The U.S. Environmental Protection Agency recently announced that it would start testing a variety of permeable pavements, surrounded by rain gardens, at an Edison, New Jersey, parking lot to see which are the most efficient at keeping pollutants like motor oil and pesticides out of storm drains.
Permeable pavement acts like a water filter, allowing water to soak through the surface into sandy soils beneath, where the water feeds lawns or evaporates back into the air. It helps reduce erosion, as well as the amount of pollution that washes into rivers and streams.
Impermeable surfaces, on the other hand, can act like log flumes, overwhelming storm systems and water-treatment facilities to the point that they overflow, and sometimes even carry raw sewage into waterways. "With asphalt, all you ask is for it to carry a load and shed water," says William F. Hunt III, PhD, associate professor in the biological and agricultural engineering department at North Carolina State University. "That's why they're so efficient, and the reason impermeable pavement was developed and became the standard."
Porous concrete and other surfaces are so efficient at managing runoff that they're used on all the interstates in Georgia and Oregon.
With winter snows and springtime snowmelts just around the corner, it might be time to rethink your asphalt, and here are three reasons why:
#1: It's simply nicer-looking. When most people think "permeable pavement" they also think "gravel driveways." But if you're not a fan of the nostalgic crunch of gravel, opt for attractive permeable-concrete paving stones that are more efficient at absorbing water than gravel, and require less maintenance, says Hunt. "The fact that they're very attractive is their big selling point. They tend to run a little more in terms of cost than pervious asphalt or pervious concrete," he says, but if you want to blend in with your neighbors, the latter two—pervious asphalt and pervious concrete—look virtually identical to their impervious counterparts, and will cost you a little bit less.
#2: It's healthier for you, too. One of the things that keeps regular asphalt impervious is a chemical sealant made from coal tar, which itself contains cancer-causing chemicals called polycyclic aromatic hydrocarbons (PAHs). The PAHs collect in dust, which you can inhale during a dry season, and they wash off into streams where they collect in mud—which then has to be treated as hazardous waste—and in fish that you eat.
#3: You may get paid for it. Montgomery County in Maryland offers homeowners $1,200 to rip up their old asphalt driveways to install permeable surfaces. Call your local county environmental protection office or department to see if similar programs exist in your area.
If you're interested in installing a porous driveway, Hunt says there are a few things you should know before switching on the jackhammer. "A lot of it comes down to what the area around your driveway is like. If the area is very stable, without a lot of windblown dust, then the systems will work a long time and work quite well," he says. Dust from gardens, fields, or deserts can clog permeable pavement and prevent the water from draining. Also, permeable options work better if you have sandy soils, which bear weight better than a soil that gets wet when it expands, like clay, he notes. That makes a difference if you're using the pavers for a driveway, but it won't matter much if they're serving as a walkway between your home and a garden.