New research from FluxLab at St. Francis Xavier University shows that Surface Emissions Monitoring (SEM), the standard method in North America for the past 30 years to measure methane emissions from landfills, can miss major sources of methane. SEM involves a technician walking over stable landfill areas in a back-and-forth pattern while using a handheld device to measure methane just above the ground. Some areas are unsafe to walk, such as active faces where new waste is added daily, explain researchers involved in the study. As a result, they say SEM cannot capture emissions from the entire site.
Athar Omidi, research associate at StFX FluxLab and the study's lead author
"Our findings show that SEM can work well under specific conditions, like at closed landfills no longer receiving waste, but it leaves large blind spots at active sites," said the study's lead author, Athar Omidi, a research associate at FluxLab.
FluxLab researchers assessed 10 landfill sites, two closed and eight active, using both SEM and vehicle-based methane surveys that measure methane across the entire landfill, including areas that are unsafe to walk. By comparing SEM results to more comprehensive vehicle-based methane surveys, FluxLab researchers found that SEM often detects only a fraction of total emissions, raising concerns about its use as the sole regulatory compliance tool.
"When regulations, like those released by the Government of Canada in December 2025, rely on SEM, we risk underestimating emissions, delaying mitigation, and missing opportunities for real climate gains."
WHY THIS MATTERS
Methane is a potent greenhouse gas. It is more than 80 times stronger than carbon dioxide over a 20-year period in terms of trapping heat in the atmosphere, Ms. Omidi says. Landfills are one of Canada's largest methane sources, making accurate measurement and reduction critical for meeting climate targets.
In December 2025, Canada released new national landfill methane regulations, identifying SEM as the standard on-site performance verification method. However, SEM cannot be used in unsafe or inaccessible areas such as active faces, leachate ponds, and composting zones: areas which can be among the biggest emitters, she notes.
METHANE LEAKING IN PLACES WE'RE NOT LOOKING
The results, they say, revealed a clear pattern. At closed landfills, SEM performed well, often pinpointing hotspots responsible for up to 67 per cent of total emissions. But at active landfills, SEM frequently missed the largest sources, detecting on average just 17 per cent of total emissions, with most undetected emissions coming from areas unsafe for technicians to access, the researchers say.
"This should have been a wake-up call for regulators," said Dr. David Risk, FluxLab director and study co-author. "Methane reductions are only as good as the measurements that prove them. For outcome-based regulations to succeed, we need monitoring approaches that see the entire site, not just the easy parts."
The study concludes that while SEM has value, it should be paired with other technologies like mobile surveying, drones, or remote sensing to ensure comprehensive site coverage. The researchers recommend establishing performance standards that guarantee at least 90 per cent of site-wide emissions are detectable. By combining SEM with newer, more flexible methods, landfill operators can improve accuracy, cut emissions faster, and strengthen public confidence in reporting, they say.
FluxLab, based at St. Francis Xavier University, specializes in advanced research on methane emissions measurement and mitigation. Through field experiments and technology evaluation and acceleration, the lab supports evidence-based policies and best practices for the waste management, oil and gas, and agricultural sectors.
