Peak Performance

Permeable Pavement

A Hole-y Responsible Choice

By Maria Harding

As populated areas expand, their roads, parking lots, and residential pavement take up more and more space. Rain runoff from these paved areas carries petroleum-based contaminants and other toxic chemicals. Traditionally designed pavement will direct runoff to gutters, gullies, and then sewer networks to eventually empty directly into natural water reservoirs such as lakes and rivers. Runoff poisons our bodies of water and can lead to dangerous flooding and erosion.

Permeable pavement is gaining attention as a partial solution to reduce the damage done to lakes and streams and the surrounding areas. As a homeowner, you can be part of the solution by replacing traditional impervious concrete with permeable pavement on your driveway, sidewalks, or garden patio.

Permeable pavement can include a variety of paving techniques, including pavers, plastic grids, and permeable poured pavement. What they have in common is that they are porous, allowing storm water to filter into the earth below, replenishing natural underground aquifers. When a large volume of water comes quickly, it is stored in reservoirs beneath the pavement, allowing the water to soak into the ground gradually.

As water filters through the pavers, through the soil sediment, and through ground roots, many pollutants are filtered out or broken down by bacteria before the water returns to an aquifer source, our primary natural source for drinking water. These aquifers have become severely depleted by the expansion of cities and impervious pavement.

Many municipalities already require that newly-constructed parking lots have green features like permeable pavement. Dense urban areas without nearby lakes and streams are using permeable pavement to reduce reliance on sewer systems. Pedestrian areas such as outdoor shopping centers and college campuses are using permeable pavement as a way to avoid puddles and dangerous slippery spots.

If trees grow near paved areas, using permeable pavement can allow them to grow to their full potential and to be more safely rooted. Permeable pavement allows for air and water to reach the rooting zone more effectively than impervious surfaces. Trees, in turn, contribute to urban canopies, soaking up stormwater and air pollution, providing cooling shade, beautifying neighborhoods, and helping to slow traffic.

Individual pavers, permeable asphalt, permeable concrete, and plastic grids are all possible paving materials. Individual pavers look like traditional cobbled surfaces, but the stones themselves are more porous and the material between individual stones allows water to pass through. Varied stones can even be used to create gorgeous mosaic patterns. Permeable asphalt and permeable concrete look very much like their impervious counterparts, but the aggregate stones tend to be larger. You may have seen similar material used around swimming pools to avoid slippery surfaces. Installation for either permeable option tends to be more expensive than traditional material because of the deeper dig and supporting rock reservoir. Plastic grids function much like individual pavers, but they are made of recycled plastic and have a more industrial geometric pattern. Many designs allow for grass or other ground-cover plants to grow right through the grid.

You may wonder if permeable pavement is more vulnerable to cracking and deterioration due to repeated cycles of freezing. In fact, because permeable pavement is porous and moisture does not remain on the surface during daytime thaws, ice buildup and expansion damage is decreased. The underlying rock reservoir also acts as an insulating layer of air, which reduces surface freezing as well as soil frost depth. Thus, permeable paving materials may offer a winter safety benefit to residential walkways and driveways.

It’s important to rely on the guidance of an experienced installation company. A professional installer will evaluate the quality of soil to be paved. When paving over clay or low-draining soils, the depth of the rock base reservoir should be increased, allowing for more water volume capacity as it absorbs slowly into the soil. A professional installer will also help you decide if there are some areas that should be left impermeable—for instance, sections of pavement that are directly at your home’s foundation.

You can ask your pavement specialist about any regular maintenance or cleaning that may be needed to keep your pavement filtering properly. Some adjustments to your seasonal routine may be required. One example is that sand should not be used on permeable pavement in the winter, as the small grains may plug the porous openings. Your installer may recommend periodic vacuuming with specialized equipment.

If the pavement at your home is in need of a face lift, consider making a conscious choice for the environment by installing permeable pavement. Speak to an experienced paving company about the varied, durable, and beautiful options available.

Sources for this article included: usgs.gov, epa,gov, and stormwater.pca.state.mn.us.