Boston's aging natural-gas pipeline system is rife with more than 3,000 leaks, some of which could pose explosion risks, researchers say.

A study by researchers at Boston University and Duke University found 3,356 separate natural gas leaks under the streets of Boston, a release from Boston University said Tuesday.

"While our study was not intended to assess explosion risks, we came across six locations in Boston where gas concentrations exceeded the threshold above which explosions can occur," BU earth and environment Professor Nathan Phillips said.

In addition to the explosion hazard, the researchers said, natural gas also poses a major environmental threat because methane, the primary ingredient of natural gas, is a powerful greenhouse gas that degrades air quality.

The leaks were distributed evenly across Boston neighborhoods and were associated with old cast-iron underground pipes, they said.

"Repairing these leaks will improve air quality, increase consumer health and safety, and save money," Duke researcher Robert B. Jackson said.

The researchers said their study, published in the journal Environmental Pollution, could guide policymakers and utilities as they work to replace and repair leaking natural gas pipeline infrastructure.