MARK GOCKE/Star-Tribune correspondent

A herd of antelope moves on winter range south of Pinedale as a drilling rig for a natural gas well looms in the background.

JACKSON - People around the Jonah natural gas field will likely notice more haze in the air during certain days, but that lessened visibility should not harm people's health.

So says TRC Environmental Corp. of Laramie, a consulting firm that analyzed air quality issues in the Bureau of Land Management's Jonah Infill Drilling Project Environmental Impact Statement.

In areas removed from the Jonah Field, such as Grand Teton and Yellowstone national parks - Class I airsheds, the most stringent on air quality stipulations - the document predicts impacts that will "potentially exceed" thresholds on a certain number of days per year.

"Whereas no violations of applicable federal or state air quality regulations are anticipated, significant project-specific and cumulative air quality impacts are anticipated to visibility at regional Class I airsheds under all alternatives," the document reads in its executive summary.

Local communities of Big Sandy and Pinedale will see the most visibility impacts, according to the extrapolative study.

The document analyzes several drilling alternatives, ranging from 497 current well pads to 3,100 new wells. The BLM favors a plan to allow 64 well pads per section as part of the project, or one well pad for every 10 acres.

Under the BLM's preferred alternative, Big Piney would see the most days with visibility impacts at seven. Boulder would have the highest changes in air quality, with an estimated five days exceeding threshold levels.

The alternative with the highest number of wells developed per year would have the most drastic visibility impacts, with Big Sandy experiencing 31 days of impacts above threshold levels, and the area also would have the most dramatic changes in air quality on those days, according to the document.

Alternative A, with the fewest new wells developed each year, would see Big Piney, Big Sandy and LaBarge having the most days above visibility threshold levels at 10 each, and Boulder would have eight days with the most dramatic changes.

The modeling scenarios used assumed the maximum field emissions that could potentially occur at the same time.

The likely biggest contributor to air quality problems is particulate matter, or PM 10s and 2.5s, coming from dust due to increased traffic and construction. Other pollutants are nitrogen oxides, carbon monoxide, sulfur dioxide, volatile organic compounds, and hazardous air pollutants such as benzene, toluene, ethylbenzene and xylene.

Flaring, occurring at a well's completion, is a factor in releasing some of these hazardous materials.

"During the completion phase, gas and condensate are both vented to the atmosphere and combusted (flared)," the document says. "Emissions from the venting of natural gas include (hazardous air pollutants) and (volatile organic compounds). Flaring emissions from the combustion of natural gas and condensate include" those items plus nitrogen oxides and carbon monoxide.

The BLM's preferred alternative would have some of the highest numbers of volatile organic compounds and hazardous air pollutant emissions, at 56,226.3 and 16,361.8 tons per year, respectively.

No adverse health affects are predicted as a result of these levels, the document states.

However, at five-acre well spacing, levels of benzene approach those considered "immediately dangerous to life or health."

Benzene can cause various forms of leukemia, and moderate levels can cause headaches, shakiness, elevated heart rate, vomiting and disorientation.

Long-term cancer risks to those living near the Jonah Field are considered extremely small, according to the document.

Environmental reporter Whitney Royster can be reached at (307) 734-0260 or at royster@mail.trib.com.