The city could be on the hook for as much as $2 million for not handing over enough trash to the operators of the HPOWER waste-to-energy plant, a Honolulu City Council committee was told Wednesday.

The city’s contract with Covanta Energy Co. guarantees that 800,000 tons of trash move through the three boilers that make up the HPOWER facility at Campbell Industrial Park. Energy generated by the incinerator-type operation is sold to Hawaiian Electric Co. with the proceeds split between the city and Covanta.

Because the city was able to dump only about 680,000 tons into HPOWER in 2013, it is now in negotiations with Covanta over how much the contractor should be reimbursed, city Deputy Environmental Services Director Tim Houghton told Council Budget Committee members Wednesday.

Activation of a $302 million third boiler in 2013 boosted HPOWER’s capacity to 3,000 tons of municipal waste a day.

Pressed to give an estimate of how much the city may owe, Houghton said "potentially" between $1.5 million and $2 million. "But that’s all subject to negotiation. It could be nothing depending on the negotiation process," he said.

Houghton said several new sources of trash will mean the city should be able to meet the 800,000-ton threshold this year. About 30,000 tons of wastewater sludge, 30,000 tons of automobile waste and 50,000 tons of coconut beetle waste from the U.S. Department of Agriculture are expected. "They will be paying the full tip fee," Houghton said of the USDA.

The issue was raised during a Budget Committee discussion of Bill 47, which would allow the owner of PVT Land Co. a waiver from paying a disposal fee for dumping processed feedstock into HPOWER.

Houghton said the city opposes the waiver because "we do not believe it is good policy to be waiving tip fees."

If, for example, the city were to accept 70,000 tons of feedstock waste annually, it would mean roughly $5 million in lost HPOWER tip fees and between $900,000 and $1 million in landfill tip fees for leftover ash residue disposal. It would cost the city even more if other companies chose to dispose of already processed waste, he said.

Councilwoman Kymberly Pine, who represents West Oahu, said "it’s hard for us to make a decision and support what you’re saying when I have no numbers to go with it." She noted that PVT estimates the city could generate up to $25 million annually from the sale of energy generated from its feedstock waste.

Steve Joseph, a PVT official, told Council members the feedstock waste it is offering would burn more efficiently than typical waste.

The committee deferred the bill after Budget Chairwoman Ann Kobayashi asked for more information from the city administration.

The bill was introduced by Council Chairman Ernie Martin.