Hill Air Force Base and Utah State University are helping to develop a new technique for cleaning up fuel spills - technology using some of the world's most ancient creatures.
Soil microbes are encouraged to munch petroleum products in the experiments, which the Environmental Protection Agency is now investigating as a potential method to clean up underground fuel spills elsewhere.One night in January 1985, an automatic shutoff valve malfunctioned while jet fuel was being transferred from a bulk storage tank farm at the air base. "It turned on and started filling these tanks and didn't turn off," said Bob Elliott, a civilian who works at Hill's Environmental Management Directorate.
Fuel spilled out all night.
"There was snow on the ground and nobody noticed there was jet fuel running underneath the snow until it was running down the street," he said. By then, 25,000 gallons had spilled.
Fortunately, the water table was about 60 feet below the surface, and that meant it would take a long time for the contamination to work its way down. The cleanup was a major headache.
Working through the Air Force Engineering Services Center at Tyndall Air Force Base, near Panama City, Fla., teams at Hill decided to use a well-venting system. In this method, which has been around for about eight years, the volatile jet fuel is literally sucked out of the ground.
Wells are dug, and blowers installed in them to force air out. That lowers the air pressure in the wells, and air flows through the porous ground to the wells. As it goes, the air lets the fuel vaporize, and it comes out, too.
The system has worked with lighter fuels, like gasoline, because they evaporate easily. "Jet fuel is a heavier type fuel; it's a kerosene-based fuel," Elliott said. "They wanted to evaluate how well this technology applied to jet fuel."
In December 1989, crews started cleaning up the underground fuel plume with the vacuum method. "It operated for a year, and one of the conditions of operating with that system is that we had to have an air quality permit," he said.
Extracted fumes can't be allowed to contaminate the air. So incinerators burn hydrocarbons as they come out, but they cost $6,000 a month to operate.
Costs skyrocket toward the end of the project, when the fumes are less concentrated and more fuel must be burned in the incinerators.
Meanwhile, Robert Hinchee, who works for Battelle Memorial Institute at Columbus, Ohio, came up with a method of destroying underground spills by encouraging soil microbes to digest it. They break hydrocarbons down - the carbon turns into carbon dioxide and the hydrogen forms water.
Samples showed the venting and incineration system was effective in removing most of the fuel, although heavier residuals weren't evaporating. Concentrations dropped from 8,000 or 10,000 parts per million, down to 500. That wasn't good enough to meet state standards.
Then the system was turned around - air was blown into the soil to ventilate the microbes. After 11 months, of 50 soil samples taken only three had any hydrocarbons, and they were only 20 or 30 parts per million.
And pumping air into the soil eliminated the need for incinerators, since fumes weren't coming out.
Having discovered the value of air injection, cleanup crews are using the technique eleswhere at Hill, a site where jet engines are tested during maintenance. Underground storage tanks spilled there since they were installed in 1942, although they apparently haven't leaked - carelessness was to blame.
Sometimes hundreds of gallons would spill when tanks were overfilled. Jet fuel seeped 95 feet down and got into the groundwater.
Under EPA auspices, a pilot study is being carried out at the new site, using air injection to stimulate the microbes.
USU's Water Research Laboratory is under contract through Battelle to analyze soil and water samples. Graduate students and researchers work both in the field and laboratory.
Ryan Dupont, associate professor in the USU civil and environmental engineering department, said, "When you inject the air, the concern there is, `Are we pushing the contaminant into buildings or up out of the ground, rather than treating it?"
Thus far, the answer is "no." The injections take place 90 feet below the surface, and the buildings' foundations reach 10 feet below the ground level.
"Just from scanning the results over that six-month period, it looks like there has been measurable removal of material from the soil samples."
Asked if "bioventing" is a promising technique, Dupont said, "We believe pretty strongly that it is."