296 11 The Disposal of Municipal Solid Wastes
- Filtering (geotextile) system
A blanket of nonwoven geotextile fabric,
composed of felt-like plastic is placed below
the gravel. This porous material allows liquid
to flow downward while preventing fine par-
ticles from clogging and blocking the drain-
age and collection systems. Underneath, a
geo net made of felt-like plastic diverts made
of mesh-like plastic diverts the leachate
toward the underlying collection pipes and a
low-lying sump. - Collection system
Six-inch perforated PVC perforated plastic
pipes surrounded by a bed of porous rock/and
sand directs the leachate to the lowest part
of each disposal cell. The liquid is conveyed
via the leachate collection system to a sump
located at the lowest point of each disposal
cell. When a small amount of the liquid has
built up, a pump automatically removes the
liquid from the landfill to specially designed
storage tanks or pond, where they are tested
for acceptable levels of various chemicals
(biological and chemical oxygen demands,
organic chemicals, pH, calcium, magnesium,
iron, sulfate, and chloride) and allowed to
settle. After testing, the leachate must be
treated like any other sewage/wastewater; the
treatment may occur on-site or off-site at
approved wastewater treatment plants.
(E) Ground Water Protection Base - The HDPE plastic (geomembrane) shield
The primary bottom shield consists of two
components. First is a man-made synthetic
thick high density polyethylene liner, the
geomembrane, which is used in MSW landfills
and consists of a thick (30–100 mm) type of
durable, puncture-resistant synthetic plastic,
polyethylene, polyvinylchloride, high-density
polyethylene (HDPE). It is impermeable, and
highly resistant, to chemicals which might
be present in the liquids leaving the landfill
(i.e., leachates) as well as gases emanating
therefrom. This plastic is also called the bot-
tom liner and is key to the achievement of the
purpose of the landfill which is to keep the
refuse or any items emanating from it from
entering the environment. The plastic liner
may also be surrounded on either side by a fab-
ric mat (geotextile mat) that will help to keep
the plastic liner from tearing or puncturing
from the nearby rock and gravel layers.
The second part of the ground water base
is the clay shield described in 13.- Clay shield
The shield consists of a minimum of 24 in. of
compacted clay. It is the second component
of the primary liner system and provides
added environmental protection, preventing
leachates and gas from entering the environ-
ment from the landfill.
(F) Monitoring Liner System - Protection against clogging of the monitor
ing layer
A blanket of geotextile fabric composed of
felt-like plastic fibers is laid below the primary
ground water protection base. Underneath, a
geonet of mesh-like plastic is used to permit
any liquids movement. These materials, col-
lectively, prevent the fine clay particles from
clogging the monitoring layer below. - Collection system
Perforated plastic pipes surrounded by a bed
of porous rock and/or sand at the lowest point
of the liner system. This feature is used to
measure the performance of the liner system
and groundwater protection base. Regular
monitoring is performed to ensure the integ-
rity of the landfill components.
(G) Secondary Protection Base - HPDE plastic shield
The secondary bottom liner consists of two
components. First is a man-made synthetic 60
mil high density polyethylene liner, imper-
meable to liquids. The second is the clay
shield described in 17 below. - Clay shield
The second component of the secondary bot-
tom liner is a minimum of 24 in. of re-com-
pacted clay. The clay and the synthetic liner
located above it provide an added measure of
environmental protection.
Operation of a Landfill
Landfills are used differently in different localities,
including different countries. In some, MSW is
dumped into landfills without much possessing, and
no attempt is made to recover recyclable items. In