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 construction project in New York 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, travels 500 feet (150 m) below street level in sections, and will cost over $6 billion. Construction began in 1970 and is expected to be completed in 2020.
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 240 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 to increase the pressure,[clarification needed] so that the water will rise through 14 vertical shafts.
Stage Two was built using tunnel boring machines and comprises two sections. The Brooklyn and Queens section runs 5.5 miles (8.9 km) and begins in Red Hook, Brooklyn, where it connects to the Richmond Tunnel for Staten Island. It passes through Park Slope, Bedford-Stuyvesant and Bushwick before reaching Maspeth, Queens. From Maspeth it runs through Woodside and Astoria, where it connects to the end of the Stage One section. The Brooklyn section is 16 feet (4.9 m) in diameter, and the Queens section - 20 feet (6.1 m).
The Manhattan section is 10 feet (3.0 m) in diameter and runs for 9 miles (14 km). It begins at a valve chamber in Central Park, run south along the west side of Manhattan, and curves around the southern end of the island to come partway through the Lower East Side. A spur of the Manhattan tunnel begins on the west side at approximately 34th Street, goes to the east side and then turns north under Second Avenue to about 59th Street. The tunnel itself was completed in 2008, and after the construction of riser shafts was completed, the tunnel opened in 2013. 
What used to be called Stage Three is now being referred to as a separate project, the "Kensico-City Tunnel." It will be 24 feet (7.3 m) in diameter, running from the Kensico Reservoir in Westchester to the Van Cortland Valve Chamber complex in the Bronx.
The largest valve chamber is in Van Cortlandt Park. It is built 250 feet (76 m) below the park surface. When completed it will control the flow of water from the city's Catskill and Delaware systems. These systems provide 90 percent of the city's current drinking water. The Van Cortlandt Park Valve Chamber is 620 feet (190 m) long, 43 feet (13 m) wide and 41 feet (12 m) high. The complex has nine vertical shafts; and two manifolds. Each manifold is 560 feet (170 m) long and 24 feet (7.3 m) in diameter and is projected to be finished in 2020.
Since 1970, when construction on the tunnel began, 24 people have died in construction-related accidents. This includes 23 workers and a 12-year-old boy, Don-re Carroll, who died while exploring uncapped water pipes in the Bronx. No deaths have occurred since 1997.
- New York City Water Tunnel No. 1, completed 1917
- New York City Water Tunnel No. 2, completed 1936
- New York City Water Tunnel No. 3, begun 1970, estimated completion in 2020
- Scenes from the 1995 film Die Hard with a Vengeance were filmed in Tunnel No. 3.
- Payback, a 1997 novel by Thomas Kelly, includes "the twenty-three men who have died building New York City Water Tunnel Number Three" among those to whom it is dedicated. Billy Adare, one of the principal characters, is a sandhog working on the tunnel whose father was killed in the early stages of its construction.
- The CSI: NY episode "A Man a Mile" deals with the death of a sandhog during construction of Water Tunnel No. 3.
- In Spider Robinson's novel Night of Power, Tunnel No. 3 is depicted as an abandoned project, taken over as the secret headquarters for a revolutionary movement.
- The Nova episode "The Hidden City" (Oct. 3, 1989) included a segment on the construction of the tunnel.
- "Tunnelers Hit Something Big: A Milestone". New York Times. August 10, 2006. Retrieved 2011-12-15. "It is the biggest public works project in New York City’s history: a $6 billion water tunnel that has claimed 24 lives, endured under six mayors and survived three city fiscal crises, along with the falling and rising fortunes of the metropolis above it. ..."
- Grann, David (1 September 2003). "City of Water". The New Yorker (Condé Nast): 88–103. Retrieved 21 October 2013.
- NYC Department of Environmental Protection (2006). City Water Tunnel No. 3 Fact Sheet (Report). http://www.nyc.gov/html/dep/pdf/factsheet.pdf. Retrieved 21 October 2013.
- water-technology.net "New York City Tunnel No. 3, United States of America". Net Resources International. Retrieved 2011-12-15.
- Flegenheimer, Mark (16 October 2013). "After Decades, a Water Tunnel Can Now Serve All of Manhattan". The New York Times. Retrieved 21 October 2013.
- NYC Department of Environmental Protection (2008). New York City 2008 Drinking Water Supply and Quality Report (Report). City of New York. p. 6. http://www.nyc.gov/html/dep/pdf/wsstate08.pdf. Retrieved 21 October 2013.
- Cohen, Noam S. (2 September 1991). "Body of Bronx Boy Retrieved From a 500-Foot Shaft". The New York Times. Retrieved 12 October 2013.
- John H. Betts The Minerals of New York City originally published in Rocks & Minerals magazine, Volume 84, No. 3, pp. 204-252 (2009).