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Thousands of gas leaks in Boston area, study finds

A screen grab of the interactive map created by Google and the Environmental Defense Fund that shows thousands of gas leaks in the region.

Environmental Defense Fund

A screen grab of the interactive map created by Google and the Environmental Defense Fund that shows thousands of gas leaks in the region.

An online map published Wednesday by Google and the Environmental Defense Fund reveals thousands of natural gas leaks under the streets of Boston and surrounding cities.

Just don’t expect a rush by utility companies to repair most of the pipes.

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The overwhelming majority of the leaks are small and do not pose immediate public safety threats. National Grid, Boston’s leading natural gas distributor, said such low-grade emissions typically are not flagged for repair right away but rather are monitored and then fixed in the normal course of pipe replacement.

“Everybody has to understand that there is a significant investment coming with these improvements and that will have impacts on our customers,” said Susan Fleck, National Grid’s vice president for pipeline safety.

Fleck called the map a helpful tool in the company’s ongoing effort to replace old pipes with flexible plastic materials and noted that National Grid assisted researchers with their work. But an immediate, wholesale repair project is unnecessary and impractical, she added.

The Environmental Defense Fund, however, is hoping its mapping project will inject utility companies and regulators with a sense of urgency about leaks that might not be severe enough to cause explosions but can harm the atmosphere and nearby wildlife. The nonprofit advocacy group, based in New York, also mapped Indianapolis and Staten Island and plans to study other cities.

“By showing how much gas is escaping, we believe we’re helping to highlight the value that can be achieved by accelerating utility efforts to find and fix leaks — not just the ones that present an immediate risk to public health, but ones that are more chronic in nature and can be a large source of greenhouse gas emissions,” said Mark Brownstein, associate vice president of the environmental group’s US climate and energy program.

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The Patrick administration pointed to a law recently signed by Governor Deval Patrick requiring utilities to repair the most serious leaks, called Grade 1 leaks, immediately and all Grade 2 leaks within 12 months. Gas companies also must file plans that include a timeline for removing leaky pipes. “Massachusetts has some of the oldest gas infrastructure in the country,” said Ann G. Berwick, chairwoman of the Department of Public Utilities.

The new maps are the result of a pilot program that outfits the same cars used to create Google’s “street view” maps with sensors that can detect methane gas. Online viewers can zoom in to see precise locations of leaks in their neighborhoods.

The Environmental Defense Fund sorted leaks into three tiers, signified on the map by yellow, orange, and red dots. Red dots, a small fraction of the total, represent the most serious leaks, which the group said cause as much environmental damage as a car driving 9,000 miles per day in the area. Leaks marked by yellow dots, by far the most common, are equivalent to a car driving between 100 and 1,000 miles per day.

On average, sensors detected one leak for every mile of road in Greater Boston. A leading cause, researchers said, is aging pipes. The project found more than half of area gas lines are more than 50 years old, and 42 percent are made of cast iron or other materials that are prone to corrosion.

In Indianapolis, where pipes are much newer, researchers found a total of just five leaks.

National Grid said it already planned to spend $1.8 billion replacing gas lines in Massachusetts over the next five years.

Callum Borchers can be reached at callum.borchers@globe.com. Follow him on Twitter @callumborchers.

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