And the project’s results suggest that some urban areas may have even more leaking pipelines than originally suspected. In fact, according to the lead author of the paper Joseph von Fischer, a biologist at Colorado State University, urban natural gas pipeline leaks have been poorly studied, meaning many cities may not be sure how much methane they’re losing each year.
“There have just been a handful of studies, and the problem is that it’s really very labor-intensive to measure the leaks from the distribution system,” he said.
But pinpointing these leaks is important. While most natural gas pipeline leaks aren’t a big hazard from a health perspective as long as they’re outdoors, they can occasionally spiral into huge problems for both humans and the environment. Just last year, a ruptured pipe at a storage facility above Los Angeles resulted in one of the biggest accidental greenhouse gas leaks in U.S. history, spewing nearly 100,000 tons of methane into the atmosphere before it was plugged months later.
The new strategy streamlines the process of looking for leaks by pairing methane-sensing equipment with Google cars. The equipment works on its own, the cars are roaming the streets anyway, and the drivers require no additional special training.
The methane-sensing instruments involve special infrared laser technology that can detect, in real time, how much methane is in an air sample. In preliminary experiments, the scientists conducted tests to determine the system’s accuracy and found that the cars were best able to detect leaks within a distance of 20 meters, or about 65 feet. But this works in urban settings where pipelines run beneath the streets and among buildings, von Fischer said.
“The distance from the middle of most city streets to the location of the front of a house is typically 60 feet or less,” he said. “We felt that that was an adequate distance range because we felt that most of the leaks we observed would be within that distance range.”
The researchers developed an algorithm for determining the rate at which methane was leaking from any detected pipeline break, and they also came up with a simple classification system for the size of the leaks they discovered: small, medium and large. This system, von Fischer said, was mainly about helping them communicate their findings to the public and providing useful information to utilities about which leaks should be addressed first.
In the paper, the researchers have described their findings in five cities: Burlington, Vt., and Indianapolis, which have more modern pipelines thanks to accelerated pipeline replacement programs, and Boston, Staten Island and Syracuse, N.Y. In each city, drivers were instructed to pass down every street at least twice.
Not surprisingly, they discovered far fewer leaks in Burlington and Indianapolis — just 11 and five leaks, respectively, compared with hundreds or even thousands in Boston, Staten Island and Syracuse. The results translated to 6 leaks per 100 kilometers of roadway in Burlington and 0.4 leaks per 100 kilometers in Indianapolis, compared with 56, 63 and 28 leaks per 100 kilometers in Boston, Staten Island and Syracuse, respectively. That said, the rate of methane escape tended to be highest in Boston. Overall, the researchers estimate that Boston is losing about 1,300 tons of methane each year in pipeline leaks, compared with 1,000 tons in Staten Island and 300 in Syracuse.
In general, most of these individual leaks can be classified as small. But the researchers note that their method is probably significantly underestimating the number of leaks — especially small leaks — in any given city. Their studies have suggested that their likelihood of detecting a small leak in any given drive-by was about 35 percent, while the probability for a medium leak was 63 percent and 74 percent for a large leak.
The researchers say that when they compare their data with leak maps assembled by utility companies, they’ve consistently identified leaks the utilities were unaware of — and vice versa. This suggests that the drive-by strategy could be used in conjunction with the leak-detection efforts used by utility companies to identify more problem spots, von Fischer said.
The near-term goal is “giving utilities a tool to be able to rank the size of their leaks and make cost-effective repairs,” he added. “This is a scientifically sound tool that brings about really rapid and low-cost ability to find the largest leaks so they can be targeted for replacement.” In fact, he said, the team has partnered with a New Jersey utility, which has used its data to make about $900 million worth of pipeline repairs and replacements.
The Environmental Defense Fund has made some publicly available leak maps for certain cities using the project’s findings. But von Fischer cautioned that these results shouldn’t cause city residents undue alarm. From a public health perspective, he said, most methane leaks are considered safe — they’re not a health hazard or an explosion risk. In outdoor spaces, where the gas is allowed to seep up through the ground and straight into the atmosphere, leaks are generally considered low-risk.
But methane leaks are wasted resources, from an economic point of view, von Fischer said. And from an environmental perspective, methane leaks can be a big problem for the climate. Methane is believed to be up to 30 times as potent as carbon dioxide as a greenhouse gas, but its global sources and emission rates are much less well quantified.
In addition to natural gas pipeline leaks, methane is leaked from oil and gas drilling operations and emitted from landfills and livestock farms, as well as from natural sources such as wetlands. Thawing permafrost is also proving to be a major source of global methane emissions. So pinpointing the human-caused sources of methane and finding ways to reduce them can be a major practical way to combat climate change.
“I think that environmental issues are inherently multifaceted — they arise from human use of technology, they arise from social and economic factors, and they arise within a political and legal framework,” von Fischer said. “It’s been fascinating for me to be on the technological and science side, but partnering with people both on the industry side and on the environmentalist side to help bring about resolutions to those issues.”