FOR IMMEDIATE RELEASE00-60
Repair Completed At Shaft 6 On New York City's Delaware Aqueduct In
Repairs on a gate valve at Shaft 6 of the Delaware Aqueduct have
been completed and the normal flow of water was restored on Wednesday
evening, December 6th, according to an announcement by Commissioner
Joel A. Miele Sr., P.E., of the New York City Department of Environmental
Protection (DEP). The Aqueduct had been taken off line on November
28th so that the gate valve could be repaired. Shaft 6 is located
adjacent to the City's Chelsea Pumping Station, near the Newburgh-Beacon
Bridge, on the east side of the Hudson River.
"This was a complex job that involved two two-man teams of divers
alternating on 12-hour shifts in a diving bell and descending, under
extreme pressure, 700 feet down a water-filled shaft," said Commissioner
Miele. "While one diver worked outside of the bell on repairing
the valve, his partner monitored the diver and life support systems.
When one team returned to the surface, the divers transferred to a
compression chamber where they remained until the next shift, at which
time they descended 700 feet again to resume work on the valve. By
maintaining the diving crews under the pressure that occurs at 700
feet, they were able to perform their work and go up and down the
shaft without suffering caisson disease, also known as 'the bends,'
a dangerous disorder that divers and tunnel workers may suffer when
they return too rapidly from the high pressure zones at the depths
to the normal atmospheric pressure at the surface."
The divers were isolated in a compression chamber and started acclimating
themselves to the increased pressure of the depths on Tuesday, November
28th. On Friday, December 1st, the first team descended to the bottom
of the shaft. The divers fixed the three-quarter-inch hole in the
valve, which allowed water to fill the shaft, and also took steps
to secure or strengthen other potentially vulnerable parts of the
valve and piping in the shaft to preclude further leaks. By Tuesday
morning, the teams had completed the repairs, and water was gradually
released into the Aqueduct. On Wednesday morning, prior to resumption
of normal flow, divers returned and inspected all components of the
valve and shaft to ensure that the repairs had been successful and
that no leaks occurred in unexpected areas.
Commissioner Miele said, "I salute the divers, who undertook
this dangerous and demanding job, as well as all the engineers, scientists
and support staff who planned the work and saw that it was carried
out safely and thoroughly."
The function of Shaft 6 is to serve as a de-watering apparatus for
the Delaware Aqueduct. Now that the gate valve is repaired, DEP will
be able to move ahead with plans to inspect the Aqueduct's condition,
ascertain the extent and type of any other leaks, and make recommendations
for future maintenance and repair efforts. Two leaks in the Aqueduct
are known to exist; both are west of the Hudson, one in Roseton and
the other in Wawarsing.
"The repair work at Shaft 6 is an important step in dealing
with those leaks," said Commissioner Miele. "The leaks,
which may be due to underground geological conditions that existed
when the deep rock tunnel was built in the 1940s, may even date to
the time when the Aqueduct went into service. While we are convinced
the leaks do not represent a threat to the safety and reliability
of the Aqueduct at present, we are taking aggressive actions to locate
and fix them. DEP has awarded a contract to the Woods Hole Oceanographic
Institute to custom build an Autonomous Underwater Vehicle (AUV),
which will inspect and photograph the interior of the tunnel. We are
also going to do geological test borings near the leaks. After the
AUV inspection and test borings are completed, we will de-water and
inspect the length of the Aqueduct. We will then determine how best
to repair the existing leaks and what maintenance work, if any, needs
to be done to ensure that the tunnel continues to serve us for many
decades to come.