NEW YORK (CBSNewYork) — From the city to the suburbs, thousands of miles of some of the country’s oldest and decaying gas mains lay just below the surface of our streets.

As CBS2’s Dick Brennan reported, experts said the consequences could be dangerous or devastating.

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In the early 20th century, there were new roads, rails, and an underground system delivered gas to buildings around New York.

More than 100 years later the landscape has drastically changed — but some of those exact same mains are still delivering our gas today.

“That infrastructure is way past its service life, which is dangerous,” natural gas expert Mark McDonald said.

McDonald, who investigates gas explosions, said aging mains like the ones we have in the northeast are at greater risk for cracks and ultimately leaks.

He pointed to a string of accidents across the country, the largest of which happened in Northern California in 2010, it killed nine people and destroyed property.

“Her house was at the epicenter where the gas line exploded,” Kimberly Archie said.

Archie’s best friend’s home was destroyed in the blast.

Her friend’s loss inspired Archie, a documentary maker, to investigate and chronicle gas explosion cases.

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“You can have a ticking time bomb under your house and you don’t even know it,” Archie said.

A Con Edison spokesperson told CBS2 that since 2014 the company has been replacing old mains at a rate of 65 miles per year, a number that is expected to increase to 100 miles in the future.

PSEG said it too has been prudently replacing old mains and will triple its rate of replacement to 510 miles this year.

Adam Forman with the non-profit group Center For Urban Future said the new lines have decreased leaks by 30 percent, but many neighborhoods may still be vulnerable.

“It’s the oldest parts, so northern Manhattan, the Bronx,” Forman said.

Both PSEG and Con Edison said they’re doing more to check for leaks.

“It essentially would involve having a specialized truck drive down city streets. It’s not a big ordeal, and it will identify gas leaks just by driving over the main,” McDonald said.

Con Ed said it increased these surveys from once a year to thirteen times a year. Critics said the number should be even higher.

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You may also want to consider installing a gas detector in your home.