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PFC level drops in Mississippi River but remains higher near 3M-Cottage Grove plant

The presence of a 3M-produced chemical has declined in the Mississippi River southeast of St. Paul but the pollutant was found at significantly higher rates downstream of the company's Cottage Grove plant.

The Minnesota Pollution Control Agency announced this week that it detected less perfluorooctane sulfate (PFOS) in the river between St. Paul and Cottage Grove, compared to similar tests conducted in 2009.

However, the testing showed that while PFOS presence also has declined in the river stretch between 3M's Cottage Grove plant and Hastings, it remains in much higher concentrations near and downstream of the manufacturing facility even as the company has undertaken cleanup operations.

MPCA testing in 2012 was conducted in four sections of Pool 2, the 32-mile stretch of river from the Ford Dam in St. Paul to Hastings. The vast majority of water samples taken in the three sections upstream of Cottage Grove found reduced levels of PFOS, said Katrina Kessler, manager of the agency's water assessment and environmental information section.

Most samples found PFOS levels of about 5 parts per trillion, lower than the current water quality criteria of 7 parts per trillion.

"One of the main messages that we want to get across is we think the water quality is improving in sections 1, 2 and 3," Kessler said. "That's a success story."

By comparison, water samples taken close to 3M's Cottage Grove plan detected PFOS levels of 142 and 155 parts per trillion. The levels dropped to between 23 and 26 parts per trillion at the lowest level of Pool 2 at Hastings.

"They were lower the further you went down that pool, but there's an obvious hotspot in the concentrations measured directly downstream from 3M," Kessler said.

The MPCA tested PFOS levels in water, fish, invertebrates and sediment.

PFOS is a type of perfluorochemical (PFC) that was manufactured by 3M for decades at its Cottage Grove plant and was used in consumer products. 3M phased out PFC production about a decade ago, but the chemical does not break down easily in the environment.

For several years 3M has been working to clean contaminated east metro dump sites and river sediment near its plant in Cottage Grove, and it has added a filtration system to catch PFCs in wastewater discharged from the facility into the nearby river.

Kessler said the MPCA does not know specifically why the PFOS numbers are higher downstream of Cottage Grove, other than that the 3M facility is a "legacy source" of the contamination. The company has been working on remediation efforts, Kessler said, but it takes time for that cleanup to be fully realized.

"It appears the 3M phase-out of PFOS manufacturing, and the MPCA-ordered cleanup of three 3M disposal sites and a landfill that received 3M wastes, are beginning to reduce levels of PFOS in the river and its food chain," MPCA Assistant Commissioner Rebecca Flood said. "But the levels around and downstream of the 3M Cottage Grove facility remain significantly higher."

A 3M spokesman did not return a call seeking comment.

The MPCA's latest findings will be used as the agency reviews its water quality guidelines and as it decides whether Pool 2 will remain on an impaired waters list the agency submits to the federal Environmental Protection Agency in fall 2013, Kessler said.

The MPCA has listed Pool 2 of the Mississippi as impaired for PFOS since 2008.

Scott Wente

Scott Wente has been editor at the South Washington County Bulletin since 2011. He worked as a reporter at other Forum Communications newspapers from 2003 to 2011.

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