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March civil engineers remove soil treatment system

Contractors guide a crane-lifted tank onto a truck bed Sept. 22, 2009, at March Air Reserve Base, Calif. The tank was part of the ground water and soil vapor extraction system that was installed on base in 1997. After cleaning an equivalent of 58,000 gallons of jet fuel, the system is no longer needed. (U.S. Air Force photo/Staff Sgt. Megan Crusher)

Contractors guide a crane-lifted tank onto a truck bed Sept. 22, 2009, at March Air Reserve Base, Calif. The tank was part of the ground water and soil vapor extraction system that was installed on base in 1997. After cleaning an equivalent of 58,000 gallons of jet fuel, the system is no longer needed. (U.S. Air Force photo/Staff Sgt. Megan Crusher)

MARCH AIR RESERVE BASE, Calif. -- Base civil engineers and contractors marked an important environmental milestone earlier this year when they began dismantling a soil treatment system. The system had been used to remove an equivalent of 58,000 gallons of jet fuel from beneath the flightline.

The Panero aircraft refueling system was the location of the contaminated site. The system was installed on base in 1952. The site originally contained 34 underground tanks, and each tank was designed to hold 50,000 gallons, said Eric Lehto, 452nd Air Mobility Wing environmental engineer.

It was typical for underground fuel tanks to leak, and these tanks were no exception, according to Mr. Lehto.

In 1991, base contractors removed all 34 underground tanks along with 15,000 tons of contaminated soil.

Although much of the contamination was removed, jet fuel still remained in the soil and groundwater, said Mr. Lehto. The civil engineers tried several follow-on processes to clean the site.

Groundwater extraction and soil vapor extraction were two of the techniques tried, said Mr. Lehto. Groundwater extraction pumps the contaminated water from an aquifer and then the water must be treated and properly disposed of.

The soil vapor extraction pulls the vapors directly from the soil. The vapors are then burned at a high temperature. The process turns the vapors into carbon dioxide and water which is released into the atmosphere, said Mr. Lehto.

The soil vapor extraction system was the most effective treatment process. It was used from 1997 to 2008 to extract as much contamination as possible.

The Santa Ana Regional Water Quality Control Board, the agency that had project oversight, agreed that the soil vapor extraction had done as much as it could and gave March ARB permission to dismantle the system.

Even with all the contamination that has been cleaned and removed, some residual contamination remains.

The good news is that the contamination that remains is stagnant, said Mr. Lehto. The water in the ground near the site is isolated. It will gradually rid itself of contamination over time.

"Fortunately, there are naturally-occurring microbes in the soil that eat the fuel, so eventually all the fuel will be gone and out by natural methods," Mr. Lehto said.

Ivan Vargas, a field engineer with MWH, agrees. The base contractor company has monitored the site for more than 10 years.

"There haven't been any problems with contamination being released into production wells," said Mr. Vargas.

The whole cleanup program has been a great success, and the rest of the contamination will ultimately be removed through natural processes, according to Mr. Vargas.

To ensure the remaining contamination doesn't infiltrate drinking and irrigation water, field engineers will continue to monitor the site on a quarterly basis, said Mr. Lehto.