BUILDING BIG: Databank: New York Third Water Tunnel

Six hundred feet below the busy streets of New York City, engineers are boring a 60-mile-long tunnel -- the largest tunnel in America. This tunnel won’t carry cars, trains, or even people, but it will deliver 1.3 billion gallons of water daily to nine million area residents. New York City’s $6 billion Third Water Tunnel is one of the nation’s largest and most complex public works projects ever attempted.

In 1954, New York City recognized the need for a new tunnel to meet the growing demand on its 150-year-old water supply system. Construction began in 1970 on the Third Water Tunnel, a tunnel designed to improve the dependability of New York City’s entire water supply system. The majority of the tunnel is being carved with a 450-ton, 19-foot diameter rock-chewing device called a tunnel boring machine. Unlike the older water supply tunnels in New York City, water control valves in the Third Water Tunnel will be housed in large underground chambers, making them accessible for maintenance and repair.

When completed in 2020, the size and length of the Third Water Tunnel, its sophisticated valve chambers, and its depth of excavation will represent the latest in state-of-the-art tunnel technology.

Fast Facts:

The equipment used to dig the Third Water Tunnel is the same that was used to dig the underwater Channel Tunnel, or "Chunnel," that connects mainland France to England.
The largest valve chamber in the tunnel, the Van Cortlandt Park Valve Chamber, is 620 feet long (longer than two football fields placed end to end), 42.5 feet wide, and 41 feet high.
The tunnel boring machine, which had to be lowered into the tunnel in pieces and assembled at the bottom, is capable of excavating 50 feet of rock per day at a diameter of 23 feet -- more than twice the rate previously achieved in tunnel construction through drilling and blasting methods.