New York City Water Tunnel No. 3

New York City Water Tunnel No. 3 is a part of the New York City water supply system and is the largest capital construction project in New York City history. It is being built by the New York City Department of Environmental Protection to provide New York City with a third connection to its upstate water supply. The tunnel will be more than 60 miles (97 km) long, travel 500 feet (150 m) below street level in sections, and will cost over $6 billion. Construction began in 1970 and was expected to be completed in 2020, but work to link the existing sections of the new tunnel with Queens and Brooklyn has been indefinitely postponed by the Bill De Blasio mayoral administration.

The project was authorized in 1954 and was imagined as "the greatest nondefense construction project in the history of Western Civilization." The city determined that it needed a third water tunnel so that Tunnels 1 and 2 could be closed for inspection and repairs. Stage One construction of Tunnel 3 began in 1970 and completed in 1993. This portion was put into service in 1998 and cost about $1 billion.

This first section was bored through bedrock between 250 and 800 feet (76 and 244 m) underground, using drilling and blasting techniques. Section one is 13 miles (21 km) long and starts at Hillview Reservoir in Yonkers, New York then crosses under Central Park in Manhattan, to reach Fifth Avenue at 78th Street. From there it runs under the East River and Roosevelt Island into Astoria, Queens. It is a concrete-lined tunnel that is 24 feet (7.3 m) in diameter and reduces to 20 feet (6.1 m) in diameter before connecting to 14 vertical shafts.

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