Tracer method to measure landfill gas emissions from leachate collection systems

This paper describes a method developed for quantification of gas emissions from the leachate collection system at landfills and present emission data measured at two Danish landfills with no landfill gas collection systems in place: Fakse landfill and AV Miljø. Landfill top covers are often designed to prevent infiltration of water and thus are made from low permeable materials. At such sites a large part of the gas will often emit through other pathways such as the leachate collection system. These point releases of gaseous constituents from these locations cannot be measured using traditional flux chambers, which are often used to measure gas emissions from landfills. Comparing tracer measurements of methane (CH4) emissions from leachate systems at Fakse landfill and AV Miljø to measurements of total CH4 emissions, it was found that approximately 47% (351 kg CH4 d−1) and 27% (211 kg CH4 d−1), respectively, of the CH4 emitting from the sites occurred from the leachate collection systems. Emission rates observed from individual leachate collection wells at the two landfills ranged from 0.1 to 76 kg CH4 d−1. A strong influence on emission rates caused by rise and fall in atmospheric pressure was observed when continuously measuring emission from a leachate well over a week. Emission of CH4 was one to two orders of magnitude higher during periods of decreasing pressure compared to periods of increasing pressure.