"There are 3 entrances. One of them can only be accessed by you and thats the roof of the bridge. You will have to fight a squad of snipers if you go that way.
Sewers are usually guarded by starfish demomen and enemy engineers, Spy could help.
And the normal way by the bridge is guarded by alot of mercernaries but teammates will probably be there. The intel probably has info of a new type of radiation that gives the dead special powers."