CASCADE TOWNSHIP, Mich. (WOOD) — The state on Wednesday sampled the Thornapple River for possible PFAS contamination after Target 8 found mounds of foam building up on a riverbank.

The foam, which a state Department of Environmental Quality called “unusual,” appears similar to what has formed on the Rogue River, just below the Rockford Dam.

The Rogue River foam had extremely high levels of PFAS, a likely carcinogen, leading to a health advisory against ingesting it.

Contractors for the DEQ used cheesecloth and Ziploc bags to scoop up the foam from the Thornapple River, just below the Cascade Dam. They also took water samples.

The DEQ said photographs of foam on the river taken by Target 8 prompted Wednesday’s testing.

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One shows foam piled high along the east bank, directly below the dam.

It was enough to worry some residents. Some said they had never seen the foam so thick on this part of the river.

“A couple weeks ago, I was out there and we had a stack of foam on the edge of the water that was probably a foot high,” said Marilyn Otte, who lives on the east bank of the river near the dam.

Another photograph shows it clinging to a stick.

“It’s not like soap suds,” Otte said. “It’s more like if you put shaving cream on the water surface.

“If my grandkids could swim down there, I probably wouldn’t allow them to do so because it’s pretty nasty looking, and I don’t know what it is,” Otte said.

The DEQ said it was a combination of PFAS in the Rogue River and agitation from the Rockford dam that created PFAS foam there. Tests found 300,000 parts per trillion of total PFAS in the foam — 4,000 times higher than the limit for drinking water.

The Rockford Dam is directly downstream from Wolverine Worldwide’s old tannery, where the shoemaker used PFAS-tainted Scotchgard for decades.

The Cascade Dam is downstream from the Gerald R. Ford International Airport, where firefighting foam containing PFAS, a likely carcinogen, was used for decades. The airport is testing its groundwater for PFAS but said results won’t be available until July.

Private tests have found 15 homes with wells with low levels of PFAS near the airport, but there had been no tests on the river itself.

“We know AFFF foam used at airports can contain PFAS and since there’s an airport nearby, we saw some foam, it made sense to come out and grab a sample,” said DEQ spokesman Scott Dean.

The state said it could take several weeks to get results from Wednesday’s tests.