This Huge Mining Pit Is About To Be A Lake

Old mines leave behind a a pressing problem: Huge holes that make the landscape look like a chunk of swiss cheese. But in Germany, some scientists and city planners are turning these into lakes. The largest one will be the biggest artificial lake in Germany when it's done, with a shoreline of 26 kilometers or about 16 miles all around. But it's not as easy as simply filling the holes with water. It takes a LOT of research to get this science right. Interested in more environmental stories? Email us at [email protected] mailto:[email protected]. We'd love to hear from you! Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:17Speaker 00

  You're listening to Short Wave from NPR.

• 0:23Speaker 00

  Hey, Shortwavers. Emily Kwong here, and I am joined by Planet Money producer Willa Rubin. Willa, hey, what's up?

• 0:29Speaker 01

  Hey, Emily. Hey, Short Wave. I come to you with a story.

• 0:33Speaker 00

  All right, let's hear it.

• 0:34Speaker 01

  So about two hours southeast of Berlin, there's a city called Kottbus.

• 0:44Speaker 01

  It's pretty small. About 100,000 people live there. For context, this is in eastern Germany, near the Polish border. And so historically, this part of Germany had a lot of lignite mining. This is a fossil fuel that is dark brown. It's soft. It's kind of like an intermediate between hard coal and petroleum coke.

• 1:04Speaker 00

  Oh, interesting. I've never heard of this. OK, lignite.

• 1:06Speaker 01

  Yeah, lignite. Then, after the Berlin Wall fell in 1989, and Germany reunified east and west in the early 90s, a lot of mines in the former East shut down, mostly for economic reasons, or they ran out of coal. Then there was this pressing problem. There were a bunch of holes in the ground that used to be mines, but now looked like a landscape of Swiss cheese, which is not awesome aesthetically or safety-wise. And so the city of Kottbus has a really interesting plan. And one sweltering day in September,

• 1:51Speaker 01

  I went to go see one of these pits.

• 1:53Speaker 00

  Ooh.

• 1:54Speaker 01

  20 minutes east of the city.

• 1:56Speaker 02

  Hello. It's great to have you here.

• 1:58Speaker 01

  At the train station, I met up with Stefan Zimonidis Nowak.

• 2:02Speaker 02

  Here we are.

• 2:05Speaker 01

  Stefan has lived in Kottbus for a long time. He works for the city council, and he's an urban planner working here.

• 2:12Speaker 02

  OK.

• 2:15Speaker 02

  Welcome to the Kotbus lake.

• 2:17Speaker 00

  Wait, did he just say lake?

• 2:19Speaker 01

  Uh huh. Because, Emily, Stefan and his colleagues are turning this giant former mining pit into a huge lake. It'll be the biggest mining pit turned lake in all of Germany. It's even in the lake's name, Kotbuser Ostsee. In German, that literally means Kotbus East Lake, okay? But it's also a play on words that means Kotbus Baltic Sea. And that is like the dream that Stefan and his colleagues are chasing. A mini Baltic Sea, right near the city center.

• 2:58Speaker 02

  I'm really a fan of the Baltic Sea and the shorelines and big sandy beaches. And we will have this here, the Kotbus beach is really huge one.

• 3:13Speaker 00

  Well, today on the show, how? How do you get from a Swiss cheese landscape to the largest artificial lake in Germany? I'm Emily Kwong.

• 3:22Speaker 01

  And I'm Willa Rubin. You're listening to Short Wave, the science podcast from NPR.

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• 4:52Emily Kwong?

  All right, Willa, so let's pick up where we left off. You get off the train and cot bus to see the lake. What does it look like?

• 4:58Speaker 01

  Emily, this lake is huge. That was my first impression. But honestly, what really took me aback were all the birds.

• 5:09Speaker 02

  And it's also planned to have natural habitat on the eastern shoreline, which will not be developed by building. We will be left for the nature like it is.

• 5:23Speaker 01

  Another thing that I noticed is that the sides of the lake were all boarded up. The lake itself is not open to the public yet.

• 5:31Speaker 02

  Everything is so slow.

• 5:35Speaker 02

  Planning takes a lot of years and but it's also exciting.

• 5:40Speaker 01

  When it is done, this is going to be the largest human made lake in Germany with a shoreline of 26 kilometers or about 16 miles all around, where people can go and swim and be in nature. There's also a little tourism boost as well. And it takes lots of research to get that science right.

• 6:06Emily Kwong?

  Yeah.

• 6:07Speaker 01

  And one scientist who has done so much work on pit lakes in Eastern Germany is Martin Schulze. When you see lakes, in your mind, do you see all of the different chemical calculations and so forth? Are you thinking about what's really happening beneath the surface?

• 6:25Speaker 05

  To some extent, of course, yes. Yeah, because I like my, my job and my, my research.

• 6:32Speaker 01

  Martin is a research professor at the Helmholtz Center for Environmental Research. He has written a lot about post-mining lakes in Eastern Germany and around the world.

• 6:41Speaker 05

  But these lakes are a beautiful piece of nature. And that is a very important driving force for me in my work. I want to keep them clean. I want to keep them in an ecologically healthy state so that

• 6:59Speaker 05

  Both nature and we as humans can benefit from them.

• 7:03Speaker 01

  He is super passionate about it. And he is one of the people who kind of wrote this playbook about how to turn a mining pit into a lake.

• 7:11Emily Kwong?

  Fascinating. Okay. Walk me through this transformation process. How do you go about turning a pit mine into a lake?

• 7:18Speaker 01

  Okay, so first, when you stop mining, groundwater starts to creep back up to the surface.

• 7:25Emily Kwong?

  And what do you mean by groundwater?

• 7:27Speaker 01

  Yeah, yeah, yeah. So when mines are operating, mines are kept super, super dry. And all that groundwater, this is water that is normally below the surface of, in this case, lignite. That groundwater is normally, when mines are operating, getting pumped out into local rivers. And it's being really closely monitored because, you know, no one wants mines to flood, especially when people are working in those mines.

• 7:52Emily Kwong?

  Absolutely not.

• 7:53Speaker 01

  Then when mining stops, that dewatering process also stops.

• 7:57Speaker 05

  Then the groundwater is rebounding and the former mining hole becomes a lake.

• 8:03Speaker 01

  Basically, they switch off some pumps and then groundwater starts coming back into these pits.

• 8:09Emily Kwong?

  Well, then that's it. Bada bing bada boom. Isn't that easy? You just like stop mining and it turns into a lake?

• 8:14Speaker 01

  Like, kind of, sort of, not really. Because you start to get water filling up the pit, which is great.

• 8:22Emily Kwong?

  Yeah.

• 8:23Speaker 01

  But a couple of problems. The first is that it can take many, many decades for all of the groundwater to come back on its own. That's problem number one. And problem number two is that the groundwater that is lying beneath the lignite, once it reaches the air, it is often incredibly acidic.

• 8:41Emily Kwong?

  Yeah.

• 8:42Speaker 01

  Because when that groundwater comes back up to the surface, it often comes into contact with oxidation products of high rite. This is a shimmery, golden-looking mineral. Sometimes it's called fool's gold. And yeah, and it can cause a lot of problems.

• 9:01Speaker 05

  As long as this mineral is deep underground and has no contact with air, and that means oxygen, everything is fine. But once it comes into contact with air.

• 9:14Speaker 05

  The oxidation has started.

• 9:16Speaker 01

  And that makes sulfuric acid.

• 9:18Emily Kwong?

  Yikes. Yeah, you do not want to be swimming in water that's sulfuric acid.

• 9:22Speaker 01

  Mm hmm. This groundwater can be like less than three on the pH scale, like lemon juice. We should be swimming in water that is close to like seven or eight on a pH scale.

• 9:36Emily Kwong?

  Oh, gosh. Okay, so when this happens, how do engineers or urban planners, scientists like react? How do they treat it?

• 9:43Speaker 01

  So there's a couple of methods. One is a sort of like break glass in case of emergency method. And that is to add limestone powder. So thinking about pH, limestone lime is a base. So then that helps to balance out the acidity. But this treatment also tends to be pretty expensive. And it also isn't like the most natural method to treat acidity.

• 10:10Emily Kwong?

  I hear that. So is there a better method for addressing this acidification issue? When when the lakes start filling up with groundwater?

• 10:19Speaker 01

  Add water from rivers, you know, get some fresh water in the mix.

• 10:23Speaker 05

  The hydrogen carbonate, also called bicarbonate, that is contained in almost all fresh waters that you find in rivers and streams. That is a major actor in that neutralizing process. And it works very well.

• 10:38Emily Kwong?

  The science of this is so cool, how to how to neutralize a lake in the making. So so how does this apply to the one in Kottbus? They're obviously trying to do this on a massive scale.

• 10:49Speaker 01

  Yes. So, okay, so part one of this playbook, which is, you know, neutralizing the groundwater's acidity. So far in Kottbus, they have managed to do this without limestone powder. Since 2019, lake designers have been flooding the pit with water from the Spray River, which goes up to Berlin. And now the pH is about eight.

• 11:11Emily Kwong?

  We love it.

• 11:12Speaker 01

  And Scheffan, the urban planner for the lake, says that the flooding is even on track to finish next year.

• 11:18Emily Kwong?

  Very cool. Okay, so the lake is almost to the level they would like.

• 11:22Speaker 01

  But Emily, they are not the only. Only ones who also want spray water. Because there are other pit lakes, smaller ones, but they also get water from the spray. Even nature preserves, like the Spray Forest outside of Berlin. Environmental groups have expressed concerns about this. Because the Spray River is drying up anyway. And then with Germany going renewable and phasing out mines over the course of the next decade. All that means that the Spray River isn't getting as much water as it used to. Like, from mines that were once pumping a lot of water into the Spray. So now, everyone is sort of taking turns, making agreements. Essentially competing for an increasingly limited resource.

• 12:06Speaker 01

  On the other hand, without water from the Spray, there would be that Swiss cheese landscape. So that's kind of the balancing act when trying to restore nature, but with limited natural resources.

• 12:18Emily Kwong?

  That is sort of a cash 22 to all of this, huh?

• 12:20Speaker 01

  Yeah, exactly. And for the Kappus or Osee, this has contributed to why the flooding has taken a while. Which has also contributed to another problem, the shoreline. Because ideally, you'd have to fill a pit with water very quickly.

• 12:40Emily Kwong?

  But why is that?

• 12:41Speaker 01

  Like, picture this. You have groundwater seeping into the lake from the bottom and sides of the pit. And then pipes and channels, they bring river water into the pit. And together, these put pressure on the pit, which then stabilizes the shoreline around it.

• 12:57Speaker 05

  Then you have the pressure against that inflow, and that is the stabilizing force.

• 13:02Emily Kwong?

  Because of the Spray, river water can't be brought in super quickly. And that makes the shorelines not super stable, it sounds like.

• 13:08Speaker 01

  Exactly. And shorelands can also be unstable because of the materials on the sidewalls or of how the waves work once there is water in the pit lake. There is a lot to monitor. And the shoreline has been this ongoing challenge. And the stakes of figuring that out are high. The city of Kappus, also the German state that it's in, Brandenburg, even private businesses, they have invested a lot of money into making this lake accessible to the public. There are plans for houses and businesses by the shoreline. Millions of euros have already been spent on a bike path around the lake. So they are determined to figure this out. With more time.

• 13:56Speaker 01

  And that's what I was struck by as we drove around the lake. Even though the lake is still in progress, there were already people there, just sitting by their cars, beers in hand, enjoying the view. They're already part of the way there.

• 14:14Emily Kwong?

  You know, Will, I hope you can go back to Koppa someday and like, take a swan dive into that lake.

• 14:19Speaker 01

  I'm looking forward to it.

• 14:21Emily Kwong?

  Thank you so much for coming on the show. It was great to have you.

• 14:24Speaker 01

  Thank you so much for having me. So fun to do this with you all.

• 14:28Emily Kwong?

  This episode was produced by Rachel Carlson. It was edited by our showrunner, Rebecca Ramirez. Tyler Jones checked the facts. Kwasi Lee was the audio engineer. Translation help from Alex Passeltiner, my boyfriend who speaks German.

• 14:42Speaker 01

  Thanks, Alex.

• 14:43Emily Kwong?

  Thank you, Alex. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. Thank you for listening to Short Wave from NPR.

• 15:06Speaker 00

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