Natural gas leaks across Washington, D.C: Their number, source, and relevance to greenhouse gas emissions

Background/Question/Methods

Natural gas use is expanding rapidly in the United States, developed through the combination of horizontal drilling and hydraulic fracturing.  Concerns over the net greenhouse gas balance and other environmental impacts have accompanied the natural gas boom.  One of the biggest uncertainties for understanding greenhouse gas emissions is the extent to which natural gas can leak out of pipelines that distribute the gas. We mapped all 1500 road miles in Washington, D.C., for methane leaks using a mobile methane analyzer.  We also sampled leaks for their isotopic composition to distinguish fossil fuel methane from other sources, including landfills, sewers, and wetlands.

Results/Conclusions

We mapped thousands of methane leaks across the streets of Washington, D.C.  Concentrations at the leaks were as high as 50-times background levels of methane in the city’s air. Based on the carbon isotope composition of the methane, all of the biggest leaks were derived from a fossil fuel source, likely coming from distribution pipelines under the roads and sidewalks. Specifically, pipeline gas had a d¹³CH₄ signature of -40.2‰. The average isotopic signature of the methane sampled at road leaks was -39.5‰, with biological sources from sewers, wetlands, and landfills being substantially different, typically -55 to 60‰. Reducing natural gas leaks will reduce greenhouse emissions, improve consumer safety and air quality, and save people money.  We call for a national program to map leaks across all major cities in the United States.