20″ Subaqueous Water Mains to City Island

This project required the replacement of an existing 100-year old water main with dual 20-inch DIP force mains beneath the Eastchester Bay. The new force mains will provide City Island with clean water. The contract consists of the installation of a temporary peninsula in the Eastchester Bay in order to facilitate the construction of a cofferdam.

We constructed approximately 4,000 LF (2 drives) of 44″ drill holes at depths up to 100 ft. beneath Eastchester Bay via HDD. The majority of the drilling through Gneiss. We installed 32″ of welded steel casing through previously drilled bore holes. The casing was installed with a pipe thruster in three separate pipe strings, up to 900 ft. in length. We sliplined 20″ DIP into 32″ steel casing on rollers, grout annulus between casing and DIP. Hydric fill was installed in abandoned 12″ and 16″ water mains. Finally, we removed the existing temporary force main on the City Island Bridge.