In a now-required quarterly update on its ongoing search to locate its next municipal solid-waste landfill by year’s end, the city Department of Environmental Services offered a list of potential future dump sites.

However, it noted all of the sites — located in West Oahu or on the North Shore — are deemed restricted and unusable as all are in close proximity to potable well water, prime agricultural lands, residential areas, schools or hospitals, or a variety of each.

During a Honolulu Planning Commission meeting Wednesday, city ENV Director Roger Babcock reported on the city’s continued need and its ongoing difficulty to find an alternative to the 35-year-old Waimanalo Gulch Sanitary Landfill in Kapolei — the city’s only solid-waste dump on the island.

“I will note that this is a task that multiple, prior administrations have not been able to accomplish over the past 20 years,” he told the panel. “But the mayor and this administration is committed to identifying the waste site before the deadline and getting this done.”

He also noted any future landfill needs to be about 100 acres in size and must last about 20 years to accommodate “our current waste load that goes there, as well as (construction and demolition) waste.”

Six sites — four in Wahiawa, one in the Kapolei and Waipahu area near Kunia Road, and one in Haleiwa — were looked at previously by Mayor Rick Blangiardi’s Landfill Advisory Committee, which issued a report on the matter in 2022.

But the mayor-appointed group recommended rejection of the six selected sites, due in part to their location over drinking water resources and because those sites are currently restricted for use under state law, he said.

Similarly, at a December 2021 meeting, the Honolulu Board of Water Supply had raised concerns of its own over siting a landfill within its “no pass zone,” an area that covers the interior of the island where Oahu’s potable water aquifer is located.

According to Babcock, use of the six sites — as well as a slew of other possible dump site locations around the island, including three different golf courses and an area near the University of Hawaii West Oahu in Kapolei — would require the state Legislature to amend or rescind an existing state law called Act 73.

That law places restrictions on locating waste disposal facilities, particularly those close to conservation lands or half-mile “buffer zones” near residential areas, schools or hospitals, as well as near airports or tsunami inundation zones.

At Wednesday’s meeting, Planning Commission Chair Pane Meatoga III asked whether the city “would be actively pursuing a bill to amend Act 73 in this next legislative session.”

“That would be what we would have to do, yes,” Babcock replied.

The city’s status update follows the state Land Use Commission’s Aug. 22 decision, which adopted formal documents related to the city’s December 2022 petition to modify the state special-use permit and extend a deadline by two years, to give the city more time to find an alternate landfill.

The prior deadline of Dec. 31, 2022, to locate the island’s next dump was extended to Dec. 31 — just over three months away.

Closure of the existing 200-acre landfill near Ko Olina is scheduled for 2028, though the city says its dump won’t reach full capacity until 2036.

Besides discussion of potential landfill sites that cannot currently be used, Babcock said the city is also investigating alternative technologies to reduce waste on Oahu.

He noted those meth- ods could include plasma arcs, gasification, thermal depolymerization, multiphase microwave and microwave plasma and pyrolysis.

“Some of the alternative technologies are basically things that would be our alternatives to HPOWER,” he said. “Those are all alternative combustion- or noncombustion-related volume reduction or elimination processes.”

Still, Babcock asserted these methods are expensive, largely unproven “emerging technologies.”

“So there are none in operation anywhere in the world at scale … and so we do continue to monitor that situation … but we don’t want to be the first in the world” using these technologies, he said.

The shipping of waste off-island is also under city consideration.

“And there was even a pilot program that was initiated that was not successful,” Babcock said. “However, just in the big scheme of things, it is still something that is worth evaluating.”

He noted that “we already do ship hazardous waste as a county and as a state; there’s no hazardous waste disposal” on Oahu.

Another landfill search update is scheduled for November.

On Tuesday the Mayor’s Office told the Honolulu Star-Advertiser that the city will no longer consider federal lands — namely, military-owned parcels on Oahu — for a landfill.

That decision comes after several attempts by the city at locating dump sites, including on Navy lands, failed.

Instead, the city asserts it might look at private properties for its next landfill.

“The city is considering sites that would require amendment to Act 73 restrictions and sites that might require eminent domain,” Ryan Wilson, a city spokesperson, said previously.