Unconventional natural gas extraction in the form of hydraulic fracturing began in the Marcellus Shale region in Pennsylvania in 2003. However, by around 2006 the number of wells drilled in the state began to increase rapidly and communities began to notice more intensively the impact of the industry (State Impact).

At the time of writing this post, permits have been given for almost 17,000 wells, and nearly 7,800 wells are in operation as sites of natural gas production, with more wells becoming active daily. As recorded by MarcellusGas.Org, a local citizen-led website that collates and provides information and data on gas well production in Pennsylvania, on average 1 new well was opened every 2 days in the state during September 2015.

Many of these wells and the related natural gas infrastructure of compressor stations, well pads, glycol dehydrators, water impoundment ponds and pipelines are densely located in northeastern Pennsylvania. Along with this infrastructure, inevitable concerns have arisen about environmental impacts, especially in relation to water and air pollution. While much attention has been given to water pollution through several high-profile cases of contaminated well water in areas of northeastern Pennsylvania, residents of this community have also had concerns about the relatively under-monitored effects of fracking on air quality.

Pollution sources at well pads

While air pollution can occur throughout the hydraulic fracturing infrastructure, including at compressor stations, pipelines and dehydrators, a recent white paper on air quality released for industry compliance also notes the different pollutants that are emitted at various stages of the natural gas well pads. While the fracturing process and the large compressor stations are well know as source(s) of pollution, the monitoring undertaken by participants in the Citizen Sense “Pollution Sensing” project has also demonstrated that well pads are possible sources of PM2.5.

As documented in the above white paper, examples of hydraulic fracturing operations that contribute to emissions of air pollution include:

  • Drilling: Engines in the drilling process are major sources of NOx and PM2.5.
  • Completions: Engines used to pump fluid and sand into a well bore during the fracturing process generate methane, NOx, VOC and PM2.5.
  • Completion Venting: The venting and removal of “debris, liquid and inert gases” from a completed well can generate VOCs, particularly at sites of wet gas.
  • Trucks: Diesel trucks are used through the fracturing process to transport “drilling and fracturing equipment, equipment, water, chemicals, waste water and other materials to and from a well site,” which can generate PM2.5 emissions.
  • Wellhead Compressors: These engines are “located at the wellhead to raise the pressure of the produced gas to that required in the gathering line. Wellhead compressors emit NOx, PM2.5, and VOCs.”
  • Condensate Tanks: These tanks “store higher-molecular-weight hydrocarbons (carbon number >5) that are separated on site from the produced gases. Emissions from condensate tanks include VOCs from tank working, breathing, and flashing losses.”
  • Pneumatic Devices: “Used for a variety of wellhead processes and a source of VOCs and methane.”
  • Equipment Leaks: Methane and VOC emissions are known to occur at well pads, but there are different estimates regarding just how high fugitive emissions may be. Numerous articles, including this study in PNAS, suggest methane emissions are significantly higher than official estimates indicate.

Reference: HRP Associates, “Managing the Requirements of Evolving Air Regulations across the Marcellus and Utica Shale Region,” white paper (September 26, 2015). Images:

  • Tower for drilling horizontally into the Marcellus Shale Formation for natural gas, from Pennsylvania Route 118 in eastern Moreland Township, Lycoming County, Pennsylvania, USA by Ruhrfisch, Wikipedia (2009).
  • Fracking diagram, Kelly Finan for Citizen Sense (2015).

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