DEP Announces Final Steel Segment Lowered Into Delaware Aqueduct Bypass Tunnel

May 14, 2020

Significant landmark for $1 billion project to repair the longest tunnel in the world

High-resolution images of the tunnel liners can be found on DEP’s Flickr page

The New York City Department of Environmental Protection (DEP) today announced that the final segment of steel lining has been lowered into the Delaware Aqueduct Bypass Tunnel, marking another significant milestone in the project to repair the longest tunnel in the world.

The last of 230 massive steel liners was lowered down an access shaft in the Town of Newburgh at 3:45pm on Wednesday. Each steel segment is 16 feet in diameter, 40 feet long, and weighs 106,000 pounds. Workers began transporting the steel liners in October from a storage site along the Hudson River in the City of Newburgh to the project site on Route 9W near Middlehope. DEP expected to complete the installation of steel liners by August, but laborers finished this vital portion of the $1 billion project several months ahead of schedule.

“I want to congratulate the engineers, laborers and other construction experts whose excellent work continues to advance the Delaware Aqueduct repair on budget and on schedule,” DEP Commissioner Vincent Sapienza said. “A project this large includes many milestones. Safely shipping, lowering and welding these massive steel segments is one of the most important because the steel lining will provide structural integrity to the Delaware Aqueduct, helping it serve New Yorkers for many generations to come.”

The Delaware Aqueduct Bypass Tunnel is the largest repair project in the 178-year history of New York City’s water supply system. Its centerpiece is a 2.5-mile-long bypass tunnel that DEP is 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, the longest tunnel in the world, typically conveys about half of New York City’s drinking water each day from reservoirs in the Catskills.

A massive tunnel boring machine completed excavation of the tunnel on Aug. 13, 2019. The tunneling machine excavated 12,448 feet over the course of 582 days, starting deep below the Town of Newburgh and pushing east to an access shaft in the Town of Wappinger. The tunnel boring machine lined the shale and limestone bedrock with precast rings of concrete as it drove the tunnel forward. The steel segments will line 9,200 linear feet of the new tunnel, and will later be coated 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.

The steel liners arrived at a deep-water port in the City of Newburgh in 2016 and 2017, where they stayed in storage until last year. Moving the massive liners 8 miles to the construction site required significant planning and coordination. A route was planned with local authorities, and utility lines were raised to allow the steel segments to pass beneath them. A craned loaded them onto special “lowboy” flat-bed trucks, and each liner was escorted to the site by police who shut down local roads and controlled traffic. The liners could only be moved between the hours of 10pm and 4am to avoid the times when local residents were typically traveling on the roads. Three liner segments were shipped to the site during a typical night of work.

Once they arrived at the construction site in Newburgh, each steel liner was picked up by a crane, turned vertically and lowered into the tunnel. A system of specially designed train cars drove each liner into place, starting at the Wappinger end and working their way back to Newburgh. Once they were fit end-on-end, workers double welded the liners together. The inside of each liner was outfitted with steel rebar to support the final concrete lining of the tunnel, which will be pumped into the tunnel and formed in the coming months.

Background on the Delaware Aqueduct repair project

DEP has monitored two leaking sections of the Delaware Aqueduct—one in Newburgh, and the other in the Ulster County town of Wawarsing—since the early 1990s. The leaks release an estimated 20 million gallons per day, about 95 percent of that escaping the tunnel through the leak near the Hudson River in Newburgh. DEP has continuously tested and monitored the leaks since 1992. The size of the cracks in the aqueduct and the rate of leakage have remained constant over that time.

In 2010, the City announced a plan to repair the aqueduct by building a bypass tunnel around the leaking section in Newburgh, and also by grouting closed the smaller leaks in Wawarsing. The project began in 2013 with the excavation of two vertical shafts in Newburgh and Wappinger to gain access to the subsurface. These shafts, 845 and 675 feet deep respectively, were completed in 2017. Workers then built a large underground chamber at the bottom of the Newburgh shaft. That chamber has served as the staging area for assembly and operation of the tunnel boring machine, and as the location from which excavated rock is brought to the surface by underground trains and a large crane.

The existing Delaware Aqueduct will stay in service while the bypass tunnel is under construction. Once the bypass tunnel is nearly complete and water supply augmentation and conservation measures are in place, the existing tunnel will be taken out of service and excavation will begin to connect the bypass tunnel to structurally sound portions of the existing aqueduct. While the Delaware Aqueduct is shut down, work crews will also enter the aqueduct in Wawarsing to seal the small leaks there, roughly 35 miles northwest of the bypass tunnel.

The project will mark the first time that the Delaware Aqueduct will be drained since 1958. In 2013, DEP installed new pumps inside a shaft at the lowest point of the Delaware Aqueduct to dewater the existing tunnel before it is connected to the new bypass tunnel. Those pumps will be tested several times before the tunnel is drained in 2022. The nine pumps are capable of removing a maximum of 80 million gallons of water a day from the tunnel—more than quadruple the capacity of the pumps they replaced from the 1940s. The largest of the pumps are three vertical turbine pumps that each measure 23 feet tall and weigh 9 tons.

The Delaware Aqueduct Bypass Tunnel is the first tunnel built under the Hudson River since 1957, when the south tube of the Lincoln Tunnel was finished.

Background on the tunnel boring machine “Nora”

The Delaware Aqueduct Bypass Tunnel was excavated by one of the world’s most advanced tunnel boring machines (TBM). The machine—which measured more than 470 feet long and weighed upwards of 2.7 million pounds—was named 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 for the City’s as a draftsperson during the construction of Ashokan Reservoir, was also the first female member of the American Society of Civil Engineers.

The $30 million TBM arrived at the worksite in Newburgh in 2017. It was delivered in 22 pieces and took four month to assemble. The 21.6-foot diameter TBM was built to withstand more than 30 bar of pressure—believed to be the most of any TBM ever manufactured. (That’s about 11 times the amount of pressure from a garden hose.) The machine needed to withstand high pressure because workers encountered huge inflows of water under immense pressure when the aqueduct was first built more than 70 years ago. The TBM was equipped with pumping equipment to remove up to 2,500 gallons of water per minute away from the tunnel as the machine pushed forward. The TBM was also 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 followed the TBM as it works. The railroad cars regularly traveled back and forth between the TBM and the bottom of Shaft 5B in Newburgh, delivering workers, equipment and rock between the two locations. The TBM was dismantled, brought to the surface in pieces, and removed from the worksite after it completed the excavation last year.

About the Delaware Aqueduct

The Delaware Aqueduct is an 85-mile-long tunnel that delivers drinking water from Rondout Reservoir in Ulster County to Hillview Reservoir in Yonkers. The aqueduct typically conveys about 50 percent of New York City’s drinking water. The Delaware Aqueduct put into service in 1944 when New York City Mayor Fiorello H. La Guardia opened a set of emergency gates to channel the Rondout Creek directly into the new aqueduct. It was placed into emergency service that year to support efforts related to World War II. The Delaware Aqueduct is the longest tunnel in the world, approximately 11 miles longer than water tunnel build in the early 1980s in Finland.

DEP manages New York City’s water supply, providing more than 1 billion gallons of high-quality water each day to more than 9.6 million New Yorkers. This includes more than 70 upstate communities and institutions in Ulster, Orange, Putnam and Westchester counties who consume an average of 110 million total gallons of drinking water daily from New York City’s water supply system. This water comes from the Catskill, Delaware, and Croton watersheds that extend more than 125 miles from the City, and the system comprises 19 reservoirs, three controlled lakes, and numerous tunnels and aqueducts. DEP has nearly 6,000 employees, including almost 1,000 scientists, engineers, surveyors, watershed maintainers and other professionals in the watershed. In addition to its $70 million payroll and $168.9 million in annual taxes paid in upstate counties, DEP has invested more than $1.7 billion in watershed protection programs—including partnership organizations such as the Catskill Watershed Corporation and the Watershed Agricultural Council—that support sustainable farming practices, environmentally sensitive economic development, and local economic opportunity. In addition, DEP has a robust capital program with $20.1 billion in investments planned over the next decade that will create up to 3,000 construction-related jobs per year. For more information, visit, like us on Facebook, or follow us on Twitter.