At the time, this was the largest spill of pentachlorophenol in United States history.

Problems, though, still occur mainly in the form of large uncontrolled spills from the reservoir.

In fact, a large spill did occur in Building 470 in 1958.

Even with improved technology and response capability, it predicted that less than half of a large spill would ever be recovered.

The disaster was the largest ever accidental spill of oil into marine waters.

"Historically, we've only been able to recover 10 to 15 percent of any large spill," he said.

In recent years, large spills have provided dramatic evidence of the damage that petroleum can do to fish, birds and the coastal environment.

As nearly as scientists can gauge, for instance, the largest spill yet known had almost no environmental impact.

The contingency plan also says chemical dispersants should be the chief method of breaking up the oil in such a large spill.

With an estimated 28,000 barrels spilled, it was Alberta's largest spill since the mid-1970s.