Federal investigators have left southern New Jersey after completing the on-the-ground portion of their probe into a train derailment that caused the release of a hazardous chemical.

The National Transportation Safety Board announced Friday that it had finished its work, nearly exactly a week after the Nov. 30 derailment in Paulsboro.

The NTSB says it will have a preliminary report completed in about two weeks.

Meanwhile, the site cleanup is continuing as crews remove derailed cars.

Officials have said they expect hundreds of evacuated residents to be able to return to their homes on Sunday.

U.S. Sen. Robert Menendez is heading to the area on Friday for a briefing on the situation.