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Dredging to remove harmful chemicals from a length of the Fox River in the Green Bay area is set to start April 2, but a company paying for much of the cleanup is putting the brakes on work this year.

Appleton Papers Inc. has told the U.S. Department of Justice that it wants to resolve who is financially responsible for the massive cleanup before it resumes the work.

The potential delay could put the cleanup of polychlorinated biphenyls from the river further behind schedule. Last year, Appleton Papers and NCR Corp. stopped work in late July over the same dispute. Dredging operations could have continued for several more months.

The cleanup is the largest of its kind in the United States, and according to court records, the cost of removing PCBs from river sediment will exceed more than $1 billion.

The aim is to stop the flow of PCBs into Lake Michigan and eventually make fish in the Fox safe to eat.

Plans call for the cleanup to be completed by 2017.

"To do this, we have to stay on schedule," said James Hahnenberg, a project manager with the U.S. Environmental Protection Agency. "We have to have a certain amount of production this year."

"It's a critically important reach of the river," where PCB concentrations and the depths of the contaminated sediments are generally greater than in other segments, said Beth J. Olson, a water resource manager with the state Department of Natural Resources.

The EPA's goal for 2012: dredging 680,000 cubic yards of sediment between a dam in De Pere and state Highway 172 at Ashwaubenon and Allouez at a cost of about $75 million, according to a letter from Appleton Papers to the EPA.

Last year, contractors dredged 232,757 cubic yards of sediment before they stopped work - 68% less than the volume of sediment dredged in 2010.

The work involves barges and large vacuums that suck up sediment at precise locations. The sediment then is pumped to a wastewater treatment plant on the banks of the Fox, where the PCBs are removed or trucked away to a landfill. Other areas of the river are being capped with rock or sand.

After stopping work last year, Appleton Papers and NCR said they had spent $315 million to date on the cleanup.

But with a little more than two weeks away from the start of this year's cleanup, Appleton Papers says it can't agree with the government's 2012 schedule.

In a strongly worded letter to the U.S. Justice Department, an attorney for Appleton Papers said the company was dismayed by the government's "abuse of power," and that after 1½ years into enforcement action by the EPA, the government has yet to establish that the company is responsible for the cleanup.

"The government is doing everything it can to avoid justice, increase the costs of this litigation and delay any resolution on the merits," attorney David R. Erickson said.

He also said the EPA has toughened cleanup standards in the middle of the project, heaping additional costs on the company.

Appleton Papers proposed to suspend dredging this year, or to carry out a "measured but significant amount" of work while the parties go to court to settle the matter.

The Justice Department declined to comment because the matter is pending in litigation. But in court documents, the government has said Appleton Papers and NCR, through acquisitions, are largely responsible for the pollution. PCBs were used in some papermaking processes from 1954 to 1971, when they were banned.

Vermont Law School professor Patrick Parenteau, an expert on toxic cleanup and a former EPA attorney, said "it's not unheard of to have this level of conflict and animosity" in a case where so much is involved.

He noted that General Electric Co. challenged the authority of some EPA actions involving cleanup of PCBs in the Hudson River in New York, but those claims were rejected in court.

Parenteau said it's not unusual for costs and remediation work to change in the middle of a large sediment cleanup project.