With New Tools, a Focus on Urban Methane Leaks

Until recently, little was known about the extent of methane leaking from urban gas distribution pipes and its impact on global warming.  But recent advances in detecting this potent greenhouse gas are pushing U.S. states to begin addressing this long-neglected problem.

For environmentalists ... even small fissures in natural gas pipelines are a cause for alarm, because methane is a potent greenhouse gas.  Methane doesn’t persist as long in the atmosphere as does carbon dioxide, which lasts for centuries.  But in the 12 to 14 years that it lingers, methane traps heat at least 30 times more efficiently than does carbon dioxide.  Which means that many small natural gas leaks — too small to cause safety problems — can pose a serious risk to the climate. 

Those many otherwise minor leaks have been accumulating at an accelerating pace ... along gas distribution lines in Los Angeles, Boston, Baltimore, and all five boroughs of New York City. Natural gas escapes into sewer lines and buildings, rides up ventilation shafts, and descends into subways.  One recent study found leaks in Manhattan occurring at a rate of 4.25 per mile — a nearly 10 times greater leak density than the same study found in Cincinnati, Ohio, where Duke Energy addressed the problem with a recently completed, 15-year, $1 billion project to replace old cast-iron pipes with reinforced steel.  In a landmark street-level analysis of Boston’s natural gas leaks published in 2012, researchers found that the city loses nearly 3 percent of its supply through cracks in its aging pipes.   A subsequent Harvard University study, which sampled air from rooftops in the Boston area from 2012 to 2013, revealed atmospheric methane concentrations two to three times higher than previous estimates, amounting in total as enough to heat 200,000 homes, according to the study’s authors. 
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Gas distribution pipelines, which begin at what engineers call the “city gate” and deliver gas to homes and businesses, are different from gas transmission pipelines, which carry natural gas from production fields to distribution hubs.  Gas flows through distribution pipelines at relatively low pressure, and they’re closer to the surface, only two or three feet deep.  Their maintenance is up to the utilities that own them, and regulated by the states.  So even though leaks from the older ones threaten to take a serious bite out of federal efforts to slow the pace of climate change, the federal government can’t do much about them.  The problem is that states haven’t either.  Like the utilities, regulators and state legislatures haven’t monitored for tiny but climate-harming leaks, concentrating instead on immediate safety issues involving larger leaks that could combust. 

“The current regulatory framework in most states doesn’t recognize distribution leaks as an environmental problem,” says Simi Rose George, a regulatory affairs expert with EDF.  “That’s something we think needs to change.” 
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In 2010 Picarro, Inc., a technology company based in Santa Clara, California, unveiled a special kind of sensor, called a “cavity ring-down spectrometer” to detect atmospheric concentrations of greenhouse gases in finer detail than ever before.  If utilities fix gas leaks for environmental reasons, they can catch leaks decades before they have a chance to explode. 
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That effort has now mapped segments of the Los Angeles metropolitan area, along with Boston, Chicago and Indianapolis, outfitting Google Street View cars with Picarro sensors, wind gauges, and GPS.  It has revealed what might be considered an obvious trend, but one that nevertheless proves a point:  Cities whose infrastructure hasn’t been shored up in the last half century lose natural gas from their pipelines at higher rates than cities with newer pipeline infrastructure. 

The natural gas escaping from Boston’s pipelines accounts for 10 percent of the state’s greenhouse gas emissions.  “We think it’s a compelling tool to help regulators assess the need for pipeline replacement programs,” says EDF’s George.  She notes that if utilities fix gas leaks for environmental reasons, they can catch leaks years, even decades, before they ever have a chance to ignite and explode. 

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