Landfill gas monitoring

Landfill gas monitoring is the process by which gases that are released from landfill are electronically monitored.

Landfill gas production results from chemical reactions and microbes acting upon the waste as the putrescible materials begins break down.^[1] in the landfill Due to the constant production of landfill gas, pressure increases within the landfill provoke its release into the atmosphere. Such emissions lead to important environmental, hygiene and security problems in the landfill. ^[2][3] Several accidents have occurred, for example at Loscoe, England in 1986.^[4] Migrating landfill gas was allowed to build up and destroyed the property. An accident causing two deaths occurred from an explosion in a house adjacent to Skellingsted landfill in Denmark in 1991Danish EPA. Due to the risk presented by landfill gas there is a clear need to monitor gas produced by landfills. In addition to the risk of fire and explosion, landfill gas migration in the subsurface and result in contact of landfill gas with groundwater. This can result in contamination of groundwater by organic compounds present in nearly all landfill gas ^[5]

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Techniques for the monitoring of landfill gas

Surface monitoring is used to check the integrity of caps on waste and check on borehole monitoring. It may give preliminay indications of the migration of gas of-site. The typical regulatory limit of methane is 500 parts per million (ppm) by volume.

Gas probes, also known as perimeter probes, are used for Subsurface monitoring and detect gas concentrations in the local environment around the probe. Sometimes multiple probes are used at different depths at a single point. Probes typically form a ring around a landfill. The distance between probes varies but rarely exceedes 300 metres. The typical regulatory limit of methane here is 50,000 parts per million (ppm) by volume.

Ambient air samplers are used to moniter the air around a landfill for excessive amounts of methane and other gases.

Types of landfill gas monitor

A monitor may be either a

• Single reading monitor, giving point readings for landfill gas composition, or a
• Continuous gas monitor, that remain in boreholes and give continuous readings over time for landfill gas composition and production.

Techniques for establishing landfill gas (rather than liquid) as the source of volatile organic compounds in groundwater samples

Several techniques have been developed for evaluating whether landfill gas (rather than leachate) is the source of volatile organic compounds (VOCs) in groundwater samples.^[6] leachate water frequently has elevated levels of tritium compared to background groundwater and a leachate (water) release would increase tritium levels in affected groundwater samples, while landfill gas has been shown not to do so. Although landfill gas conmponents can react with imnerals and alter inorganic constituents present in groundwater samples such as alkalinity, calcium , and magnesium, a frequent major leachate constituent, chloride, can be used to evaluate whether leachate has affected the sample. Highly soluble VOCs, such as MtBE, diethyl ether, and tetrahydrofuran, are evidence of leachate fefects, since they are too water-soluble to migrate inlandfill gas. The presence of highly soluble semi-volatile organic compounds, such as phhenols, are also consistent with leahctae effects on teh sample. Elevated concentrations of dissolved CO2 have been shown to be a symptom of landfill gas effects - This is because not all of the CO2 in lanbdfill gas reacts immediately with aquifer minearls, while such reactions are complete in leahcate due to the presence of soils as daily cover in the waste. Top assess whether VOCs are partitioning into groundwater in a specific location, such ass a monitoring well, the headspace gas and dissolved VOC concentrations can be compared. If the Henry's Law constant multiplied by the water concentration is significantly less than the measured gas concentration, the data are consistent with VOCs partitioning from landfill gas into the groundwater.

See also

• Anaerobic digestion
• Biogas
• Biodegradability
• Landfill

References

1. ^ Burdekin, O. (2003) An investigation into the continuous monitoring of landfill gas and the commercial viability of the Intelysis landfill gas monitor, Manchester University, Unpublished thesis
2. ^ Brosseau, J. (1994) Trace gas compound emissions from municipal landfill sanitary sites; Atmospheric-Environment 28 (2), 285-293
3. ^ Christensen, T. H., Cossu, R. & Stegmann, R. (1999) Landfilling of waste: Biogas
4. ^ Williams and Aitkenhead (1991) Lessons from Loscoe: The uncontrolled migration of landfill gas; The Quarterly Journal of Engineering Geology 24 (2), 191-207
5. ^ Kerfoot, H.B., Chapter 3.5 In Christensen, T. H., Cossu, R. & Stegmann, R. (1999)Landfilling of waste: Biogas
6. ^ Kerfoot, H.B., Chapter 3.5 In Christensen, T. H., Cossu, R. & Stegmann, R. (1999)Landfilling of waste: Biogas
7. ^ Basic Information on Biogas.