People canoeing on a river

Protecting the Middle Fork from coal ash: How long is ‘perpetuity?’
Everyone agrees on the 'P' word

Dynegy is planning to close the coal ash ponds at its shuttered Vermilion Power Station near Oakwood, Illinois. The company may propose to remove the toxic coal ash from the banks of the Middle Fork River, or cap the ponds and leave them in place. The Illinois EPA says the river must be protected "in perpetuity." But after Dynegy walks away from the site, what does perpetuity mean?