PAVILLION — Data from a monitor near the Pavillion natural gas field showed no problems with air quality, according to results of a Wyoming Department of Environmental Quality study.
The agency placed a mobile monitoring station just east of the field — owned by Encana Oil and Gas — to measure levels of nitrogen oxides, hydrocarbons, particulate matter and ozone. In more than a year of testing, none of the results exceeded regulator-set levels.
Steve Dietrich, air quality administrator for the DEQ, presented the study to a group of 11 area residents at a meeting in Pavillion Wednesday night.
The agency set the mobile air quality monitor near Pavillion after resident complaints about air quality. The monitor continuously collected data from January 2011 to March 2012.
The agency measured the constant presence of several pollutants created by or associated with oil and gas drilling, but nothing exceeded air quality standards set by the U.S. Environmental Protection Agency. The agency moved the monitor to another location earlier this year.
“We didn’t get any indication from these results that we needed to take another step,” Dietrich said.
According to the data, only ozone — a pollutant created by the interaction of nitrogen oxides, oxygen and volatile organic compounds — bumped up against the legal limit. The eight-hour average of ozone met but never exceeded the standard for one day in mid-2011.
Nitrogen oxides — or NOx — reached about a fifth the legal limit at its highest. The annual average for the gas — generally emitted by combustion — was less than 2 percent the allowable amount.
Measurements of particulate matter were below dangerous levels. Larger matter reached about 80 percent the legal limit in its peak but averaged less than a tenth the legal limit over the year. Smaller matter also fell below what the EPA considers safe, averaging about 20 percent the legal limit annually and reaching just more than half the standard at its highest.
The monitor also detected levels of methane and nonmethane hydrocarbons, which aren’t governed by a state or federal standard.
The results disappointed several residents at the meeting, who questioned whether the monitor’s location — on a hill about 20 feet higher than much of the well field — skewed results. Some also wondered whether an unseasonably wet spring could have affected the data.
“We can tell we’re being impacted,” said Jeff Locker, a Pavillion-area resident with wells on his property. “I don’t think we’re getting a fair sample.”
Agency representatives said siting the monitor was a difficult process, adding they considered wind direction, access to electricity and topography before deciding where to place it.
“The real difficulty is there’s no such thing as a perfect space,” said Kirk Billings, an air quality analyst. “That’s just the nature of the beast.”
Some at the meeting wondered why hydrocarbon emissions aren’t limited by the EPA. Dietrich said he wasn’t sure, but would guess they’re governed by permitting processes and included as volatile organic compounds.
The state and EPA have also launched an investigation into whether activity in the same field contaminated several water wells in the area. A preliminary report released by the federal agency in December seemed to implicate the industry for water contamination, but the study was disputed by Encana and state and industry officials.
Data from another test by the U.S. Geological Survey was released in late September, and the EPA said it considered them consistent with the agency’s earlier testings — a claim disputed by the industry. The results are expected to be peer-reviewed in January.
Dietrich said the air near the field could be retested, but it would take some time to secure another monitor. The DEQ owns three mobile units, but they’re already committed to other projects.
“You want to put monitors everywhere you can,” he said. “But your pocket is only so deep.”