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New science, new threat
The decision to shut down groundwater pumping in 2010 was part of increased calls by General Mills to end cleanup efforts and switch to “natural attenuation,” a technical term for letting nature take its course with contaminated groundwater. MPCA officials appeared willing to agree, records show — until the emerging science of vapor intrusion changed matters.
Vapor intrusion — when fumes from contaminated groundwater begin rising through the soil — was first discussed by researchers in the 1990s. It gained notice in Minnesota in 2007, when pollution of an Edina water well was traced to a plume that also caused vapor problems in homes in St. Louis Park.
General Mills had conducted crude vapor tests in sewer lines beneath the Como neighborhood in 1997, but, after the St. Louis Park incident, the MPCA asked for more sensitive testing of the soil itself.
The results showed high TCE levels in the soil vapor — and shocked General Mills officials, said Larry Deeney, the company’s senior technical leader for global environmental issues. Based on the declining groundwater contamination, he said, they hadn’t expected a problem.
General Mills proposed installing remediation systems in all homes that were potentially affected, but the MPCA told the company to first outline the vapor plume by testing soil gas below their foundations. Properties with TCE concentrations of more than 20 parts per billion would receive remediation. Properties with lower levels would not.
As of Feb. 26, high TCE levels had been found in 120 homes, 90 of which received remediation. Some homes have presented costly complications for General Mills. Ebert and Krauze, for example, need a new basement floor. Cracks in the existing floor will prevent the air-pressure system from sucking contaminants from below their foundation.
In other cases, property owners are being denied fixes, because TCE tests were low in their homes even though they were high next door.
The homeowners’ attorneys want remediation systems installed in all homes above the plume, just as they were at vapor intrusion sites where they represented homeowners in Attica, Ind., and Madison, Wis.
MPCA’s Neve said that is a possibility. After 30 years, the original cleanup agreement with General Mills was amended Tuesday, giving the company 90 days to propose a new long-term plan for monitoring the removal of any contaminants. The company will need to determine whether TCE is indeed sitting below the ground in contaminating blobs, Deeney said, and figure out how to get it out. Solutions could include burning TCE out, trapping it in filters, or neutralizing it with bacteria.
“We’re just trying to go in and make things right,” he said.
Jackie Milbrandt lives across the street from Ebert and Krauze, in a house her parents bought when she attended the U. Milbrandt slept in the basement as a student and later bought the home, where she lives with her husband and two children.
TCE readings of 16 and 17 meant General Mills didn’t have to install a remediation system in her home. Unsettled, Milbrandt bought an $800 air purifier and keeps her children upstairs. A treadmill in the renovated basement sits unused.
“We stopped going down there,” she said, “though of course laundry has to be done.”
Jeremy Olson • 612-673-7744