What are the guys on the ground checking for?
Never mind, just found this:
More important are the post-landing procedures and checks. The ground equipment cooling lines have to be connected to the shuttle, so the electronics can be cooled again. Also, technicians have to make sure that no RCS, OMS or APU propellant is leaking out, because all three substances used (MMH, N2O4 and Hydrazine) are toxic and cause dangerous fumes.