In Western Canada, tens of thousands of oil wells have been out of service for decades but never plugged. Activists and experts say the existence of these inactive oil and gas installations -- often dug hundreds of meters below the surface in Alberta province -- is a ticking ecological time bomb for the vast country. "Every single one of them is simply steel and concrete. They erode and break down," said Regan Boychuk, the founder of Reclaim Alberta, a group advocating for the clean-up of such wells. IMAGES AND SOUNDBITES ARRANGED IN SEQUENCES