By MATT HUNT GARDNER

SYDNEY - The Domtar tank cleanup was halted Monday so the contractor could figure out how air filters keeping the Whitney Pier neighbourhood safe from gases might have let elevated levels of a chemical seep into the air.

"Why weren't the people warned?" area resident Ann Ross asked, adding that she didn't understand why news of the leak was made public three days after it happened.

On Friday, test results from one of the air monitoring stations at the Whitney Pier site, near the coke ovens, reported an elevated level of naphthalene, a polycyclic aromatic hydrocarbon.

Ms. Ross said she thought the aroma of mothballs, which she and a neighbour smelled over ther weekend, was coming from the tar ponds.

"But this smell was different and more intense," she said. "Everyone was suffering from headaches, and some people were nauseous."

A sample collected the week before measured the level of naphthalene at 12.3 micrograms per square metre of air, said Parker Donham, a representative for the Sydney Tar Ponds Agency, the provincial agency charged with cleanup of the tar ponds and coke ovens sites.

The Sydney standard is three micrograms per square metre, but Mr. Donham said that level is particularly strict and that other areas in Canada have looser guidelines.

He said the site has rigid guidelines in order to be "extra-cautious" and uses two types of air monitors to measure 30 to 40 types of PAHs, volatile organic compounds and particulate matter.

The United States Environmental Protection Agency says naphthalene can cause hemolytic anemia, cataracts and jaundice. It can be found in mothballs and cigarettes.

The Canadian guideline for naphthalene in soil is 22 milligrams per kilogram of soil.

The Domtar tank, now housed inside a sealed building, contains about 4,000 tonnes of water, oily sludge and raw materials from the coke ovens, as well as railway ties, cables and other junk.

The provincial and federal governments are paying to ship 1,000 tonnes of the coal tar oil to a licensed incinerator in Quebec.

Clean Harbours Canada Ltd. has the $3.6-million contract to clean up the site and is shipping material to its site in Ontario.

Mr. Donham said elevated levels of naphthalene coincided with a new heating process that created more gases inside the building.

Previously, cleanup crews used hot coils to heat little puddles of the toxic sludge, then pumped it into trucks, but the process was too slow.

They built a large heating tank to warm up more of the sludge at a time, but it released more gases like naphthalene into the air, Mr. Donham said.

He said the chemical might have been released because the activated-charcoal filters used to clean the gas-filled air might have been gummed up.

He also said the exhaust fan that pushes air through the filters could be malfunctioning.