They could even introduce subterranean farming or an industrial mining complex simialr to one of the episodes in Star Trek where the rock eating mother alien that lays her spherical eggs everywhere, but the miners keep destroying them without realising and she defends her future babies the only way she can. Spock mind melds with her and they resolve the conflict with both parties involved benefitting from the new arangement.
A fast track monorail system set in their own tunnel above the existing tunnel network or straight and parallel to a station departure lounge in desired locations. That would give more significance for a marine outfit to move quickly where needed if any infestation occurs.
Hope you enjoy the reading, but please don't let it distract you from the serious matter of playing this game. Mothership values your input i'm pretty sure.