Lt. Col. George Bivens said Tuesday the pipe bombs were fully functional and could have been set off by either a trip wire or fuse, but appear to be among items that were hastily discarded.
The truck was reportedly cleared and normal operations resumed around noon.
Police in Atlantic County have arrested a student after explosive material was reportedly found inside his home.
Kenneth W. Smith, Jr., 26, of Philadelphia, was indicted on Monday in relation to the September 2012 incident.
A Bucks County man was found dead in a home containing explosives Tuesday.
A bail hearing was postponed Friday for a northeastern Pennsylvania man accused of trying to board a cross-country flight with explosives in his bag.