Amid mounting pressure to solve O'ahu's trash disposal problems quickly, Mayor Mufi Hannemann yesterday announced plans to expand the H-Power garbage-to-energy plant rather than build a new facility based on a different technology.

A third boiler could be added to the plant by 2011 and could cost $100 million less than a new facility, he said.

"This is really the prudent way to go, financially speaking," Hannemann said.

The price of the new boiler must be negotiated, so officials declined to publicly estimate the cost.

The city also hopes to start shipping some of the island's trash to the Mainland by 2009, he said.

The announcements came one day after the city's Planning Commission agreed that the controversial Waimanalo Gulch landfill near Kahe Point should remain open for up to two years, pending state approval.

Hannemann said he wants to reduce the amount of trash headed to the landfill as quickly as possible.

It's too early to tell whether the plans for H-Power and trash shipping would affect a separate city proposal to expand the size of the landfill and keep it open at least 15 years longer, he said.

"I'm trying to do everything I can to obviate the need for a landfill," Hannemann said. "Everything is evolving."

Some neighbors, including state Senate President Colleen Hanabusa and the Ko Olina resort, have long complained of windblown trash and other problems associated with the site, and are pushing to close it down.

The H-Power decision means the city will end its evaluation of several proposals that could have led to construction of a new waste-to-energy facility. Officials said they could not legally disclose the cost of those proposals or names of the companies involved.

Covanta Energy Corp., which operates H-Power, was one of them. Under terms of the city's bid request, the firm had not been allowed to propose adding a third boiler instead of building a new plant.

The city will now negotiate with the company over the cost of adding the boiler, which is allowable under Covanta's existing contract to operate the facility.

H-Power business manager Rodney Smith said the new plan is a good one.

"Covanta is very happy to go ahead with that," he said. "We can get it done for a better price and get it built faster than anyone else, we believe."

H-Power uses trash combustion to heat two huge boilers, which produce steam that powers a turbine to generate up to 46 megawatts of electricity.

The plant burns about 600,000 tons of trash each year. Hannemann said it would be able to handle 300,000 tons more with the third boiler.

If the new boiler is not added, the island will end up sending more than 200,000 tons of combustible trash to a landfill each year by 2020, officials estimated.

A new plant based on a different technology could still be built in the future if that is found feasible, Hannemann said.

The city hopes to award a contract by July to ship at least 100,000 tons of trash to a Mainland landfill each year, starting in 2009.

City Councilwoman Ann Kobayashi said she had opposed a third boiler in the past because H-Power's combustion technology produces tons of ash that are disposed of at the landfill, and because the boilers must be shut down periodically for maintenance.

Council Budget Chairman Todd Apo, who has long opposed keeping the landfill open, said the shipping option should help alleviate pressure until the H-Power work is complete.

"I don't think it's a long-term solution for us, but I think it's an interim solution," he said.

Council Planning and Sustainability Chairman Gary Okino said he was very pleased with the mayor's announcements.

"We've been pushing very hard for solutions to our refuse problems," he said. "We're never going to get another landfill, so we've got to make this one last."

Apo disagreed on that point.

"We're not going to keep that landfill open forever, nor are we going to keep it open for 20 or 30 years," he said.

Former Mayor Jeremy Harris had long pushed to build a third boiler but ran into opposition from some council members who favored building a new plant based on a different technology.

Several companies had lobbied council members and others about gasification technologies, especially plasma arc, which produces less ash than the combustion process used by H-Power but is not used elsewhere to handle such a large volume of trash.

None of the proposals that were being evaluated by the city included plasma arc, officials said.

Reach Johnny Brannon at jbrannon@honoluluadvertiser.com.