Constructed between 1937 and 1945, the Delaware Aqueduct draws from four reservoirs – the Cannonsville, Pepacton, Neversink and Rondout – to provide between 50 and 80 percent of the City’s daily water demand. The 84-mile aqueduct consists of three distinct pressure tunnels connecting the Rondout Reservoir in Ulster County to the Hillview Reservoir in Yonkers, and crosses the Hudson River at a depth of 600 feet below the river’s surface. With the bulk of New York City’s drinking water supplied by the Delaware Aqueduct, restoration of its deteriorating condition is critical.
Two leaks in the Rondout-West Branch Tunnel, located at Wawarsing and Roseton, threaten the aqueduct with significant water loss or catastrophic collapse. Leak data indicates that the 33 to 37 million gallons per day escaping from the two leaks does not account for all of the water missing from the aqueduct. A leak below the Hudson River is an even more worrisome prospect.
Although DEP has known of these leaks for more than 10 years, progress in rehabilitating the aqueduct has been slow. Rehabilitation work has been limited to shaft repair, as the DEP conducts a water dependability study to ensure that when the aqueduct is taken off-line, New York’s 9 million residents have a sufficient alternative water supply. There is also concern that draining the aqueduct could lead to a tunnel collapse, as the internal pressure of the water decreases relative to the pressure exerted by the rock on the outside of the tunnel.
In January of 2007, the DEP released a Revised Environmental Assessment for work to be done at six shaft locations along the aqueduct. This work, which has already begun, is to be performed in preparation for tunnel repairs, which according to the assessment may not be undertaken for another eight to ten years because of the current lack of an alternative water supply. Work to be performed at each shaft site is estimated to take 6 months, except for work at Shaft 6 in Wappingers, NY, where repairs are estimated to take place over 48 months. Improvements to each site vary, but include the installation of monitoring equipment and data acquisition systems to transmit pressure readings from inside the tunnel, as well as the routing of electrical service and other interior and exterior repairs.
In June of 2003, DEP sent a self-propelled submersible vehicle (an Autonomous Underwater Vehicle or AUV) through the 45-mile Rondout-West Branch Tunnel on a 16-hour mission to record data from inside the tunnel. The vehicle, built by the Woods Hole Oceanographic Institute, reportedly took approximately 160,000 digital images inside the aqueduct and measured pressure, velocity and other conditions, using sensors. Although the AUV run through was initially viewed as a success, it soon became clear that the untethered vehicle passed through the tunnel too quickly to complete a full inspection of the aqueduct. A second, tethered submersible vehicle has not yet been built.
In February of 2008, a team of divers was employed to inspect the structural and mechanical components of a tunnel unwatering shaft. The inspections, which took place over approximately two weeks, required divers to be lowered 700 feet in order to take measurements and collect other information DEP will use in creating its ultimate aqueduct repair program.
Although steps are being taken in preparation of the tunnel repairs, the DEP’s early inaction has only added to the sense of urgency in dealing with the impending crisis. Some residents of the Wawarsing area have experienced first hand, how the deteriorating conditions of the aqueduct can wreak havoc.
With unexplained flooding in their basements, after weeks without rain, residents are left asking the DEP whether the water is from the leak in the aqueduct and wondering why it has not been fixed. It is imperative to the individuals being affected by the leak presently and to those who may be affected in the future, the people who depend on the Delaware Aqueduct’s water, that alternative water sources be identified and repairs take place as soon as possible.