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For years, communities in the east Twin Cities metro have treated their drinking water to remove PFAS, sometimes called "forever chemicals." The water coming from the tap is safe to drink. But the PFAS contamination remains underground, and continues to show up in lakes, streams and groundwater.

A new study from the Minnesota Pollution Control Agency recommends the state take action to contain the underground contamination plume and keep it from spreading to new areas.

It’s still unclear who would pay for the plan, which could cost hundreds of millions of dollars in addition to what’s already being spent to treat drinking water.

PFAS — or per- and polyfluoroalkyl substances — are human-made chemicals that resist breaking down in the environment. Studies have linked exposure to PFAS to several health problems, including kidney and thyroid disease, liver damage, low birth weight and cancer.

Decades ago, 3M disposed of chemical waste containing PFAS at several sites in the east Twin Cities metro, including one in Oakdale and the Washington County Landfill. Over time, that contamination spread underground across more than 120 square miles. 

The contamination continues to spread in the groundwater. The chemicals are also showing up in connected lakes, rivers and streams.

“Now we are dealing with PFAS at an aquifer level, at a surface water level and in sediment,” said Jeff Holtz, who serves on the Lake Elmo City Council and the state’s 3M settlement work group. “And none of those issues are going away.”

For decades, Minnesota’s main approach to PFAS has been treating water taken from the ground before it’s sent to residents for drinking. 

But a new study from the Minnesota Pollution Control Agency suggests a broader response: not just treating groundwater destined for people’s taps but also removing PFAS from the environment itself.

Oakdale Mayor Kevin Zabel said it’s a shift in approach.

"For the longest time, the philosophy has been, treat the water you use out of the aquifer before it goes into our drinking water distribution system,” he said. “That's not changing."

But Zabel said the study reflects “the reality that we need to do more to get PFAS out of the aquifer faster, otherwise we’re going to be facing long-term and downstream effects — which we’re already starting to see.”

Pumping water, returning it to the ground

 examined options for reducing PFAS from both groundwater and surface waters, including lakes and streams.

It focused on how a flood control project built in the 1980s is contributing to the movement of PFAS in the east metro. Called Project 1007, it's a network of stormwater pipes, channels and dams that extends from the Tri-Lakes area in Lake Elmo to the St. Croix River. 

Experts believe that the system acts as a pathway, helping PFAS travel more quickly through the region.

The study recommends several possible actions to reduce the spread of contamination. 

The most ambitious one would involve installing a system of wells that would pump contaminated groundwater, remove PFAS, then distribute it to cities and inject some back into the underground aquifer.

Returning the treated water to the ground would help slow the movement of the contaminants, and also make sure the groundwater supply is sustainable, said Kirk Koudelka, assistant commissioner at the Minnesota Pollution Control Agency.

"What we're trying to do is making sure we're recharging the aquifer if we’re taking water from it,” he said.

Koudelka said the MPCA does use wells to pump contaminated groundwater at some of the 3M disposal sites, but this would be a much larger system. And the concept of injecting water back into the aquifer would be new for Minnesota.

The agency has worked with the University of Minnesota to study how much water it could draw from different aquifers and how much would need to be returned to make sure levels remain steady, said Andri Dahlmeier, the MPCA’s East Metro Unit supervisor.

More testing is needed before the state could start using the injection process, Dahlmeier said.

The technology isn’t new, said Peter Kang, an associate hydrogeology professor at the University of Minnesota. It’s commonly used in coastal areas, such as California, where seawater intrudes into a groundwater aquifer, he said.

The process works better in places where water flows more easily through the ground, Kang said. And close investigation is needed to make sure it’s not causing changes to the chemical makeup of the water, he said.

Other recommendations in the study include continuing to clean up the Oakdale disposal site and the Washington County Landfill, which are still leaking PFAS.

And it suggests installing barriers into streams that would capture PFAS but allow the water to pass through, the way a furnace filter traps dust.

“It's supposed to be constructed so that the water can flow quick enough through it, so you don't cause any damming or any flooding like that,” Dahlmeier said.

It’s not clear where the funding would come from to carry out the PFAS cleanup plan.

The study estimates the cost of building the pumping and injection system at between $227 million and $404 million, plus operating expenses of $12 million to $84 million annually. 

Pumping and treating the groundwater without injecting it back into the aquifer would cost less but still has a considerable price tag.

In 2018, 3M agreed to pay $850 million to settle a lawsuit with the state of Minnesota over PFAS contamination. That settlement money, along with a 2007 order signed by 3M, are paying the water treatment costs for east metro cities.

But those settlement funds will run out soon, and there’s no additional money for the Project 1007 recommendations, state officials said. 

Meanwhile, cities in the east metro continue to treat their drinking water, trying to stay ahead of the spreading PFAS plume.

In Oakdale, east of St. Paul, a treatment plant has been using carbon to filter out PFAS from the city's water supply for 20 years.

Built in 2006, the filtration plant was the first of its kind in the U.S. designed to remove a class of chemicals that Minnesota health officials were just beginning to understand.

Untreated water flows through pipes into massive tanks, where it's filtered through a grainy carbon material that resembles fine black sand. 

The PFAS is attracted to the carbon and sticks to it, said Cory Tietz, Oakdale's public works director. The water then flows into a second backup tank to catch any chemicals the first one missed.

Within the next couple of years, the city plans to build a larger, centralized filtration plant to treat water from additional wells. 

Tietz said as the plume of PFAS moves north, trace amounts are showing up in city wells that historically weren't affected.

"We're seeing it creep in other places,” he said. “So where we don't have filtration now, as we potentially get to where we're going to need it, we're prepared.”

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A new study from the Minnesota Pollution Control Agency recommends the state take action to contain the underground contamination plume and keep it from spreading more. It’s still unclear who would pay for the plan, which could cost hundreds of millions of dollars.

New study outlines costly steps to control ‘forever chemicals’ in east Twin Cities metro

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