Publish Date: 2007
Landfill gas (LFG) is formed as a natural byproduct of the decomposition of wastes in landfills. To recover its energy value and minimize its pollutant emissions, many landfill managers have installed LFG recovery and utilization systems. Recovery of 100 percent of the gas generated is generally considered infeasible due to the permeability of the waste and the inefficiencies, as well as the timing of installation, of the recovery system.
The goal of this project was to document what is known about actual LFG collection system efficiencies based on recent research programs, case studies, and field experience. This report presents the results of an investigation into the topic of gas collection efficiencies of LFG recovery systems that was conducted by the SWANA ARF staff with input and guidance provided by the ARF LFG Project Sponsors.
Of the numerous publications that were reviewed for this project, three directly addressed the issue of LFG collection system recovery efficiencies and provided quantitative estimates of LFG recovery efficiencies that were significantly higher than the 75 percent average recovery efficiency stated in AP-42.
Detailed reviews of these three publications • two of which were published in 2006 and the third in 2005 • are presented in the report along with summary reviews of two other recent publications.
The four approaches to determining LFG collection efficiency that are reviewed in this report are significantly different.
Two of these approaches require the installation of flux chambers or monitoring probes, whichmust be installed at specific locations that may not be representative of the entire landfill.
The third approach appears to address two significant issues that were reported to EPA in a 2002contractor memorandum • namely the temporal and spatial variation in LFG generation and
emission rates - by taking numerous measurements over the entire surface of the landfill and
conducting monitoring events on a quarterly basis.
The fourth approach relies heavily on the computer modeling of LFG generation to estimate gas collection efficiencies and does not attempt to determine the gas collection efficiencies at a given landfill.
The three field studies reviewed in this report provided quantitative estimates of the LFG collection efficiencies at five closed, capped landfills.