The Navy has recommended to federal and state environmental regulators that it conduct limited upgrades to its Red Hill Underground Fuel Storage Facility where 27,000 gallons of fuel leaked from one of its 20 underground tanks in January 2014. The leak alarmed state lawmakers and officials charged with protecting the state’s water supply and tipped off a major review of the facility’s safety.

The long-awaited recommendation from the Navy includes sticking with the facility’s single-walled steel tank liners while permanently adopting its program for cleaning, inspecting and repairing the tanks that Navy officials say was significantly improved upon after the 2014 spill. The Navy also plans to decommission tank nozzles, put protective coatings on the tanks and implement improved monitoring in the event of a spill.

By 2022, the Navy says, it also will evaluate the possibility of installing a water treatment plant in case of spills.

The Navy evaluated a range of options for improving its World War II-era tanks, including double-lining them, but ultimately decided against the more elaborate and costly alternatives. Navy officials say that double-lining the tanks would increase costs significantly while providing minimal benefits.

“Since 2014, we have substantially improved prevention, detection and miti­gation measures to ensure the facility is operated safely and to protect against a potential release of fuel,” Navy Capt. Marc Delao, commanding officer of Naval Facilities Engineering Command Hawaii, said by email. “Our proposed tank upgrade plan will further reinforce and add to those layers of protection. Analysis shows that the other tank upgrade alternatives provide minimal reduction to risk while requiring significant additional cost to taxpayers.”

The Navy redacted the cost estimates for the various alternatives from its report, citing procurement reasons. But the report notes that double-walling the tanks is expected to cost 10 times more than the current option.

The Navy’s recommendation must be approved by the U.S. Environmental Protection Agency and state Department of Health. Keith Kawaoka, the Health Department’s deputy of environmental health, said his department had recently received the Navy’s report and needed more time to review it before commenting.

Ernie Lau, manager and chief engineer of the Honolulu Board of Water Supply, said he was “disappointed” by the Navy’s decision.

“In simple terms it looks like (their recommendation) is basically kind of the status quo, what they are already doing,” said Lau.

Lau said the Board of Water Supply’s position on Red Hill remains the same: that the Navy needs to double- wall its tanks within 10 years or find a new location for them away from Oahu’s underground water supply.

The 20 massive tanks, 18 of which are in operation, are situated just 100 feet above an aquifer that supplies drinking water to residents from Moanalua to Hawaii Kai.

The Navy has said that it’s unlikely that the water source would be polluted by a major spill at its facility, but this hasn’t assuaged the concerns of environmental groups and state regulators.

Hawaii Health Department Director Bruce Anderson told lawmakers in April that ultimately the Navy should move its tanks away from the aquifer, but said the state doesn’t have the power to force the Navy to do so. Anderson said a major release at the facility that contaminated the drinking water aquifer would be impossible to clean up.