Typical Problems
Most landfills are highly heterogeneous environments, both physically and biologically, and the gas composition sampled can vary radically within a few metres.
Near-surface monitoring is additionally vulnerable over short time periods to weather effects. As the atmospheric pressure rises, the rate of gas escape from the landfill is reduced and may even become negative, with the possibility of oxygen incursion into the upper layers (an analogous effect occurs in the composition of water at the mouth of an estuary as the sea tide rises and falls). Differential diffusion and gas solubility (varying strongly with temperature and pH) further complicates this behaviour. Tunnelling effects, whereby large items (including monitoring boreholes) create bypass shortcuts into the interior of the landfill, can extend this variability to greater depths in localised zones. Such phenomena can give the impression that bioactivity and gas composition is changing much more radically and rapidly than is actually the case, and any series of isolated time-point measurements is likely to be unreliable due to this variance.
Landfill gas often contains significant corrosives such as hydrogen sulphide and sulphur dioxide, and these will shorten the lifespan of most monitoring equipment as they react with moisture (this is also a problem for landfill gas utilization schemes).
Physical settlement as waste decomposes makes borehole monitoring systems vulnerable to breakage as the weight of the material shifts and fractures equipment.
Read more about this topic: Landfill Gas Monitoring
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