News•September 21, 2015

Study: EPA May Be Underestimating Landfill Methane

Landfills may be emitting more methane than previously reported because the Environmental Protection Agency may be drastically underestimating how much garbage is being deposited in landfills across the U.S., according to a new Yale University study.

Banana peels, coffee grounds, plastic bottles and other detritus tossed in the garbage usually ends up in a landfill and emits methane as it decomposes. Methane is a greenhouse gas up to 35 times as potent as carbon dioxide as a driver of climate change over the span of a century, and landfills are the United States’ third largest source of methane emissions, according to the EPA. The Obama administration is focusing on cutting methane emissions as part of its Climate Action Plan.

A landfill in Arizona.
Credit: Alan Levine/flickr

The study, published Monday in the journal Nature Climate Change, examined more than 1,200 solid waste landfills, including those that are open and those that are closed and no longer accepting waste.

Using previously unavailable data from individual landfills, the study found that in 2012, about 262 million metric tonnes of waste were deposited in landfills across the country, more than double the 122 million tonnes estimated by the EPA. The agency may be underestimating the amount of waste landing in landfills because small waste disposal facilities are not required to report how much refuse they accept.

The study also found that open landfills emit 91 percent of all landfill methane emissions, while closed landfills are 17 percent more efficient than open landfills at capturing methane so it does not escape into the atmosphere.

EPA spokesman Robert Daguillard said the EPA has not yet reviewed the study.

“Our principal findings provide a more accurate estimate of municipal waste disposal in the United States compared to previous estimates,” study co-author Jon T. Powell, a Yale doctoral student, said.

The study’s primary goal was to learn more about the efficiency of methane capture systems at landfills, which are more effective after a landfill stops accepting new waste, he said.

“When a landfill reaches the end of its life, an engineered cap or barrier system is installed to seal off the waste material from the environment,” Powell said. “Open landfills typically have some areas that are ‘closed’ in this manner, but also have areas that do not have permanent caps, and it is more difficult to extract methane and other gases that are generated in these areas.”

Methane capture systems at open landfills aren’t installed quickly enough to capture methane from rotting food waste, he said.

Scientists unaffiliated with the study said it shows better data is needed to fully understand the extent of the climate challenge posed by landfill methane emissions.

“The overall significance is that although we already know that reducing methane emissions can bring great societal benefits via decreased near-term warming and improved air quality, and that many of the sources can be controlled at low or even negative cost, we still need better data on emissions from particular sources,” Duke University climate sciences professor Drew Shindell said.

A landfill gas collection system in Wisconsin.
Credit: Wisconsin Dept. of Natural Resources/flickr

The study implies that the solution to landfill methane emissions is better gas capturing technology, but there’s a simpler solution, Shindell said: Composting.

“We could simply not throw organics into the trash,” Shindell said. “So, behavioral change by composting our organics could prevent virtually all the methane emissions from landfills without requiring any of the technological fixes and complex regulations.”

Oxford University atmospheric physicist Raymond Pierrehumbert, who is among the scientists who believe cutting methane should be less of a priority than cutting carbon dioxide to tackle climate change, said the study is useful in evaluating methane capture systems at landfills. But it primarily underscores that landfill gas should be used more widely as an energy source and that people should throw less in the trash, especially organic matter.

“This study focuses on what comes out of landfills,” he said. “But what is more important is what goes into them. The less readily decomposable organic materials that go into landfills, the less methane will be produced.”

But improperly managed compost heaps produce methane, too. In Europe, many compost facilities use the gas they produce to generate electricity, he said.

“So, there is a very intimate connection between what people put in their trash and what comes out of landfills, but people also need to think about the fate of what doesn’t go into the trash,” Pierrehumbert said. “Plastic also decomposes, and worse, some of it only decomposes well in anaerobic conditions. Recycling helps, but the first line of defense is making less waste to begin with.”

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