How landfills work
By Marshall Brain
http://www.JewishWorldReview.com | (MCT) Every day the average American creates four to five pounds of trash. That's more than half a ton per person per year. If a million people live in your city, its more than a billion pounds of trash per year city-wide. And we don't really think about it. The trash truck comes once a week and takes it all away.
But your trash doesn't evaporate once it leaves your house. It goes to a landfill. A landfill has to act like vault that holds billions of pounds of trash essentially forever. A good bit of the trash you generate today will be around for centuries. Because your trash will last so long and because it contains all sorts of bad stuff - chemicals, diseases, heavy metals, etc. - the technology behind landfills has gotten pretty sophisticated. A landfill a lot more than a big hole in the ground. Let's take a look at how a modern landfill really works.
A typical landfill today starts with a huge piece of land. The landfill itself might be 200 acres, and it will be surrounded by many more acres to provide access and buffers. The first step to creating a landfill is to create a giant waterproof area where the trash will go. To do that, the entire landfill area is covered with two feet (or more) of hard-packed impermeable clay, and then the clay is covered with a thick layer of plastic.
The reason for this waterproof layer is to stop anything inside the landfill from leaking out. Think of all the things that end up in a landfill - stuff like diapers, strong cleaning solutions, paint, rusting metal, motor oil, corroding batteries, electronic components covered in lead and all sorts of other nasty stuff. Plus there is rain falling on the landfill all the time and percolating through the trash to hurry these chemicals along. If this kind of stuff leaks into the groundwater or nearby streams and rivers, it creates a major environmental disaster. The clay and the plastic liner keeps all the toxic liquids where they belong.
However, there needs to be a way to drain all of the water and chemicals off the liner. If you just left it there, the landfill would become a giant stinking lake of toxic ooze. So on top of the liner goes a thick layer of gravel and dirt and miles of perforated drainage pipes. These pipes gather and drain away any liquid that collects in the landfill. A big landfill will create tens of thousands of gallons of drainage every day. The pipes collect it and send it to a treatment plant.
Now that you have a waterproof basin and a system of collection pipes, the trash trucks can start arriving. They dump their trash into the landfill in a very organized way. The landfill will take a day's worth of trash and compact it into a "cell". Compacting the trash is important because it means that the landfill will last longer. The usual way to compact the trash is to drive over it again and again with heavy bulldozers. Then the cell is covered with six inches of dirt and compacted again.
The dirt seals the cell and does three things: 1) it keeps the smell down, 2) it keeps animals like seagulls and rats away from the trash, and 3) it helps the rain to run off the trash rather than soaking in. New cells are added to the landfill and sealed every day, and the landfill gets a little taller every year.
As the landfill fills, a new problem appears: The landfill starts to produce methane. Bacteria begin digesting the trash and methane is one thing that the bacteria produce. The methane is almost identical to natural gas, so a modern landfill will drill wells into the landfill, harvest the methane and either burn it off or use it as a source of energy. The landfill will produce methane for decades.
Eventually the mountain of trash will become hundreds of feet high and it is time to close the landfill. The landfill is covered with a thick layer of plastic and a couple feet of dirt. Then it is planted with shrubs and grasses. You can't plant trees because their roots would punch through the plastic and ruin the seal. The municipality will usually continue to handle the wastewater flowing out the bottom of the landfill, to harvest the methane coming up to the top, and to manage the grassy mountain as some kind of park.
Obviously this is not a perfect system. In an ideal universe, every single piece of trash would be recycled and there would be no need for landfills. But the universe is not ideal today. Perhaps in the future we will come up with a way to process all of this trash and recycle it. Then we will be able to dismantle all of these landfills and do something useful with the trillions of pounds of trash that they contain.
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