The Navy has notified the state Health Department that Tank 5 at Red Hill, which experienced a 27,000-gallon jet fuel leak in 2014, is being brought back into service, the U.S. Environmental Protection Agency said Wednesday.

Since 2014, Tank 5 has remained out of service, but has “undergone extensive evaluation, repairs, and testing,” the EPA said in a news release. “The Navy has made significant changes to their inspection, repair, and quality control processes as well as improved their approach to quality assurance of their contractor’s work.”

The EPA said in contrast to the filling process in 2014, Tank 5 “is being filled very slowly, with numerous points throughout the process where filling is stopped, and testing for leaks is performed.”

“The Navy is prepared for emergency draining of the tank if a leak is identified by having adequate empty capacity available in other tanks. This is in sharp contrast to the events of 2014 when the tank was filled rapidly with limited testing and the inability to address leaks quickly,” the federal agency said.

Although the Navy considers the Red Hill Bulk Fuel Storage Facility to be critical for national security, the 2014 leak and fuel losses before it led to drinking water safety concerns from the Sierra Club of Hawaii and Honolulu Board of Water Supply. The Board of Water Supply wants the Navy to double-line the tanks, and if that is not possible, to relocate them.

The Sierra Club, meanwhile, is calling for a shutdown of the facility.

Sierra Club of Hawaii Director Marti Townsend called the tank reuse announcement “outrageous” and “illegal.”

“The laws governing underground storage tanks prohibit leaks into the environment, even by the U.S. military. Yet, that is exactly what the Navy’s plan calls for: filling these antiquated tanks till they leak into the environment,” Townsend said in an email.

The Navy is proposing “comprehensive tank restoration” with epoxy coating applications and improved monitoring and a 2045 deadline for “double-wall equivalency containment” to boost safety using technology that it admitted doesn’t yet exist.

Each of the 20 tanks at Red Hill can hold 12.5 million gallons of fuel. The Navy said it has 18 tanks in service. Of those, 13 are considered active, with Tank 5 returning to service. The remaining four are in a clean, inspect and repair status.

“Regulators report that the Red Hill facility continues to meet or exceed requirements,” the Navy said in a statement. “The layers of protection in place continue to show the tanks are not leaking.”

The EPA and the Hawaii Department of Health are monitoring the process of bringing Tank 5 back into service at Red Hill “to prevent a repeat of mistakes made in 2014,” the EPA said.

An “administrative order on consent” was entered into by the Navy, Defense Logistics Agency, EPA and state Health Department to make improvements after the 2014 fuel spill from the World War II-built tank farm.

Much of the concern centers on the tanks’ location 100 feet above a water supply aquifer, which is in saturated volcanic rock.

The Southern Oahu Basal Aquifer is the principal source of drinking water for more than 400,000 Oahu residents.

The Navy thinks deep, claylike barriers to any leaked fuel extend through the saturated rock aquifer into valleys separating the Board of Water Supply’s Halawa and Moanalua water shafts from Red Hill.

The Board of Water Supply, however, said some groundwater modeling shows a flow gradient across the valley toward the Halawa water shaft.