The company poised to buy the former General Motors plant by the end of the year would take over cleanup of contaminated sediment found in the Rock River nearby, City Manager Mark Freitag said.

It’s unclear when cleanup would begin, but Commercial Development Company would work with the city to get rid of the contamination if the deal to buy goes through. The company already has asked the city about when it plans to remove the Monterey Dam so the two projects could possibly be coordinated, Freitag said.

“We’re excited about that because that takes a lot of community concern right off the table,” he said.

The state Department of Natural Resources believes there could be time and cost savings by doing the projects together, but they could be done independently. The contamination can be handled safely with or without the dam, department officials said.

The city has made it clear it will draw down the river slowly—no more than 6 inches a day—to help prevent the contaminated sediment from rushing downstream. Once the dam is removed in September, the affected sediment would be exposed, making it easy for crews to scoop it up with excavators and dispose of it, Freitag said.

That’s only one of a few options available.

General Motors, which still owns the shuttered plant, submitted to the DNR a few weeks ago a remedial options report. The report details the methods that could be used to take care of the contamination, said Bill Fitzpatrick, department water resources engineer.

Besides excavating the sediment and disposing of it in a landfill, an engineered barrier could be built between the contamination and environment. The two methods could be combined, Fitzpatrick said.

It’s uncommon for the department to deal with the removal of a dam and contaminated sediment at the same time, but it’s handled such scenarios before, he said.

“It doesn’t happen every day, but yes, we believe we can safely manage the contaminated sediment and the removal of the dam,” Fitzpatrick said.

The Monterey Dam Association, a nonprofit group of residents opposed to the dam’s removal, has voiced concerns about removing the dam before the contamination is taken care of. At least one member has said exposing the contamination by removing the dam would make it airborne and cause cancer.

The department believes the contamination is not that dangerous.

“It’s not at levels that are a risk to humans,” Fitzpatrick said.

Once the dam is gone, all newly exposed sediment has to be stabilized with natural vegetation or possibly a cover crop to prevent sediment—contaminated or not—from washing into the river. The riverbed has a seedbank that will readily spring up once exposed, Fitzpatrick said.

“In this case, we would watch it very carefully,” he said.

The contamination was first found in 2015 when the city hired a consultant to evaluate the dam’s condition and take samples upstream. Contamination was found in a two-acre portion of the river’s south shore just north of a General Motors stormwater drain, Fitzpatrick said.

The department believes the source of the contamination has since been eliminated.

The contamination comprises heavy metals such as mercury, lead and zinc and polycyclic aromatic hydrocarbons. If the contamination isn’t taken care of, the river’s quality would further degrade, Fitzpatrick said.

“The concern at this site is to the aquatic food chain,” he said.

Contaminants also were discovered at the former General Motors plant. The department told the company it was likely responsible.

General Motors conducted its own investigation of the site. Earlier this year, it announced it had found contamination and took responsibility, Fitzpatrick said.

General Motors cleaned the southern half of its property, which was deemed clear this summer. The contamination in the northern half of the plant site and in the river would be cleaned by Commercial Development as part of its pending deal to buy the site, Freitag said.


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