Per- and polyfluoroalkyl substances

The Social Discovery of a Class of Emerging Contaminants

Washington County (Cottage Grove, Woodbury, Oakdale), Minnesota

Suspected contamination source: The 3M Company’s Cottage Grove facility (MDOH, 2016)

Screen Shot 2017-06-05 at 2.27.20 PM

The 3M Company produced per- and polyfluoroalkyl substances (PFASs) at its Cottage Grove facility from the late 1940’s until 2002. Perfluorooctanoic acid (PFOA) was a prominent type of PFAS made at this site.

Click here to view our timeline for Washington County, MN 

Waste from the production process were disposed on site in a specially prepared pit; there may be other disposal sites. The on site water treatment plant that processed waste water did not remove PFAS, so these compounds eventually entered the Mississippi River. Some sludge left over from the water treatment process also contained PFASs and was disposed on site. On the west side of the site, firefighting foams containing PFASs were used in training exercises. PFASs may also have been released into the air.

Environmental testing shows that the groundwater beneath the 3M Cottage Grove site is contaminated with PFOA, and other PFASs including perfluorooctane sulfonate (PFOS) and perfluorobutanoic acid (PFBA). In some areas, the levels of PFASs exceed the Minnesota Department of Health (MDH) drinking water criteria, which as of May 2017 is:

  • 35 ppt for PFOA
  • 27 ppt for PFOS

Groundwater beneath the site flows south and discharges to the Mississippi River. Sampling of river sediments near the site and the water within those sediments detects PFASs at levels of concern for humans and wildlife, but concentrations in the river water are much lower due to dilution.

Workers at the facility were exposed to PFASs in the course of their work and also through the facility’s water supply.

In 2008, 2010, and 2014, MDH completed biomonitoring studies of selected residents in Cottage Grove, Lake Elmo, and Oakdale who were known to have been exposed to PFOA and/or PFOS in their drinking water. The average concentration of PFASs in the participants’ samples were higher than the averages for the general U.S. population. The studies found that over time, as the participants drink treated water, the PFAS concentrations in their bodies decreased. More information about the biomonitoring studies can be found at PFC Biomonitoring: East Metro.

Additional Resources

Media Coverage:

Full citations are available on the second page of the full contamination site tracker. We ask for your additions, changes, questions and comments be sent to

%d bloggers like this: