3M has discovered elevated levels of perfluorinated chemicals in monitoring wells at its Woodbury clean-up site, but drinking water wells do not appear to be affected.
3M pumps groundwater contaminated with PFCs from a former landfill in Woodbury to its Cottage Grove plant, where it's used as a coolant.
In March, the company slowed down its pumping rate, to avoid depleting the underlying aquifer. Then in May, 3M found higher levels of PFCs in the monitoring wells.
No significant changes were found in drinking water wells nearby. The Minnesota Pollution Control Agency's remediation supervisor, Sandeep Burman, said that means the clean-up system works.
"Essentially it's an early-warning system, because the main focus here is to make sure we know of changes before private wells are impacted, and that's exactly what happened in this situation," Burman said. "We had time to respond and make sure the private wells are safe."
For now, the MPCA has directed 3M to return to the higher pumping rates. Burman said the two organizations will try to learn whether it was the slower pumping rate, an exceptionally dry summer, or some other factor, that caused the spike in the monitoring wells.
PFCs were used for decades in 3M's industrial operations, and the company disposed of wastes from those operations at several locations in the east metro.