Precise measurements of leaks from natural gas pipelines across metropolitan Boston have shown that almost one-sixth of the leaks qualified as potentially explosive, and that a handful emitted half of the total gas lost.

The findings by CAS researchers differ significantly from results gathered by gas companies and other monitoring groups, says Margaret Hendrick (GRS’16). They also highlight the risks these fugitive gas emissions pose to safety and the environment.

Hendrick is lead author on a paper published in Environmental Pollution that emphasizes the need to develop standardized ways to detect leaks and prioritize their repair.

“We know we have a problem with aging natural gas infrastructure, but we need a better understanding of how big the problem is.” —margaret hendrick

Natural gas is considered a relatively clean fossil fuel—though methane (its main component) is a major contributor to atmospheric warming—but a substantial amount of the gas is lost in production and distribution. In Boston and other East Coast cities, gas pipelines may date back to the mid-19th century. About a third of the installed pipelines use leak-prone materials such as cast iron, wrought iron, or unprotected steel.

Hendrick—who joined the Institute for Sustainable Energy as a postdoctoral associate after receiving her PhD in September 2016—and researchers from BU and industry looked at emissions from cast iron pipelines at 100 sites in Greater Boston where leaks had been detected in the air along roadways.

“Even a very small leak can be a great safety concern,” says Hendrick. A 2014 gas explosion in Boston’s Dorchester neighborhood injured 12 people. There were 113 gas distribution pipeline incidents, with 18 fatalities, in the United States that year.

“We know we have a problem with aging natural gas infrastructure, but we need a better understanding of how big the problem is and the best ways to solve it,” Hendrick says.

One major issue is a lack of agreement on the number of gas leaks. In 2013, Nathan Phillips, a CAS professor of earth & environment, published a survey on all Boston roads that found 3,356 gas leaks. The most recent estimate from an annual report filed by National Grid with the Massachusetts Department of Public Utilities, which regulates natural gas in the state, is about half that number. Massachusetts categorizes gas leaks by risk, with potentially explosive leaks given a Grade 1 classification. The National Grid annual report cited 36 Grade 1 leaks—but the BU fieldwork, identifying 15 out of 100 leaks as Grade 1, suggests that figure may be low.

Even if all parties agree on how to assess gas leaks and prioritize their repair, fixing them will be expensive, and the cost would be borne by gas customers. “We’re stuck in this conundrum where if we were to retrofit this infrastructure quickly, there would be huge rate increases, and families might not be able to pay their utility bills,” Hendrick says. “But it isn’t if these old pipes will start leaking, it’s when.”

While the priority in dealing with leaks is to ensure public safety, it’s also critical to consider the climate implications, Hendrick says. In her most recent study, seven “super-emitter” leaks released half the methane. On average over a 20-year period, a methane molecule released into the atmosphere traps about 86 times as much heat as does a carbon dioxide molecule, says Phillips. Hendrick proposes a leak classification scheme that includes both safety and climate risks.

“We are consuming more natural gas than ever before in the United States,” she says. “We need research to try to characterize fugitive methane emissions across the entire natural gas system.”