Study finds gas utilities’ methane emissions lower than EPA estimates

Metering and regulating station upgrades, changes in pipeline materials, better pipeline leak-detection instruments, and regulatory changes helped US natural gas utilities reduce methane emissions in the last 20 years to levels 36-70% below US Environmental Protection Agency estimates, a new study found.

The study by Washington State University researchers also showed significant variations by region, with some areas showing higher-than-average emissions because of large differences in the age and type of pipe in different parts of the US.

“A concerted effort by gas utilities to upgrade our nation’s pipeline network in order to enhance safety has contributed significantly to a declining trend in emissions from the gas distribution system,” American Gas Association Pres. David K. McCurdy said on Mar. 31 as the study’s results were released.

Safety is AGA members’ top priority, McCurdy said. “As we strive to make our systems safer by upgrading and modernizing our infrastructure, we are also making them cleaner.”

AGA sponsored the emissions measurement research with major gas utilities and the Environmental Defense Fund. WSU Regents Prof. Brian Lamb, from WSU’s Atmospheric Research Laboratory, led the study with assistance from Conestoga-Rovers & Associates, an engineering and environmental consulting firm.

Their work followed similar methane emissions measurement studies earlier at gathering stations, processing plants, pipelines, and storage facilities (OGJ Online, Feb. 11, 2015) and production sites (OGJ Online, Sept. 17, 2013).

The new study showed that:

• The measured local distribution system methane emissions were 393-845 gigagrams (Gg)/year, or 0.1-0.2% of nationwide totals.

• EPA’s higher 1,329 Gg/year estimates were based on a 1992 study in which Lamb and his colleagues participated that EPA used to develop its 2011 methane inventory.

• Out of 230 measurements, three large leaks accounted for 50% of the total measured emissions from pipeline leaks. In these types of emission studies, a few leaks accounting for a large fraction of total emissions are not unusual.

• When WSU researchers visited nine metering and regulation stations used in the 1992 study, they found an average of 10 times fewer emissions than what was measured 20 years earlier. Lamb attributed the decrease to changes in equipment and better inspection and maintenance.

AGA said the study’s results suggest that the number of pipeline leaks from mains decreased 20% and from services 16% because of better pipe materials, efforts to seal cast iron joints, and enhanced leak detection and repair procedures.

Gas utilities have installed modern plastic pipes since 1990 at a rate of 30,000 miles/year and installed cathodically protected coated steel mains at 1,500 miles/year, both connecting new customers and upgrading existing pipeline infrastructure, the trade association said.

Nearly 600,000 miles of distribution mains and service lines to serve 17.5 million additional customers also have been added, it noted. Pipes that may no longer be fit for service are being replaced with ones made from more modern materials, AGA said.

Jonathan Peress, EDF’s air policy director for natural gas, said on Mar. 31 that while the study shows definite improvements by utilities, up to an estimated $195 million/year of gas continues to leak nationwide.

“The new findings reinforce the fact that when regulators and companies both set their minds to fixing a problem, they can get some pretty good results,” Peress said.

Contact Nick Snow at

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