Landfill gas monitoring
Landfill gas monitoring is the process by which gases that are released from
landfillare electronically monitored. Landfill gasproduction results from chemical reactions and microbes acting upon the wasteas the putrescible materials begins break down. [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monitoring of landfill gas and the commercial viability of the Intelysis landfill gas monitor, Manchester University, Unpublished thesis] in the landfillDue to the constant production of landfill gas, pressure increases within the landfill provoke its release into the atmosphere. Such emissions lead to important environmental, hygieneand securityproblems in the landfill. [Brosseau, J. (1994) Trace gas compound emissions from municipal landfill sanitary sites; Atmospheric-Environment 28 (2), 285-293] [Christensen, T. H., Cossu, R. & Stegmann, R. (1999) Landfilling of waste: Biogas] Several accidents have occurred, for example at Loscoe, Englandin 1986. [Williams and Aitkenhead (1991) Lessons from Loscoe: The uncontrolled migration of landfill gas; The Quarterly Journal of Engineering Geology 24 (2), 191-207] 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 1991 [http://www2.mst.dk/common/Udgivramme/Frame.asp?pg=http://www2.mst.dk/Udgiv/publikationer/2001/87-7944-831-3/html/kap30.htm Danish 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 [Kerfoot, H.B., Chapter 3.5 In Christensen, T. H., Cossu, R. & Stegmann, R. (1999)Landfilling of waste: Biogas]
Techniques for the monitoring of landfill gas
Surfacemonitoring 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 off-site. The typical regulatory limit of methaneis 500 parts per million(ppm) by volume (in California, AB 32may push this limit down to 200 ppm). Surface monitoring can be broken down into Instantaneous and Integrated. Instantaneous monitoring consists of walking over the surface of the landfill, while carrying a flame ionization detector(FID). Integrated consists of walking over the surface of the landfill, while pumping a sample into a bag. The sample is then read with a FID or sent to a lab for full analysis. Integrated reulatory limits tend to be 50 ppm or less.
Gas probes, also known as perimeter or migration probes, are used for
Subsurfacemonitoring 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 monitor the
airaround a landfillfor 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. [Kerfoot, H.B., Chapter 3.5 In Christensen, T. H., Cossu, R. & Stegmann, R. (1999)Landfilling of waste: Biogas] Leachate water frequently has elevated levels of tritiumcompared to background groundwaterand 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 components can react with minerals 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 effects, since they are too water-soluble to migrate inlandfill gas. The presence of highly soluble semi-volatile organic compounds, such as phenols, are also consistent with leachate effects on the sample. Elevated concentrations of dissolved CO2have been shown to be a symptom of landfill gas effects - This is because not all of the CO2 in landfill gas reacts immediately with aquifer minerals, while such reactions are complete in leachate due to the presence of soils as daily cover in the waste. To assess whether VOCs are partitioning into groundwater in a specific location, such as a monitoring well, the headspace gas and dissolved VOC concentrations can be compared. If the Henry's Lawconstant 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.
* [http://www.ciwmb.ca.gov/LEACentral/LandfillGas/Monitoring/Screening/default.htm CIWMB policy]
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