"Closing a valve reveals the ladder in area 2 and reduces climbing DC to 9. This also causes sewage backflow to flood the labeled area. "
I just searched for a couple of minutes on the dungeon map for this "labeled areas". I just realised you meant the areas mentioned on the labels of the valves. Maybe it's because I'm not a native speaker but in my opinion "labeled areas" in this case is wrong. The valves are labeled with names of areas.