Page 328 - Materials Chemistry, Second Edition

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The Sanitary Landfill 299

FIGURE 10.4 Geomembrane materials.

The thickness of geomembrane liners range from 30 to 120 mil. The recommended thickness
for all geomembrane liners is 30 mil (0.75 mm) with the exception of HDPE, which should be set
at 60 mil (1.5 mm) (Qian et al., 2002).

10.4.8 COMPATIBILITY OF LINERS WITH WASTES

The chemical compatibility of a geomembrane with waste leachate is a critical consideration
regarding choice of material. Materials used in landfill construction must be expected to withstand
a wide range of natural stresses for very long periods. Many materials deteriorate over time when
exposed to chemicals occurring in leachate. Landfill owners and operators must anticipate the com-
position of leachate that a site will generate and select the appropriate liner materials. The chemi-
cal resistance of any geomembrane materials as well as LCR pipes should be thoroughly assessed
prior to installation.
The EPA Method 9090A test (U.S. EPA, 1986b) is used to evaluate the chemical compatibility
of synthetic materials used in liner and leachate collection and removal systems. A primary objec-
tive of chemical compatibility testing is to ensure that liner materials will remain intact during the
operating lifetime of a landfill, and also through the postclosure period and beyond. EPA Method
9090A is used to predict the effects of leachate under field conditions. The test is performed by
immersing a synthetic membrane in a chemical mixture for 120 days at two different temperatures,
i.e., ambient and elevated. Samples are removed every 30 days and evaluated for changes in phys-
ical properties. Tests performed on geomembranes are listed in Table 10.4.
Intuitively, the results of a 120 day test under controlled conditions should be considered to be
of limited predictive capability to a real-world landfill situation. Method 9090A has been verified,
however, with limited field data. The U.S. EPA conducted a 5 year study of the impact of MSW on
common liner materials and measured little if any deterioration within that period. In other studies,
however, the results of chemical exposure on geomembranes can range from minor effects such as
discoloration to more serious problems such as swelling. In extreme cases, the liner may dissolve,
or tearing, cracking, or puncturing may occur. The waste may react with the liner causing degrada-
tion of the polymer or its additives or the waste may dissolve into the liner, resulting in swelling of
the membrane without degrading it (Butler et al., 1995).