Minnesota's Vapor Trail: Tracking toxic gases in basements

  • Article by: JEREMY OLSON , Star Tribune
  • Updated: March 31, 2014 - 9:26 AM

Discovery that contamination in soil can vaporize and seep into homes has prompted a statewide review of polluted sites.


Homes along 20th Avenue SE in Minneapolis are among those affected by toxic chemicals.

Photo: Jim Gehrz, Star Tribune

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The discovery that toxic vapor can rise from contaminated groundwater has undercut decades of pollution cleanup efforts in Minnesota, prompting state regulators to revisit 293 cleanup sites to determine if contaminants that once seemed contained underground are producing health hazards today.

While cleanups in southeast Minneapolis and St. Louis Park have been well publicized, the Minnesota Pollution Control Agency has quietly undertaken a much broader review, and found another 53 pollution sites, from Bagley to Rochester, where vapor intrusion is being addressed. The review is ongoing at 80 additional sites.

State pollution officials also must decide whether to revisit 268 Superfund sites that were closed out years ago, because old cleanup strategies didn’t account for vapor risks.

“We will deal with these sites and we will do a professional job of responding to them to protect public health and improve and restore the environment,” said John Linc Stine, MPCA commissioner. “Unfortunately, the legacy of past actions is something that all of society is living with.”

Among the 53 known problem sites, at least eight were old dry cleaning businesses, where it was common practice to dump cleaning chemicals out the back door.

Others include the Duluth Air Force Base and the Tonka Corp. toy manufacturing site in Mound — where a primary issue had been preventing contamination of nearby Harrison Bay on Lake Minnetonka. The review of these sites has been ongoing since 2008, when the state issued its first guidance for dealing with soil vapor.

Data requested by the Star Tribune regarding the 53 problem sites shows that 68 adjacent residences and 92 businesses received testing. Mitigation systems have been installed in 11 homes.

None of the sites are as large or problematic as Minneapolis’ Como neighborhood, which is adjacent to an old General Mills research plant where 1,000 gallons of toxic chemicals such as trichloroethylene, or TCE, were dumped yearly from 1949 to 1962.

Since November, testing of soil vapor has been completed beneath more than 270 Como properties, largely single-family homes or rental apartments for students at the University of Minnesota. General Mills has agreed in 144 cases so far to pay for mitigation systems — mostly negative air-pressure systems that draw vapors out of the soil and prevent them from building up in basements.

Measured in micrograms per cubic meter of air, TCE levels that reached the thousands in a few cases have created anxiety for Como residents who wonder what they have been breathing and whether their houses will be sellable ever again.

“I don’t feel safe living there,” said Coral Sadowy, 66, who wonders if TCE exposure is related to her uterine cancer. A TCE reading of 3,370 below her basement grossly exceeded General Mills’ threshold of 20 for a mitigation system.

Shift in the science

The common thread at these sites is the use of solvents or other compounds known as “volatile organic chemicals” such as TCE and perchloroethylene, or PCE.

Research has linked these compounds to higher rates of cancer, birth defects and other disorders when people are exposed to high levels of them over long periods.

These chemicals tend to sink into the groundwater and sometimes collect in dense globs that contaminate the water unless removed. For years, the primary environmental concern has been whether the chemicals were contaminating drinking water supplies. If not, the strategy often was to contain the chemical plumes below the ground and slowly remove the chemicals by pumping and airing out the groundwater.

While this satisfied scientific knowledge of the time, it didn’t address facts discovered in the late 1990s — namely, that these chemicals could vaporize underground and rise through the soil in potentially harmful levels to basements of homes and businesses.

Minnesota is slightly ahead of the curve nationally in reviewing its pollution sites for vapor risks, though New York completed the process several years ago and other states in New England are farther along, said Lenny Siegel of the Center for Public Environmental Oversight in Mountain View, Calif.

“The reason vapor intrusion to me is a high priority is because it is an intrusion,” he said. “Something that doesn’t belong in people’s homes is getting in there and they can’t do anything about it.”

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