Elevated benzene readings cause for concern in Gunnison
12-12-07

GUNNISON—Analysis of some air samples collected in buildings impacted by the Top Stop gas leak show instances of benzene concentration more than 470 times greater than the level set as an objective in state remediation operations.
Last week in a meeting of the Gunnison City Council with the city’s environmental consultant Lance Hess, city councilman Rod Taylor expressed a wide-felt sentiment when he said, “There’s been a lot of fear with this gas and what’s going on. I’m still quite confused at what’s safe and what isn’t. You see ‘parts per million’ and ‘parts per billion’ and all sorts of things. Is there some kind of chart out there that tells you what your exposure is?”
Answering Taylor, Hess recited exposure levels listed in a letter given to Gunnison residents who had air samples from homes and businesses tested for toxic fumes. The letter was distributed in tandem with the results of those tests.
Rather than parts per million or parts per billion, the letter explained benzene concentrations in terms of micrograms (one-millionth of a gram) per cubic meter. That letter lists levels of concentrations that, if exposed to them over certain lengths of time, could result in a one-in-a-million cancer risk (see table).
“It ranges from 0.29 micrograms per cubic meter over a 30-year period, all the way up to 8.8 micrograms per cubic meter [over a one-year period],” Hess said.
Lab results from Gunnison air samples have shown benzene concentrations ranging from 0.77 micrograms per cubic meter to 4,200 micrograms per cubic meter, Hess said in another interview this week.
That measurement, he said, was from the Casino Star Theatre’s basement dirt floor in what Hess called a “hot spot.” He said that the sample yielding the result was collected after the theater had already been closed down, and that such levels were not found in the auditorium or lobby areas.
Nevertheless, the measurement points out the hazardous potential of the leak.
Typically, the letter accompanying analysis results stated, the common practice following a petroleum release is to reduce benzene exposure levels to those that would yield a less-than one-in-a-million risk level for cancer.
However, because of background levels of benzene, sometimes that cannot be accomplished. In that case, “benzene concentrations are then cleaned up to levels consistent with concentrations generally found in the area.”
Environmental consultants such as Hess and Wasatch Environmental—the company hired by Top Stop and directed by the state to remediate the leak—are still trying to determine background levels in the Gunnison area.