ROCKFORD, MI -- The Environmental Protection Agency is making a small but significant entrance into the toxic fluorochemical pollution investigation in Kent County, Mich.

The EPA will begin sampling groundwater and drinking water wells polluted with per- and polyfluoroalkyl substances (PFAS or PFCs) from Wolverine World Wide tannery waste starting next week.

The agency confirmed its involvement on Friday, Dec. 22.

Aside from some consultation visits by advisors, sample collection would be the first federal boots on the ground in the investigation.

An EPA spokesperson characterized the agency's role as "supporting" the Michigan Department of Environmental Quality's response to the multi-plume, multi-township PFAS investigation sparked by discovery of contaminated wells in Belmont in April.

"While MDEQ is taking the lead on drinking water issues, EPA is assisting the state in collecting water samples to verify data provided by Wolverine," the agency said.

"EPA personnel have coordinated with MDEQ and will sample groundwater and well water at impacted residences during the week of December 25. EPA will notify residents of their individual sampling results as soon as they are available."

People with knowledge of the investigation say the EPA has been a regular presence on conference calls this month as pressure mounts on the state to devote more resources and seek federal assistance for the bulging Wolverine response and the 28 sites so far with PFAS contamination in 14 communities around Michigan.

This week, the governor signed a supplemental appropriations bill for $23.2 million to aid the PFAS response statewide.

The DEQ says the EPA has been advising the Wolverine investigation for a while, but the federal presence has loomed larger since the Kent County Health Department asked Gov. Rick Snyder to get the EPA more involved, suggesting it might if the state wouldn't.

Michigan's Congressional delegation also asked the EPA to take a larger hand in the PFAS response and the county's letter caught the attention of some state lawmakers in Lansing, who questioned the state's apparent reluctance to seek more EPA involvement.

It's unknown whether the EPA plans to remain involved in the investigation beyond the scope it has disclosed.

The DEQ referred questions to the EPA on Friday.

Wolverine said the EPA expects to sample a handful of monitoring wells at the House Street landfill and former tannery site in Rockford, and about 15 residential wells.

"These confirmation samples are collected by EPA and sent to an independent laboratory to confirm that the results are the same as those received from laboratories used by Wolverine and the MDEQ," the company announced on its blog.

Test results confirm both the House Street landfill and the tannery are major sources of PFAS contamination.

Total combined PFOS and PFOA concentrations at the 1855 House Street NE dump are more than 668 times the EPA's health advisory level of 70-ppt -- a non-enforceable threshold for what's considered safe in drinking water, for which the groundwater under hundreds of residences in the dump's vicinity is used.

Total combined PFOS and PFOA concentrations under the tannery grounds in Rockford are 7,000 times the EPA level. Although nearby properties are connected to Rockford municipal water, which has tested clean, the tannery is adjacent to the Rogue River and upstream of the city's former surface water treatment plant river intake.

Rockford stopped drinking from the river in 2000.

The Kent County Health Department, which has argued the Wolverine investigation is stretching its resources, said it "welcomes the additional resources that the EPA brings."

We are confident that the agency's expertise and efforts can only hasten the ultimate goal of solving the issues associated with groundwater contamination as it now exists," said department spokesperson Steve Kelso.