Emissions from wastewater recycling at oil and gas drilling sites likely contributed to a string of high-ozone events in the winter of 2011 in Wyoming's Upper Green River Basin, according to a study released this week.
By studying the chemical signatures in emissions from oil and gas operations, the study, led by researchers at the University of Wyoming, found that wastewater treatment was a major source of non-methane pollutants that spurred ozone formation.
"What we've done is hopefully just highlight that it's an important source that should be considered," said Robert Field, an atmospheric sciences professor at the University of Wyoming and lead author of the report.
The study comes after research led by the National Oceanic and Atmospheric Administration last October linked oil and gas production in eastern Utah's Uinta Basin to high wintertime ozone levels in 2012-2013 (Greenwire, Oct. 1, 2014).
Ozone typically forms in the summer, when intense sunlight and humidity prompt chemical reactions between airborne nitrogen oxides and volatile organic compounds. It's far less common in the winter, but the NOAA study found that VOCs released by oil and gas activities built up to high enough levels to trigger reactions.
The study, released this week, was published Tuesday in Atmospheric Chemistry and Physics, a journal of the European Geosciences Union. The University of Wyoming School of Energy Resources and the Pinedale Anticline Project Office provided funding for the research, while the Wyoming Department of Environmental Quality provided data and external auditors.
The Upper Green River Basin is a sparsely populated area in southwest Wyoming that has two of the nation's top proved wet natural gas fields. Almost all the emissions in the area come from oil and natural gas activities, according to Department of Environmental Quality data.
Field and his team began studying the region's wintertime ozone levels and the mix of non-methane hydrocarbons in 2009.
They measured several high-ozone events in the winter of 2011, with ozone topping 85 parts per billion numerous times. The national standard for ozone is currently 75 ppb.
By measuring condensate in the non-methane VOCs during those episodes, the researchers say they were able to pinpoint a wastewater treatment facility as a major source of the ozone-causing emissions. According to the study, the facility, which is located in Sublette County and handles wastewater from drilling operations, releases toluene, xylene and other VOCs that are high in condensate.
"When we first started there ... I was not fully aware of the water treatment facility," Field said. "It was actually as we started to do the analysis of data and stated finding this condensate signature -- it was like, 'Where is this coming from?' It wasn't until we did the actual data analysis we realized it must be coming from this facility."
Wastewater treatment operations weren't the only hot spot for emissions at the oil and gas operations, but they're a significant factor that often goes overlooked in calculations of emissions, Field said.
He added, however, that it was difficult to apply the study's specific results to other oil and gas operations because they have different systems -- including those with smaller pumps -- for dealing with recycling wastewater. And the team has not yet studied how different factors might cause changes in the emissions released by the facilities.
He also noted that the team did not notice any high wintertime ozone levels in the winter of 2012. According to the study, 2012 coincided with reduced levels of total non-methane hydrocarbons. It's unclear yet what drove that reduction.
"Wyoming requires really, really specific conditions and levels of emissions to get ozone production going, and it's different from the Uinta," Field said. "There's a lot of other stuff going on in the background."
The research team is planning a future project in which regulatory agencies, an energy company and an advocacy group will participate in sampling the air for pollutants.
Field said that the team is hoping to use future research in Wyoming and Utah to get a better picture of the emissions profiles of oil and gas operations.
"We're hoping to use these measurements to get a better understanding of the geographical distribution of these pollutants and how they might vary from one place to another," he said.
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