U.S. environmental and emergency response teams are cleaning up jet fuel that spilled Thursday at Kunsan Air Base, South Korea, according to base officials.

Early reports estimated 6,000 to 7,000 gallons of fuel spilled into an overflow-containment system and about 700 gallons leaked out of it. Officials said the spilled fuel was contained within about 100 feet of where the aircraft was being fueled.

But those reports are premature and officials have not determined how many gallons actually spilled, said Capt. Alisen Iversen, Kunsan public affairs officer.

“We may not actually know until next week,” she said.

Iversen said Kunsan City environmental officials were alerted and South Korea’s 38th Fighter Group, also located on the base, volunteered to assist with cleanup efforts.

Lt. Heather Healy, deputy chief of public affairs, said about 20 to 30 personnel from the base civil engineer, bioenvironmental and fuels-management flights worked overnight on that process as well.

Healy said engineers using backhoes will remove about up to 12 inches of soil from the area where the fuel spilled and dig test spots around the contaminated site to see if the leak spread.

An environmental accident board is being formed to determine the spill’s cause.

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