The company operates four wells that act like giant wet-vacs at the dump. For almost 40 years, they've sucked out enough groundwater to fill six Olympic-sized swimming pools -- every day. The system is supposed to halt the chemicals' underground movement. The extracted water is piped to 3M's plant in Cottage Grove, where some is used in production. It eventually ends up in the Mississippi River.
Regulators long believed such systems were slowly remedying the groundwater problem near the Woodbury site and two other disposal areas used by 3M in Washington County in the late 1950s and early 1970s.
That optimism has faded since 2004, when state officials began testing residential wells for 3M's perfluorochemicals, once used for nonstick cookware, stain-resistant fabrics, fire-suppression foams and film coatings. PFCs have been found in drinking water wells near the disposal sites, raising the question: Did the chemicals slip past the pump-out wells?
"It's soluble, it gets into the water and it goes," said Douglas Wetzstein, Superfund unit supervisor for the state Pollution Control Agency, which is still investigating how PFCs spread. "... We don't have all the answers, and the thing about PFCs is that every week or month that comes along, there seems to be some other angle that needs to be investigated."
One possibility is that PFCs escaped into Washington County's groundwater before any cleanup efforts began.
3M, the Maplewood-based manufacturer of Scotchgard, Post-It notes and thousands of other products, says it phased out PFCs by 2002 because the chemicals don't break down and had been detected in people and animals around the world. High concentrations of some PFCs have caused liver, thyroid and developmental damage in animals. One compound, PFOA, likely causes cancer, a federal scientific panel said last year.
In May, the company signed a new agreement with state regulators to investigate and to remedy the problems. It also has alerted 3M stockholders that another $121 million will be needed to deal with PFCs in Minnesota and at a plant in Alabama.
Paying the price, for years
At the Pine Bend oil refinery in Rosemount, pollution has trickled underground for years -- straight toward the Mississippi River 1½ miles a way.
After paying a record $6.9 million fine in 1998 for water and air pollution violations, the refinery owner Flint Hills Resources says it is working harder to prevent spills and leaks, and has spent $30 million cleaning up the old ones.
So far about 4.1 million gallons of product have been sucked out of the ground, using various methods. That's enough to fill nearly 500 tanker trucks. The waste is treated, incinerated or refined on site.
Workers periodically recover petroleum from a trench near the river, said John Hofland, a company spokesman. Some of the cleanup will go on another 10 years or more, he added.
Even low concentrations of pollution are worrisome -- and expensive.
In Oakdale, 3M last year paid $3 million to build a carbon-filtration plant that removes the chemical PFOA. The new plant is expected to cost $350,000 a year to operate.
The level of PFOA in the groundwater entering the plant is about 1 part per billion, slightly above the state drinking water limit. The chemical is undetectable after filtration. Each year, the city supplies 1 billion gallons of water to customers.
The net result: Filters will remove about a gallon of PFOA each year.
"That's the amount somebody threw in the ground years ago," said city public works director Brian Bachmeier.