Investigators confident extent of gas leak has been found
By John Hales
2-13-08

GUNNISON—Environmental consultants working on the Gunnison Top Stop gas leak are feeling confident they have identified the extent of the leak.
At a meeting last week to update the city and residents about cleanup efforts, Lee Barrus of Wasatch Environmental said his company had “pretty much defined the plume [leak] area,” based on extensive samplings in the area.
“We’ve gone to tremendous lengths to find out where the plume is. We feel very confident that our map is accurate as to where the plume is,” Barrus said.
That map, which Barrus distributed as a visual aid at the meeting, shows the plume extending in a southwesterly direction from Top Stop’s lot, and at one point splitting into two branches.
Identification of the plume has been a primary objective in cleanup efforts to date, along with the reduction of fumes in homes and residences.
In January, Wasatch Environmental found free-phase gasoline floating on top of the water table in one area, something that had not been significantly found before. The discovery was a breakthrough, said Lance Hess, the environmental consultant hired by Gunnison City.
“This is exciting because it represents a very dense ‘center of mass’ of the plume. … It is the central mass of petroleum we have been anticipating,” Hess wrote on the city’s website dedicated to gas leak information.
Barrus offered more bits of good news. He said apparently the plume had not reached the river, or if it had, it was going underneath it rather than into the water itself.
Wasatch Environmental has installed a system, called a curtain system, near the river that will both monitor contamination levels and filter and clean the water underground.
He said monitored levels of contaminants were “so low we’re not even calculating removal rate.”
As to removal of contamination, Barrus reported significant gains in the rate at which gasoline was being removed from the soil.
“We’ve almost doubled the extraction rate we had before,” he said.
From the time that extraction units first began removing gasoline from the soil until Jan. 6, about 4,060 gallons had been cleaned up, an average of roughly 1,000 gallons per month.
In just slightly less than three weeks after that, however, another 1,500 gallons were removed.
In addition, Barrus said, Wasatch Environmental had hauled away 25,000 tons of contaminated dirt, but didn’t know how much fuel was contained therein.
“In that dirt was who knows how much fuel. It’s hard to say how much,” he said.
Barrus was also unable to offer any kind of timetable for the cleanup, when asked how much of the approximately 20,000-gallon leak he expected to be able to extract.
“I think it’s a little early to be able to say ‘this is how much we’re going to get out, and this is how long it’s going to take,’” he said.
In other developments not discussed at the meeting, Lance Hess sent a letter to the city that gave evidence that the leaking tank may have had not one hole but two, lending credence to the idea that the tank had been leaking prior to July.
Hess arrived at his conclusion after examining statistical inventory reports (SIRs) from the leaking tank.
With the SIR method, a stick measurement is taken at the beginning of each day. The number of gallons is determined by where on the stick the fuel level reaches. At the end of the day, another stick measurement is taken, and that level is compared to where it ought to be as derived from the number of gallons dispensed from the tank. The method does allow a certain margin of inaccuracy, meaning that a difference between the measured amount and the derived amount does not necessarily indicate a leak.
However, Hess said, he found instances of “statistically significant” fuel loss at levels below where the hole is supposed to have been.
It had been maintained that the hole in the tank was located about three feet up from the bottom along a welded seam. However, in the early days of the leak, depending on who one talked to, there was also mention of a hole at the bottom of the tank.
Hess said this “second hole theory” could account for those divergent accounts, as well as for the inventory discrepancies.
Hess said, however, that even if the theory turns out to be true, that does not mean that Top Stop necessarily knew about it, because of the inadequacy of the SIR method.
However, Hess did note that Top Stop continued to sell gas and fill the leaking tank even after significant losses were indicated in July.
Inventory reports bear that out.
Daily fuel losses exceeding 1,000 gallons were recorded three different times in the first eight days of July, yet Top Stop did not stop its sales, empty the tank or report a suspected leak until Aug. 9.