Assessing Accuracy of Tracer Dilution Measurements of Methane Emissions from Landfills with Wind Modeling

During the last decade regulators and the landfill industry expended considerable effort developing methods for measuring methane (CH4) emissions from landfills. These efforts are intended to better quantify greenhouse gas contributions from landfills, with data perhaps used to refine landfill operations for emission reduction. With the advent of a new measurement technology for quantifying trace gases in the atmosphere, the Tracer Gas Correlation Technique has emerged as the most promising tool for measuring whole-landfill CH4 emissions. Over the last two years Waste Mangement Inc. and the US EPA have embarked on a campaign to use this method to measure CH4 emissions at landfills with different climates, in different operational stakes, and with or without landfill gas collection systems. While these data provide invaluable insight into CH4 emissions, they are limited by the requirement that data be collected under “ideal” conditions, i.e., with a wind direction suitable for the existing road and measurement layout, a landfill gas plume that intersects the ground, daylight and absence of inclement weather. In addition, because of measurement costs at ay given landfill measurements are taken only a few times in a single year. Because data are limited, we propose use of a land-atmostphere model to predict CH4 emissions from landfills during non-ideal conditions and non-measurement periods. Preliminary results demonstrate this modeling framework can match measured wind and tracer data at a test landfill where the Tracer Gas Correlation Technique was applied. This is the first application of a land-atmosphere model for assessing landfill gas emissions and has the possibility of dramatically improving our understanding of CH4 emissions. I this project we will:

• Couple a 1-D model for advective/diffusive CH4 transport and reaction in landfill cover soils to an existing atmospheric model that we successfully applied to landfills;
• Using this new model, simulate CH4 emissions, tracer release from the landfill surface, and downwind gas plumes at two landfills with different cover soils and with existing CH4 emission data from the Tracer Gas Correlation Technique; and
• From this modeling work assess the representativeness of CH4 emission data from limited measurements for calculating year-round CH4 emissions for any given landfill, and develop guidelines for using limited CH4 emission data to predict annual emissions.

Publications
Final Report

Taylor, D., Chow, F., Madjid, D., and P. Imhoff, Atmospheric modeling to assess wind dependence in tracer dilution method measurements of landfill methane emissions, Waste Management, Available online 2 November 2017, ISSN 0956-053X, https://doi.org/10.1016/j.wasman.2017.10.036. (https://www.sciencedirect.com/science/article/pii/S0956053X17307821)