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Last week, I talked a little about the large numbers that are being bandied about these days and there was one over the holidays that certainly caught my attention.

It occurred in a news item. A holding pond at a coal-powered electric plant in Tennessee failed and over a billion gallons of sludge spilled out.

I couldn't imagine what a million gallons of sludge would look like, let alone a billion. So I went to work to put this into some sort of perspective to help me comprehend the size, scope and impact of the spill.

To start with, there are at least two different types of gallons in use around the world. Canada, England and most commonwealth countries use the imperial gallon, which is 4.54 litres in volume. The United States uses the U.S. gallon, which is 3.7854 litres in volume. So a U.S. gallon is about three quarters the size of an imperial gallon. The rest of the world of course uses litres, which is theoretically the system we now use in Canada.

The spill in Tennessee was over a billion U.S. gallons which would make it over 3.7854 billion litres. In the metric system 1,000 litres is equal to one cubic metre. So that would make it over 3.785 million cubic metres in size and one news item stated that, in fact approximately four million litres had been spilled.

The trick now was to put four million cubic metres into a shape that one could visualize. If you took a block of sludge one hundred metres high by two hundred metres long and two hundred metres wide, then that is the amount of sludge we are talking about. That is a mighty impressive pile of sludge. You could also envision it as two metres high, one thousand metres or one kilometre wide by two thousand metres or two kilometres long.

If that mass of sludge was coming at you, you would certainly want to get out of the way. A person can tread water but treading sludge might be a problem.

Now that you have a reverence for the amount of sludge, just what is this sludge and where did it come from? The power plant had been in operation for over 50 years burning coal. The stuff that was left behind after the coal was burnt made up part of the sludge. Also the fly ash, which at one time went up the smoke stack but now most of it gets caught with scrubbers, forms a slurry which then gets put into waste or tailings ponds. Coal fired power plants do pump a lot of other pollutants up into the atmosphere but that's a whole other issue.

This plant had three large ponds held in place by earthen dikes. Heavy rains, probably combined with a lack of adequate care and maintenance, caused one of the 20-metre high dikes to fail and the sludge in the 40-acre pond spilled out. The spill covered 300 acres of land, destroyed three homes and damaged 42 other properties. It also buried 4,500 feet of a main road that had to be dug out.

This was a pretty big spill but it was only covered in the national news for a couple of days because by today's standards it just wasn't very exciting or newsworthy: No one was injured or needed saving. There were no pictures of animals or birds floundering in the sludge. Visually, it just looked like acres of barren sludge and it wasn't particularly toxic, so no one was being poisoned.

The company assured everyone that they would clean the mess up - and you have to imagine that that will take a while. An ecologist called it an ecological disaster but if you rated disasters on a scale from one to ten, this one was probably less then a one - unless of course it was your house or property that got buried. However, try to imagine all the coal-fired plants around the world and try to calculate just how long it will be before the entire planet is covered in a metre of sludge.

- Walt Humphries is a well-known Yellowknife artist and prospector