A contractor punctured the iron casing around the Queens-Midtown Tunnel in New York City, but fortunately thousands of motorists escaped a horrible death:
Workers for the Metropolitan Transportation Authority, which owns the tunnel, first noticed the curious downpour in the eastbound tube around 10 a.m. Leaks are not unheard of, and at first it appeared routine. An initial report indicated that officials suspected that the water was coming from a broken main on the Queens end of the tunnel.
But there was no evidence to support that guess. So, as the water continued to pour in, a tunnel worker performed a simple test using the most sensitive of instruments: his tongue.
The water, the worker discovered, was salty.
Immediately, it was clear that this was no burst pipe. City mains carry fresh water; salt water could only be rushing in from the river above.
[T]he cause of the Queens-Midtown Tunnel’s sudden failure was ... clear. Floating on the river, high above the tunnel, was a barge working on an entirely different infrastructure project, probing deep into the water with a large, red drilling rig.
When contractors punctured Chicago's Loop tunnel network in 1992, we got flooded basements. A QMT failure could have drowned thousands of people.