Excavation of two vertical shafts will provide access for construction workers to build the 2.5-mile-long Delaware Aqueduct Bypass Tunnel. Image: New York City Department of Environmental Protection
In early April, New York City Department of Environmental Protection (DEP) Commissioner Emily Lloyd joined town, county, and state officials in Wappinger, N.Y., to mark the next phase of construction at Shaft 6B, a key component of the $1 billion bypass tunnel project that will address leaks in the Delaware Aqueduct. A ceremonial first blast at the construction site marked the beginning of bedrock excavation to build a 700-foot-deep shaft on the east side of the Hudson River.
The Delaware Aqueduct conveys more than half of New York City’s drinking water from four reservoirs in the Catskill Mountains. DEP has been monitoring two leaks in the aqueduct
since the 1990s. The leaks — located in Newburgh and Wawarsing — release a combined 15 million to 35 million gallons a day (mgd), depending on the rate of flow inside the aqueduct. To address the leaks, DEP has begun construction of a 2.5-mile bypass tunnel that will run 600 feet below the Hudson River, from Newburgh to Wappinger. The bypass tunnel, which is scheduled to be complete in 2021, will convey water around the leaking portion of the Delaware Aqueduct in Newburgh. That existing part of the aqueduct will be taken out of service once the bypass tunnel is finished. The smaller leak in Wawarsing will be sealed shut by grouting from inside the aqueduct.
The bypass tunnel is the central component of DEP’s $1.5 billion Water for the Future program, which aims to ensure clean, safe and reliable drinking water for future generations of New Yorkers. Water for the Future also includes structural upgrades to the Catskill Aqueduct, rehabilitation of the Queens Groundwater System to supplement upstate supplies, and water conservation initiatives in the city.
The 85-mile-long Delaware Aqueduct — the world’s longest continuous tunnel — was constructed between 1939 and 1944. The aqueduct runs as deep as 1,500 feet below ground, varies in diameter from 13.5 to 19.5 feet, and was constructed by drilling and blasting.
In most areas, the Delaware Aqueduct is lined only with reinforced concrete. However, two sections of the tunnel that run through limestone formations were lined with steel. The ongoing investigation of the structural integrity of the aqueduct found that small cracks formed where this steel lining ended.
DEP has continuously tested and monitored the leaks by using dye, backflow, and hydrostatic tests; hourly flow monitors provide near real-time data on the location and volume of the leaks. In 2003 and 2009, DEP used an Autonomous Underwater Vehicle (AUV), built in partnership with engineers at Woods Hole Oceanographic Institution in Massachusetts, to conduct a detailed survey of the entire 45-mile length of tunnel between Rondout Reservoir and West Branch Reservoir. The AUV took 360-degree photographs while gathering sonar, velocity, and pressure data to assist in determining the location, size, and characteristics of the leaks. The AUV is scheduled to launch again in fall 2014 to update that data. All the data gathered thus far clearly show that the rate of water leaking from the tunnel has remained constant and the cracks have not worsened since DEP began monitoring them in 1992.
Excavation of two vertical shafts will provide access for construction workers to build the bypass tunnel. The shafts in Newburgh and Wappinger will be 900 and 700 feet below surface level, respectively, and will measure roughly 30 feet in diameter. Both shafts are expected to be complete by 2016. An underground chamber at the bottom of the Newburgh shaft will serve as the staging area for the bypass tunnel. DEP expects to use a tunnel boring machine (TBM) to drill the 22-foot-diameter bypass tunnel, progressing at roughly 50 feet a day. The tunnel will be about 14.5 feet in diameter once it is lined with concrete and steel and will stretch 2.5 miles — including beneath the entire width of the Hudson River.
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. This work is anticipated to happen late in the year 2021. Engineers expect it will take roughly eight months to connect the bypass tunnel. While the Delaware Aqueduct is shut down, work crews will also fix cracks at three segments in Wawarsing, about 35 miles northwest of the bypass tunnel. These segments, totaling about 500 feet, will be sealed by injecting grout into them.
Years of preparation and planning for the Delaware Aqueduct bypass project led to the Water for the Future program, a portfolio of related projects that will ensure New York City has high-quality and reliable drinking water while the aqueduct is out of service.
• Catskill Aqueduct repair and rehabilitation — The 74-mile-long Catskill Aqueduct, which conveys water from the Ashokan and Schoharie reservoirs, will undergo a repair and rehabilitation project starting in 2016. Along with replacing more than 30 valves that are decades old, the interior lining of the tunnel will be scrubbed to decrease friction, which will increase the tunnel’s capacity by approximately 30 to 40 mgd.
• Queens groundwater — To augment the city’s upstate water supplies, DEP will also rehabilitate the Queens Groundwater System, formerly the Jamaica Water Supply, which will sustainably provide more than 33 mgd in southeast Queens. The Queens Groundwater System comprises 68 wells at 48 separate well stations.
• Water conservation — Between now and the Delaware Aqueduct shutdown in 2021, DEP will implement a number of initiatives to reduce water consumption in the city by as much as 50 mgd. As part of the Municipal Water Efficiency Program, DEP is identifying opportunities to conserve water at city-owned properties and facilities. To help encourage water conservation in private residences, DEP will sponsor a voucher program that aims to replace as many as 800,000 inefficient toilets with high-efficiency models that will save as much as 30 mgd by 2018.
• Croton System — The Croton Water Filtration Plant is entering its final stage of construction in the north Bronx, and testing of the filtration system and water lines is nearly complete. Once online, the filtration plant will allow the city to once again use water from the reservoirs in Putnam and Westchester counties that comprise the Croton System. DEP expects this will provide nearly 300 mgd.
View updates on construction, milestones, and other information related to Water for the Future at www.nyc.gov/waterforthefuture.
Information provided by New York City Department of Environmental Protection