This is a partial transcript of "The Big Story With John Gibson," September 6, 2005, that has been edited for clarity.

JOHN GIBSON, HOST: Members of the Army Corps of Engineers (search) are busy pumping contaminated floodwater out of New Orleans into Lake Pontchartrain (search). We're looking at live pictures there of exactly what the problem is.

This is coming after they managed to get two levee breaks plugged. But the water is still up to seven feet deep in some places, as you can see in the pictures, not to mention just the plain destruction of the physical structures everywhere.

Joining us now on the phone to talk about the huge engineering effort is William Marcuson, president-elect of the American Society of Civil Engineers and the director emeritus of the Geotechnical Laboratory of the Waterways Experiment Station.

So, Mr. Marcuson, tell us what's involved in pumping out the city of New Orleans.

WILLIAM MARCUSON, PRESIDENT-ELECT, AMERICAN SOCIETY OF CIVIL ENGINEERS: Well, first the city is basically divided into 12 or 13 compartments. Not all of these compartments are flooded. They've got 22 pumping stations, I think. And these are huge pumps, capable of pumping something like 6,000 cubic feet a second. If they're all working, they could pump the Superdome full in about 30, 35 minutes, something like that.

I don't expect all of them to be working. They have got, oh, some of them are old. Some of the pumps have special electrical requirements needing 25 hertz current, as opposed to 60 hertz current. I expect some of them will be clogged with debris. And there are other problems, getting electrical power to them and all sorts of things.

GIBSON: Yes, but can you say if they were working and they weren't clogged with debris and the electrical problems weren't a problem, how long would it take to de-water New Orleans?

MARCUSON: Under the best of circumstances I expect we're looking at three or four weeks. And under the worst of circumstances, it's probably three or four months.

GIBSON: William Marcuson — this is somebody who should know. There you've got it: three or four weeks, to three or four months, depending on the circumstances.

Mr. Marcuson, thanks a lot.

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