Nora Holes Through
We reached a significant milestone last August when we completed excavation of the Delaware Aqueduct Bypass Tunnel, the $1 billion effort to repair leaks in the longest tunnel in the world. Read the Press Release.
The moment, known as “holing through,” happened at 6:51 a.m. on August 13 when Nora, the tunnel boring machine, broke through a wall of shale bedrock nearly 700 feet beneath the Town of Wappinger in Dutchess County.
The Bypass Tunnel
The Delaware Aqueduct Bypass Tunnel is the largest repair project in the 177-year history of New York City’s water supply system. Its centerpiece is a 2.5-mile-long bypass tunnel that we are building 600 feet under the Hudson River from Newburgh to Wappinger. When the project is finished in 2023, the bypass tunnel will be connected to structurally sound portions of the existing Delaware Aqueduct on either side of the Hudson River to convey water around a leaking section of the tunnel. The 85-mile-long Delaware Aqueduct typically conveys about half of New York City’s drinking water each day from reservoirs in the Catskills.
Nora’s Stats
Nora began to excavate the tunnel on Jan. 8, 2018. She pushed eastward from her starting point nearly 900 feet below the surface in the Town of Newburgh in Orange County. She mined 12,448 feet over 582 days. She excavated 89.8 linear feet on her most productive day, 354.8 feet during her best week, and 945 feet during her most productive month. As she forged ahead, she also lined the shale and limestone bedrock with 2,488 precast rings of concrete.
What’s Next
Now that mining is finished, we will begin to install 16-foot diameter steel liners inside the first layer of concrete. After the 230 steel liners are installed and welded together, we will be coat them with a second layer of concrete. This “triple-pass” design will provide the bypass tunnel with structural stability and prevent leaks from occurring again in the future.
