A federal judge has appointed former South Carolina U.S. Rep. John Spratt to mediate a lawsuit challenging the $650 million deepening of the Savannah Harbor shipping channel.

U.S. District Judge Richard Gergel issued the order Wednesday. Spratt served for 28 years as congressman from South Carolina's 5th Congressional District.

Environmental groups have sued the U.S. Army Corps of Engineers saying dredging the river's shipping channel to accommodate larger container ships requires a South Carolina pollution permit. They say that the dredging will mean toxic cadmium form river silt will be deposited in a site on the South Carolina side of the river.

On Tuesday, Gregle agreed that both the South Carolina Savannah River Maritime Commission and the Georgia Ports Authority could take part in the suit.

Tags: U.S. Army Corps of Engineers, toxic cadmium, Savannah Harbor shipping channel, deepening suit, South Carolina U.S. Representative John Spratt