As of today, it's been around 69 days since the Deepwater Horizon drilling rig exploded and sank to the bottom of the Gulf of Mexico, taking the lives of 11 men and setting off what is arguably America's worst environmental disaster, a disaster that is ongoing today and that won't stop — even by best-case estimates — until the end of the summer. If you assume that BP's leak has been pumping out an average of 100,000 barrels of oil a day, you're looking at 2.89 million gallons so far.

The TVA coal ash slurry spill in Harriman, Tenn., was more than three times as large.

In the early hours of Dec. 22, 2008, an earthen containment wall burst at the TVA Kingston Fossil Fuel Plant, unleashing a massive wave of toxic coal ash slurry, more than a billion gallons in all, into nearby rivers and covering hundreds of acres of land with sludge up to 6 feet deep in places. Homes were destroyed and roads washed out. TVA will be cleaning up the area for a long time, and they'll never get close to restoring the area to it's pre-spill state.

There were reports of large fish kills after the spill, and tests have since found elevated levels of toxic chemicals like lead, copper, barium, cadmium and thallium.

You can read more about the spill here on MNN:

• Toxic coal ash pond bursts and floods Tennessee town

Checking in on the TVA coal ash spill

Assignment Earth: Coal ash spill in Tennessee

How many catastrophic fossil fuel-related disasters do we need before we get serious about breaking ourselves of the habit? Big Dirty Energy has a firmly entrenched position, huge bank accounts, and legions of lawyers, lobbyists, and pocketed politicians at their beck and call. Big Dirty Energy is a fierce opponent that will not go silently to its grave.

Will BP's oil spill be the big catalyst that will drive us towards finally diversifying away from dirty energy like oil and coal and towards cleaner sources like efficiency, solar and wind?

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Shea Gunther is a podcaster, writer, and entrepreneur living in Portland, Maine. He hosts the popular podcast "Marijuana Today Daily" and was a founder of Renewable Choice Energy, the country's leading provider of wind credits and Green Options. He plays a lot of ultimate frisbee and loves bad jokes.

The TVA coal ash spill: The other big leak
It's worth remembering that at the end of 2008, more than 1 billion gallons of toxic coal ash slurry was spilled by the Tennessee Valley Authority. When will ou