Despite concerns by the Navy, a Honolulu City Council committee unanimously passed an updated resolution Wednesday asking regulators to reject Navy plans to pursue single-wall tank upgrades at the Red Hill Bulk Fuel Storage Facility.

The resolution also seeks secondary containment tank upgrades, and if that is not possible, relocation of the tanks away from the Southern Oahu Basal Aquifer, which lies below the 20 giant underground fuel tanks and is the principal source of drinking water for more than 750,000 Oahu residents.

The full City Council will consider the resolution on Nov. 6.

Part of the discussion before the public infrastructure, technology and sustainability committee centered on exactly what the Navy proposed in a Sept. 9 tank upgrade alternative decision that still has to be approved by the U.S. Environmental Protection Agency and state Department of Health.

A public meeting will be held in November to get public input.

The Navy proposed “comprehensive tank restoration” with coating applications and improved testing, monitoring, modeling and sampling, but the plan falls short of the Board of Water Supply’s call for relocation away from the aquifer or double- walled tank-within-a-tank containment.

“We have an opportunity here to prevent contamination — tank-within-a-tank is the best solution,” said Erwin Kawata, program administrator in the Board of Water Supply’s water quality division. “If that is unfeasible, the fuel should be removed and relocated away from the groundwater.”

The Navy is proposing an extended timeline to 2045 for what it calls “double-wall equivalency secondary containment” — or removal of the fuel if that is not possible. The deadline for tank upgrades currently is 2037.

“While the proposed resolution and our understanding of the way ahead both include secondary containment, we believe the proposed resolution could be misinterpreted as implying that single-wall constructed tanks are the Navy’s final solution,” said Capt. Marc Delao, regional engineer for Navy Region Hawaii. “In fact, the Navy is pursuing technologies … that will provide secondary containment of the fuel.”

Delao admitted that while “this technology does not currently exist to allow a fiscally­-responsible approach, the Navy is committed to finding that solution for secondary containment” in the future.

Kawata said the Navy’s double-wall equivalency is “talking about single-wall tanks working with other things to try to maintain or try to keep fuel from escaping from the facility. … So this ‘equivalency’ is not the same thing as tank-within-a-tank.”

The tank upgrade plan is part of an “administrative order on consent” entered into by the Navy, Defense Logistics Agency, EPA and state Health Department after 27,000 gallons of fuel spilled in 2014 from the World War II-built tank farm.

Much of the concern over Red Hill centers on the tanks’ location 100 feet above the water supply aquifer, which is in saturated volcanic rock. The Navy thinks deep claylike barriers to any leaked fuel extend through the aquifer in 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.

The Navy said Russia’s and China’s militaries “have become increasingly aggressive” and Red Hill provides access to fuel for mission readiness across U.S. Indo-­Pacific Command.

Beneath Red Hill’s 20 feet of concrete is lava rock that in some cases is solid and elsewhere is like cinder blocks. Past leaked fuel may have become bound up in concrete and rock or attenuated by microbial action, the Navy said.

Council member Carol Fukunaga said it was “very concerning” that earlier in the process the Navy indicated that a tank-within-a-tank approach was feasible and now it is “backsliding” with its latest proposal and extended timeline.

Delao said from technology and fiscal standpoints, tank-within-a-tank “is not a practical application at this point, so ergo, looking at other technologies, other ways of achieving secondary containment.”

The full City Council will consider the resolution on Nov. 6.