Comprehensive Study Shows Decreasing Emissions from Local Natural Gas Distribution Systems

Washington, D.C. – A study published today in Environmental Science & Technology led by a team from Washington State University (WSU) found that emissions from local natural gas distribution systems in cities and towns throughout the U.S. have decreased in the past 20 years, to levels 36 to 70 percent lower than current estimates. This reduction reflects significant upgrades at metering and regulating stations, improvements in leak detection and maintenance activities and replacement of older pipeline materials.

“A concerted effort by natural 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 natural gas distribution system,” said AGA President and CEO Dave McCurdy. “Natural gas utilities are leading a fact-based dialogue about our nation’s energy future. Better data informs that conversation and help us to continually improve the delivery of natural gas to homes and businesses safely and reliably.”

Led by Regents Professor Brian Lamb in WSU’s Laboratory for Atmospheric Research with assistance from Conestoga-Rovers and Associates, an engineering and environmental consulting firm, the study provides the most comprehensive set yet of direct measurements of emissions from the distribution system. They estimate that emissions from the distribution system range from approximately 393 to 854 gigagrams per year, which is between 0.1 and 0.2 percent of the natural gas delivered nationwide.

The U.S. Environmental Protection Agency’s annual Inventory of U.S. Greenhouse Gas Emissions and Sinks currently uses data collected in the 1990s in a study sponsored by the Gas Research Institute and the EPA. The WSU researchers found dramatically lower emissions, particularly, at metering and regulating (M&R) stations. In fact, because of the significant differences they saw from data from the early 1990s, the researchers revisited nine sites from the previous study and found an average of one-twelfth fewer emissions than 20 years ago from those M&R stations. The researchers also measured reductions in emissions from individual pipeline leaks as compared to earlier studies.

“Because of its abundance and inherent efficiency, natural gas is a foundation fuel for our nation’s clean and secure energy future. Safety is our top priority and as we strive to make our systems safer by upgrading and modernizing our infrastructure we are also making them cleaner,” said McCurdy.

Results from the study by WSU suggest that the number of pipeline leaks have decreased 25 percent for mains and 16 percent for services due to the use of better pipe materials, efforts to seal cast iron joints, and enhanced leak detection and repair procedures.

Since 1990, natural gas utilities have installed modern plastic pipes at a rate of 30,000 miles per year and installed cathodically protected coated steel mains at 1,500 miles per year, both connecting new customers and upgrading existing pipeline infrastructure. They have also added nearly 600,000 miles of distribution mains and service lines to serve 17.5 million additional customers. Pipes that may no longer be fit for service are being replaced with ones made from more modern materials.

Decisions to replace pipe are rooted in enhanced risk-based integrity management programs. America’s natural gas utilities work with their state regulators, legislators and other key stakeholders to advance important safety policies that both enhance system integrity and support increased access to natural gas service for homes and businesses.

AGA and many of its member companies were involved in the development of, and have been partners in the EPA’s Natural Gas STAR program since its inception in 1993, and the industry is working with EPA to develop a new voluntary Gold STAR certification for the natural gas distribution sector. In May 2014, the AGA Board of Directors also approved a set of voluntary guidelines for the purpose of further emissions reductions.

Dr. Lamb’s project is part of a group of ongoing studies that are looking at the entire natural gas supply chain, from the production wells to the transmission pipeline system to local distribution systems. The study was done in coordination with major natural gas utilities and the Environmental Defense Fund.

As part of the study, the research team carefully measured numerous sites selected from lists of known leaks provided by the twelve participating utilities in various regions around the country that met specific criteria to ensure a comprehensive and representative dataset. The researchers took direct emissions measurements of 230 randomly selected, representative leaks from underground pipelines as well as at 229 metering and regulating stations where natural gas is measured and regulated from higher pressure pipelines to lower pressure distribution pipelines.

The group also used different methods than in the previous study, which Lamb believes results in a more accurate assessment of the actual emissions. The researchers made twice as many measurements as in the previous study and carefully checked their results with back-up methods.