National Physical Laboratory (NPL)

Measurements of Methane Emissions and Surface Methane Oxidation at Landfills: WR1125


Methane emissions from landfill were estimated to account for around 3% of the UK‟s total greenhouse gas emissions in 2009. The reported figure for methane emissions from landfill in the UK represents 41.5% of all UK methane emissions. The IPCC guidelines indicate that measurement of methane emissions is necessary to validate models and to provide confidence in country specific model parameters for waste management emissions. Previous studies have concluded that DIAL (Differential Absorption Lidar) is the best techniques for measuring methane emissions and a method for selecting a representative sample of UK landfill sites has been developed. A further requirement for measurement of methane oxidation in the capping layers was identified.

This report presents the results of measurement campaigns carried out using the NPL DIAL system to monitor emission fluxes of methane from nine landfill sites in UK from February to May 2011. NPL also collected air, subsurface and flux box samples for methane isotope analysis. This analysis and surface methane oxidation data have been provided by Royal Holloway University of London using an isotope measurement technique.

Three of the sites were active landfill sites and six were closed; all sites had gas collection systems in place. Site selection was carried out in conjunction with the Environment Agency and Defra. The help of the landfill site operators is gratefully acknowledged.

Methane emissions, as measured by DIAL, were significantly higher for active sites than closed sites due to the methane emitted directly to air from the uncapped active areas. There was no significant observable difference between methane emissions from sites closed before and after implementation of the Landfill Directive which came into force in 2001. Two of the sites, F and D had very low emissions, however site F was not operating under normal conditions during the measurement period. Site I stands out as having larger emissions than would be expected from a closed site. Methane emissions from the closed sites were not generally uniform across the whole site. This implies that there were areas of the site where the gas collection system may not have been operating efficiently.

Methane is emitted from landfill sites by passing directly through the soil cap, through cracks in caps, through leaking boreholes, leaks in gas collection systems or directly from uncapped operational areas of a landfill site. In landfill cover soils methanotrophic bacteria consume methane emitted from the landfill waste degradation below, and may even consume atmospheric methane.

In general the fraction of methane oxidised at the closed sites as identified in the plume was higher (18.4% average) than at the active sites (9.5% average) because much of the methane emitted to the atmosphere from the active sites was from the operational areas with no cover soil.

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