In coming weeks a dredge will appear on the Potomac River near Alexandria, drag its mammoth bucket through the greenish-brown water and begin deepening the river's shipping channel for the first time since 1965.

The machine won't stop until it has scoured seven miles of river bottom at the waterfront and two sites downstream--scooping up enough clay and sand to fill a hole the size of a football field 300 feet deep.

Alexandria leaders say the work will provide a crucial and long overdue boost for their historic port, allowing bigger cruise ships to visit and letting freighters carry heavier loads, including newsprint for The Washington Post.

Others worry about what will become of all that muck pulled up from the bottom.

The dredged spoil, amounting to 357,000 cubic yards, is to be dumped in what federal officials call a deep hole near the Virginia waterfront off Fort Belvoir, at Gunston Cove about 12 miles south of Alexandria.

Officials with the U.S. Army Corps of Engineers, which is overseeing and financing the project, say extensive environmental studies show the area, with depths of 35 feet to 50 feet, to be a safe place to deposit the spoil.

Critics say the dumping site is in fact a deep trench harboring unusual aquatic life that would be smothered by the spoil. Some fear the same currents that keep the trench free of silt will carry away spoil placed there, clouding nearby waters with harmful sediment and other pollutants.

"I wish they weren't" using the site, said Donald P. Kelso, a George Mason University associate professor who has studied the trench and its clams, aquatic snails and shrimplike creatures called scuds. "I don't think [the dredged material] is going to stay there."

Critics of the plan say at least some of the spoil should be taken to landfills or other sites on dry land--an option the Engineers call too expensive.

The discussion over the Fort Belvoir site is but a whisper compared with arguments over plans to dump spoil from the Baltimore Harbor's approach channels into the Chesapeake Bay at a place called Site 104.

The difference in the volume of debate could be attributed to the difference in project scale. Site 104 would receive 18 million cubic yards over many years, according to a state proposal. Gunston Cove is to receive one-50th that amount, with deposits limited to one season.

The Corps of Engineers eventually wants to dredge 11 shallow areas, or bars, between the mouth of the Potomac River and the Alexandria waterfront 108 miles away. But it has enough money to dredge only three areas now: Alexandria, the Hunting Creek Bar about two miles south and the Mattawoman Bar another 14 miles downstream.

The $2.6 million project, to begin the week of Dec. 5, aims to restore the channel to a depth of 24 feet set by Congress in 1899.

The Great Lakes Dredge & Dock Co., based in Oak Brook, Ill., will bring in roughly 30 workers, two dump scows that can hold 4,000 cubic yards of material and the dredge with its bucket that can nearly fill two dump trucks in one scoop.

Corps officials said they have been eager to start work on the channel. "We've been trying for years now" to find an acceptable spoil site, Bob Blama said.

As it considered the Fort Belvoir site, the Corps of Engineers studied bottom-dwelling fish, surveyed for fish that stay over the winter, tested the muck to be dredged and asked the U.S. Fish and Wildlife Service to search for sturgeon, a rare species.

"We basically cleared all those obstacles," Blama said. "The material's clear."

Yet some remain skeptical.

"This stretch of the river is a prime spawning and nursery area for American shad and other important . . . fishes such as river herring and striped bass," the Interstate Commission on the Potomac River Basin said in a letter to the Engineers.

The commission, which monitors the Potomac watershed for the localities that line it, said dredged material might move into the river under strong spring flows. That could interfere with spring spawning as shad eggs and sperm are covered with muck.

"We're going to be looking and watching," said Joseph K. Hoffman, executive director of the commission.

The dredging is to be restricted to cold weather months in order to avoid hurting fish such as shad, a depleted species, said corps officials. Cloudiness from sediment usually does not spread beyond a spoil site, Blama said.

U.S. Rep. James P. Moran Jr. (D-Va.), whose district includes Alexandria, called environmentally based opposition to the project "just knee-jerk."

"You've got a big hole. You haven't found any sturgeon. And there's a need to dredge the river," Moran said. "It ought not to cause the environmentalists to lose any sleep." Moran said it was "past time" to begin the project.

Some freighters make the trip upriver riding high, with less than a full load. Even so, they often must await high tide to move through shallow portions of the channel.

"It's a big disadvantage," said Robert Taylor, president of the Robinson Terminal Warehouse Corp. The Washington Post subsidiary dominates Alexandria's commercial shipping, bringing in a little more than two dozen ships a year.

Robinson Terminal owns and operates two docks on the riverfront. The city has a smaller pier that also can accept commercial vessels. The three facilities are the remnant of a commercial trade that was among America's busiest in the 18th and 19th centuries.

With increased channel depth, Alexandria could attract large cruise ships, said Ed Didion, president of Washington-based Didion World Cruises, which matches tourists to cruise trips and charter liners.

"Oh, they are going to dredge the Potomac? Finally? It's been a long time coming," Didion said.

Potomac River Dredging

The Corps of Engineers is planning to dredge three sites on the Potomac River in an effort to deepen the river's shipping channel for the first time since 1965. Critics are concerned with the 357,000 cubic yards of spoil that will be deposited at Gunston Cove.

DREDGING SITES:

Alexandria waterfront

Hunting Creek Bar

Mattawoman Bar

SPOIL WOULD BE PLACED:

Gunston Cove

SOURCE: U.S. Army Corps of Engineers