Evidence of emissions from oil and gas drilling operations in northeastern Colorado

Since 2007, air samples collected regularly at NOAA tall towers and from aircraft across the US have been analyzed for over sixty different species, including greenhouse gases (CO2, CH4, N2O, SF6), CO, several hydrocarbons (propane, n-butane, pentanes, benzene, acetylene), and ozone-depleting substances. The Boulder Atmospheric Observatory (BAO) is a 300-m tall tower located 35 km north of the Denver metropolitan area in the northern Colorado Front Range. The BAO sits on the southwestern edge of the Denver-Julesburg Basin (DJB), home to over 15,000 oil and gas wells. Using in-situ meteorological data, we analyze the air composition of the BAO samples for three different wind sectors: the North and East sector (with strong contributions from oil and gas production operations and cattle feedlots), the South sector (dominated by the Denver urban area), and the West sector (containing the foothills of the Rocky Mountains and a few oil and gas wells). Air samples from the BAO North and East sector exhibit enhanced levels of alkanes that are strongly correlated with each other. To put these BAO samples in a regional context, we drove a mobile laboratory around BAO during the summer of 2008. A continuous methane analyzer was used to detect regional enhancements in methane and local plumes from point sources (including a natural gas processing plant, feedlot, and waste water treatment plant). Targeted air samples within and outside of plumes were collected and later analyzed in the NOAA lab. Samples collected over the DJB show very similar molar ratios of alkanes as the BAO samples from the North and East sector. These alkane ratios compare very well with the ratios measured in over 70 natural gas samples collected at various wells in the DJB in 2006.