A scale that weighs incoming loads of trash at the city's Waimanalo Gulch dump has been giving faulty readings — raising concerns that the city could be losing revenue from garbage haulers or underestimating the dump's intake while seeking a time extension of its operating permit.

Problems with the scale were first detected in May, and immediate repairs proved unsuccessful, according to Waste Management Inc., which operates the site for the city.

Another company was called in Tuesday to make further repairs, which should be completed by tonight, the company said. The scale then will be recalibrated.

But a scale attendant who recently retired said the problems began at least two months before she retired six months ago — and that nothing was done when she and another attendant reported the problems to managers.

"The weight could have been off 300 to 1,000 pounds per transaction," said Betty Nathaniel. "They were informed. This wasn't just one-time only, and two people were telling them."

Trash haulers are normally charged $92 for every ton of debris dumped there, but the weight of such loads has been estimated since the scale broke, said city spokesman Bill Brennan.

Environmental activist Carroll Cox said he is concerned the city may be losing money by miscalculating the loads, and that the amount of accumulated trash could be distorted.

Accurate measurement of volume is important because the city is seeking a 20-month extension of its state permit to operate the dump, which expires in less than a year. The city says it believes there is room for more trash without immediately increasing the dump's size.

Brennan said the city is confident that the weight and volume are being estimated realistically, and that the city is not losing revenue.

"The repairs probably will be done by this weekend," he said. "In the meanwhile, the scale attendants have been making checks to ensure that the weights applied to each transaction are acceptable."

Officials told a City Council panel this week that the dump has plenty of room because it has been receiving less trash than anticipated.

"We have not reached the permitted elevation" of piled trash, assistant refuse division chief Wilma Namumnart told the council's Planning and Sustainability Committee.

The city plans to seek permission later to expand the dump's size and operate it for at least 15 more years, she said. The site is near Kahe Point on the Leeward Coast.

An environmental study for the expansion has been complicated by the discovery of three large stones that may be Hawaiian artifacts, officials said.

The faulty scale was last calibrated in August 2006, as part of a routine schedule, said Paul Burns, who oversees the dump for Waste Management.

"The issue with the scale is a result of corrosion of a 17-year-old scale, as would be expected at a facility like this one that is near the ocean," he said. "Most scales last between 15 to 20 years. This scale is nearing the end of its useful life and WM plans to replace the scale soon."

Meanwhile, the company has been investigating allegations that a different manager received payoffs from companies that use the dump.

The FBI has interviewed at least one person in connection with the case, and Honolulu police also have made inquiries. Waste Management placed the manager on administrative leave two weeks ago.

Nathaniel, the former scale attendant, said her supervisor told her that problems with the scale had been reported to the manager who is now on leave.

"Nothing happened," she said. "The scale still was not functioning properly. There's a lot of layers at the landfill. I guess something is starting to wash the layers away."

About 300,000 tons of trash and other debris are deposited in the dump every year, according to a recent study of O'ahu's waste stream. Another 168,000 tons of ash and residue from the H-Power garbage-to-energy plant are buried there each year.

Reach Johnny Brannon at jbrannon@honoluluadvertiser.com.