This Huge Mining Pit Is About To Be A Lake
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Hey, Short Wavers. Emily Kwong here, and I am joined by Planet Money producer Willa Rubin. Willa, hey, what's up? Hey, Emily. Hey, Short Wave. I come to you with a story. All right, let's hear it. So about two hours southeast of Berlin, there's a city called Cottbus.

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. Oh, interesting. I've never heard of this. Okay, lignite. 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 Cottbus has a really interesting plan.

And one sweltering day in September, I went to go see one of these pits. Ooh! 20 minutes east of the city. Hello. It's great to have you here. At the train station, I met up with Stefan Simonidis-Noak. Here we are. Stefan has lived in Cottbus for a long time. He works for the city council, and he's an urban planner working here. Okay.

Welcome to the Kotbuss Lake. Wait, did he just say lake? 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, Kotbusser Ostsee.

In German, that literally means Cottbus East Lake, okay? But it's also a play on words that means Cottbus Baltic Sea. And that is like the dream that Stefan and his colleagues are chasing. A mini Baltic Sea right near the city center. I'm really a fan of the Baltic Sea and the shorelines and big sandy beaches and waterfalls.

And we will have this here. The Cottbus Beach is a really huge one. 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. And I'm Willa Rubin. You're listening to Shortwave, the science podcast from NPR. ♪

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Learn about this comprehensive approach to planning at edwardjones.com slash findyourrich. Edward Jones, member SIPC. All right, Willis, so let's pick up where we left off. You get off the train and caught bus to see the lake. What does it look like? Emily, this lake is huge. That was my first impression. But honestly, what really took me aback were all the birds.

And it's also planned to have natural habitat on the eastern shoreline, which will not be developed by building. It will be left for the nature like it is. 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. Everything is so slow. Planning takes a lot of years and time.

But it's also exciting. 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. 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? To some extent, of course, yes.

Yeah, because I like my job and my research. Martin is a research professor at the Helmholtz Center for Environmental Research. He has written a lot about post-mining leaks in eastern Germany and around the world. 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

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

When you stop mining, groundwater starts to creep back up to the surface. And what do you mean by groundwater? 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. Absolutely not. Then when mining stops, that dewatering process also stops. Then the groundwater is flooded.

rebounding and the former mining hole becomes a lake. Basically, they switch off some pumps and then groundwater starts coming back into these pits. Well, then that's it. Bada bing, bada boom. Isn't that easy? You just like stop mining and it turns into a lake. Like kind of, sort of, not really. Because you start to get water filling up the pit, which is great. Yeah. 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. Because when that groundwater comes back up to the surface, it often comes into contact with oxidation products of pyrite,

This is a shimmery, golden-looking mineral. Sometimes it's called fool's gold. And it can cause a lot of problems. 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,

And that makes sulfuric acid. Yikes. Yeah, you do not want to be swimming in water that's sulfuric acid. 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. Oh, gosh. Okay. So when this happens, how do engineers, urban planners, scientists like react? How do they treat it? So there's a couple 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. I hear that. So is there a better method for addressing this acidification issue when the lakes start filling up with groundwater? Add water from rivers. You know, get some fresh water in the mix. 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. The science of this is so cool, how to neutralize a lake in the making. So how does this apply to the one in Cottbus? They're obviously trying to do this on a massive scale. Yes. So, okay, so part one of this playbook, which is, you know, neutralizing the groundwater's acidity, so far in Cottbus, they have managed to do this without limestone powder.

Since 2019, lake designers have been flooding the pit with water from the Spree River, which goes up to Berlin. And now the pH is about 8. We love it. And Stefan, the urban planner for the lake, says that the flooding is even on track to finish next year. Very cool. Okay, so the lake is almost to the level they would like. But

But Emily, they are not the 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, it's

All that means that the Spree River isn't getting as much water as it used to, like from mines that were once pumping a lot of water into the Spree. So now everyone is sort of taking turns, making agreements, essentially competing for an increasingly limited resource.

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. That is sort of a cash 22 to all of this, huh? Yeah, exactly. And for the Codbuster Osei, this has contributed to why the flooding has taken a while, which has also contributed to another problem.

Oh.

And together, these put pressure on the pit, which then stabilizes the shoreline around it. Then you have the pressure against that inflow, and that is the stabilizing force. Because of the spray, river water can't be brought in super quickly, and that makes the shorelines not super stable, sounds like. Exactly. And shorelines 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 Cottbus, 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. 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. You know, Willa, I hope you can go back to Cottbus someday and, like, take a swan dive into that lake. I'm looking forward to it. Thank you so much for coming on the show. It was great to have you. Thank you so much for having me. So fun to do this with you all. This episode was produced by Rachel Carlson. It was edited by our showrunner, Rebecca Ramirez.

Tyler Jones checked the facts. Kweisi Lee was the audio engineer. Translation help from Alex Paseltiner, my boyfriend, who speaks German. Thanks, Alex. 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 Shorewave from NPR.

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