Because the owner and developer remain at odds, the fate of much of the 16-acre World Trade Center site in Lower Manhattan may now be in the hands of a third party. The site’s owner, The Port Authority of New York and New Jersey, and New York City developer Larry Silverstein, who has a 99-year lease on the property, failed to reach an agreement by March 12 on a financing plan and schedule for three towers on the property’s eastern side. Structural-steel placement on the site’s structural centerpiece, One World Trade Center, reached the 20-story milestone in February, with construction set for completion in 2013. Of the remaining four planned towers, construction has begun on only one. An arbitration panel has said that if the deadline was not met, it would impose a binding resolution.