Section 2 of City Water Tunnel No. 3

Rank #1
Cost: $750 million

Digging began in October for the Manhattan leg of City Tunnel No.3, considered the largest capital construction project in New York history.

Located 550 ft. under the streets of Manhattan, the tunnel is all about delivery safe drinking water to city residents. Its sophisticated control system, the placement of its valves in special chambers and the depth of its excavation represent state-of-the-art technology.

The tunnel originates from 30th Street on the west side of Manhattan and will run downtown to the Holland Tunnel. A second section will loop north from that point up the west side to Lincoln Center.

This 8.5-mi. section of the tunnel will be activated by 2011 at a cost of $750 million, according to Commissioner Christopher O. Ward of the New York City Department of Environmental Protection.

Planning for City Tunnel No. 3 began in the early 1960s and actual construction commenced in 1970. As part of a four-stage tunnel project, tunnel No. 3 is expected to be completed by 2020 at a total cost of $5.5 billion to $6 billion, according to the DEP.

At conclusion, the tunnel will be more than 60 mi. in length.

Stage 1 - which is already delivering drinking water - was completed in 1998 and is a 24-ft. diameter concrete-lined pressure tunnel that steps down in diameter to 20 ft. It runs 13 mi. from the Hillview Reservoir in Westchester, through the Bronx, northern Manhattan and Queens.

The first section of Stage 2 - the Brooklyn-Queens section running through Red Hook, Brooklyn, to Woodside and Astoria, Queens - is complete and will be activated in 2007.

Construction of stages 2, 3 and 4 has been accelerated by a tunnel boring machine known as "the mole," which has been lowered in sections and assembled at the bottom of the shaft. The TBM has chipped off sections of bedrock through the continuous rotation of a series of steel cutters mounted on a large-diameter, full-circular, welded steel cutter head.

The TBM is expected to allow tunnel workers to excavate at an average of 50 ft. per day at a diameter of 23 ft. - more than twice the rate possible through drilling and blasting methods. Because the TBM bores into the rock, there is less damage at the point of excavation and no noise at the surface to disturb surrounding communities.

City Tunnel No.3 is 800 ft. underground at its deepest and 400 ft. at its shallowest point. While No. 3 will not replace tunnels No. 1 and No. 2, it will enhance and improve the adequacy and dependability of the entire water supply system and improve service and pressure to outlying areas of the city.

The operation of No. 3 will also allow for the inspection of Nos.1 and 2 for the first time since they were put into service in 1917 and 1936, respectively, according to the DEP.

When completed, tunnel No. 3 it will include four large underground valve chambers, numerous riser shafts with riser valve and distribution chambers and surface access facilities.

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