Comparison of Field Measurements to Methane Emissions Models at Municipal Solid Waste Landfills

Project Sponsor: Environmental Research and Education Foundation

Project Cost: $46,000

Investigators: Florentino De la Cruz (PI) and Morton Barlaz (co-PI)

Institution: North Carolina State University

Overview and Objectives

Landfills are the dominant disposal alternative for municipal solid waste (MSW) in the U.S. In 2018, U.S. landfills were estimated to emit 180 Tg (million metric tons) CO2 equivalents (CO2e), making landfills the third and fourth largest sources of anthropogenic methane in the U.S. and globally, respectively. With the exception of the California Landfill Methane Inventory Model (CALMIM), which models methane emissions directly, models estimate emissions by reducing methane production by the fraction of the methane that is collected and the fraction of uncollected methane that is oxidized in the landfill cover soil.  This approach can lead to considerable error due to uncertainty in methane production, the time-varying collection efficiency and the fraction oxidized. In a 2016 paper, we showed that models [EPA Greenhouse Gas Reporting Program (GHGRP), Intergovernmental Panel on Climate Change (IPCC) and California Air Resources Board (CARB)] overestimated measured emissions by a factor of 4 to 31 for a young landfill with no gas collection.

The overall objective of the proposed research is to quantitatively evaluate the relationship between measured and modeled methane emissions for at least 4 landfills.  In the proposed work, we will extend the 2016 analysis from one young (<3 years old) landfill without gas collection to a set of at least 4 landfills that are more typical (i.e., waste of varying ages and gas collection installed).

Landfills are considered the third largest emitter of methane in the US. Methane is an important greenhouse gas 28 times more potent than CO2


Research Approach

For each landfill, we will obtain measured data for methane emissions and collected methane.  We will also obtain information required to apply models to calculate production and emissions (e.g., waste quantity and composition, well coverage, soil cover types and coverage).  The site-specific data will be used with multiple models (GHGRP, IPCC, CARB, SWICS) to compare modeled and measured emissions. Sensitivity analysis will be conducted to identify critical model inputs and their impact on predicted emissions.

The potential for additional regulation of greenhouse gas emissions is high and it is unlikely that site-specific measurements will be used at each landfill at a useful frequency.  Thus, any regulatory scheme is likely to rely on the prediction of emissions using models.  It is therefore critical for the waste industry to understand the relationship between measurements and predictive models to effectively comment on proposed regulations.