The world’s longest tunnel needs a $1.2 billion fix. Built during World War II, the Delaware Aqueduct supplies approximately half of New York City’s drinking water and has been leaking 15 million to 35 million gallons daily since the 1990s.
Now construction workers are using a custom-made boring machine to create a 2.5-mile bypass tunnel around the leak 55 stories underground. The city is also preparing for a months-long shutdown of the Delaware Aqueduct to divert water. If all goes well, officials say, nobody will notice any difference in the water supply.
Here’s a closer look at this massive infrastructure project.
Completed in 1944, the 85-mile aqueduct carries more than 500 million gallons of water from four upstate reservoirs into the city every day. One million people in Ulster, Orange, Putnam, and Westchester counties who also rely on this supply, according to the city’s Department of Environmental Protection (DEP).
In the early 1990s, leaks were discovered in Newburgh and Wawarsing at a weak point where it crosses through limestone instead of shale. They were exacerbated by floods and high water tables, causing the state and the city’s DEP to spend millions, Judy Rife reported in the Times Herald-Record.
The leaks were stable, but what if they got worse?” Paul Rush, the DEP’s deputy commissioner for water supply told the paper. “We were putting half the city’s water supply at risk. If we lost the Delaware, it would be a disaster. Water is the economic lifeblood of the city. That’s what I saw.”
Constructing the bypass tunnel and completing internal repairs will cost around $1.2 billion, and water projects to supplement the city’s supply during part of the construction period will cost approximately $900 million, according to the department.
“It’s really the largest and most complex water tunnel repair that the city of New York has ever done,” Vincent Sapienza, DEP commissioner told the Associated Press’ Michael Hill.
Repair work on sections of the Delaware Aqueduct began last year. In October 2022, the main tunnel will need to close for five to eight months, but officials say they don’t anticipate any reduction in water delivery to the city.
NYC Water Reduction Efforts
“Cutting off half the city’s water supply for up to eight months sounds like a recipe for disaster, but the environmental agency has been preparing for years,” Hill reported. Despite a growth in population, New York City has managed to lower water usage through efforts such as the installation of low-flow toilets in 10 City University of New York buildings.
This month the DEP announced that through a number of strategic initiatives, the city has gone from a per-capita peak demand of 213 gallons per day in 1979 to 115 gallons per day in 2017, saving 10 million gallons of water daily. Over the next five years, the department plans to double that.
Projects include installing timers on 400 spray showers in Parks Department playgrounds, upgrading bathroom fixtures in public schools, upgrading wastewater treatment plants, distributing nearly 100,000 home water saving kits, and replacing more than 12,600 inefficient toilets in private residences.
New opportunities identified call for replacing water fixtures across the city’s public hospitals and clinics, retrofitting plumbing fixtures in the New York City Department of Citywide
Administrative Services portfolio, and upgrading the infrastructure in several city parks.
A bypass tunnel is being bored with a machine named for civil engineer Nora Stanton Blatch Deforest Barney. It has a cutter head 21.6 feet in diameter. Altogether the entire machine is more than 470 feet long and weighs upward of 2.7 million pounds, according to the DEP.
The cutter head turns at 8.8 RPM maximum, and as the machine excavates, it partially lines the tunnel using 9,000-pound concrete segments. The tunnel is expected to be completed in 2022, reducing the water shutdown from years to months, Hill reported.
Boring isn’t without risk. “Tunnel boring machine work can be tricky and one misstep can derail a project for years,” Construction Dive’s Kim Slowey wrote, citing how Bertha, the machine used to carve out the tunnel for the $2.2 billion Alaskan Way project in Seattle, broke down and caused a two-year delay. “Bertha finally completed her tunneling work in April 2017, almost 30 months past the originally scheduled finish date.”
However, officials in New York have confidence in the project, which has been years in the making. By 2023, water should be flowing through a bypass tunnel built to last, Hill wrote. Rush told him that after that, the DEP doesn’t plan to come down again anytime soon.