Comparison of Three Different Landfill Surface Methane Mapping Techniques: Lessons Learned and Policy Implications

Three different landfill methane surface emissions monitoring (SEM) techniques were compared at active and inactive landfills and in separate controlled release tests.  The deployed SEM techniques included traditional walking surveys with a human operator equipped with a portable methane concentration analyzer with a sampling pump, the drone-based equivalent of this traditional survey where the methane analyzer is instead mounted to a drone and a long sampling tube drags on the landfill surface, as well as a recently introduced laser-based sensor that mounts beneath a drone and measures path-integrated methane concentration between the drone and the ground.  Both drone-based solutions have received commercial interest as they address safety concerns with humans traversing challenging terrain on foot, and can increase the area covered by the survey, especially with the path-integrated sensor which can probe landfill areas with active machinery.  

 

Testing at landfill sites showed that while the drone-mounted, downward-facing laser was the easiest solution to implement in the field, it was also the least effective at identifying hotspots.  Although the walking survey and drone-based equivalent produced generally comparable hotspot mappings, the latter was faster to implement and also gave the cleanest and most repeatable indication of hotspots.  However, critically, results of the controlled release tests revealed poor correlation between methane surface concentration and emission rate for all techniques.  Additionally, parameters such as drone flight speed and the response time of the gas analyzer will affect the absolute magnitude of collected methane concentrations.  This is problematic for the likely success and efficiency of current and proposed regulations that require mitigation action based on specific volume fraction (concentration) thresholds such as 500 ppm.  Based on these results we recommend that site-total emission quantification techniques should be prioritised in both research and regulations, such that problematic landfills can properly be prioritise for action, which can then be supported by SEM data to identify where on the landfill the emissions are occurring.