PFCs found in northern wells near Woodbury disposal site
Although levels of 3M-manufactured chemicals have been consistent in wells on the south end of a former disposal site in Woodbury, recent testing showed an increase in perfluorochemicals (PFCs) to the north.
Testing at monitoring wells near the site this fall showed a slight increase in chemicals that prompted a round of sampling in private wells in all compass directions. The Minnesota Pollution Control Agency sampled three nearby residential wells located north of the site starting Nov. 28.
"The test results have come back and we haven't seen anything that would require an advisory," said Jerry Stahnke, project manager for the 3M Woodbury disposal site.
But he added that levels of PFCs shown at private wells are significant enough for the MPCA to continue monitoring the site.
Additionally, it is unknown why the chemicals seem to be moving to the north.
Sentinel wells, or monitoring wells, are being tested on a biweekly basis, mainly concentrating on the southern boundary of the disposal site because that's where the increases were originally found.
However, the MPCA asked 3M to do a comprehensive round of sampling in all directions surrounding the site in October, Stahnke said.
It then revealed increases in two types of the PFC family - perfluorooctane sulfate (PFOS) and perfluorooctanic acid (PFOA) - in four of the northern wells.
Samples were sent to both the MPCA lab and 3M's, he said.
"The test results are quite comparable between the two labs," Stahnke added.
Southern wells often show PFCs, which is typical due to groundwater flow, but rarely do they end up on the north side.
"It was unexpected because that's upgradient," Stahnke said. "We wouldn't expect these results on the northern end."
That's why the MPCA looked into sampling five nearby private residential wells in Woodbury late last month.
The agency was only able to test three of them because one was an abandoned household and another refused testing, he said.
"We saw that some of the results have come down a little bit but there is still at least one that suggests we should continue to investigate that area," Stahnke said.
To figure out why the northern end contains PFCs, 3M is currently trying to find anything that could cause the water to go in a different direction, he added.
"Groundwater is expected to go to the southwest and here we're finding it in the north," Stahnke said.
The MPCA is expecting a report from 3M in the first quarter of 2012 once the actual physical work is completed and the company had a chance to do an analysis, he said.
Stahnke explained that reasons behind finding PFCs on the south and the north may not be related at all, but said there are three possibilities why contamination is happening.
Sentinel wells were installed in 2007 and 2008 and have been tested over time, but the increases in PFCs started showing up in May of 2011, he said.
Contamination could be related to significant weather change in the first half of the year, the cleanup work that was done over the last two years, or barrier wells, he said.
The cleanup opened up the disposal site, which left a pit that may have mobilized contamination, while barrier wells could've released some of the chemicals that they were meant to capture, Stahnke added.
Drinking water limits for contaminants is 0.3 parts per billion, or one-third of a part per billion, according to state standards. Private well testing results were not made available by press time.
"It's hard to imagine that anybody can detect levels that low," Stahnke said, adding, "We're acting within an abundance of caution because the levels we saw on the north end were not that high but yet significant enough."