A mix of volatile organic chemicals coming from the process of fracking oil and gas wells poses a health risk to people living within a half-mile of a drilling site, according to a new study by the University of Colorado-Denver School of Public Health.

The three-year study in Garfield County detected levels of chemicals such as trimethylbenzenes, aliaphatic hydrocarbons, and xylenes in the air. All those chemicals can have neurological or respiratory effects, the study said.

Those effects could include eye irritation, headaches, sore throat and difficulty breathing.

"Our results show that the non-cancer health impacts from air emissions due to natural gas development is greater for residents living closer to wells," the report said. "The greatest health impact corresponds to the relatively short-term, but high emission, well completion period."

Completions involve hydrofacturing, a process in which water, sand and trace chemicals are forced down the well under pressure to crack the rock to release more oil and gas and flowback, when the frack fluid and hydrocarbons return to the surface.

The study will be published in an upcoming edition of Science of the Total Environment.

"Our data show that it is important to include air pollution in the national dialogue on natural gas development that has focused largely on water exposures to hydraulic fracturing," said Lisa McKenzie, the study's lead author and research associate at the CU-Denver School of Public Health.

Mark Jaffe: 303-954-1912 or mjaffe@denverpost.com