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Landfill Gas Monitoring Systems - Emissions Monitoring

3.5 Emissions Monitoring

Unlike soil gas and near surface gas monitoring, which measure the concentrations of chemicals in landfill gas, emissions monitoring measures the rates at which chemicals in landfill gases are released from landfills. Emissions sources at landfills that are most frequently monitored are the landfill surface itself and landfill gas combustion units (e.g., flares or other combustion devices).

Emissions monitoring can be used to judge the need for, or the effectiveness of, a landfill gas control system. It is also used to determine the volume of air contamination over time releasing from the landfill.

 

 3.5.1 Flux Chambers

 Flux chambers are used to collect the passive release of landfill gases for later analysis, either on site or in a laboratory to determine the emission rate. Surface flux chamber is set up to enclose a known surface area. It is placed directly on the surface for a known time period. It should be well-sealed against the surface. All of those chambers are designed to create good mixing and sampling conditions, minimizing the disturbance of the gas emission. A broad expanse of volatile compounds can be monitored by surface flux measurements, such as VOCs, mercury, methane, carbon dioxide, NOx, and sulfur compounds.

Static flux chamber looks like a container constructed of an inert and non-adsorbing material. It is also connected to the appropriate sampling system. The gas concentration changes with time in the chamber without intrusion of any gas outside the chamber. Contaminant flux increases over the sampling period. Discrete samples should be withdrawn at regular intervals during the whole sampling period. Static flux chamber measurement lasts from some minutes (using PID or FID) to one hour or less (using sorbent tubes for example).

  

Figure 13

Figure 15. Static-flux-chamber with PID monitoring (INERIS)

 

Scanning surface flux chambers are connected to an inert gas supply system and an exit fitted out with measurement points. The system gathers contaminant gas emitted from soil within the inert gas flow. Before sampling, it is necessary to reach the stabilization of the flow regime of inert carrier gas into a chamber in contact with the ground. Therefore the measured parameters (concentrations and outgoing air-flows) allow for the test to quantify the flow of emitted vapors outgoing from the chamber, and thus to deduce the flow released through the concrete slab or the ground.The surface flux chamber needs a longer period of equilibration due to its size and the gas injection. Flux measurement lasts around three or four hours.

  

Figure 14

Figure 16. Scanning flux chamber with PID monitoring (INERIS)

 

3.5.2 Spectroscopic Sampling Techniques

 Surface emissions are also being measured by Fourier-transformed infrared-red (FTIR) or ultra-violet spectroscopy (UVS) sampling techniques. These techniques can detect and identify contaminants in the air along a straight line (e.g., the boundary of a landfill or across the landfill surface). UVS is typically set up for specific compounds (usually inorganic gases), but FTIR can be used for multiple compounds (usually organic gases). The spectroanalysis can identify specific compounds and concentrations in the space between the source and the receptor. (Agency for Toxic Substances and Disease Registry, 2001)

The website of Emission Measurement Center (EMC) of EPA compiles a long list of the test methods available for emission measurement.

  

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