The World Trade Center is leaking, and it's not one of those "Oh, we'll just patch it right up," leaks, either—officials are concerned that a faulty slurry wall is to blame, and if that's true it will be quite the project to fix.

A slurry wall is a technique used to keep a desired area blocked from water —in this case, the Hudson River. According to DNAinfo, workers recently began hearing the sound of gushing water within the complex, and quietly called in engineers to trace its source. The excavation process, while itself costly, will be nothing compared to the cost of fixing the slurry wall, if that is indeed the culprit—the 3,200-foot-long partition is hidden behind other walls that comprise offices and retail stores expected to be open next year.

Port Authority has already spent millions repairing the slurry wall post-9/11, which was built in the '60s and praised at the time as an engineering feat. It held under the attacks on the World Trade Center, staving off groundwater and preventing subway tunnels below the subterranean PATH tubes from flooding.

If the slurry tubes are found to have been improperly insulated, it will delay the opening of the building's sections that were expected to open next year.