CHARLESTON, S.C. (AP) — The state commission overseeing South Carolina's interests on the Savannah River joined environmental groups Monday in asking that a federal judge rule the $650 million deepening of the river's shipping channel is subject to South Carolina's environmental laws.

The Savannah River Maritime Commission filed documents in federal court in Charleston saying U.S. District Judge Richard Gergel should settle the question.

Environmental groups in both Georgia and South Carolina originally sued the U.S. Army Corps of Engineers, saying the deepening work needs a permit under South Carolina's Pollution Control Act. The plaintiffs last week then asked the judge to consider the wider issue of whether all South Carolina environmental law applies.

Maritime interests say the river deepening is needed so the Georgia ports can handle the larger container ships that will routinely be calling when the Panama Canal is expanded in 2014.

The lawsuit was brought by the Southern Environmental Law Center on behalf of the Savannah Riverkeeper, based in Augusta, Ga., as well as the South Carolina Coastal Conservation League and the South Carolina Wildlife Federation.

The original suit said the corps needs a state pollution permit because toxic cadmium in river silt will be dumped in a dredge spoils area on the South Carolina side of the river.

Court documents note there are two exemptions under which the corps might not be subject to the permitting requirements of the Clean Water Act, which requires federal agencies to adhere to state environmental rules.

One of them is that if information about discharges is included in an environmental impact statement submitted to Congress before the work begins or before money is appropriated. The second is that the Secretary of the Army has the authority to maintain navigation.

The maritime commission is seeking to intervene in the suit.

Commission attorneys noted in court documents the corps has said the matter of exemptions is a question for the federal, not state courts.

"The corps cannot now hide from its own admissions in seeking to defeat the intervention or the amendment of the complaint" brought in federal court, the documents said.

The corps had a Monday deadline for responding to the motion to widen the complaint.