The worst thing about this posting had to be the swamp itself. The ancient flooded forest produced an enormous amount of methane from its decomposing base, and the smell, combined with some particularly aromatic local animal defense mechanisms was nearly enough to burn the eyes.
Despite the air being safe to breathe, most of the infantry had taken to wearing at least a cloth mask and goggles to keep down the smell and reduce the effects of the fumes on their eyes while on patrol.
While off patrol, they retreated to the mine shafts, where an air purification and radiation mitigation system had been set up to keep them safe while the construction machines reinforced the tunnels so that they wouldn't collapse when under attack.