AREA A/B ENGINEERING REPORT - Waste Management

3.6.1 Landfill Gas Collection Efficiency
Geosyntec Consultants
The majority of potential GHG emissions from a landfill are controlled by the LFG management
system, as previously discussed in Section 3.5. The collection efficiency of a gas control system is
the percentage of the total LFG generated in the landfill that is recovered by the
system. Gas collection systems at modern landfills with well-engineered final
cover systems have been demonstrated to have very high efficiencies and thus
are proficient at reducing GHG emissions 18 . However, gas collection efficiencies
are dependent on the type of cover being used during the operation of the
landfill. State-of-the-practice literature regarding gas collection efficiencies under different
cover conditions are summarized in the recently completed study published by SWICS (2009),
which also provides collection efficiency values obtained from a comprehensive field-testing
program.
Effects of Cover Conditions: The conclusions of the field tests performed for SWICS (2009)
relating gas collection efficiencies to cover conditions are summarized below (it should be noted
that test data on daily soil covers was limited, as stated by the experts involved with the creation
and review of that document):
• Daily Cover: Collection efficiencies are in the range of 50-70 percent, with a mid-range
default of 60 percent, for portions of a landfill that are under daily soil cover with an
active LFG collection system installed;
• Intermediate Cover: Collection efficiencies are in the range of 54-95 percent, with a
mid-range default of 75 percent, for a landfill or portions of a landfill that contain an
intermediate soil cover with an active LFG collection system installed; and
• Final Cover: Collection efficiencies are in the range of 90-99 percent, with a mid-range
default of 95 percent, for landfills that contain a final soil and/or geomembrane cover
system with an active LFG collection system.
Effects of Gas System Design and Operation: The effectiveness of a gas collection system is
dependent upon its intended design and mode of operation. If a gas collection system is
designed for compliance with the USEPA’s New Source Performance Standards (NSPS), or to meet
similar air quality requirements, it will likely be capable of greater collection efficiencies than a
system whose design basis was to control subsurface gas migration. Similarly, a landfill with a
gas collection system installed voluntarily as part of an energy utilization project may not be
capable of collection efficiencies as high as NSPS-compliant systems simply because it is often
difficult to maximize gas quality (needed for optimal energy production) at maximized levels of
gas collection across the entire wellfield.
In summary, the actual collection efficiency of the LFG collection system is dependent on the
operational phase of landfill development and the type of cover in place. A recent white paper
18 Appendix B provides an in-depth discussion and several references regarding the ability of landfills to control
methane emissions through effective gas collection.
MD10186.doc 55 29 March 2009