A jet fuel storage tank at Sand Island may have been leaking for weeks before it was reported Jan. 21, a state official said Wednesday.

The fuel spill has already hit the water table, which is just 2 1/2 to 3 feet below ground, and has begun spreading slowly across the surface of the groundwater.

Crews are working to recover about 42,000 gallons (1,000 barrels) of jet fuel released from the aboveground tank, just 200 feet from the ocean.

Terry Corpus, the on-scene coordinator for the state, said he thinks the fuel had been leaking "many days to a couple of weeks" from the bottom of Tank No. 2 before Aircraft Service International Group reported it to the state Department of Health.

"I’m greatly concerned about the release," he said. "Even though it’s a lot, none of it could be seen on the ground. All of it was underground."

Personnel from the Health Department’s Hazard Evaluation and Emergency Response Office and the U.S. Environmental Protection Agency have recovered 16,000 gallons so far.

Keehi Lagoon is the closest body of water to the spill. Crews have set up hard booms and an absorbent sweep at Keehi Boat Harbor in the event the fuel reaches the ocean.

It took three days to drain the remaining fuel out of the leaking tank, which was aired out and cleaned, and the fuel was put into other tanks, Corpus said.

He said crews are using an air knife, which uses compressed air to bore holes into the ground until they reach fuel, to assess where the fuel has spread.

A trench is being dug around the tank. The fuel, rather than sinking, floats to the surface of the groundwater, and a wet/dry vacuum cleaner of sorts is being used to suck the fuel from it.

In 2009, a jet fuel spill occurred at the same facility, said EPA spokesman Dean Higuchi.

He said the leaking tank has a 2.8-million-gallon capacity and the facility can hold a maximum of 44 million gallons in its tanks.

Jet fuel is similar to kerosene, is not as flammable and does not evaporate as quickly as gasoline, Corpus said.

The EPA sent two on-scene coordinators, who arrived Sunday from its San Francisco office. The EPA did the same after the 233,000-gallon molasses spill in Honolulu Harbor in 2013 that caused a massive die-off of fish and other marine life.

Whether it is runoff, an oil spill or a molasses spill, "any time you have a pollutant entering and degrading the water quality, you could have impacts to the marine environment," Higuchi said. "We are working to prevent that from happening.

ASIG, which has another jet fuel facility at the Honolulu Airport, has airport facility services in more than 80 cities around the world.