Regulators and researchers alike have long been trying to accurately estimate leakage rates from natural gas infrastructure, in order to understand the potential effects of such emissions on climate and human health.   EPA’s Office of Inspector General reported last year that methane leaks from distribution pipelines accounted for more than 10% of total methane emissions from natural gas systems, and it recommended, among other things, that EPA work with PHMSA to address methane leaks from a combined environmental and safety standpoint.  Earlier this year, the Obama administration announced as part of its Climate Action Plan new goals to cut methane emissions from the oil and gas sector 40 to 45% from 2012 levels by 2025, and stated that new PHMSA standards for natural gas pipelines expected in 2015, while focused on safety, “are expected to lower methane emissions as well.”

A new study (led by Brian Lamb at the Laboratory for Atmospheric Research at Washington State University) posits that EPA’s model for estimating the amount of methane leaked from the nation’s gas distribution systems is outdated.  Direct Measurements Show Decreasing Methane Emissions from Natural Gas Local Distribution Systems in the United States, Lamb et al., at p. 5161.  EPA does not directly measure methane emissions for its yearly estimates.  These emissions figures are instead based on a 1992 study in which the Agency, in conjunction with the Gas Research Institute (GRI), compiled “emissions factors” for natural gas industry components, which are multiplied by an estimate of the number of such components across the U.S. to create a national estimate of methane emissions for the industry.  Id.  EPA annual emissions inventories are based upon the original emissions factors from the EPA/GRI study, which have not been revised in more than 20 years to reflect replacement and/or upgrades of metering and regulating facilities, reduction in miles of older cast iron and unprotected steel pipeline, increases in protected steel and plastic pipeline miles, and improvements in leak survey methods.  Id. at 5162. 

The study’s authors implemented a national sampling program, directly measuring methane emissions from underground pipeline leaks and metering and regulating facilities of 13 local distribution companies (representing 19% of distribution pipeline mileage) across the country.  Id.  Sampling results led to the development of emissions factors generally lower than those used in the 1992 EPA/GRI study (particularly for underground pipeline leaks and plastic mains), attributable to improvements in leak detection technology, replacement of older pipes, and better maintenance since the 1990s.  Id. at 5163.  The study concludes that between 0.10% and 0.22% of total gas delivered via the national’s distribution pipeline network is lost through leaks, an estimate 35% to 70% lower than EPA’s estimate in its 2011 emission inventory.  Id. at 5167. 

The study comes on the heels of recent efforts in several states (California, Massachusetts, and New York, for example) to require natural gas pipeline operators to monitor and/or address leaks on their systems, both for environmental and public safety reasons.  Despite indications in the study that methane emissions from gas distribution systems have decreased in recent years, given the current interest in climate change and safety impacts associated with gas pipeline leaks, EPA and PHMSA regulatory efforts to address pipeline-related emissions are likely in the near future.  System operators and the public should be aware of this new information when new rulemaking proposals are made available for comment.