NYC DEP starts $1 billion tunneling project to repair Delaware Aqueduct

New York — In early September, the New York City Department of Environmental Protection (DEP) began tunneling for the Delaware Aqueduct Bypass Tunnel — the largest repair project in the 175-year history of New York City’s drinking water supply. The $1 billion project will repair two areas of leakage within the 85-mile Delaware Aqueduct, the longest tunnel in the world. The primary leak will be eliminated through the construction of a 2.5-mile bypass tunnel, which will be drilled 600 feet below the Hudson River from Newburgh to Wappinger.

The tunnel will be driven by one of the world’s most advanced tunnel boring machines. The machine — which measures more than 470 feet long and weighs upwards of 2.7 million pounds — was dedicated in honor of Nora Stanton Blatch Deforest Barney, a noted suffragist and the first woman in the United States to earn a college degree in civil engineering. Nora, who worked as a draftsman on the City’s first reservoir and aqueduct in the Catskill Mountains, was also the first female member of the American Society of Civil Engineers.

“The start of tunneling to repair the Delaware Aqueduct is a major milestone in the history of New York City’s water supply system,” DEP Acting Commissioner Vincent Sapienza said. “While the City has added new facilities to its water supply over the past century, repairs approaching this magnitude have been few and far between. The effort to fix the Delaware Aqueduct is by far the most complex DEP has undertaken, and it highlights the absolute need to keep our public works in a state of good repair.”

The next phase of construction for the bypass tunnel will begin when construction workers in Newburgh begin to lower the $30 million tunnel boring machine (TBM) into a subsurface chamber that is located 845 feet below the ground. The machine is currently being stored in 22 pieces. It will take workers approximately four months to assemble the TBM.

The TBM is an integral part of DEP’s program to fix two leaks in the Delaware Aqueduct. The largest of the two leaks is located along the western bank of the Hudson River in Newburgh. The TBM will be used to build a 14-foot diameter bypass tunnel alongside this section of the aqueduct. The 2.5-mile bypass will be constructed 600 feet below the Hudson River, from Newburgh to Wappinger. Once finished, it will be connected to structurally sound portions of the existing Delaware Aqueduct to convey water around the leaking section. The leaking stretch will be plugged and permanently taken out of service.

The TBM was built to withstand 30 bar of pressure — believed to be the most of any TBM ever manufactured. The machine needs to withstand that much pressure because workers encountered huge inflows of water under immense head pressure when the aqueduct was first built more than 70 years ago. The TBM is also equipped with dewatering equipment to pump 2,500 gallons per minute away from the tunnel as the machine pushes forward.

In addition, the machine is outfitted with equipment to install and grout the concrete lining of the tunnel, and to convey pulverized rock to a system of railroad cars that will follow the TBM as it works. The railroad cars will regularly travel back and forth between the TBM and the bottom of Shaft 5B in Newburgh, delivering workers, equipment and rock between the two locations. Once the TBM begins its work, DEP expects it will drive about 50 feet of tunnel per day. Work on the tunnel will continue 24 hours a day, five days a week. Tunneling is expected to take 20 months.

Over the past several months, workers have already blasted 130 linear feet of “starter tunnel” in the direction that the TBM will work.

The finished bypass tunnel will be reinforced by 9,200 linear feet of steel and a second layer of concrete after the TBM is finished driving its path beneath the river. Once those are in place, DEP will shut down the Delaware Aqueduct to connect the bypass tunnel to the existing aqueduct. The approximately six-month shutdown is planned for October 2022. The project is expected to be finished in 2023.