Five months after the U.S. Navy announced that one of the tanks at its Red Hill Underground Fuel Storage Facility on Oahu may have leaked some 27,000 gallons of jet fuel, military officials say they may have discovered the source of the leak.

Inspectors found three small holes in the massive tank, according to a Navy press release issued Thursday. They aren’t big enough to be visible to the naked eye, but were discovered during a tank examination that included “vacuum box testing,” which indicates whether air can flow through the tank’s wall.

“The small holes were located in prior welding repairs and may explain the reason for the fuel loss,” Capt. Mike Williamson, chief engineer for Navy Region Hawaii, said in the press release. “We’ve got the right experts working meticulously to determine the full extent of the leak as the inspection continues.”

Security fence at Red Hill Underground Fuel Facility. 1.29.14 ©PF Bentley/Civil Beat

Gates leading up to the Red Hill Underground Fuel Storage Facility.

PF Bentley/Civil Beat

The Navy reported the 27,000-gallon leak to the Hawaii Department of Health in January, turning over evidence that included a drop in the tank’s fuel level, elevated soil vapor levels and pictures of fuel seeping out of a concrete wall near the tank.

However, Navy officials said in subsequent weeks that they weren’t sure if there was a leak after all.

There are 18 active tanks at the underground facility, each big enough to contain the Aloha Tower.

After the Navy reported drops in fuel levels at Tank 5 in January, a review of documents by Civil Beat found that there had been dozens of leaks at the facility over the years, dating back to the 1940s.

The Navy’s own reports also indicate growing concerns about the integrity of the aging tanks, and their potential to pollute drinking water sources. Such contamination could take decades to clean up, according to the reports.

The tiny holes recently found in Tank 5 indicate the scale of the challenges that the Navy faces in monitoring leaks in its tanks, each of which are 250 feet tall and 100 feet in diameter. Despite their tiny size, the holes could have leaked the equivalent of all the fuel stored in a modern-day gas station over the span of a few weeks.

Past Navy inspection reports show that tanks taken offline in recent years for repairs have been riddled with hundreds of defects, though it’s not clear if the flaws led to fuel leaks. For instance, a 2007 report indicates that Tank 6 had 684 defects, about two-thirds of which required repairs such as patching and welding.

The state health department is currently working on an “enforcement remedy” that may require the Navy to implement better leak prevention and detection technology and drill more test wells to determine whether past contamination is migrating toward county wells that supply about one-quarter of Oahu’s drinking water.

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