To address the problem WSP, in a joint venture, was engaged by the New York City Economic Development Corporation (NYCEDC) to manage the construction of a single new tunnel and water main to replace the two existing pipes that provide critical backup water supply to Staten Island.
The new siphon is a six-foot diameter steel water transmission main within a two-mile-long, 12-foot in diameter tunnel that runs beneath the New York Harbor from Brooklyn to Staten Island, parallel to the Verrazano-Narrows Bridge. The water main can deliver up to 150 million gallons of drinking water to the borough in the event of a disaster, significantly increasing its water security and ability to bounce back.
Located under the water table, soil conditions were extremely soft. The project required the use of a 300-foot-long, 110-ton tunnel boring machine (TBM) known as an earth pressure balance machine (EPBM), which mines and pushes the soil and muck through a screw conveyor system that transports the residue away from the machine. The Harbor Deepening Program was the first in New York City to use an EPBM. Additionally, the starting point in Staten Island and the end point in Brooklyn were both located in densely populated urban areas. The tunnel passed 80 feet below the Belt Parkway, a six-lane highway along the South Brooklyn shoreline where the ground conditions were particularly challenging.