What pedestrians perceive as the solid ground level around the 16-acre trade center is in fact the roof of a 70-foot-deep underground complex that includes much of the hub, including the PATH platforms and many of Westfield’s spaces, most of the memorial museum, 1,000 feet of the No. 1 subway line and enormous mechanical areas.

As many roofs do, this one began springing leaks. The Port Authority traced the sources of the water to the constant spraying done by workers to reduce dust levels as they break up concrete, and to the fact that Tower 3, still under construction, is open to the elements.

Coincidentally or not, DNAInfo reported on Aug. 25 that workers at the trade center were hearing the sound of water behind the walls in the lower concourses and said there were fears the seepage was coming from the slurry wall lining the foundations. The authority replied at the time that “its most recent inspection did not identify any leak in the slurry wall,” a situation that would have required a full-scale evacuation of the site. It did not elaborate on other possible leak sources, however.

On Tuesday, Steven Plate, the director of World Trade Center construction for the Port Authority, said: “The dripping has been reduced dramatically. We’ve made some significant progress. Several spaces are dry.” He said the leak had affected only four of Westfield’s retail spaces.

Westfield, for its part, is reluctant to take possession of any spaces until all of them can be delivered in acceptable condition. The leaks have proved to be one of several sticking points.