A recent study by the Colorado School of Public Health has linked hydraulic fracturing to elevated levels of petroleum hydrocarbons in the air near drilling sites. The study, to be published in Science of the Total Environment, identified cancer and non-cancer impacts to residents living within a half-mile of drilling sites in Garfield County, Colorado. According to a press release issued by the University of Colorado, the researchers apparently found the greatest impact to be during the "relatively short-term, but high emission, well completion period." The researchers relied upon ambient air sample data from monitoring stations in the vicinity of the drilling sites in reaching their conclusions. What is unclear, however, is whether the elevated emissions are attributable to releases from the wells themselves or from emissions associated with the well drilling equipment and associated vehicle traffic.