The aqueduct, the world's longest continuous tunnel, was constructed between 1939 and 1944 and crosses Ulster, Orange, Dutchess, Putnam and Westchester counties. The aqueduct is a concrete-lined tunnel that varies in diameter from 13.5 to 19.5 feet and runs as deep as 1,500 feet beneath the ground. It was constructed by drilling and blasting, and in most areas, it is lined only with unreinforced concrete. In areas where the rock is not as strong, a steel reinforcement liner was added to the concrete liner.
Since the 1990s, DEP has been monitoring leaks in a portion of the aqueduct that connects the Rondout Reservoir in Ulster County to the West Branch Reservoir in Putnam County, specifically in the towns of Roseton and Wawarsing. The leaks release between 15 and 35 million gallons of water a day, depending on the amount of water the aqueduct is carrying. Years of comprehensive inspections, testing, and study indicate that cracking and leakage are occurring in the aqueduct where it passes through limestone, a rock more susceptible to wear and tear than sandstone, shale, gneiss and granite that form the vast majority of the tunnel.
DEP is continuously testing and monitoring the leaking areas using dye, backflow, and hydrostatic tests, and hourly flow monitors that provide near real-time data on the location and volume of the leak. The data clearly show that the rate of leakage has remained constant since DEP began monitoring in 1992.
In 2003 and 2009, DEP launched an Autonomous Underwater Vehicle (AUV) - a cutting-edge, self-propelled submarine-shaped vehicle 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 from Roundout to West Branch reservoirs. The AUV took 360-degree photographs every eight feet, while also gathering sonar, velocity, and pressure data to assist in determining the location, size, and characteristics of the leaks. During the same period, DEP considered a number of alternatives to fix the leaks, and has more than $300 million of construction underway to build the equipment necessary to take water out of the tunnel to complete the repairs.
DEP's construction experts and tunnel designers have prepared a plan to address the leaks by building a bypass tunnel around the most significant leaking portions of the aqueduct, and will repair parts of the concrete liner in the existing tunnel in other areas, including Wawarsing. The tunnel will need to be shut down and emptied for a period of time to facilitate the bypass connection and perform the repair work.
Preparation for the repair work is currently underway, including: purchasing equipment for the repair; working on the design of the repair; preparing contract documents for the repair, including the bypass tunnel; performing physical investigations of geology at the site of the shafts and bypass tunnel; and assessments of environmental impacts of the project. The current repair plan is based on the following schedule:
* Construction of new shafts that connect to the aqueduct and the bypass tunnel to begin in 2013 and to be completed in 2016. A shaft is a vertical pipe that connects the tunnel to the surface. There will be two shafts at both ends of the new three-mile bypass tunnel. These shafts will provide access points for construction of the bypass tunnel and to facilitate connecting the bypass to the existing tunnel. The shafts will be from 700 to 900 feet deep, and have a diameter of 15 to 20 feet and will be located in the Town of Newburgh, which is on the west side of the Hudson River and in Wappinger, which is on the east side of the river.