New York -- The World Trade Center towers reached six stories below ground level, incorporating a shopping center and subway station, among other things. As workers dismantle the wreckage from the Sept. 11 terrorist attacks, they are finding instability issues with the WTC's basement walls.
According to an ABCNews.com report, most of the soil surrounding the WTC site originally was a landfill, some of it trash and dirt dating back to the time of the American Revolution.
The trash originally was dumped into the Hudson River to give New York City more room. Consequently, the original shoreline of the river runs directly under the WTC site.
If nothing has been holding the containment wall up from the inside, some engineers fear the soil and nearby river will try to push the wall over. Now, some members of the team that constructed the towers 30 years ago are working on how to take it apart safely. One theory is to anchor the wall with thousands of steel cables, drilled deep into the ground.