A school in the area of a massive oil pipeline leak in northern Alberta remained closed for a fourth day Wednesday after students complained of headaches and nausea from gassy, tarry smells.

"Friday morning, there was a strong smell ... of a propane or gas odour within the atmosphere," said Lubicon Cree Chief Steve Nosky. "The kids were getting sick. They were getting nauseous. They were getting headaches and they were sent home."

Energy regulators say 28,000 barrels of crude oil spilled from the Rainbow pipeline, owned by Plains Midstream Canada, before the leak was discovered and the flow was shut down Friday morning. It's the largest pipeline leak in Alberta in 36 years.

The Lubicon live in the community of Little Buffalo northeast of Peace River. The town is about 14 kilometres from the spill site, said Alberta Envirionment Minister Rob Renner.

Davis Sheremata, spokesman for Alberta's Energy Resources Conservation Board, denied that problems in Little Buffalo were connected to the leak.

"We often will get complaints like this and sometimes it is a feedlot nearby. Sometimes it's an asphalt operation. Sometimes it's not oil-and-gas related. We're looking into it," he said.

Nokey insisted there are no possible sources for the smell other than the crude-soaked soil and pond, where the oil has collected.

"As soon as the wind shifts, we experience the smell," he said.

The community of 350 is deeply worried, said Veronica Okemow, who works in the school's kitchen and whose six-year-old son is a student.

"A lot of children aren't (outside) as normal," she said. "As soon as we see someone else, that's the first thing we talk about.

"I'm sure if we knew what the effects would be in the long term, I'm sure we'd be doing more."

Okemow's son was one of the students who felt sick Friday. On Wednesday, she said, he asked her what the effects of the odours could be.

"He came in from outside and asked me, 'Will that smell affect my walking?' I said 'Why do you say that?'

"Then he said, 'I'm not feeling well. My legs are starting to bother me and my throat is really sore.'"

Alberta New Democrat environment critic Rachel Notley wondered why the problem took so long to come to light. She pointed out that while the leak was discovered and the school closed on Friday, it wasn't until Tuesday that the extent of the leak was disclosed.

At first it was estimated that a few hundred barrels had leaked. Notley suggested that was underplayed to avoid raising an environmental issue for the federal Conservatives before Monday's federal election.

"Either they're grossly incompetent or there's political interference."

Sheremata says it takes time to estimate how much has really leaked from a pipeline, especially when most of it has soaked into the soil.

About 100 workers continued to clean up the site Wednesday.

The affected section of the 44-year-old pipeline, which runs 772 kilometres from the Norman Wells pipeline in Zama, Alta., to Edmonton, was shut down and both ends were sealed off. Sheremata said the oil remains about 300 metres from any flowing water and is pooling in the soil and in a stagnant pond.

Seen from the air over the site, the oil appeared to be running down a cutline into a muskeg area about the size of two football fields. The odour of oil was heavy in an aircraft passing overhead.

The black outline of the oil was clearly visible around the edge of the water, which also contained a beaver pond.

Air quality monitors were set up Monday at both the spill site and in Little Buffalo near the school. The monitors haven't detected any hydrocarbon levels above air quality guidelines, said Sheremata.

Nor have workers at the site had similar problems.

"We have not had any headaches or nausea at the site."

Renner acknowledged smells can cause health problems but wouldn't say if that's how he would describe the problems at Little Buffalo.

"That's the reason Alberta Health has been activated. Odour from a health-quality issue can be a significant issue, but from an overall health perspective it may not be," he said.

Renner said the notification and cleanup process has been operating as intended. He defended Alberta's pipeline monitoring system.

"I'm confident those inspections are taking place and the appropriate maintenance is taking place."

The pipe leaked 7,500 barrels of oil in late 2006, but has been inspected since then.

Renner acknowledged the death of several beaver and waterfowl and noted that it was the beaver dam at the end of the stagnant pond that kept the oil from spreading further.

"There is a beaver dam in the area and that initially contained the spill," Renner said. "Once the area has been isolated there will be additional measures put in place to contain the spill."

It's not the first time people in that part of the province have made odour and health complaints related to the energy industry.

Residents in the rural area of Three Creeks, near Peace River, have complained for more than a year about powerful gassy, tarry smells that waft over their fields, pastures and yards.

There, too, officials pointed to air quality monitors that weren't finding problems. Eventually the government acknowledged the odour came from the oilpatch and that it was causing headaches and nausea.

Repairs to the Plains Midstream line were expected to be complete by the end of the week, although restart depends on regulatory approval. The lower half of the line into Edmonton has continued to operate, delivering about half the line's normal volume.

The company said it had not yet diagnosed the cause, but noted on its website that the leak appears to be a singular failure and not a systemic problem.

Sheremata said investigators were digging out the pipe to get their first look at the hole. Early indications were it was a large break, he said.

The pipeline was built in 1965 and has a capacity of 220,000 barrels a day. Average daily volumes were 187,000 barrels a day during 2010.

Enforcement action will result if regulations weren't followed, Sheremata promised.

In 2009, Alberta hit a low for pipeline failures of 1.7 leaks for every 1,000 kilometres of pipe. Alberta has more than 377,000 kilometres of pipeline.

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