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Hi-Tech Mini-Sub Seeks Delaware Aqueduct Leaks - 2002-03-24


A recent study shows that the Delaware Aqueduct, the huge underground tunnel that carries almost two billion liters of fresh water south from the Catskill Mountains to New York City every day, is leaking. VOAs Adam Phillips spoke to an expert on the aqueduct about the plumbing problems and the high tech scientific plans underway to help solve it.

Before becoming Commissioner of the New York City's Department of Environmental Protection the agency which oversees all the city's reservoir and water systems, among other things, Joel A. Miele Senior often marveled at the technical accomplishment the Delaware Aqueduct represents. "Unfortunately, you can't look at it," he pointed out. "It's not that simple because it's essentially buried below the ground deep in the rock that underlies the watershed area and the path from the watershed area down into the City of New York. It's essentially a large hole in the rock."

The Delaware Aqueduct is also a very long hole in the rock. Completed in 1945, its 135-kilometer length makes it the longest continuous tunnel ever built. It is over four meters in diameter. However, recent tests showed the aqueduct is leaking about 136 million liters of water every day, a full two percent of its output. While no major rupture is anticipated for at least twenty years, Commissioner Miele decided the time to repair it is now. "It just disturbed me as an environmentalist and as an engineer that this quantity of water would be being lost," he said.

But finding and repairing the leaks will not be easy. "It's not very accessible," Mr. Miele observed. "I mean, if you have a plumbing leak in your building or in an office building or even if we have a leak in the street, we dig up a hole in the street, we find the leak, we shut off the water at both ends, we put a clamp on it, we replace a piece of pipe, we close the street and we go on. This thing, again, is 300 meters below the ground in solid rock. There's no way to get at it from the outside and it's got a lot of water flowing in the inside. So it's not your normal plumbing repair."

To help solve this problem, Mr. Miele's Department had the famed Wood's Hole Oceanographic Institution build an unmanned, self-propelled submarine less than three meters long. The device cost a half million dollars. "And what we are going to do is introduce it before the end of this year into the upstream access to the tunnel," he said. "Let it flow through the tunnel under its own power completely, disconnected from any other outside source of power or communication, and let it take some photographs and instrumentation readings as it travels through the tunnel [while] tracking it's location by onboard equipment and computers."

With the submarine providing what will essentially be 360-degree photographs of the tunnel's interior, engineers will be able to pinpoint trouble spots within about thirty centimeters. But the machine's ability to detect sound will also help Commissioner Miele's investigators. "Because," said Mr. Miele, "Whenever there is a leak in a pipe like this, and this is essentially a pipe, there is a noise to the release of water to a pipe. That is how we test the leakage in our street system. We listen with a sonar device for the rushing of water."

Commissioner Miele adds that, once the locations of the leaks in the tunnel are identified, workers will attempt to bore into the rock precisely above them and fill the leaks with mortar, in essence fixing the cracks from the wall's perspective. "If we can do that and it works, then our problem is solved and we can go on to other problems."

While recent tests with a submarine prototype have been successful, the Delaware Aqueduct may have to be completely drained and repaired from the inside if the craft proves unworkable during the actual project; not exactly your everyday plumbing problem. But Commissioner Miele of New York City's Department of Environmental Protection has high hopes that the miniature sub will find the leaks and engineers will be able to repair the aqueduct without massive disruptions to New York City's precious water supply.

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