Several different technologies can be used to measure landfill gas emissions. But it is important that landfill operators find the most cost-effective and effective method for their site. Since methane forms the largest component of landfill gas, it is also the primary gas found in LFG emissions. Methane is also a potent greenhouse gas that contributes to climate warming. Monitoring methane emissions will give an indication as to how much landfill gas is being emitted from a site, in terms of both methane and total LFG emissions.
Methane emissions can be measured above the surface of a landfill to gauge potential LFG emissions or it can be measured directly by testing the rate of emissions or changes in the rate of emissions. Techniques used for monitoring LFG emissions above the surface of a landfill include surface emission monitoring, ground-based imaging and low-altitude, and aerial and satellite imaging. We will be covering each of these monitoring techniques in a series of articles, starting with surface emission monitoring in this first article.
Surface emission monitoring
Surface emission monitoring (SEM) is a method whereby a portable methane measuring meter is used to measure methane levels on or near the surface of a landfill as the operator transverses the landfill site.
Landfills generating more than 50 megagrams of non-methane organic compound emissions per year were required to conduct surface emission monitoring under the New Source Performance Standards (NSPS) regulation; however, recent changes by the EPA now require landfills that generate 34 megagrams/year to conduct surface emission monitoring. California’s surface emission monitoring requirements are even stricter than those set by the EPA, requiring more extensive methane monitoring and lower methane levels.
Both the EPA’s and California’s LFG emissions regulations require set standards to be followed in terms of how the surface emissions monitoring should be conducted. Some of the key requirements include:
- Pathway spacing — the EPA requires a serpentine pathway to be used for monitoring, with 30-meter intervals; while California requires a much-reduced spacing of 7.6-meter intervals.
- Instantaneous and integrated monitoring — Instantaneous monitoring of methane levels on the surface of a landfill at a specific location and time to record methane emissions at specific locations, whereas integrated monitoring refers to average methane concentrations from aggregated methane measurements collected across a specific area or grid of a landfill. While both types of monitoring can be conducted simultaneously, additional data processing is required.
- The action level for reducing emissions
- Monitoring cover penetrations such as gas wells — As cover penetrations are points where LFG is most likely to leak out from, both the California and new NSPS require cover penetrations (such as wellheads and vents that penetrate the landfill cover) to be monitored for potential LFG leaks.
- Monitoring frequency — While both the California and NSPS regulations require surface emissions to be monitored quarterly, California does allow for less frequent monitoring if certain conditions are met. The EPA only allows less frequent monitoring for closed landfills that meet certain requirements.
The costs associated with meeting the California LFG surface emission monitoring requirements are estimated to be around three times more expensive than the costs associated with meeting the EPA requirements. This is largely due to California’s requirement for a reduced path spacing, together with costs associated with additional equipment and data processing that is required under the Californian regulation, and costs associated with monitoring cover penetrations. The costs associated with surface emission monitoring can range from a couple of thousand dollars to over ten thousand dollars per monitoring event.
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