Contact: Ralph Pribble, 651-757-2657
St. Paul, Minn. — Responding to recent monitoring results that showed increased perfluorochemical (PFC) levels in the groundwater at the 3M Woodbury dump site, the Minnesota Pollution Control Agency (MPCA) has conducted a new round of sampling of private wells in residential areas of Cottage Grove and Woodbury near the site.
Testing results returned this week indicate none of the wells tested had levels of PFCs that exceed state drinking-water standards. However, the MPCA continues to work with 3M to determine the reason for the increase and determine if changes in the site cleanup plans are necessary.
MPCA Commissioner Paul Aasen said the agency moved quickly to sample private wells last week to determine whether the water from the wells is meeting state drinking-water standards for PFCs.
"We contacted homeowners for permission and fast-tracked the sampling and lab analysis. This week we called residents back to let them know that the wells that were tested were below the health-based drinking-water levels for PFCs,” Aasen said.
Some of the wells have had amounts of PFCs below drinking-water standards, but there were no corresponding increases related to what was seen at the site.
Aasen added it is unclear why PFC levels at the dump site have increased, but the agency is investigating.
The 3M Woodbury site received PFC-containing wastes from 3M decades ago, and this former dump site is a source of groundwater contamination in the eastern Twin Cities metro area. 3M has been cleaning up the Woodbury site under MPCA oversight.
While contaminated soil has been removed from the site, groundwater beneath it remains contaminated with PFCs. Part of the cleanup involves continuously pumping large volumes of groundwater from a series of barrier wells at the site to prevent contaminated groundwater from leaving the site.
3M advised the state in 2010 that to optimize groundwater pumping and use, pumping volumes at the site should be scaled back.
The MPCA approved a pumping-rate reduction of up to 25 percent. In March 2011, 3M shut off one of the barrier-well pumps at the site which had showed no trace of PFCs for several years. The MPCA approved the request based on a number of engineering studies submitted by 3M that showed that the reduced pumping rate would keep PFCs from migrating off-site in groundwater.
Analysis of on-site groundwater sampling results completed by 3M last month showed that levels of two of the PFCs of concern, known as PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfate), had increased in monitoring wells at the site. 3M notified the MPCA of the findings on Sept. 14 and immediately restarted the shut-down well.
The MPCA notified the cities of Woodbury and Cottage Grove about the findings and began planning for sampling of private drinking-water wells in residential areas downgradient from the site.
MPCA remediation supervisor Sandeep Burman said, “The agency will require 3M to determine the causes of the increase in PFOS and PFOA levels at the site. There is an intensive evaluation underway that will be completed in November. While that work continues, the barrier system will operate at previous pumping rates and groundwater monitoring at the site will be enhanced.”
