hazardous waste landfill is
shown in Figure 6.3.
According to Slack et al. (2005), the codisposal of hazardous and nonhaz-
ardous wastes is a practice soon to be banned in EU member states through
the implementation of the landfill directive, effective from July 2004. This will
potentially reduce the volume of leachate created in an atmosphere where there
is mixed waste storage.
In a hazardous waste landfill, the primary purpose of liners is to minimize
leakage of landfill leachate and gas into the subsurface and to allow collection
of leachate for treatment and disposal. Liners consist of successive layers of
compacted clay and/or geosynthetic material designed to prevent migration of
landfill leachate and landfill gas. Most commonly used materials for liners include
one or all of the following:
• Geomembrane (Hydraulic barrier)
• Geosynthetic clay liner (GCL) (hydraulic barrier)
• Compacted clay (hydraulic barrier)
• Geotextile (for cushion or separation)
To promote removal of leachate from the liner, the landfill bottom is sloped
and sufficient drainage pipes are provided to ensure that the leachate depth over
the liner does not exceed 1 feet. Typical slope of base liner is 2 to 10 percent and
typical slope of sidewall liner ranges from 20 to 40 percent in a landfill (McBean
et al. 1995).
The main function of a leachate collection system (LCS) is to collect leach-
ate for treatment and disposal. Most commonly used materials for LCS include
pea gravel or coarse sand, geocomposite drainage layer (GDL), perforated
HDPE/PVC pipes, leachate sump, and a submersible pump. Due to the leakage