Denver International Airport is planning an $11 million deep cleaning of its fabled tunnel system. A proposed contract would have Belfor Environmental do six months' worth of cleaning across the 3.5 million square feet tunnel network beneath the airport. While the tunnels get routinely cleaned, an airport spokesperson said this is the first time they have been deep-cleaned. (Tests for lead in the airport tunnels have detected a level of lead that isn't toxic to humans.) But the official story is that tunnels are only home to those dust bunnies — soon to be swept away.