When the party ends

WHEN AN OIL or gas well reaches the end of its lifespan, it must be plugged. If it isn’t, the well might leak toxic chemicals into groundwater and spew methane, carbon dioxide and other pollutants into the atmosphere for years on end. But plugging a well is no simple task: Cement must be pumped down into it to block the opening, and the tubes connecting it to tanks or pipelines must be removed, along with all the other onsite equipment. Then the top of the well has to be chopped off near the surface and plugged again, and the area around the rig must be cleaned up.

There are nearly 60,000 unplugged wells in Colorado in need of this treatment—each costing $140,000 on average, according to the Carbon Tracker, a climate think tank, in a new report that analyzes oil and gas permitting data. Plugging this many wells will cost a lot—more than $8 billion, the report found.

Companies that drill wells