CHARLESTON — A second South Carolina state agency has asked to be part of a federal lawsuit brought by environmental groups in two states challenging the $650 million dredging of the Savannah River shipping channel.

Attorneys for the state Department of Health and Environmental Control, in court documents filed late last week, say the agency should be allowed to participate because DHEC would have to issue a Pollution Control Act permit if the court were to require one.

The permit is at the center of the lawsuit brought by the Southern Environmental Law Center against the U.S. Army Corps of Engineers. It was filed 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 lawsuit contends that because toxic cadmium from river silt will be dumped on the South Carolina shore of the river dividing the two states, the state permit is required.

Last month U.S. District Judge Richard Gergel agreed that both the South Carolina Savannah River Maritime Commission and the Georgia Ports Authority could also enter the case.

The authority wants the shipping channel deepened so the river can handle the larger container ships that will routinely be calling when the Panama Canal is enlarged in 2014.

“This case directly implicates DHEC’s authorities and responsibilities,” attorneys for the agency wrote, noting that when Gergel allowed the Maritime Commission to enter the suit he noted “the state agency has a vital interest” in the channel deepening project.

“The same must be said of DHEC,” attorneys wrote, adding that “no existing party can adequately represent DHEC’s interests.”

DHEC said it disagrees with the conservation groups that review of the deepening project has been inadequate; does not agree with the Maritime Commission’s view of the authority of the South Carolina two agencies; differs with the Georgia Ports’ that amendments to the Pollution Control Act are unconstitutional and said the Corps of Engineers cannot be expected to represent DHEC interests.

The judge also last month appointed former South Carolina U.S. Rep. John Spratt to mediate the case. An attempt at mediation is required in federal civil lawsuits.

Spratt, from York, was chairman of the House Budget Committee and a member of the House Armed Services Committee during his 28 years in the U.S. House representing South Carolina’s 5th Congressional District. He lost his re-election bid to Republican Mick Mulvaney two years ago.

Gergel has now set a Nov. 19 court hearing on the suit.