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CATHY WURZER: Let's talk a little bit now about groundwater is becoming a precious commodity in parts of the Northern and Eastern Twin Cities suburbs. Demand comes from industry, drinking water, lawns and golf courses. And then there's pollution. More than 10% of the groundwater being pumped in this area is used to clean up polluted sites.

State officials say it has to be cleaned up. But in a place where concerns over long-term sustainability are rising, they're looking for ways to use some of that water again. Elizabeth Dunbar reports, as part of our Beneath the Surface project, examining the state's groundwater.

ELIZABETH DUNBAR: This windswept field right on the border of Woodbury and Cottage Grove belongs to 3M. The company hasn't dumped any waste here since the 1960s, but when it did, Perfluorinated Chemicals, PFCs, seeped into the groundwater below. If you visit the site today, you'll see trees and a spot where 3M employees fly model airplanes and there are four small well houses that pump 3 to 5 million gallons of contaminated water a day.

It prevents a polluted groundwater plume from spreading and threatening drinking water supplies. The water makes a 6-mile trip in an 18-inch pipe to the 3M Cottage Grove plant. It arrives at a huge water treatment building with two long rows of tanks roughly the size of cement truck mixers. Hi.

MIKE ROGERS: Hi. How are you doing?

ELIZABETH DUNBAR: Good. You work in a cool building.

MIKE ROGERS: Yeah.

ELIZABETH DUNBAR: 3M's Mike Rogers shows me what the water arriving at the treatment plant looks like.

MIKE ROGERS: This is what comes directly out of the well.

ELIZABETH DUNBAR: It looks pretty clean, but the PFCs are invisible and they have to be filtered out. That's what the tanks are for. Rogers calls them vessels. Each one is filled with 20,000 pounds of tiny grains of carbon.

MIKE ROGERS: Simply, we bring in all of the water from the site wells or the wells that you visited in Woodbury earlier, and they'll go through the vessels in a lead leg orientation. We have the--

ELIZABETH DUNBAR: OK, it sounds kind of complicated, but the process is similar to something many of us have at home. Are these fancy Brita water pitcher filters?

MIKE ROGERS: I'd say pretty close. Yeah. Just very large size.

ELIZABETH DUNBAR: The treated water is distributed throughout the 3M plant for chemical processes leading to products like reflective coating for road signs and adhesives for Scotch Tape and post-it notes. Water is also used for cooling. State officials monitoring groundwater use in the metro say 3M's pollution remediation site is one of the few where groundwater is not only being pumped and treated, it's also being reused.

But 3M site manager Mike Baima says the plant doesn't really need to use that much water, so the company is working with the Minnesota Pollution Control Agency to reduce the amount of contaminated groundwater being pumped in Woodbury.

MIKE BAIMA: Technically, we do use it all right now. And we have a number of projects ready to go that are scoped and feasible to allow us to reduce water usage. If we can come to an agreement to reduce that level, we're always looking to reduce our impact on the environment, whether it be air, water, raw materials, things like that.

ELIZABETH DUNBAR: Reducing pumping volumes at groundwater remediation sites is tricky. And MPCA officials say the last time it was attempted at the 3M site in 2011, it didn't quite work.

KLAY ECKLES: Over here it gets treated with some fluorine and some fluoride and then it goes right into the city water system.

ELIZABETH DUNBAR: Klay Eckles, Woodbury's Public Works director, will be watching closely if 3M and the MPCA try to reduce pumping again. He's showing me one of the city's 18 wells that provide drinking water. Eckles says the city has had to make sure its pumping doesn't affect the Valley Creek trout stream. And now the state has set up a groundwater management area in the North and East Metro because of concerns about whether groundwater pumping is sustainable.

The new area covers Ramsey County, part of Anoka County, and all of Washington County, where Woodbury is located. Back at Public Works headquarters, Eckles says there's more scrutiny than ever on how much water cities use. The city wants overall groundwater use to stay flat between now and 2030, even as the number of residents is expected to increase by 30%.

On some days, the water being pumped from the 3M remediation site is as much as the entire city of Woodbury uses. Cities are restricting lawn watering and looking for creative ways to keep golf courses green. So Eckles says pollution containment sites like 3M's should also be tapped for solutions.

KLAY ECKLES: That's a lot of water. And it's not that we shouldn't remediate, that protects our groundwater. So you have to do it. It's just are we doing it in the most effective way?

ELIZABETH DUNBAR: The 3M remediation site isn't the only example where polluted water is being cleaned up and used again. In New Brighton, they're drinking it.

DEAN LOTTER: Our water is, I might argue, the safest, at least most monitored water in the state.

ELIZABETH DUNBAR: New Brighton city manager Dean Lotter says that's because raw groundwater pumped from the city's wells contains Trichloroethylene, TCE, from polluted groundwater that migrated from the Twin Cities Army Ammunition Plant, TCAAP, in Arden Hills. Under an agreement with the city, the army helps pay for the more expensive water treatment system that's needed to ensure the water is safe to drink.

The city pumps and treats about 500 million gallons more per year than it needs, enough to share some with neighboring Fridley. Lotter says as state officials ask cities within the groundwater management area to implement conservation measures, his city is in a unique position.

DEAN LOTTER: While a lot of communities are being told stop using so much, stop pumping so much, we have a commitment that we have to honor where we actually pump way more than we need to get rid of that contamination.

ELIZABETH DUNBAR: TCAAP and 3M own the biggest pollution containment sites in the North and East Metro. But there are about a dozen other sites that altogether account for 10% of the area's groundwater use. Another big containment site is in Fridley, where a combined 300 million gallons of groundwater is pumped each year to remove TCE and other pollutants from two former Navy manufacturing and waste sites.

DNR hydrogeologist Paul Putzier is overseeing the North and East Metro groundwater management area. He says the water being pumped to contain pollution is an unfortunate reality and will be with us for decades to come. Not only does it take a long time to clean up a site, state officials are also discovering new groundwater pollution sites or reopening old cleanup sites based on health guidelines for newer or lesser known contaminants.

PAUL PUTZIER: It's just kind of like living next to the railroad tracks or something, it's just something you have to deal with. But I think putting our minds together on it is going to bear fruit in the long run. I mean, the way that we think about it is with groundwater, right now most of our groundwater use, we use it once, then we're done and it goes out.

So we think about it if we could find ways to use our groundwater, which is such a pure and beautiful resource a second time in any situation, we would solve many of our long-term sustainability problems.

ELIZABETH DUNBAR: Back in Cottage grove, 33-year 3M veteran Tom Flicker takes me to the edge of the company's property on the Mississippi River.

TOM FLICKER: It's fairly common to come down here and see deer and geese and bald eagles.

ELIZABETH DUNBAR: This tranquil place is where the millions of gallons of groundwater the company pumps and treats each day meanders down a ravine and discharges into the river. The river is also where cities discharge their treated wastewater, billions of gallons that flow down to the Gulf of Mexico.

But if groundwater sustainability concerns persist, someday we might be using that water a second, third, or fourth time, or find a way to safely inject it back into the ground. Elizabeth Dunbar, Minnesota Public Radio News, Cottage Grove.