Work on the remaining major milestone--completion of excavation work in the Tower 2 and Tower 4 areas--is continuing. In a release, the Port Authority says it's working cooperatively with Silverstein Properties Inc., which is developing Towers 2 and 4, "to get this work done as quickly as possible." Delays in completing the work led an arbitration panel ruling last month that the authority had not yet met its obligation to turn over a construction-ready site to SPI.

The milestones were established last October as part of the World Trade Center Assessment, a review of all the major public projects at Ground Zero. They encompass work on the WTC Transportation Hub, the National September 11 Memorial & Museum, the vehicle security center and the Freedom Tower, also known as One World Trade Center.

On the transportation hub, the authority has turned over final construction documents to Phoenix Constructors, begun procuring 22,000 tons of structural steel and started installation of steel on the south mezzanine pavilion. For the memorial, the authority has completed design work on the memorial's pavilion and finished installing steel on the northern part of the West Bathtub. The authority has mobilized contractors to construct the foundation walls for the vehicle security center. On the Freedom Tower, the authority has completed foundation work and brought the South Core shear walls up to grade level.