Map of the District of Columbia showing where researchers found natural gas leaks under city streets, with colors indicating the concentration in parts per million of methane at each location. Duke University

A dozen leaks were so serious they posed a high risk of explosion. But, more worryingly, having brought these leaks to the attention of the city authorities, when the teams returned to re-assess gas escapes four months later, they found nine of the worst leaks were still emitting dangerous levels of methane, the main constituent of natural gas.In some of the worst cases, when manhole covers were lifted, methane concentrations as high as 500,000 parts per million were found. That’s roughly 10 times the level at which explosions may occur.Quite apart from the risks of explosion such leaks pose, the researchers also highlight the economic cost of the leaks to utility companies and how such leaks contribute to global warming. Like carbon dioxide, methane is a greenhouse gas — except methane is 20 times more potent a GHG than CO2 when it comes to trapping heat from the sun in Earth’s atmosphere.The researchers published their findings last week in the peer-reviewed journal Environmental Science & Technology The study quotes statistics from the U.S. Pipeline and Hazardous Materials Safety Administration (PHMSA) that natural gas pipeline failures cause an average of 17 fatalities, 68 injuries, and $133 million in property damage annually.Add to that PHMSA figures which, in a report issued 2009, titled, “Barriers to Implementation of Methane Emissions Reduction Projects in Gas Transmission and Distribution,” (PDF) said oil and natural gas systems in the US were the second largest man-made source of methane emissions at 23 percent.Highlighting that the technologies to reduce methane emissions were mature, in other words, fixing leaks isn’t rocket science, the PHMSA was critical of how methane leaks were being addressed, stating, “The issue seems to be more policy and precedent related than technology related.”The study released this week echoes PHMSA concerns that a potent greenhouse gas was leaking into the atmosphere yet the wherewithal to stop these leaks was readily available. Quite apart from methane also being known to catalyze the production of ozone (O3), a less life-giving version of oxygen, known to cause tissue inflammation , methane leaks are costing natural gas companies an estimated $3 billion per annum. The researchers estimated that between 2000 and 2011, natural gas customers in the US absorbed the cost of escaping gas to the tune of $20 billion.For the study a team from Duke University, led by Robert B. Jackson, professor of environmental sciences at Duke, collaborated with researchers from Boston University and Gas Safety, Inc. The team mapped gas leaks under all 1,500 road miles within Washington, D.C., using a high-precision Picarro G2301 Cavity Ring-Down Spectrometer installed in a car equipped with GPS.Subsequent laboratory analyses confirmed that the isotopic chemical signatures of the methane and ethane found in the survey samples closely tied in with that of pipeline gas. On average, analysis disclosed that methane in the leaks was about 2.5 times higher than in background air samples collected around the city. But in some leaks, methane levels registered as high as 89 parts per million, about 45 times higher than normal background levels.At four individual street-level sites, the volume of methane leaking out was measured. The readings came in at between 9,200 to 38,200 liters per day for each leak, comparable to the amount of natural gas used by between 2 and 7 homes.In a parallel study last year, more than 3,300 natural-gas pipeline leaks were logged beneath 785 road miles in the city of Boston.Commenting on the two studies, Nathan G. Phillips, a professor at Boston University's Department of Earth and Environment, said , “The average density of leaks we mapped in the two cities is comparable, but the average methane concentrations are higher in Washington."In common with many US cities, Washington and Boston’s city streets hide an aging pipeline infrastructure, ever more prone to leaks the older it gets. In cities where such infrastructure is judged to be at risk, the research team recommends comprehensive gas-leak mapping to assess the extent of the problem and associated hazards.Already, the aging pipeline problem has come to the attention of legislators. In November 2013, Sen. Edward J. Markey (D-Mass.) introduced two new bills aimed at accelerating the replacement of natural gas pipelines in states with older infrastructures. The proposals also offered new federal programs and incentives to help defray the costs associated pipeline replacement and repairs.