DEP Announces Significant Progress on Project to Upgrade and Rehabilitate Catskill Aqueduct

February 5, 2020

The New York City Department of Environmental Protection (DEP) today announced significant progress on a $158 million project to clean, upgrade and rehabilitate the Catskill Aqueduct, which delivers approximately 40 percent of the city’s drinking water each day. The aqueduct was shut down for 10 weeks in November, December and January to facilitate work inside the structure and at facilities connected to it. During that time, upwards of 200 workers were deployed at more than a dozen locations in Ulster, Orange, Putnam and Westchester counties to clean the inside of the aqueduct, repair cracks and other defects, and replace valves that are connected to the aqueduct.

“This complex project to rehabilitate the Catskill Aqueduct has required more coordination and flexible planning than perhaps any in the history of our water supply,” DEP Commissioner Vincent Sapienza said. “I want to thank the laborers who worked around the clock for 10 consecutive weeks, the communities north of the city who prepared and activated their backup water supplies while the aqueduct was out of service, and our DEP engineers and planners who coordinated activities during the shutdown. While we are pleased with the significant progress that was made this year, much work remains to complete the project and ensure this critical aqueduct can serve New Yorkers for generations to come.”

The 92-mile-long Catskill Aqueduct stretches from Ashokan Reservoir in Ulster County to Hillview Reservoir in Yonkers. The rehabilitation project focuses on the 74 northernmost miles of the aqueduct, from Ashokan to Kensico Reservoir in Valhalla. To safely perform the work, DEP must periodically shut down the Catskill Aqueduct for weeks at a time. The first shutdown, which occurred in the fall and winter of 2018-2019, allowed experts to inspect the inside of the aqueduct, test methods for cleaning its concrete lining, and repair a few areas where leaks were known to exist.

The most recent shutdown for the project—known as the Catskill Aqueduct Repair and Rehabilitation Project—started on Nov. 10, 2019, and continued until Jan. 23. The following work was accomplished during that time:

  • The Catskill Aqueduct was shut down for 74 days, 9 hours and 20 minutes without affecting the reliable supply of water to New York City or the 20 communities in Ulster, Orange, Putnam and Westchester counties that usually draw their drinking water from the aqueduct.
  • A total of 32.5 miles, or 171,500 linear feet, of the aqueduct’s concrete lining was cleaned from the inside. The cleaned area stretched from a facility near the Wallkill River in Ulster County to the Croton Reservoir in Westchester County. Workers removed a harmless, organic film from the inside the aqueduct by using stiff scrapers that are similar to squeegees. They scraped the walls of the aqueduct clean from a rolling, modular scaffold that was specially manufactured for the project. Cleaning the aqueduct will restore some of its historic transmission capacity. The organic film creates a rough surface within the Catskill Aqueduct. That rough surface creates friction, causing the water to move slower and thereby reducing the amount of water that can flow through the aqueduct each day. DEP estimates it will regain roughly 40 million gallons of transmission capacity in the Catskill Aqueduct by cleaning its concrete lining. A total of 800 tons of organic film was removed during the latest shutdown.
  • Leaks and other defects, such as surface cracks, along the aqueduct were repaired at several locations. These were repaired by a variety of methods. A total of 14,036 linear feet of holes were drilled into the aqueduct to seal leaks by injecting them with a special grout that filled the cracks.
  • Workers also removed and replaced the first two of 35 century-old valves along the aqueduct. These valves are located at chambers that allow the aqueduct to drain into local bodies of water. The remaining valves will be removed and replaced in future shutdowns.

DEP worked in close coordination with communities in the Hudson Valley where aspects of the construction were happening. DEP also collaborated with 20 towns, cities, villages and water districts north of the City that draw all or some of their drinking water from the Catskill Aqueduct. DEP worked with all these communities to prepare and confirm the readiness of their backup water supplies before and during the shutdown.

Preparing for the Delaware Aqueduct Bypass Tunnel

DEP’s work on the Catskill Aqueduct is key to preparing for a shutdown of the Delaware Aqueduct in 2022. The 85-mile-long Delaware Aqueduct is the longest tunnel in the world. It begins at Rondout Reservoir in Ulster County and conveys about half of New York City’s drinking water every day.

DEP is currently working on a $1 billion project to repair two areas of leakage from the Delaware Aqueduct. The primary leak will be eliminated through the construction of a 2.5-mile bypass tunnel that is now being built 600 feet under the Hudson River from Newburgh to Wappinger. Excavation of the bypass tunnel was completed on Aug. 13, 2019, and workers are now lining the tunnel with steel and concrete. The bypass tunnel will be connected to structurally sound portions of the existing Delaware Aqueduct to convey water around the leak. The Delaware Aqueduct will stay in service while DEP works on the bypass tunnel parallel to it. Once the bypass tunnel is nearly complete, DEP will shut down the Delaware Aqueduct for 5-8 months to finish the connections on either side of the Hudson River. The leaking section of the existing aqueduct will be plugged and taken out of service forever.

Over the past decade, DEP has worked on several projects to ensure New York City will have a reliable supply of drinking water during the Delaware Aqueduct shutdown. The rehabilitation of the Catskill Aqueduct, including the additional transmission capacity that it will yield, is key to those efforts.

Background information on the Catskill Aqueduct

The Catskill Aqueduct is a 92-mile conduit that carries drinking water from Ashokan Reservoir in Ulster County to Hillview Reservoir in Yonkers. The aqueduct conveys about 40 percent of New York City ’s drinking water on an average day, and it can currently deliver up to 590 million gallons per day.

The Catskill Aqueduct was built from 1907-1915. It first delivered water to New York City on Dec. 27, 1915, starting with water to the Bronx only. Water from the Catskill Aqueduct first reached all five boroughs of the city in 1917. The majority of the aqueduct—about 55 miles of its total length—was built above ground using a “cut-and-cover” method that involved excavating a trench and building the aqueduct at the surface. The remainder of the aqueduct includes grade tunnels that cut through mountains and pressure tunnels that plunge below creeks and rivers before coming back to the surface. The portion of the Catskill Aqueduct that runs 1,114 feet beneath the Hudson River is the deepest part of New York City’s entire water supply.

The aqueduct conveys water from Ashokan Reservoir, which was the first reservoir New York City built in the Catskills. Water that came from the Catskills, through the aqueduct, was key to allowing New York City to grow through the industrial and population booms that followed World War I.

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.