Permeable paving sounds like a great idea. It has all the strength of traditional pavement, but it allows water to drain straight through it. This eliminates the need for overflow channels and gutters, which can make projects from driveways to streets significantly faster to install, and less costly in terms of time and materials. But what about contaminants in the water? After all, pavement is covered in substances you'd rather not have in your water table, from motor oil to antifreeze spills.
How Does Permeable Paving Filter Water?
What happens when water drains through permeable paving? Well, it starts at the top layer. The surface of permeable paving is solid enough to drive on, but it lacks the filler of traditional concrete. So there are little holes that allow water to drain, but don't allow larger debris to enter the pavement. There can still be contaminants in the water, though, such as chemical runoff.
That's where the subsequent layers come into play. These lower layers are designed to catch and trap contaminants the same way filters in water treatment plants do. The idea is to separate clean water from all the baggage it drags down with it, which is why several layers (often meant for catching different kinds of contaminants) are necessary. Once the water has travelled through the entire system, it comes out clean, and ready to rejoin the water table.
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