The Army Corps of Engineers' plan to deepen the Delaware River shipping channel has sustained another blow.

Motiva Enterprises LLC which operates a large refinery in Delaware City, Del., had been neutral about the controversial project but now says it cannot support it.

Spiros Mantzavinos, a spokesman for the company, said preliminary studies suggest deepening the channel could alter circulation in the river and exacerbate shoaling of sediments that could increase the refinery's berth maintenance costs.

"It will add to the cost of our operation on an ongoing basis, so we are concerned about the project," Mantzavinos said Thursday.

He raised the concerns a day earlier during an Army Corps workshop at Delaware State University in Dover.

The workshop was part of Delaware Department of Natural Resources and Environmental Control review of permits that have held up the start of the $311 million project, sponsored by the Delaware River Port Authority.

The Army Corps says a deeper channel will benefit refiners in the Philadelphia area by saving them $32 million per year in costs associated with unloading oil onto smaller ships for the final leg up the bay and river.

Six refiners in Philadelphia, Marcus Hook, Pa., Greenwich and West Deptford have not committed to deepening their own berths to take advantage of a deeper channel. Opponents argue this raises questions about the project's economic benefits.

The General Accounting Office, the investigative arm of Congress, is auditing the Army Corps' economic analyses and environmental studies justifying the project.

An Army Corps official downplayed the concerns raised by Motiva, saying the refiner has never been included in economic benefit analyses.

"If two (of the six Philadelphia-area) facilities associated with benefits from the project came out totally opposed to it, that would have a direct bearing. But this really does not," corps spokesman Ed Voigt said.

The main shipping channel splits off to the east of Pea Patch Island, across from the Motiva refinery. Army Corps regulations prohibit deepening the channel to the west of the island to accommodate a single deep-draft user, Voigt said.

Additionally, this area has silting problems created by the island and twists in the river that make deepening the channel to the Motiva refinery unfeasible, Voigt added.

The deepening will create 32 million cubic yards of sediments, much of which will have to be disposed in Gloucester and Salem counties unless the Army Corps and DRPA come up with alternatives.