Thirty years ago, state regulators let General Mills leave a swimming pool's worth of chemicals beneath the Como neighborhood of southeast Minneapolis.

They soon came to regret it.

Today, the result is a house-by-house search beneath basements for chemical vapors that could be threatening the public's health.

A Star Tribune review of agency documents and cleanup records shows decades of hand-wringing by state and federal pollution officials after a 1984 agreement that required General Mills to pump and clean contaminated groundwater in the neighborhood surrounding its defunct research facility — but not remove any of the material that was causing it.

The lessons learned in Como could have implications across Minnesota, where dozens of other communities may harbor similar underground soil contamination.

Whether leaving the pollution behind caused health problems is unclear. A few Como residents have suffered disorders such as lymphoma that have been linked to long-term exposure to trichloroethylene, or TCE, the chemical that trickled into groundwater below their homes and vaporized into a gas that rose toward their basements. But no link between the pollution and illnesses has been proven, and no elevated rates of cancer or birth defects have been detected.

Nonetheless, attorneys suing General Mills on behalf of Como residents are criticizing environmental agencies — both the Environmental Protection Agency for its hands-off approach to a site it deemed hazardous and the Minnesota Pollution Control Agency (MPCA) for its oversight.

"Both of the government agencies charged with the protection of these people bailed on them in the 1980s," said Shawn Collins, a Chicago environmental attorney.

State officials acknowledge that the agreement — one of the first Minnesota made under the 1980 federal Superfund law — would never be made today, given modern understanding of contaminated groundwater and of the soil vapors that can rise from it. Just last week, they amended the deal in a way that requires additional steps by the company.

Discovery of the soil vapors prompted General Mills to announce in November that it would test the soil below 200 Como-area houses and businesses; those with high TCE levels will receive air-pressure systems that pull harmful vapors out and into the open air.

But as Como's testing nears completion, an old question is resurfacing: Can the remaining chemicals just be left in the ground?

"It doesn't seem like, here, it is going to be adequate," said Hans Neve, an MPCA site remediation manager.

Meanwhile, anxiety has spread in the Como plume, a 20-block section of homes largely owned by families or rented by University of Minnesota students between the General Mills site and Van Cleve Park.

Wendy Sangren can't help wondering if her home, where her husband was raised, was related to her in-laws' cancer deaths.

Millie Caspersen, a 77-year-old retired psychiatric nurse, hasn't suffered illnesses she could trace to any vapors, but testing found TCE beneath her home at 750 times the threshold for remediation.

"We've lived here, raised our kids here, for 44 years," she said, noting her husband stomped grapes for winemaking in the basement. "And now we're wondering, 'What have we been actually breathing?' "

A place called 'away'

The answer requires a look back to 1947, when General Mills started chemical research at its site at 2010 E. Hennepin Av. Chemical residue was dumped there in barrels that were stacked in the ground and perforated so the contents could drain away.

That mind-set was common at the time, Neve said — chemicals could just go "to a place called away" and presumably not harm anyone.

About 1,000 gallons of chemicals were dumped each year from 1949 to 1962. They included TCE, an industrial solvent linked in cases of long-term exposure to higher risks of birth defects, cancer and other disorders. Disclosure of the pollution came after General Mills sold the property in 1977.

Under the new regulatory muscle of the Superfund program, the EPA put the General Mills site on its National Priority List, which meant that cleanup was urgent. But lacking staff, the EPA passed oversight of the situation to the state.

The MPCA and General Mills ruled out removing tons of contaminated soil, concluding it would be expensive, ineffective and disruptive to roads and a railway line. Ignored for two decades, the bulk of the chemicals already had sunk below the top layer of soil and scattered downstream in the groundwater or in clumps.

Instead, they agreed on pumping groundwater to air out the contaminants. The area had no drinking water wells, records showed, but pumping would stop the chemical plume from expanding under the U campus to the Mississippi River.

"The focus at the time was … containment," said Neve, explaining an agreement his MPCA predecessors made when he was 12.

General Mills agreed to bear the $100,000 annual cost of pumping but reimburse MPCA no more than $5,000 in any year for related costs.

Second-guessing of the deal came quickly, according to records reviewed by the Star Tribune.

Five years in, state officials were rethinking whether contaminated soil should be removed but found General Mills unwilling to make a change that would expose the Golden Valley-based food maker to more costs.

"The window of opportunity to do cost-effective and environmentally sound soil removal appears to have passed us by," an MPCA official said in a 1990 memo.

State officials also suspected much of the TCE was in chemical blobs that weren't addressed by the pumping and were simply recontaminating the groundwater.

Staying away from basement

Around this same time, Karl Ebert and Carol Krauze moved to Como, unaware that a Superfund site sat across a railroad berm from their yard. The house was affordable, between their offices in St. Paul and Minnetonka, and close to the U, where they intended to pursue master's degrees.

Later, Ebert worked from home as a computer programmer — and for years he spent eight-hour days in a basement office. That ended in November, when the couple learned of the TCE risk and when testing found elevated levels of the chemical beneath their basement. Now Ebert shares the upstairs playroom with his three children and tries not to think about whether TCE exposure will result in a health problem someday.

"I've already been exposed to it for 20 years," he said. "Whatever I've got from it, I've got."

How much 25 years of pumping groundwater beneath Como has helped is a matter of dispute. The MPCA and General Mills agreed the pumping should reduce TCE groundwater concentrations to below 270 parts per billion in the shallow "glacial aquifer," and to below 27 parts per billion in the deeper aquifer beneath it.

TCE levels dropped as planned, records show. One pumping station saw shallow groundwater TCE levels drop from more than 600 in 1999 to less than 100 in 2011.

Those targets, however, exceed the five parts per billion now recommended by the Minnesota Department of Health — although that recommendation is for groundwater that serves as a drinking water supply.

The EPA has indicated that it won't remove the site from its high-risk list, with groundwater levels so high. And the attorneys suing General Mills expect a "rebound" in TCE levels, because the company halted pumping in 2010 and they believe there are remnants of TCE in the soil that will recontaminate the groundwater.

"They really haven't stabilized anything," attorney Norman Berger said. "They set an unprotective cleanup objective that they realized they could hit and then shut things down."

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