The cost of shipping some of O'ahu's trash to a Mainland dump could be far less than estimates included in a new garbage management plan, consultants who prepared the document conceded yesterday.

Honolulu should seek competitive bids for such a deal and decide whether any are feasible, representatives from the R.W. Beck firm told City Council members during the first public discussion of the draft plan released 12 days ago.

The company agreed to revise the document and include a contingency plan for disposing of trash if the city's Waimanalo Gulch landfill near Kahe Point is forced to close in May, when its operating permit expires.

Shipping trash out of Hawai'i or dumping it at a private landfill in Nanakuli are options briefly mentioned in the draft plan, but the city has not prepared any firm alternatives to Waimanalo Gulch.

The consultants had estimated it would cost between $245 and $341 per ton to ship trash to Washington state — far higher than the $91 that trash haulers now pay to dump each ton here.

Councilman Todd Apo called the figures "outrageous" and "misleading."

"If that were the range, nobody would be looking at doing it," he said, adding that three companies are working to set up such garbage shipping operations.

One firm offered a few years ago to charge less than $80 per ton, said Apo, who's pushing for the closure of Waimanalo Gulch.

R.W. Beck solid waste expert Robert Craggs said the company had not been aware of that offer, but he agreed that costs could be much lower than the plan's estimates, which are meant to be conservative.

It's hard to know how much such an operation would really cost, because there are no closely comparable ones anywhere else in the United States, Craggs said.

The plan calls for shipping bales of plastic-wrapped trash to Portland, Ore., then trucking them to the Roosevelt Regional Landfill in Washington.

But two companies have filed plans with the state Health Department that call for shipping the bales up Washington's Columbia River to a point much closer to the landfill. Another company wants to ship trash to an Oregon site.

The consultant plan estimates it would take until 2011 to start shipping the trash from Hawai'i, but at least one firm has indicated it could be ready in about six months.

Councilman Romy Cachola said he was skeptical about offers to ship trash for low prices.

"If they're not making money, they might end up not doing the job they're supposed to do," he said.

He said he's also worried a company could submit a "low-ball" bid for a contract that leaves the city dependent on a trash-shipping operation that could cost much more in the future.

The consultant plan assumes the Waimanalo Gulch landfill will be expanded and continue to operate for at least 15 years.

Reach Johnny Brannon at jbrannon@honoluluadvertiser.com.