It takes detective work to track the path of chemicals in groundwater. Sometimes, the mystery goes unsolved.
Eight years ago, Jim and Judith Blackford got a letter from the Minnesota Pollution Control Agency. It said they needn't worry that their well water might be polluted by an old landfill a half mile from their Lake Elmo home. The groundwater flowed the other way. Last year, the Blackfords found out their well water carried traces of a 3M chemical probably discarded in the landfill more than three decades ago. The Blackfords' experience illustrates one of the abiding mysteries of groundwater pollution: Chemicals dumped in soil sometimes end up in surprising places.
"You feel kind of sullied," said Judith Blackford, who lives with her husband and son on a 5-acre remnant of her parents' former farm. The family now drinks bottled water.
Across the metropolitan area, groundwater laced with chemicals lies beneath at least 35 communities. Hidden pollution from dumps and industrial sites has slid beneath lakes, crept up to river banks and slipped through subterranean valleys to contaminate far-off wells.
It takes detective work to find out how it got there and where it might be going next. Engineers often probe the ground with dozens of wells, drawing water samples to analyze for a cocktail of pollutants. They study that data and the flow of groundwater to map the extent of pollution, which is called a plume.
Two adjacent plumes of a 3M compound called PFBA contaminate groundwater beneath a quarter of Washington County. To find those plumes, the state Health Department sampled 1,338 residential wells, and detected 3M chemicals in 56 percent of them. Even so, scientists still don't fully understand how the chemicals spread so far and wide.
'Some of it we are not going to be able to answer with any certainty," said Virginia Yingling, a hydrologist who has mapped the plumes for the state Health Department. "There are places where we will be sampling intensively because we just don't know what is going on."
Until recently, other state officials were sure nothing was going on with Judith and James Blackford's well.
"Your well ... is not impacted by the landfill," hydrogeologist Ingrid Verhagen of the Minnesota Pollution Control Agency wrote them in 2004.
But their well and 12 neighbors' -- once thought not at risk because they were essentially uphill from the landfill -- have tested positive in the past year for PFBA, a chemical 3M once made for coating photographic film.
Now, Verhagen and others believe that the government's decades-long cleanup program at the landfill inadvertently raised the water table, and redirected pollution into the wells.
It didn't help that PFBA seems to zip through groundwater, outpacing other pollutants in the same landfill, such as volatile organic compounds (VOCs).
"Those compounds are amazing," said Verhagen. "They travel to places a VOC would never go."
The water table near the landfill now is dropping, but it could take three years for residents' wells to be rid of PFBA, she said. Meanwhile, the state is supplying homeowners with in-house filtration systems, though the Blackfords are holding out for municipal water hookup.
They don't think the chemical has harmed them or their two adult children, one of whom still lives at home. The risk of low-level contamination is that a lifetime of drinking the water might increase their odds of disease.
"We've always been really aware of chemicals in our environment," said Judith Blackford. "It kind of sucks some of the joy out of life knowing that it is in your water system. You can't quantify it. You can't say what it is going to do."
Surprise beneath a lake
In North Oaks, the exclusive suburb in Ramsey County built on a farm once owned by railroad magnate James J. Hill, residents thought their problems with buried chemicals were behind them in 1994.
That's when the last chemical drums were dug out of an old dump on Hwy. 96, and 60 residents on the east side of Gilfillan Lake stopped using wells contaminated by a pollution plume. The residents switched to municipal water.