NYC Completes Excavation of Third Water TunnelMayor of New York City Michael Bloomberg turned off on 9th August, 2006 a tunnel boring machine and announced that the excavation of Stage 2, or the Manhattan leg, of City Water Tunnel No. 3 was complete. Stage 2 of the project is a 13.7 km water tunnel built since October 2003. The project is important because Water Tunnels No. 1 and No. 2 have never been checked up on or had service inspections. Tunnel No. 1 was built in 1917 and Tunnel No. 2 in 1936, but neither cannot be inspected or maintained because turning them off can cause a water shortage. The completion of the second stage will nearly double the capacity of the city's water supply, currently 4.5 billion litres a day, and provide a backup to the two other ageing water tunnels, allowing them to be closed, inspected and repaired for the first time since they opened. The third water tunnel originates at the Hillview Reservoir in Yonkers, just across the border between the Bronx and Westchester County. The reservoir is fed by aqueducts that carry water from the Catskill and Delaware water systems, which usually provide 90% of the city's water supply. From the reservoir, the first stage of the tunnel reached south into the centre of the Bronx, then west across the Harlem River into Upper Manhattan and then down the west side of Manhattan and east into Central Park, crossing under the East River and into Astoria, Queens. That 20.9 km first stage cost about USD1 billion. It was begun in 1970, completed in 1993 and began delivering drinking water to some residents of the Bronx, Manhattan and Queens in 1998.The second stage, which extends the first stage south into Midtown and Lower Manhattan and east and south into Queens and Brooklyn, is complicated. The 16.7 km Brooklyn-Queens section - actually two separate tunnels, linking Red Hook, Brooklyn, via Maspeth, Queens, to Astoria - was completed by 1999 and is scheduled to begin transmission of water in 2009 which will supply water to areas in all five boroughs of NYC (the Bronx, Brooklyn, Manhattan, Queens and Staten Island).The new 13.7 km Manhattan section resembles three spokes radiating from a central point roughly below the intersection of West 30th Street and 11th Avenue. One spoke travelled north to Central Park, the second went to Lower Manhattan, and the third spoke, 4 km long, travelled east to Second Avenue and then north to East 59th Street and First Avenue. That third section was the last to be fully excavated, a step completed when mayor Bloomberg sat at the controls of a 213 m-long 3.81 m-diameter Robbins hard rock main beam TBM, as it excavated the last 20 centimetres of quartz, granite and silica. Tunnel depths range from 122 m to as deep as 244 m below Roosevelt Island. The contractor in charge of the Manhattan section of the tunnel is a joint venture of Schiavone Construction, J.F. Shea and Frontier-Kemper Constructors. The TBM's 27 disc cutters, weighing 158 kilogrammes and each 43 cm in diameter, have chipped through the bedrock at a rate of 16.8 to 30.5 metres a day, more than double the 7.6 to 12.2 metres that could be excavated each day under the drill-and-blast method used on Stage 1. Visit www.robbinstbm.com The rock has been removed from the face of the tunnel through the TBM's trailing gear by a conveyor into muck cars. A locomotive pulled the cars on rails through the tunnel to the head of the shaft at its opening, and the rock was then sifted, crushed and raised to the surface by a vertical conveyor belt. The new section must be lined with a 35 cm concrete layer, tested, fitted with instruments and sterilized before water can gush through it in 2012. 60,400 cubic metres of concrete will be used to line the Manhattan tunnel. The city is also installing at least 10 shafts that will link the tunnel with the water distribution grid. Construction of the shaft network, which brings water from the tunnel at depths of 183 to 244 metres up to the distribution system's water mains in Manhattan, will continue for the next three years.Even after 2012, two more stages of the project will remain. Stage 3, a 25.7 km segment 6.1 m in diameter and 244 m beneath the ground called the Kensico City tunnel, will join the Kensico Reservoir in Mount Pleasant in Westchester County with the Van Cortlandt valve chamber in the northern Bronx. It is in the final planning stages. The tunnel would allow the city to shut down, inspect and repair its two other aqueducts south of Mount Pleasant, the Delaware aqueduct, completed in 1945 and the Catskill aqueduct, completed in 1915.A proposed Stage 4, extending south from the Hillview Reservoir, through the eastern Bronx and under the East River into Queens, is still under review. This final stage will be 22.5 km long. The entire tunnel is scheduled to be completed in 2020 at a total cost of USD5.5 to USD6 billion. During the 36 years of construction, the third water tunnel has claimed 24 lives. Click us/17. Visit www.nyc.gov/html/dep/html/news/3rdtunnel.html 35/06. Mayor Michael Bloomberg switching off the Robbins TBM after breaking through Stage 2 of Water Tunnel No. 3 in NYC on 9th August, 2006