Some 14,000 gallons of fuel and water were released from a drain line that’s part of the fire suppression system in a tunnel about a quarter mile downhill from a fuel storage facility at Red Hill, the Navy said Sunday.

The incident was “initially assessed as a water leak shortly after 5 p.m. Saturday,” but fuel was mixed into the release overnight, according to a press release.

The Navy said it was investigating the cause of the “water and fuel mix release,” but stressed the pipe was not connected to fuel tanks or the main fuel pipelines at the Red Hill Bulk Fuel Storage Facility, “all of which are secure.”

“Approximately 14,000 gallons of a mix of water and fuel was contained in the lower tunnel and has been recovered and transferred to an above ground storage tank as of midday Sunday,” the press release said. “The rate of release has reduced considerably and continues to be captured.”

“There are no signs or indication of any releases to the environment, and the drinking water remains safe to drink,” it added.

The Navy said it notified the state Department of Health about the incident when Fleet Logistics Center Pearl Harbor responded to the initial leak on Saturday and provided updates on Sunday.

The release occurred amid safety concerns related to the beleaguered Red Hill facility, which was built during World War II and is made up of 20 gigantic underground fuel tanks and a network of pipelines that deliver fuel to Pearl Harbor and other places.

Numerous fuel leaks in the past have raised fears about impacts on the environment and a drinking water aquifer beneath the tanks.

In late October, the state announced it had fined the Navy $325,000 for violations of environmental rules at the underground fuel storage facility last year.