Letter to U.S. EPA re: Regulation of methane emissions from oil and gas development

2 Feb 2015

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Seth B.C. Shonkoff, PhD, MPH

Executive Director | PSE Healthy Energy

436 14th Street, Suite 808

Oakland, CA 94612  

(510) 899-9706


February 2, 2015


The Honorable Gina McCarthy

U.S. Environmental Protection Agency

Office of the Administrator 1101A

1200 Pennsylvania Avenue, N.W.

Washington, DC 20460


Re: Regulation of methane emissions from oil and gas development


Dear Administrator McCarthy,


As a national organization comprised of physicians, scientists, and engineers, PSE Healthy Energy ( appreciates the opportunity to share with you our scientific judgment regarding the regulation of methane emissions from oil and gas development and transmission. As you know, natural gas and petroleum systems are the largest industrial source of methane in the United States, accounting for approximately 29% of emissions. Upgrading equipment used to produce, store, and transport oil and gas is essential and promulgating federal regulations aimed to cut methane emissions from the oil and gas sector by 40-45% by 2025 (from levels recorded in 2012) is a step in the right direction. However, there are a few substantial weaknesses in this rule as it is currently proposed.


While climate change mitigation strategies will create their own economic, public health, and safety benefits, regulations aimed to reduce methane emissions will also reduce associated primary and secondary health-damaging air pollutants which are co-emitted (Petron et al. 2012; Petron et al. 2014; Gentner et al. 2014; EPA NSPS 2013). Reducing methane co-pollutants such as volatile organic compounds (VOCs) will reduce public health risks among populations living among oil and gas operations. This will only be possible, however, if regulations apply to existing infrastructure, which is projected to account for nearly 90% of methane emissions by 2018 (ICF International 2014).


Modern oil and gas development has expanded dramatically in recent years and an increasing number of people live, work, and play in close proximity to its operations. Consequently, the probability of acute and chronic exposures to associated air pollutants such as benzene, toluene, ethylbenzene, xylene, formaldehyde, and hydrogen sulfide have increased (Adgate et al. 2014; Shonkoff et al. 2014). Many of these air pollutants present direct risks to public health. For instance, benzene is a known carcinogen and chronic exposure to benzene has been shown to increase the risk of leukemia in workers (Vlaanderen et al. 2010) and children (Whitworth et al. 2008). Maternal exposure to airborne benzene has been associated with decreases in birth weight and head circumference in pregnancy and at birth (Slama et al. 2009) as well as neural tube defects among offspring (Lupo et al. 2011). Regional scale air quality studies have shown that oil and gas operations are a significant source of ambient benzene levels (Gilman et al. 2013; Pétron et al. 2012).


There are numerous health risks from other primary and secondary air pollutants that are co-emitted with methane during oil and gas development and transmission as well. For instance, elevated levels of formaldehyde have been found near upstream oil and gas operations in several states (Macey et al. 2014). Formaldehyde is a suspected carcinogen with a range of acute (mucus membrane irritation, dermal allergies, asthma) and chronic (pulmonary function damage, reproductive toxicity) health effects (Kim et al. 2011). Additionally, methane and many non-methane VOCs are also precursors to tropospheric (ground-level) ozone (Smith et al. 2009). Ozone is a secondary air pollutant and strong respiratory irritant associated with increased respiratory and cardiovascular morbidity and mortality (Jerrett et al. 2009). Modeling and measurement studies in Texas (Kemball-Cook et al. 2010; Olaguer 2012), Utah (Edwards et al. 2013), and Wyoming (Schnell et al. 2009) show high levels of ozone pollution associated with oil and gas development. These air pollution hazards could be reduced with a strong rule on methane emission reductions that includes existing infrastructure.


The scientific literature on air pollution associated with oil and gas development has grown significantly in recent years alongside the increase in domestic production. Air pollution studies from states with active oil and gas development have focused primarily on methane and VOC emissions and the formation of ground-level ozone. While additional investigations are needed, the majority of primary research on non-methane VOCs indicates significantly elevated emissions and/or atmospheric concentrations in areas of active oil and gas development. Although local exposure to emissions from oil and gas development have not been well-characterized, modeling and preliminary empirical studies indicate that intermittent spikes in emissions may pose additional risk to nearby human populations (Brown et al. 2014; Colborn et al. 2014; Macey et al. 2014).


While few epidemiological assessments have been undertaken, there is a growing body of literature that examines health hazards and health outcomes among populations in close proximity to oil and gas development. A risk assessment in Colorado suggested that those living in closer geographical proximity to well pads were at an increased risk of acute and subchronic respiratory, neurological, and reproductive health effects as well as slightly elevated cancer risks, driven primarily by benzene (McKenzie et al. 2012). Another study showed a greater prevalence of some adverse birth outcomes including congenital heart defects and neural tube defects for neonates born to mothers who live in higher compared to lower densities of oil and gas development (McKenzie et al. 2014). More recently, an association study using survey data showed higher reported health symptoms per person among residents living closer to shale gas wells in Pennsylvania (Rabinowitz et al. 2015).  


Many of the health risks associated with air pollutant emissions from oil and gas development can be dramatically cut by regulating methane emissions. However, the proposed regulations only cover new and modified sources associated with the production, processing, and transmission natural gas. In order to be effective these regulations must apply to existing infrastructure. Methane emissions from existing sources account for a significant proportion of greenhouse gas inventories (Kang et al. 2014), including emissions from decommissioned and abandoned wells which continue to leak even when plugged (Bishop 2013; Kang et al. 2014; Ingraffea et al. 2014). Again, it is estimated that nearly 90% of projected 2018 emissions from oil and gas development will come from existing infrastructure (ICF International 2014). The Clean Air Act (CAA) gives the EPA authority to craft greenhouse gas regulations for existing major stationary sources (42 U.S. Code §7411). Therefore, we strongly recommend the U.S. EPA extend its proposed rules for methane emissions to cover existing oil and gas infrastructure. 


In addition to public health hazard mitigation potential of a strong rule, there are several other areas that require further consideration if the new regulations will be effective from a climate change mitigation perspective. First, the U.S. EPA must update the global warming potential (GWP) used for methane to reflect the current scientific consensus from the IPCC AR5. The US Code of Federal Regulations currently assigns a GWP of 21 to methane, which is based on climate science from the mid-1990's. While the EPA has proposed to increase the GWP to 25 (based on consensus science in 2007 (IPCC AR4)) this is still well out of date. Current climate science (IPCC AR5) places the GWP of methane at 34 for a 100-year timeframe and 86 over a 20-year timeframe (Intergovernmental Panel on Climate Change 2013). Furthermore, IPCC AR5 also suggests that we do not have 100 years before a 2°C warming that is projected to result in a climate tipping point with positive feedback loops. Therefore, using the 20-year timeframe in addition to a 100-year timeframe is recommended. 


Second, the U.S. EPA must use accurate leakage rates to ensure an appropriate baseline for measuring reductions. To do so the U.S. EPA must incorporate top-down measurements from more recent analyses (Brandt et al. 2014; Miller et al. 2013; Pétron et al. 2014; Schneising et al. 2014), which consistently find significantly more elevated leakage rates than bottom-up estimates (Allen et al. 2013). Bottom-up estimates often fail to account for all sources of methane emissions associated with oil and gas development (Caulton et al. 2014).


The leakage rate defines the scope of the issue and the stringency of mitigation required. If the U.S. EPA estimates the 2012 leakage rate at 2%, this would entail finding and fixing 0.9% of the leakage. However, if a more accurate leakage rate as found in recent studies of 3.6% were used, this would entail finding and fixing 1.6% of the leakage, a far more difficult and time-consuming task. In the end, whichever 2012 leakage rate the U.S. EPA chooses to adopt will ultimately determine the effectiveness of the methane rules; therefore, it must be based on sound science.     


Our organization, PSE Healthy Energy, is dedicated to supplying evidence-based, scientific information and resources on energy choices including oil and gas development to a variety of stakeholders. We maintain formal affiliations and relationships with faculty members across a range of disciplines at a number of national institutions, including Cornell University, University of Pennsylvania, Stanford University, George Washington University, and the University of California, Berkeley. Our mission is to bring scientific transparency to important public policy issues surrounding such methods by generating, organizing, translating, and disseminating scientific information. We invite you to contact us or visit our website at, where we provide high-quality resources and analyses on modern forms of energy development.


Once again, thank you for the opportunity to share with you our views regarding the regulation of methane emissions from oil and gas production. Please feel free to contact us with any questions.





Seth B.C. Shonkoff, PhD, MPH

Executive Director | PSE Healthy Energy

Visiting Scholar | University of California, Berkeley

Affiliate | Lawrence Berkeley National Laboratory, Berkeley, CA



Jake Hays, MA

Director, Environmental Health Program | PSE Healthy Energy




Cc:      Dan Utech

            Special Assistant to the President for Energy and Climate Change

            The White House

            1600 Pennsylvania Avenue NW

            Washington, DC 20500 





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