Vast quantities of muck are dredged each year from the busy shipping channels in Philadelphia, New York and New Jersey - some years, enough to cover a football field with a pile a half-mile high.

Vast empty craters are found in parts of Pennsylvania, the ugly remains from a century of coal mining.

Now state officials are allowing the muck to be treated and placed in the abandoned mines - using one problem to help solve the other.

The concept is hailed not only as an environmental two-for-one, but as a tool for economic development: on one end, removing a key obstacle in the way of deepening the Delaware River, and on the other, giving a boost to older communities where the economic engine of coal mining has long since sputtered to a halt.

"Frankly, it's a very, very good match," said Pennsylvania State University engineering professor Barry Scheetz, a mine-reclamation specialist.

But, so far, the promise has not materialized, amid questions about how to pay to ship the stuff up to mine country - primarily the northeastern anthracite region, home to more than 50,000 acres of abandoned mines - and whether there are dangers posed by small amounts of toxic contaminants in the material.

In Hazleton and Tamaqua, two Northeastern Pennsylvania towns where the use of dredged material has been proposed, opposition has been fierce. Many call it an example of Philadelphia trying to dump its problems on the rest of the state.

"Why do it here?" asked Joe DaPrato, 65, who has a "STOP THE DUMPING" sign in the window of his Tamaqua flower shop. "We're worried it's going to ruin our water."

So far, tests by the Pennsylvania Department of Environmental Protection have not found a threat to human health. Agency scientists say any contaminants are locked into the dredged mud because it is mixed with fly ash - a byproduct from burning coal - which helps solidify the material.

Tests for possible leaching of contaminants have been conducted only for several years, at a pilot site in Clearfield County called Bark Camp. Critics worry pollutants could leach into waterways in the long run. At most sites, testing will be required only for two or three years.

One groundwater well shows an increase in certain heavy metals since the dredged material was placed nearby, though not to dangerous levels.

Charles Norris, a hydrogeologist hired by the group Army for a Clean Environment, warned that the levels might keep rising.

"You can make a rational, reasoned decision if you know what is the final story that's going to happen," said Norris, who is based in Denver. "But they don't know that now."

DEP secretary Kathleen A. McGinty said the agency would not allow the use of dredged material if it weren't safe. She said she is not advocating its use over any other substance.

"We need clean, safe material to heal a tremendous environmental scar on our landscape," McGinty said. "We have thousands of holes in the ground and nobody still standing to take responsibility for them."

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Each year, up to 3.5 million cubic yards of silty clay is dredged from the Delaware River by the U.S. Army Corps of Engineers and its contractors. The material is sucked into giant ships and then pumped into one of nine riverside disposal areas, mostly in New Jersey.

That's just to maintain the shipping channel at its current depth of 40 feet. Industry officials would like the corps to dig out an additional 5 feet, saying they will lose business to deeper harbors. Baltimore and Norfolk are 50 feet deep; the port of New York and New Jersey is being deepened to that level now.

"Deeper water means bigger business" and lower consumer prices, said William B. McLaughlin 3d, spokesman for the Philadelphia Regional Port Authority.

For now, many Philadelphia-bound tankers carrying oil - the port's chief cargo - are so big they must transfer some cargo to smaller ships before they can head all the way to port.

If the Army Corps were to deepen the channel, it would have an additional 26 million cubic yards to handle in five to seven years. That's where the mines might come in handy.

Gov. Rendell, a key supporter of deepening, thinks the mines are "a good option," said spokeswoman Kate Philips.

Of the 26 million yards of material from deepening, some 18 million is sand and could be used to replenish beaches in Delaware, said Tom Groff, a dredging project manager for the corps. The other 8 million yards of silty clay was destined for New Jersey, where officials balked partly because none was going to Pennsylvania.

Now that the stuff is approved for mine disposal, project supporters hope that New Jersey officials - who must sign off on the roughly $300 million deepening proposal - will come around.

So far not, though they are not ruling it out.

Jeffrey L. Nash, the state's lead representative on the Delaware River Port Authority, which must approve the project, said he still questions whether the project is worth the cost, and whether it would harm water quality and wildlife in the Delaware.

An initial Army Corps analysis estimated economic benefits from the project at $1.40 for every dollar spent. A Government Accountability Office report countered with a benefits estimate of just 50 cents on the dollar. The Army Corps later revised its estimate to $1.18.

Still unclear is who would pay to get the material up to mine country, as there are cheaper disposal sites near the ports.

The idea of using the mines was hatched in 1995, as the U.S. government was moving to ban the dumping of dredged material into the ocean off New York.

The proposal came from Andrew Voros, executive director of New York/New Jersey Clean Ocean and Shore Trust, a bistate agency charged with protecting the states' coastal waters.

At first, Pennsylvania officials were skeptical. "When I first heard it, I thought 'Oh my god,' " recalled J. Paul Linnan, then a DEP manager for abandoned mine reclamation.

But after seeing test results, Linnan and others became convinced that the material was safe. After consulting with Scheetz, the Penn State engineer, DEP officials suggested adding fly ash to solidify the mixture.

Today, Linnan works as a consultant for Global Remediation Technologies, one of the companies proposing to take dredged material to the mines.

But since 1995, other projects far closer to dredging sites have claimed the material.

Some was used to cover a contaminated area and build the RiverWinds golf complex in West Deptford, Gloucester County, with no ill effects, according to the state Department of Environmental Protection. Across the river, 1.9 million cubic yards were used as foundation for a runway extension at the Philadelphia International Airport.

A mixed-use development under way at the Meadowlands has room for much more.

The Army Corps awards dredging and disposal contracts to the lowest qualified bidder. Pennsylvania's mines are farther away, and transportation costs money.

The mine project will likely need one ingredient to make it work: more government funds.

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Northeastern Pennsylvania is dotted with aging towns that owe their existence to anthracite coal. One is named Coaldale, where an old bus shelter has been repainted with slogans that wistfully recall a mighty past, such as "Everybody's Goal Is Mine More Coal."

In nearby Tamaqua, a sign marks the former site of Carroll's Saloon, a supposed meeting spot of the Molly Maguires - the sometimes-violent secret society that fought bad working conditions in the mines.

Today, acidic discharges from abandoned mines have rendered many area waterways unlivable for fish. Little active mining remains, and the Northeast is scrambling to reinvent itself.

In Hazleton, where a mine pit sits near downtown, Mayor Louis Barletta wants to do more than just fill it up. He has enlisted a developer to build a 20,000-seat amphitheater on top.

"The question that I keep asking is, what's the alternative? And nobody can give me that answer," said Barletta, a twice-elected Republican in a Democratic community. "This is the one chance we have."

Yet it's the word chance that bothers Dante Picciano, head of the group fighting the Tamaqua project. He favors mine reclamation, but not with unproven material.

"We don't know whether it's safe or not," Picciano said. "I just don't think we should take a chance with all this uncertainty."