An industry-backed study of methane emissions from natural gas pipeline and storage infrastructure has found that the majority of measured emissions came from only a handful of the sites studied. This suggests that such emissions generally result from faulty equipment and are not endemic to natural gas infrastructure.
The study was led by researchers at Colorado State University (CSU) and sponsored by the Environmental Defense Fund, Dominion, Dow Chemical, Enable Gas Transmission Co., Kinder Morgan Inc., Columbia Pipeline Group, TransCanada Corp. and Williams. The Interstate Natural Gas Association of America (INGAA) also participated. The effort began in 2013 (see Daily GPI, Oct. 15, 2013; June 12, 2013).
Published Tuesday in the journal of Environmental Science & Technology, the study involved researchers from CSU, Carnegie Mellon University and Aerodyne Research taking measurements of methane emissions at 45 transmission and storage facilities throughout the country.
"This is the most comprehensive on-site study conducted to date on these types of facilities," INGAA said. "A second study will use this data to build a model of nationwide estimates from this sector, which can be compared with Environmental Protection Agency (EPA) greenhouse gas estimates. This study will be released in the coming months."
The study indicated that a few sites accounted for the majority of the measured emissions, INGAA said. "At the 45 sites researchers sampled, just two sites accounted for almost as much methane as the other 43 sites combined. The higher emissions at the two sites were likely due to a faulty valve," the association said.
"This finding indicates a need to focus methane management measures on sites and equipment with the highest emissions profile," said INGAA CEO Don Santa. "It's also very consistent with the direction INGAA members are voluntarily taking to reduce emissions."
The CSU-led study also identifies sources of emissions from natural gas transmission and storage that are under-reported in or excluded from another EPA emissions measurement program, called the EPA's Greenhouse Gas Reporting Program (GHGRP). Emissions reported in this study were higher than the emissions level reported in the GHGRP because the GHGRP excludes many sources and its reporting methods can underestimate emissions, INGAA said.
"This finding isn't surprising," Santa said. "The GHGRP only covers a small portion of the nation's natural gas compressor facilities. Under EPA reporting rules, only those facilities with emissions of 25,000-metric-ton carbon dioxide equivalent submit emissions data to EPA. In addition, some facility sources of methane measured for this new study are not included in the GHGRP, such as compressor and valve-related leaks in certain operating modes."
Santa said INGAA members have committed to develop industry guidelines for directed inspection and maintenance (DI&M) of natural gas pipeline facilities. DI&M is an EPA-recognized tool for detecting and mitigating leaks in a cost-effective manner, according to INGAA. "While most INGAA member pipeline companies use DI&M, the guidelines will improve consistency and uniformity, which should result in further emissions reductions and help focus efforts on reducing emissions from the pipeline equipment that has the potential to release the most methane," the association said.
According to INGAA, the natural gas transmission industry reduced the number of leaks along pipelines by 94%, preventing 122 million metric tons of carbon dioxide-equivalent emissions over the past three decades.