SOMBA K'E/YELLOWKNIFE - It took workers nearly two days to report an arsenic spill at the Giant Mine site but the person in charge of overseeing the clean-up project at Indian and Northern Affairs (INAC) said he doesn't think it will happen again.

Bill Mitchell, acting director of the contaminant and remediation directorate, said the amount of arsenic released last month when contract workers drilled into an arsenic chamber was less than a kilogram.

The drilling was being carried out by a Calgary-based company, North West Sequoia Drilling, working on behalf of the contractor Deton'Cho/Nuna Joint Logistics.

"It's dangerous but we cleaned it up immediately," he said. "It's still more or less below the threshold for reporting a toxic material."

According to the spill report, at 1 a.m. on Oct. 22, an unknown quantity of arsenic dust escaped from a drill hole when workers were drilling a second hole into the arsenic chamber. An environmental coordinator at the site filed the report to the NWT spill line at 5:15 p.m. on Friday, Oct. 23. The department released a statement about the incident on Oct. 29.

"It was compressed air that caused the pressure in the chamber that caused a puff of arsenic to come out of one of the holes," said Mitchell, who is a geologist by training and a former project manager at Giant Mine.

The report said the hole that released dust was secured by plastic sheeting and duct tape.

From now on, said Mitchell, workers won't be drilling with a drill that uses compressed air.

The report listed the area covered with arsenic as between five and ten metres wide. A worker who was drilling had to be washed down with a pressure washer.

Mitchell said crews cleaned up the dust and placed it in a plastic drum with a top that screws on. He said it will be later put back underground with other contaminated materials.

He said since it was a relatively small spill, the contractor waited to report the incident until workers used an x-ray analyzer to measure the amount of material.

The regulations say that spills should be reported as soon as possible to the NWT spill line, said Mitchell.

"It should have been reported sooner and we have had a lot of discussions with the contractor. Now the contractor is fully aware of the protocols and procedures. We do not expect this to happen again," he said.

After the Giant mine site closed, the federal department decided to freeze the estimated 237,000 tonnes of arsenic trioxide stored in 15 underground chambers. The compound is a by-product of gold mining and is poisonous, even in small quantities.

Mitchell said drilling into the arsenic chamber is necessary in order to measure how quickly the arsenic will freeze. Once the testing stage is finished, they will insert freeze pipes and connect them to a freeze plant.

"It would be very similar to what you have in a hockey rink, but instead of making a flat piece of ice, we're freezing the vertical walls," he explained. Mitchell said there is only minor drilling left to do this year and he hopes the department will start freezing the arsenic in the early summer of next year.

The arsenic spill sent up red flags for former city councillor Kevin O'Reilly. He said he's concerned about the frequency of spills on the site, noting this was the third spill since July at the Giant Mine site.

A spill report was filed after July 11, when drill mud seeped into Baker Creek. He said drill mud spilled again on Aug. 12.

He said waiting until the evening of Oct. 23 to report the incident to the spill line showed a lack of accountability.

O'Reilly said having a land-use permit would make the project more accountable.

"There would have been a way to catch this sort of thing," he said. "We need to have someone independent serve as a watch dog on what is going on out there."

In September, Darnell McCurdy, INAC's acting director of the territory's South Mackenzie district, said the project isn't required to have a permit.