Contractors on Thursday finished ballasting the 431-foot Davy Crockett, pumping 600,000 gallons of water into enclosed compartments in the stern to better stabilize the vessel.
The process is intended to allow divers to access previously unreachable compartments to determine the location of additional pollutants aboard the barge.
The barge is beached on the north bank of the Columbia River between Vancouver and Camas.
The U.S. Coast Guard is leading a recovery effort that began after it was discovered last month leaking PCB-tainted oil into the river. State authorities said a scrapping operation by owner Brett Simpson weakened the vessel, causing it to buckle and sink.