SGC Rapport 204 Detection and quantification of methane leakage from landfills Sven-Åke Ljungberg, Jan-Erik Meijer, Håkan Rosqvist, Stig-Göran Mårtensson 2009 Landfills make a significant contribution to anthropogenic emission of greenhouse gases through emission of methane. Greater knowledge is needed about how methane leakage occurs and how to calculate its magnitude.The purpose of this project was to detect gas leakage and to measure and quantify methane emission from landfills using modern remote sensing techniques. In this project, a handheld laser instrument and an IR camera were used. The overall objective was to develop cost-effective methods for detecting and quantifying methane emissions from landfills. There are many methods available for measuring the methane concentration in air, both from close-up and from long distances. Combined with the use of a tracer gas, the methane emission from entire landfills can be measured relatively accurately. A number of methods are used to detect leakage from parts of landfill surfaces, but there are few methods for quantifying leakage from sub-zones.The laser instrument used in the project (Siemens AG, CT PS 8 laser system) can detect methane concentrations of ≥10 ppm, and has a maximum range of 30 m that can be extended to 150-200 m using reflective material as a backscatter surface. The concentration of methane is measured in ppm x m and can be stored in logs together with supplementary field data, such as landfill and atmospheric pressure, and weather and radiation conditions, for subsequent analysis after the fieldwork. The IR camera (FLIR ThermaCAM™ GasFindIR LW) has recently been introduced to the market, and was used in the project for detection and visualisation of gas emissions from landfills. The camera produces a thermal image of the gas emission. The thermal image data is stored digitally on a DVD unit connected to the camera.Field measurements with the laser instrument and the IR camera were carried out at seven Swedish landfills and two landfills in France. The investigated surfaces at the Swedish landfills were divided into different zones, such as top surface, slope, crest and toe of slope. The field measurements in France were taken over entire landfills. The methane emission varied between the different landfills in the project, and also between the different landfill zones. The results from repeated field measurements indicated that a landfill with a final cap and a successful gas recovery system produces barely measurable emissions. The weak points at a landfill are generally slopes, including crests and toes of slopes. Where the covering of the waste is inadequate, leakage often occurs at lift joints and in areas where waste protrudes through the cover. Other weak points are deficiencies in the gas recovery system. Leachate systems can lead landfill gas and thereby cause methane leakage.The laser instrument detects point source emission of methane by measuring the methane concentrations above the emission points. The IR camera detects and visualises the occurrence of methane emissions, and can be used to trace emission points and to illustrate the dispersion pattern of methane. Both laser and the IR instrument can be used to determine the exact position of the leakage source. Diffuse emission can only be detected if the emission is large, such as at the tipping face. Both the laser instrument and the IR camera are easy to use. The laser instrument can scan over an area of approximately 1 ha per hour. The smallest measurable point source emission gives a concentration level of approximately 60 ppm, which corresponds to a point source methane emission of the order of 35 – 290 m3 CH4/year.Scanning of the landfill surfaces showed that leakage could stop, increase or slow down. There are many reasons for these dynamics. Wind conditions, air pressure changes, and changes in the moisture content of the covering layer seem to be the most important. Along with wind velocity and variations in atmospheric pressure, moisture content in the ground is an important factor that affects methane emissions from landfill surfaces. Results from field measurements of the same feature/surface at different points in time and with different ground humidity showed that pores in the surface layer close when the moisture content is greater, reducing the landfill gas leakage. The large and sometimes rapid changes make it very difficult to get a picture of the distribution of the methane leakage over the landfill surfaces. Methane emissions were measured in different seasons, and also when the landfill surfaces had snow cover. The results showed that methane is emitted easily through porous snow. The same methane concentrations were recorded for GPS-fixed leakage features with and without snow cover. In the project, the chamber method was used to try to quantify methane leakage detected by the laser instrument. When chamber method results were correlated with the corresponding laser measurements, a relationship was evident. This produced a figure for emission. The relationship between the respective figures from laser and chamber method measurements was used to quantify the detected point source emissions at the French landfills. The total emissions detected with the laser instrument at the two landfills were estimated at 41 and 30 tons of methane respectively per year. These quantified methane emissions from detected points were smaller than the total emissions as reported by the landfill operators. The relationship indicates that it is the diffuse emission of methane that is predominant, and not the point source emission through holes, fissures, etc.If the objective is to produce a reliable measurement of gas emission from a landfill, the combination of laser/chamber method is not probably sufficiently accurate. However, if the objective is, for example, to determine and prioritise where measures should be taken at different landfill surfaces to reduce emission, the combination of laser and the chamber method is very usable. The measurement method tested was application-oriented, and the aim was that the measurements would provide information on which to base the planning and implementation of short- and long-term measures. Manuals were produced for the laser instrument and the IR camera, showing how the two instruments are to be used for detecting methane emissions from landfills.The project demonstrated how the laser instrument could be used by bouncing the beam off a simple reflector. Measurement using a beam path length of up to 200 m is possible. Examples of such applications are measurements over leachate ponds, beside a landfill and on parts of a landfill. Such measurements can give important information about emission conditions that are difficult to measure in any other way.Geoelectrical measurements have several areas of application for landfills, primarily in studies of groundwater pollution. In recent years, interest has also grown in investigating processes inside landfills. Based on results from previous studies, one of the aims of this project was to examine whether three-dimensional evaluation of resistivity measurements could be used to provide better measurements and understanding of the processes below the surface. According to previous studies, landfill gas movements can be visualised through geoelectricity measurements. In the experiment, resistivity was measured along eleven lines in an area 10 m x 10 m on a slope adjacent to a biocell reactor.The resistivity measurements showed results similar to or somewhat lower than the results shown in previous studies. High water content, ion content and high organic content can explain low resistivity, while high gas pressure in the ground partly explains high resistivity. It should also be noted that temperature variations affect resistivity. When the results from the resistivity measurements was compared with results from static chamber measurements and the laser instrument, no clear correlations were observed. The gas movements below the ground surface shown by resistivity measurements at the toe of the slope could not be confirmed with measurements above ground with the laser or static chamber methods. The results from the project show that combinations of laser, IR, chamber method and geo-resistivity measurements are a successful way to describe and map methane emissions from landfills. The mapping of emissions provides precise information useful for planning maintenance or improvement measures on landfill surfaces and gas recovery and leachate systems.