Michelle Thompson was stunned to hear that the roughly 30-foot-high mound of dirt and muck that blocks her view of the Delaware River may double in size.

On a recent, chilly day, the National Park resident said she knew about the Army Corps of Engineers' plan to deepen a 102.5-mile stretch of the river. But she thought the "dredge spoils," dragged from the bottom under the proposed deepening, were headed in another direction.

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"They're going to be dumping there? I thought they were going to be dumping it at the coal mines in Pennsylvania," said Thompson, standing in her doorway just a few feet from the weed-strewn hill created by earlier dredging.

It has not been an easy issue for Thompson and others to follow. The project has been talked about for decades, and New Jersey and Pennsylvania officials have clashed over where to dump the silt, clay, and sand that will be brought up if the river is deepened from 40 to 45 feet.

In May 2007, New Jersey officials who had blocked the project backed off after Gov. Rendell and Gov. Corzine reached an agreement that Pennsylvania would "accept all spoils material."

Before that agreement, the corps had planned to deposit nearly all of the dredge spoils at sites it owns along New Jersey's riverbanks, but officials in that state balked at becoming the region's dumping ground.

"Excuse us if we don't want a mountain of mud on our side of the river. We don't want to be Pennsylvania's landfill," U.S. Rep. Rob Andrews (D., N.J.) said Friday.

Now, the deal has unraveled, and the destination for much of the 16 million cubic yards of dredge material is back to being New Jersey. Some of it would be dumped in Delaware, but none would be dumped in Pennsylvania.

The story behind what happened to the deal and how the corps got to this point is revealed in documents obtained under Pennsylvania's and New Jersey's public-disclosure laws, in terse statements issued by spokesmen for the two sides, and in interviews with various officials involved with the project.

Currently, New Jersey and Delaware are heading to federal court to stop the proposed $379 million project, saying the corps plans to proceed without obtaining required environmental approvals. The first hearing is scheduled for tomorrow in Wilmington.

Five environmental organizations have filed their own lawsuit, saying the deepening of the river could pollute it, contaminate drinking water sources, harm wetlands, and threaten endangered and protected fish and wildlife.

The groups do not oppose maintenance dredging, needed to clear the channel of debris for ships' passage, but they say the deepening will stir up toxins such as PCBs and heavy metals that have long been dormant in the riverbed.

The corps argues that it has conducted numerous studies over the last two decades that show the deepening will not hurt the environment. Though the last full study was performed in 1997, the corps says it is exempt from doing an updated study because the project will promote interstate commerce and has undergone sufficient scrutiny.

Pennsylvania officials, including Rendell and U.S. Sen. Arlen Specter, have lined up with union leaders to support the project. They say it will create thousands of jobs.

Oddly, the governors' agreement, which the corps says is not binding, is not an issue in the litigation. But without it, the project would not have moved forward.

Documents obtained under public-disclosure laws by the Delaware Riverkeeper Network, an environmental advocacy group, shed new light on the way the Rendell-Corzine deal was crafted and how it unraveled last year.

The unsigned two-page "Cooperation Agreement," which reads like a legal document, starts by saying its purpose is to "resolve a dispute" over the deepening.

Among other provisions, the pact says: "Pennsylvania has agreed to accept all spoils material from the project, except to the extent that New Jersey seeks spoils materials for New Jersey port facility projects."

Less than a year later, the corps and the Philadelphia Regional Port Authority, the project sponsor, said they were not bound by the deal and would go forward with the original plan to use six disposal sites in New Jersey and one in Delaware.

Dan Fee, spokesman for the PRPA, said the corps owns these disposal sites and already uses them for maintenance dredging. The PRPA urged the corps to move forward with the plan, as proposed two decades ago, rather than make changes that could slow the process.

Gary Tuma, Rendell's spokesman, said Rendell and Corzine understood the pact meant that New Jersey would initially accept the spoils, and Pennsylvania later would take them to use as fill, possibly in abandoned mines.

"The governor said Pennsylvania would be willing to take the dredge material after it had been de-watered in New Jersey," Tuma said, referring to the draining process after the spoils are dumped. If New Jersey wanted the fill for its own projects, it would have priority.

Robert Corrales, spokesman for Corzine, did not return e-mail and phone requests for comment on Corzine's interpretation.

But a June 27, 2008, letter that Corzine sent to the corps said the agreement specified the spoils "would be deposited entirely in Pennsylvania." He said New Jersey would enforce the agreement.

And several documents refer to a letter Corzine sent to Rendell on Oct. 21, 2008, that apparently asked what happened to their deal.

Seven months later, on May 15, 2009, Rendell wrote Corzine to say he had never personally received that letter and learned of it from the corps. He noted that the letter "implies that we agreed to design a dredged material management plan." Rendell goes on to say that wasn't the case, and that their agreement "dealt with the beneficial reuse of the materials."

Rendell also said he found it "particularly troubling" that it appeared Corzine was withdrawing support for the project, though the deal called for him to not "raise objections."

Andrews, who has long opposed the deepening, said he had warned Corzine not to go along with the agreement. He told Corzine it was "not legally enforceable" because the corps and the sponsor were not included.

"It was a public relations exercise," said Andrews, explaining that Corzine went ahead with it because he was under political pressure from Rendell and others to move the project along.

Andrews says the agreement never mentioned de-watering in New Jersey. "The agreement is implicit that there would be no spoils dumped on New Jersey," he said. And trucking the spoils from New Jersey's shores to the mines in Pennsylvania, he said, is "fantasy."

The pact also said both sides would "support the effort to obtain an update to the Environmental Impact Statement" that New Jersey is requiring before digging can start.

But Pennsylvania officials now want the project to proceed without such studies, saying they would create a long delay.

"There have been numerous environmental studies performed, and a full EIS takes years," said Fee, of the PRPA.

But the Department of Environmental Protection says the last such study was conducted 12 years ago, and environmental conditions have changed in the project area. Some species have been newly listed as endangered or threatened, and the riverbed has not been properly analyzed after a massive oil tanker spill in 2004 polluted the river. And, the impact to recovering oyster beds has not been examined, the DEP says.

Andrews says no one knows whether the project will cause serious environment issues, but that is why it is important for the corps to conduct studies to find out.

"If they're so confident it is environmentally sound, why won't they go through with the environmental review?" he asked. His biggest concern is that the deepening could hurt the aquifer beneath the river, which provides vital drinking water.

Maya van Rossum, head of the Delaware Riverkeeper Network, says the height of the spoils is also a concern. "By increasing the size of the piles you're increasing the amount of toxins there," she said, noting the runoff could pollute the river. And, wildlife would be exposed to the poisons, she said.

But Ed Voight, spokesman for the corps, said the spoil sites would not substantially increase because of the deepening. In National Park, for example, he said that over a 50-year period the deepening will contribute only 15 percent of materials that will be dumped there.

Thompson, a lifelong resident of National Park, laughed when told that Pennsylvania may take the dredge spoils later.

"It would be too expensive to double dump them," she said. "I don't believe that for a minute."

Contact staff writer Jan Hefler at 856-779-3224 or jhefler@phillynews.com.