Dangerous methane levels detected in D.C.

This map shows 5,800 places where a scientific survey sniffed out evidence of natural gas leaks. The scientists, who drove methane gas-detection equipment along all 1,500 miles of D.C. streets, also pinpointed a dozen manholes with enough gas to explode. Read related story.

The study pinpointed gas leaks where street measurements found methane concentrations significantly above background levels.

Gas leaks were most common in the Districts's oldest neighborhoods north of downtown around Logan and Dupont circles, as well as neighborhoods east of the Capitol. Study author Robert Jackson said such leaks are usually associated with old cast iron pipe that can corrode or buckle or open at joints.

The national Mall was relatively free of leaks.

NOTE: Normal background level for methane in D.C. is two parts per million.

SOURCE: Duke University's Nicholas School of the Environment.

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