Models to calculate landfill methane emissions fail to account for the benefits of waste diversion projects, including Waste-to-Energy (WTE) facilities, which now must count CO2 emissions in the Emissions Trading System (ETS).
Landfill methane dominates waste sector greenhouse gas (GHG) emissions. Yet, waste management professionals have not reached a scientific consensus on a reliable method to estimate methane emissions and the reductions from diverting organics from landfills.
Lifecycle assessment models estimate the long-term benefits of different waste management strategies. Still, they cannot produce realistic estimates of landfill methane generation and emissions to guide short-term planning efforts or monitor their progress. Landfill gas (LFG) emissions vary widely over time due to changing conditions that impact generation and the efficiency of LFG collection and control systems.
LFG models have the capability to account for such variability, but few go beyond the simple methods required for reporting emissions. Emissions estimates depend on assigned values for waste decay rates (k), methane generation potential (Lo), and LFG collection system efficiency, which have little empirical basis due to the inability to measure LFG generation directly or to find a valid way to solve simultaneously for these variables.
In the U.S., landfills have relied on a simple model, the EPA’s LandGEM, which used default k values developed in 1996 for “bulk” wastes disposed in dry or wet climates for three decades. Starting in 2010, U.S. landfills were required to report GHG emissions using slightly higher model k values for three climate categories assigned without referenced research.
The default input assumptions to model LFG generation in LandGEM and the GHG Reporting Rule persisted until 2025. Recent reports on satellite-based methane emissions measurements suggested that EPA methods often underreported landfill methane emissions and fueled efforts by environmental groups to force changes to the requirements for GHG reporting. However, the EPA solved for k using reported estimates of collection efficiency treated as valid “data” for model calibration. Nevertheless, the final version of the revised GHG Reporting Rules published in April 2024 (40 CFR 98 – see Table HH-1) used this method to assign values of 0.033, 0.067, and 0.098 for model k values in dry, moderate, and wet climates in the U.S., respectively. When run in the “AP-42 Emissions Inventory Mode,” the new LandGEM (3.1) version released in January 2025 now assigns k and Lo values based on the new GHG Reporting Rule.
Most European countries use the 2006 IPCC model, which applies multiple waste categories to estimate landfill methane emissions. Like LandGEM, IPCC’s model fails to recognize that waste decay rates vary incrementally across a wide range, reflecting different climates and moisture levels in landfills. IPCC offers four climate categories but only two for moisture levels, putting all landfills in Europe in the dry, temperate group.
Underestimating landfill methane emissions also undervalues the benefits of diverting organic waste from disposal. The inclusion of CO2 emissions from waste-to-energy in the EU Emissions Trading System will increase the costs of WTE and could drive an increase in landfilling unless avoided methane emissions are fully credited.
The best public tools for estimating landfill methane generation and emissions are country-specific LFG models developed by the Global Methane Initiative and EPA’s Landfill Methane Outreach Program and created by SCS Engineers between 2007 and 2014, which use IPCC’s multi-phase structure and improve on the k values to cover up to five climate zones.
About the Author: Alex Stege is a Vice President, Senior Project Advisor, and SCS Engineers’ National Expert on Landfill Gas Modeling. He leads SCS’s non-regulatory landfill gas (LFG) recovery modeling services, which have for decades supported developers and investors in LFG-to-energy and renewable natural gas (RNG) projects. Over nearly three decades, Mr. Stege has developed and updated the SCS LFG Recovery Model and led the team that applied it to prepare LFG recovery projections for methane utilization projects at hundreds of landfills in North America.
