Page 348 - Materials Chemistry, Second Edition

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The Sanitary Landfill 319

FIGURE 10.15 Portable organic vapor analyzer.

Methane measurements are made in the field with a portable methane meter or organic vapor
analyzer (Figure 10.15). Gas samples may also be collected and brought to the laboratory for
analysis. Measurements, for example with gas chromatography-mass spectrometry, can confirm
the identity and concentrations of landfill gas. In addition to measuring gas composition, other
indications of gas migration may be observed. These include odor (described as either a strongly
‘sweet’ or a rotten egg [H S] odor), septic soil, and audible or visual venting of gases, especially
2
in standing water. Stressed vegetation is a useful indicator of gas migration. Landfill gas in soil
pores creates anaerobic conditions by displacing oxygen. Plant roots require sufficient oxygen to
carry out normal respiration processes, and methane gas acts as a simple asphyxiant to roots
(Flower et. al., 1982).

10.4.15 TRACE GASES
Table 10.13 lists many trace gaseous compounds detected at most MSWLFs. The amounts of these
gases in leachate is a function of their initial concentrations and their solubility in aqueous liquids.
The occurrence of significant concentrations of volatile organic compounds (VOCs) in landfill gas
is associated with older landfills that had accepted industrial and commercial wastes containing
VOCs. In newer landfills in which the disposal of hazardous waste has been banned, concentrations
of VOCs in landfill gas have been very low.

10.4.16 LANDFILL GAS CONTROL

Landfill gas may vent naturally or be directed to the atmosphere by engineered controls. Systems
used to control or prevent gas migration are categorized as either passive or active. Passive systems
provide preferential flow paths by means of natural pressure, concentration, and density gradients.
Active systems use mechanical equipment to direct or control landfill gas by providing pressure
gradients, in essence, forcing landfill gas out by applied convective forces. The choice of system is
based on the design and age of the landfill unit and on the soil and hydrogeologic conditions of the
facility and surrounding environment. In other words, the degree of potential gas hazard plays a role
in the choice of the particular system.