Fixing the Delaware Aqueduct Leaks

Preparation Underway to Fix Leak in Delaware Aqueduct
Progress towards goal set in PlaNYC

The New York City Department of Environmental Protection (DEP)
announced today that preparation is underway to repair the 45-mile
Rondout-West Branch Tunnel, which has been leaking for nearly two
decades. For approximately two weeks - beginning February 20th - a team
of divers, working 24 hours a day in rotating shifts, will be lowered
700 feet in order to inspect mechanical and structural components of a
tunnel shaft and to take measurements for new equipment. The
Rondout-West Branch (RWB) Tunnel is part of the Delaware Aqueduct,
which, at 85 miles, is the world's longest continuous tunnel, and a
vital component of the City's drinking water supply system. The results
of these investigations will inform the development of a comprehensive
repair program for the Delaware Aqueduct.

“The Bloomberg Administration has made planning for the repair of the
Delaware Aqueduct a pivotal part of the PlaNYC goal to improve the
reliability and long-term sustainability of New York City's water
infrastructure,” said Commissioner Lloyd. “DEP has closely monitored
the Aqueduct since its construction, which allowed us to discover the
leaks in the late 1980s. Since then, DEP has continuously monitored,
studied and tested the leaks and their effects, using dye tests,
backflow tests, hydrostatic tests, and hourly flow monitoring. This
dive is an important step in developing a repair strategy for the
tunnel and preparing to undertake this work.”

The Delaware water supply system, constructed between 1937 and 1965,
originates more than 100 miles north of New York City and consists of
four reservoirs: Cannonsville, Neversink, Pepacton, and Rondout. The
Delaware Aqueduct conveys drinking water from these reservoirs to the
City's distribution system, and currently provides approximately 50
percent of the City's daily water needs. The Aqueduct is a 13.5-foot
diameter, concrete-lined tunnel that varies in depth from 300 to 1500
feet beneath the ground and crosses the Hudson River at nearly 600 feet
beneath the ground. The Rondout-West Branch (RWB) Tunnel is a 45-mile
portion of the 85-mile Aqueduct, and connects the Roundout Reservoir in
the Delaware system to the West Branch Reservoir, located in Putnam
County, in the City's Croton watershed.

Since the late 1980s, DEP has been monitoring two leaks in the RWB
Tunnel portion of the Aqueduct that collectively release between 10 and
36 million gallons of water a day (mgd), depending on the amount of
water the Aqueduct is carrying. Monitoring has shown that the leakage
rate is stable and has not grown.

Seattle-based Global Diving, will perform the inspection work as a
subcontractor to Rondout Constructors. Global Diving is utilizing a
Saturation Dive System to perform this deep water work- meaning the
divers live 24 hours a day in a sealed, pressurized environment. The
Earth's surface atmosphere is approximately 78% Nitrogen and 21%
Oxygen, but because of the immense pressure at 700 feet beneath the
surface of the shaft (nearly 300 pounds per square inch), the divers
are required to live in an environment composed of 97% helium and 3%
oxygen for the duration of the work - approximately three weeks. Even
when they are not underwater, the divers live in a specially-designed,
pressurized chamber, outfitted with sleeping accommodations. The divers
must stay under pressure while they move from the saturation chamber to
their diving bell, which is lowered to the bottom of the shaft so the
divers can exit and perform their work. The underwater work is being
observed and monitored using closed circuit cameras and audio attached
to the diver's helmets and the diving bell. After the work is complete
the divers must remain in the confinement of the saturation chamber for
an additional eight days so they can gradually and safely return to
standard atmospheric pressure.

In addition to beginning the work at the unwatering shaft and designing
the long-term repair program, DEP has also developed an emergency repair
plan, and through its Dependability Study is developing plans to
diversify the City's water system. In addition to creating redundancy
for our aqueducts, PlaNYC provides for the stewardship of the City's
entire water supply and distribution system by modernizing the in-city
distribution network (completing Tunnel 3), protecting drinking water
at the source -- through rigorous watershed protection programs -- and
building the Croton Filtration Plant.

New York City's water supply system provides 1.2 billion gallons of
water daily to approximately nine million people in New York City, as
well as a number of communities in Orange, Putnam, Ulster, and
Westchester counties. Water for this system is derived primarily from
three reservoir systems known as the Croton, Catskill, and Delaware
systems, which are operated and maintained by the New York City
Department of Environmental Protection (DEP).


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