The Navy is working to contain a spill at its Red Hill fuel facility near Pearl Harbor that has so far released 14,000 gallons of a mix of fuel and water from a drain line that’s part of the facility’s fire suppression system.

The Navy said in a news release issued Sunday afternoon that the rate of release had slowed “considerably and continues to be captured.”

The cause of the spill is under investigation.

Shortly after 5 p.m. on Saturday, Navy personnel believed the release was a water leak, according to the Navy.

But overnight, fuel was detected within the mixture and increased into Sunday morning. The Navy says that the fuel was contained in the lower tunnel and has been transferred to an above ground storage tank.

“There are no signs or indication of any releases to the environment, and the drinking water remains safe to drink,” according to the Navy news release.

The spill occurred about one-quarter of a mile downhill of about 20 underground fuel tanks, each capable of holding 12.5 million gallons of fuel.

The tanks sit just 100 feet above an aquifer that serves as a major source of drinking water for Oahu.

The Navy says it notified the Hawaii Department of Health, which regulates the facility, on Saturday night.