We’re missing one of landfills’ main methane sources

Landfills’ work faces, the areas where fresh waste is dumped, are responsible for a huge share of methane emissions in US landfills, yet work face emissions have largely gone uncounted by traditional methods for monitoring greenhouse gases, according to a new study (Environ. Sci. Technol. 2024, DOI: 10.1021/acs.est.4c07572).

Most landfills do not measure these methane emissions because doing so is unsafe where heavy machinery is continually on the move. “You can’t really have someone walking around the site with a handheld instrument,” says Tia Scarpelli, a research scientist at the environmental monitoring organization Carbon Mapper and one of the study’s authors. “You don’t want to get hit by a bulldozer.”

To overcome this problem, Scarpelli’s team used sensors attached to aircraft. After taking a bird’s-eye view of 217 landfills across 17 states in the continental US, the paper’s authors detected methane emissions at over 50% of the sites. And at the ones with methane coming from their work faces, “we saw that the work face tended to dominate the total emissions,” Scarpelli says.

Landfill sites with gas capture operations were some of the worst emitters. “It’s not surprising that we see more emissions at landfills that have gas collection. The reason they have gas collection is because they’re larger and generate a lot of methane,” Scarpelli says. Even with gas capture technology, she adds, it’s inevitable that some methane will find its way into the atmosphere.

Yet some landfills don’t emit methane from their work faces, and that’s more of a head-scratcher. “I don’t think we necessarily have an answer to this,” Scarpelli says. “We did look to see if there was any potential environmental driver to it, but we didn’t see any clear answer there. So to me it seems like it’s at least somewhat driven by operational practices at the landfill.”