NY Harbor Water Siphon Replacement
A vital component of the Borough of Staten Island's water supply is a system consisting of two water transmission mains, or siphons, which connect main supply lines in Brooklyn with a pump station on Staten Island, and ultimately feed Staten Island's Silver Lake Reservoir. Critical to ensuring a backup water supply to Staten Island, the siphons run in the seabed under the Anchorage Channel, an important part of New York City's water transportation infrastructure. The Channel provides the international shipping trade with access to New York Harbor and the rest of the Port of New York and New Jersey, one of the most heavily used water transportation arteries in the world. The Channel must be deepened in order to accommodate a new generation of cargo mega-ships, and to ensure the City's ability to benefit from the anticipated increase in this sector of the economy. As the existing siphons could be compromised by the increased channel depth, a new, deeper siphon tunnel is required to permit the channel dredging work to proceed. The existing siphons, installed in 1917 and 1925, are located at depths of approximately 60 ft below the surface; the new siphon will be installed at a depth of 100 ft.
LiRo, in a joint venture, is providing resident engineering inspection and construction management services to the NYCEDC for the removal of the two existing mains and installation of the new siphon. Utilizing an Earth Pressure Balance (EPB) tunneling machine specifically designed and built for this project, a 12.5 ft diameter, 9,500 ft long tunnel is being bored under Upper New York Harbor. To enable installation, a 95 ft deep launching box was constructed in Staten Island at the intersection of Murray Hulbert Avenue and Front Street, and a 150 ft deep tunnel receiving shaft was located in Brooklyn on Shore Road Park between 83rd Street and Shore Road Lane. The new tunnel extends through silts, clays, glacial soils, and weathered and decomposed rock. Once the tunnel is complete, a 6' diameter steel water transmission pipeline will be installed, and the annular void between the pipeline and the tunnel face will be backfilled with concrete.
To connect the new siphon to the existing water supply system, an additional 4,000 lf of steel trunk main and 4,300 lf of transmission main will be installed in adjacent mainland area; the installation on the Staten Island side includes a 330 ft long micro-tunnel below the Staten Island Railroad tracks, installed with the use of a pressurized-face Micro-tunnel Boring Machine (MTBM). The project also includes the replacement of 3,500 lf of sewer mains in Staten Island and 400 lf of water mains in both Staten Island and Brooklyn, as well as the installation of 8,000 lf of piles to support the mains. Valve chambers, meter chambers, insulated flange chambers, regulator chambers, connection valve chambers, blow-off structures, access manholes, and other related appurtenances are also being constructed.
As part of the project a chlorination station, incorporating sustainable features, will be constructed. The roof, as well as the north and south facades, will incorporate plant material to integrate the building into the surrounding landscape. To further minimize environmental impact, the chlorination process will take place in an underground structure, and the area surrounding the building will be landscaped. The project also includes landscape restoration, tree protection, and replacement of sidewalks in areas affected by the construction.
The new siphon will provide 5 million gallons per day (mgd) of daily water supply to Staten Island under normal conditions. In emergency situations, up to 150 mgd could be supplied, thus ensuring a redundant and reliable supply of water to Staten Island. Once installation of the new siphon is completed, the existing siphons will be decommissioned and abandoned in place.
To properly support the project, LiRo's staff possesses the technical skills to understand the anticipated ground behavior, and is well versed in the construction methodology and monitoring techniques necessary to handle these specialized conditions. Independent monitoring of the TBM and the Contractor's QA/QC program ensure safe working conditions.
Resident/ Construction Engineering & Inspection