Umm, you may not like to find this out, but there are places where the NYC water supply mains are within 3 feet of the surface. Not all of the line is deep rock tunnel.
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That I know - I used to wn property where Tunnel 2 was directly in back under shallow cover (Across the street from the Old Atwood Schoolhouse) - that said, it'd be hard to take out the whole system - too much redundancy, and there is a LOT of water