By Joe Joyce, WBZ-TV

BOSTON (CBS) – Boston has the second oldest and largest natural gas infrastructure in the nation. These aging pipes are leaking explosive methane gas and it may be occurring in a neighborhood near you.

“Across Massachusetts there are approximately 20-30,000 gas leaks at any given time.” says Bob Ackley of

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In the past, we have seen home explosions in Somerset, Gloucester, Hopkinton and North Reading because of the leaking odorless gas. Now for the first time, new video is revealing where methane concentrations are highest in the city of Boston. So far Only 1% of the city has been mapped.

WBZ-TV’s Joe Joyce reports.

“We have mapped out leaks which no one can see. This now allows us to see where they are.” says Nathan Phillips of Boston University. “What we need to do now in a systematic fashion look at all streets of Boston and greater Boston and cities beyond that to document this problem.”

Bob Ackley is a gas safety inspector and is used to grading these leaks on a scale of 1 to 3.

“A grade one leak is a hazard to person or property,” said Ackley.

He said the leaks are being incorrectly graded and continue to do damage to people’s property

“The gas companies are ignoring the fact that the gas is damaging property and not fixing the leak,” said Ackley.

Like a leak in West Newton which has been here for over one year.

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By taking measurements, Ackley measured how much Methane has leaked into the ground.

“It is saying there is 5% gas inside the manhole. That is a grade 1 explosion hazard. If that manhole explodes and comes off it could go right through a car,” said Ackley.

The gas is not only an explosive hazard but is also killing trees in surrounding neighborhoods by hardening the root system. The damage can be seen along Commonwealth Avenue.

“We have a newly planted tree here, and elm tree in severe decline, another elm in decline and some dead trees down here,” said Ackley.

The policy of the gas companies is to fix these grade one leaks as soon as possible. The problem is some people feel like the these leaks are not being addressed or fixed at all. So, there is a bill pending on Beacon Hill which will require the gas companies to fix all of the leaks within three years.

Marblehead’s Lori Erlich is fronting the effort.

“Without the bill they are left to drag their heels. This makes them hurry up and get these leaks fixed. To protect the public, protect the public’s purse and to protect the environment,” said Erlich.

Not all gas leaks are dangerous, but experts say if you have a gas leak near where you live, you should call immediately to get it fixed.

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Methane leaks are not just a problem in Massachusetts as over 800 billion cubic meters of the gas are lost annually across the nation from leaking pipes.