Nearly 6,000 Natural Gas Leaks Reported Beneath Washington DC Streets, Some With Explosion Risk

Beneath the streets of Washington, D.C., a network of thousands of aging natural gas pipelines is leaking, and several of the gas leaks are so concentrated that they pose the risk of igniting, according to researchers.

A team from Duke University and Boston University documented close to 6,000 leaks coming from the city's aging natural gas pipelines. Some leak locations had methane concentrations as high as 500,000 parts per million (ppm) of natural gas, an amount that's 10 times beyond the threshold at which explosions can occur.

The research team alerted Washington officials of the leaks, highlighting 12 that posed the risk of explosion. Four months after alerting the city, the researchers found that dangerous levels of methane were still being emitted in nine of the locations.

"Finding the leaks a second time, four months after we first reported them, was really surprising," study leader Robert B. Jackson, a professor of environmental sciences at Duke, said in a statement.

"Repairing these leaks will improve air quality, increase consumer health and safety, and save money," Jackson said. "Pipeline safety has been improving over the last two decades. Now is the time to make it even better."

In addition to being a contributor to global warming, methane escaping into the atmosphere as an economic impact. Methane leaking from pipes is the largest source of human-caused methane emissions in the US, amounting to about $3 billion worth of lost and unaccounted for natural gas each year, the researchers said.

To map the methane leaks beneath Washington's streets, the researchers used a car rigged with a GPS tracking system and a high-precision instrument that can detect natural gas.

The average methane concentration observed in the leaks was about two and a half times greater than in background air samples collected around the city. In some instances, methane concentrations were recorded at 89 ppm, about 45 times greater than then average background levels of methane in the city.

Additionally, four street-level leaks proved to be the source of a significant amount of methane.

"Methane emissions from these four leaks ranged from 9,200 to 38,200 liters per day for each leak -- that's comparable to the amount of natural gas used by between two and seven homes," said Duke Ph.D. student Adrian Down.

Last year, the researchers conducted a similar study in Boston. They found that the average density of leaks in the two cities was comparable, but in Washington the average methane concentrations were higher.

The research, which is published in the journal Environmental Science & Technology, may prompt city officials to take greater action to repair the leaks and upgrade aging infrastructure.

"We need to put the right financial incentives in place," Jackson said. "Companies and public utility commissions need help to fix leaks and replace old cast iron pipes more quickly."