6 December 2001
nytimes.com December 5, 2001
By JAMES GLANZ
In its efforts to clear ground zero with as little disruption as possible to the surrounding area in Lower Manhattan, the city is exploring the use of ground-penetrating radar to map the tangle of underground utilities without digging them up first, a spokesman for the Department of Design and Construction said yesterday.
The project, which will be aided by a contribution of about $145,000 from a regional government in Sweden, where some of the technology was developed, could allow the city to speed the cleanup and reconstruction and cut through the confusion and danger often created by old maps of underground electrical lines, phone lines, gas pipes and even submerged trolley tracks.
The radar could also be used to identify the undiscovered damage to underground utilities caused by the Sept. 11 terrorist attack. That is because the technique was used last summer to do some experimental mapping of the area around the World Trade Center, and a comparison of before-and-after pictures could reveal changes.
City utilities, like Consolidated
"It's a technology that allows nonintrusive investigation into the subsurface," Mr. Toscano said. In less rarefied terminology, he said, holes do not have to be dug.
Mr. Toscano said the city had already used the technology to aid a complicated project. The radar, he said, had been used to identify submerged cables and pipes during the construction that took place at the northern edge of Central Park.
The technology the city is considering to undertake the mapping project can see about six feet into the ground and would probably come from Witten Technologies of Boston. Originally developed by Mala GeoScience of Sweden, the necessary hardware involves a small trailer dragged behind a sport utility vehicle. Claes Jernaeus, the press counselor for the Swedish Consulate General in New York, said the financing would be offered this week from the Vasterbottens region of the country, which is Mala GeoScience's home.
The chance to map the city's underground in three dimensions would be intriguing, said Matthew G. Monahan, a spokesman for the Department of Design and Construction.
The radar technique produces pictures much like those of satellite imaging, said Michael Oristaglio, chief scientist at Witten Technologies. "We have radars that are riding just above ground level," Mr. Oristaglio said. "We create a 3-D image down from the surface."
He said that the radar senses density changes underground and converts them into a picture. In one limitation, the radar sees only the edges of pipes and conduits and cannot tell whether there is, say, cables or high-pressure gas inside.
For that reason, said Brian M. Wiprud, a utilities specialist at Weidlinger Associates in Manhattan, the radar information often must be combined with utility maps to create a complete picture of the submerged jungle of wires and tubes.
But he said that being able to peer directly into the ground could be invaluable during what will almost certainly become a sprawling reconstruction project, involving miles of new utility lines. "It would be almost as good as opening the ground and looking at it," Mr. Wiprud said.
The technology could also have drawbacks, he and others said. For one thing, the maps are not created quickly; just collecting the necessary data along a street one city block in length can take more than an hour, Mr. Oristaglio said.
Unusual underground structures can also be difficult to find and identify in the radar maps, said Paul M. Lastoff, national sales manager at Geophysical Survey Systems of Salem, N.H., which tried its own ground-penetrating radar on the pile at ground zero. The system searched for voids, or empty pockets in the rubble that could potentially collapse, Mr. Lastoff said.
But in the giant recovery project at ground zero, where utilities will be the lifelines for new buildings, the ability to look into the earth before digging could save some headaches, Mr. Toscano said. "This may be a device you would use before you start blazing away," he said.