AREA A/B ENGINEERING REPORT - Waste Management

3.5.3 Key Environmentally Protective Features of Gas Control Systems
Geosyntec Consultants
Both active and passive gas management systems play a major role in protecting human health
and environmental media at a landfill. The major environmental benefits of installing a GMS can
be broadly categorized as follows:
• Control of subsurface gas migration in the vadose zone, which
leads to protection of on-site or adjacent buildings and
structures, protects groundwater from potential impact from
water-soluble pollutants contained in LFG, and reduces
vegetative stress in landfill buffer areas; and
• Control of surface gas emissions and nuisance odors, protecting air quality
and reducing vegetative stress on the cover system.
In addition, as discussed further in Section 7.3, because of its rich methane content, LFG
offers numerous opportunities to provide renewable, green energy through landfill
gas-to-energy (LFGTE) strategies. Landfill methane may also be used directly to fuel
boilers, furnaces, engines, and vehicles, or as a feedstock for chemical processes.
3.5.4 Long-Term Performance of Gas Management Systems
Because an active GMS is an operational system in which all components can
be repaired or replaced as necessary, its long-term performance and
operational efficiency is most closely related to its level of maintenance.
Similarly, the long-term performance of a passive GMS is directly related to
maintenance – passive systems will continue to perform as designed for as long as
they are properly maintained. Because many passive LFG management strategies rely wholly on
natural processes such as methane oxidation in soil covers, landfill designers can develop very low
maintenance or even self-sustaining passive systems.
As first discussed in Section 1.4.1, LFG generation from MSW landfills decreases with waste age;
LFG generation rates typically reach a peak about one year after cessation of waste placement
(closure) before tapering off following a well-documented exponential decay curve. Peak LFG
generation and the rate at which LFG generation decreases is affected by how much water
infiltrates the landfill and is available for waste biodegradation processes. Therefore, the
duration for which significant LFG management will be required at a site is largely driven by two
factors:
• Operational conditions (most significantly, whether the landfill was operated as a “wet”
landfill to enhance biodegradation rates or as a conventional “dry” landfill); and
• Cover system design and maintenance.
As the supply of LFG from an aging landfill decreases, a landfill operator may be able to phase
MD10186.doc 53 29 March 2009