Damage To Base Of WTC Site

Workers digging into rubble of the World Trade Center have discovered a 90-foot gap in the retaining wall that keeps the Hudson River at bay, but there was no imminent danger of collapse or flood.

"Falling debris took a bite out of the top of the wall, but there are engineering remedies that are being implemented," Matthew Monahan, spokesman for the city's Department of Design and Construction said Thursday.

The retainer, called the bathtub, is a 3-foot-thick concrete slurry wall that surrounded the foundations of the twin towers to a depth of seven stories below ground. As sections are laid bare by digging equipment, repair crews patch small leaks and shore up the wall with steel cables.

As for any threat of flooding, "there is no danger whatsoever," said Paul Ashlin, a senior vice president of Bovis Lend Lease, the company managing the trade center cleanup.

Ashlin said the seepage has been mainly limited to "minor leaks, trickles" at the joints of the wall's 22-foot panels.

The extent of damage became clear as diggers removed a dirt ramp that had been built for moving debris, exposing the wall to within a foot of the underground water table, Ashlin said.

"It turned out to be a bigger bite than we first thought," he said.

As a first step to ease pressure on the retaining wall, workers are drilling two wells, and pumps should be up and running in a few days, Ashlin said. He said this standard method will lower the water table to about 30 feet below the surface.

Meanwhile, engineers are designing a large patch of steel-reinforced concrete to fill the breach; it will be a permanent part of the wall, anchored in bedrock.