Methane leaks from city pipes have dropped sharply, study finds

WASHINGTON — The amount of methane escaping from local natural gas distribution systems in cities and towns across the United States has dropped significantly in the past two decades, according to a nationwide field study released Tuesday.

The study, led by Washington State University researchers and published in the peer-reviewed journal Environmental Science and Technology, suggests that advancements in equipment, better maintenance and government regulations are helping drive down emissions of the potent heat-trapping gas, even amid a big jump in the miles traveled by distribution pipelines.

According to the research, methane emissions are 36 percent to 70 percent lower than current Environmental Protection Agency estimates — though the eastern United States, where distribution systems are older, has higher-than-average leaks. The EPA’s estimates are derived from a 1992 national study of the natural gas system — including sites revisited by the Washington State University researchers in 2013.

Methane, the primary ingredient of natural gas, is a short-lived but potent greenhouse gas believed to be 28 to 34 times more powerful than carbon dioxide at warming the atmosphere over a 100-year period. Although natural gas produces less carbon dioxide than oil or coal when it is burned for energy, leaks of non-combusted methane can undermine those environmental advantages.

The Obama administration is taking aim at methane leaks from the oil and gas industry, with plans for new Environmental Protection Agency rules clamping down on the emissions and coming Interior Department restrictions on venting and flaring natural gas produced from wells on public land.

Read more: Feds delay decision on methane mandates

Dave McCurdy, president of the American Gas Association that represents local energy companies and provided some funding for the study, said the findings reflect “a concerted effort by natural gas utilities to upgrade our nation’s pipeline network.”

The research published Tuesday is part of a broad series of 16 studies coordinated by the Environmental Defense Fund that aim to examine methane emissions across the oil and gas value chain. Funding for the new research came from the AGA, Con Edison, EDF, National Grid, Pacific Gas & Electric and Southern California Gas.

The research focused on underground pipeline leaks and the metering and regulating stations that make up local gas distribution systems ferrying natural gas to consumers. Sampling essentially began at the metering and regulating stations, where gas is measured and transferred from transmission companies to local distribution systems, and ended at customer meters at houses and businesses.

Researchers conducted direct measurements of methane at the 230 leaking underground pipelines and 229 metering and regulating stations. Thirteen different local distribution companies were involved in the project — a group that provides about 20 percent of the services nationwide and is responsible for 16 percent of the pipeline miles.

Ultimately, the researches estimated that methane emissions from the distribution system range from about 393 gigagrams to 854 gigagrams per year — about 0.1 percent  to 0.2 percent of the methane that is delivered nationwide.

The EPA estimate, based on the 1992 study, is 1,329 gigagrams.

Related story: Report finds methane emissions climbing from federal lands

The two studies used differing  techniques, but lead researcher Brian Lamb said the newer approach should be a more accurate assessment, reflecting how much methane is actually escaping into the atmosphere.

The older study involved digging down to pipelines, isolating leaking sections, measuring the emissions and then subtracting those that would have been lost in the soil. The newer approach used by the Washington State University team involved measuring known pipeline leaks on the surface.

The results were also validated by revisiting nine sites from the earlier study, where emissions were reduced by more than a factor of 10, Lamb said.

Lamb said he was surprised by the results — which demonstrated decreasing emissions despite a 44 percent increase in distribution pipeline mileage since the 1990s.

Lamb suggested the improvements could stem from utilities’ replacement of older, leakier infrastructure, as well as 2011 EPA requirements for utilities to measure and report methane leaks from their metering and pressure regulating stations.

But the Environmental Defense Fund said the study shows there is still too much methane gas escaping local distribution systems despite the improvements, with the losses comparable to the carbon dioxide from as many as 19 coal-fired power plants and valued at up to $195 million.

“While they remain a serious problem, the ongoing utility emissions also represent an important opportunity for companies and regulators to make a big dent in greenhouse pollution,” said Jonathan Peress, the EDF’s air policy director for natural gas.

Because a small number of leaks accounted for a disproportionately large share of overall emissions, targeted changes could yield big benefits.