ALBUQUERQUE, N.M. (AP) — A decades-old jet fuel spill threatening Albuquerque's water supply could be as large as 24 million gallons, or twice the size of the oil spill from the Exxon Valdez, New Mexico environment officials acknowledged Tuesday.

Officials previously estimated the spill from Kirtland Air Force Base to be about 8 million gallons. But state geologist William Moats, who made the original calculations, recently estimated the spill could be up to three times larger.

By comparison, the Exxon Valdez spilled 11 million gallons of crude oil when it ran aground in Prince William Sound in Alaska in 1989.

Jim Davis, head of the New Mexico Environment Department's resource protection division, calls the newest calculation a "first-order estimate" based on new data from Air Force monitoring wells. He emphasized that the calculations have not been reviewed, and said no one will really know how large the spill is until it has been remediated.

"It is not knowable," Davis said.

But he said he is confident the spill can be cleaned up, no matter how large. And while the fuel threatens groundwater, officials have said it poses no threat to people living above the plume.

"The bottom line is this ... we take it very seriously," Davis said. "We are pushing the Air Force and we are going to stay on top of it until it is fixed."

Kirtland spokeswoman Marie Vanover did not dispute the new estimate.

"There is really no way to carefully measure how much fuel is in the ground," she said. "What's important here, as far as the Air Force is concerned, is that regardless of the amount of fuel in the ground we are committed to two things: that the water stays safe and to continue our remediation efforts."

The fuel came from what officials now believe was a 40-year leak from underground pipes at a Kirtland aircraft fuel loading facility.

The leak was discovered in 1999. In 2007, Air Force investigations revealed the fuel had reached the water table and was moving off the Air Force base, beneath the neighborhoods of southeast Albuquerque and toward the city's water wells.

Since then, the Air Force, under pressure from the Environment Department, has cast an ever-wider net of monitoring wells, trying to figure out how far the fuel has spread.

Davis said officials still believe no contamination will reach city wells for at least five years. He said the Air Force has removed about 400,000 gallons and he hopes broader remediation targeting the largest concentration of the spill can begin this summer.

Environmental activists planned to raise the issue Wednesday at an Albuquerque-Bernalillo County Water Utility Board meeting.

"Basically they have a larger problem than they thought," said Dave McCoy of Citizen Action New Mexico. "... They need to begin planning for construction of a water treatment plant to protect Albuquerque's water supply."

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