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December 7, 2000

Contact: Geoff Ryan (718/595-6600)

Valve Repair Completed At Shaft 6 On New York City's Delaware Aqueduct In Chelsea

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.


More Information

NYC Department of Environmental Protection
Public Affairs

59-17 Junction Boulevard
19th Floor
Flushing, NY 11373

(718) 595-6600