Not their first giant hellpit sinkhole. The city's sewage system is about as up to date as a bog mummy and it's basically just eating out the rock beneath the city. It's really just a matter of time before things really get bad.
They actually have a sewage system that's very similar to DC -- the single-pipe system that channels both storm runoff and sewage. It gets clogged -- especially, say, when a tropical storm comes through -- and is in such bad repair, the sewage spills out and dissolves the rock around it.
I know too much about this because I enjoy reading stories about how motorcycles and small cars are frequently washed down the DC main pipe and need to be hauled out of this foul sewage freakout mix.