Lawyers for the State of Delaware are in federal court in Wilmington today, arguing for an injunction to stop the U.S. Army Corps of Engineers from deepening the Delaware River an additional five feet to accommodate larger ships and vessels with more cargo.

U.S. District Judge Sue L. Robinson will be asked by Delaware - joined by New Jersey and five environmental groups - to bar the river deepening to 45 feet immediately, even before a full hearing on the merits or main issues of the case.

To persuade the judge, Delaware must demonstrate convincingly that, if the Corps proceeds without a state permit, Delaware will suffer significant and irreparable environmental harm.

Delaware's case also hinges on a state's rights issue, the notion that Delaware will be harmed as a state if its role in regulating the waters offshore is tossed aside.

Justice Department lawyer Kent Hanson, representing the Army Corps, will argue that there is no irreparable harm if the dredging proceeds, and that Delaware cannot win on the merits of its case.

In court papers, the Corps said applicable water-quality laws have been complied with, and the river bottom sediments have had "numerous rounds" of biological and chemical testing.

The Corps said it will monitor water impact from the dredging, as well as examine water discharged back into the river at disposal facilities. The Corps has also designed a groundwater monitoring program to ensure that disposal of dredged material won't impact the major drinking water aquifers.

Only attorneys for Delaware and the Army Corps will present oral arguments.

Other interested parties - environmentalists, the State of New Jersey, Philadelphia Regional Port Authority, and Sen. Arlen Specter (D., Pa.) - as a friend of the court were permitted to file court briefs but not testify.

Delaware Riverkeeper Network, and other environmental groups, say the Corps' decision to proceed, after Delaware denied a permit in July, is "arbitrary and capricious," an "abuse of discretion" and violates laws governing clean water, clean air, water pollution control, coastal zone management, water resources development, and endangered species.

Environmentalists say that past studies were inadequate and outdated, that the river's ecosystem has changed, and that more scientific study is needed.

On Oct. 23, the Corps decided to proceed with deepening a 102.5-mile stretch of river after Delaware denied a permit application that had been pending since 2001.

Jo-Ellen Darcy, assistant Army secretary for civil works, concluded, as had her predecessor John Woodley in April, that federal supremacy trumped the need for state approval to protect navigable waters used in interstate commerce.

New Jersey says it is concerned about possible contaminants in the dredge material that will dumped in the Garden State. Deepening the river's main navigation channel to 45 feet, as early as January, could increase air pollutants and cause air quality deterioration, the state said.

The Philadelphia Regional Port Authority, local sponsor of the project, said in a court filing that the "actual irreparable harm" will be to the region's economy if the "20 years-in-the-waiting project" is further delayed.

"Millions of dollars have been spent to determine whether the project should go forward as a matter of economics, human health and safety," the PRPA said.

"That money, for which Delaware apparently has little consideration, would be for naught, to be replaced with expense of additional studies, reports and layers of regulatory review," the state agency said. "If the Corps has to comply with the additional work, it will be the PRPA that has to foot the bill as the local sponsor."

Meanwhile, Delaware is divided, with political leaders Gov. Jack Markell and Attorney General Joseph R. "Beau" Biden 3d, the vice president's son, leading the effort to stop the Corps until it gets a proper environmental permit from Delaware.

On the opposite side, the Port of Wilmington, labor and business groups say the project is important to preserve jobs and keep Delaware River ports competitive as ships get bigger and steamship companies go to ports with deeper waters.

About 8.7 percent of Delawareans are out of work, with the latest job losses including decision by Valero Energy Corp. to shutter its Delaware City refinery and shed 550 jobs.

Contact staff writer Linda Loyd at 215-854-2831 or lloyd@phillynews.com.