By Daisy LeBlanc, Clean Water Institute Intern, Summer 2022
What is Permeable Pavement?
Permeable pavement is a mitigative stormwater management strategy that allows water to pass through the surface of the pavement into a stone reservoir before infiltrating into the ground. Permeable pavement prevents stormwater generation, allows stormwater to infiltrate the ground once it’s created, and removes pollutants from stormwater. As a result, permeable pavements reduce contamination from and in stormwater runoff by reducing the stormwater and pollutant concentrations going into storm drains. This also resupplies the groundwater while circulating water and air into plants’ root systems. They also lead to less salt on the roads, another ecological benefit, because they cause snow and ice to melt faster.
Pervious pavement is designed with three layers for water to move through. First, water meets a layer of permeable surface and drains into the underlying second layer of uniformly graded stone bed which provides temporary storage and promotes infiltration. The water then slowly drains into the third layer of uncompacted soil, which acts as an infiltration bed. This bed is top-lined with geotextile fabric to separate it from the stone bed. From here, water can return to groundwater supplies.
Types of Permeable Pavement
There are a few different types of permeable pavements. The first are porous asphalt and pervious concrete, which both are similar to traditional pavement, but have a reduced sand concentration to create better porosity. These pavements have better traction than traditional asphalt or concrete. Next, Permeable Interlocking Concrete Pavement (PICP) utilizes spaces in the concrete to allow water to infiltrate to the ground.
Homeowners can achieve meaningful environmental benefits by installing pervious structures to areas that otherwise do not allow for drainage (driveways, parking areas, walkways). This can be done by installing impervious materials like asphalt, concrete, or brick with gaps between for pervious materials like gravel, sand, and vegetation. Traditional gravel driveways, though, do no qualify as permutable pavement because they do not allow for infIltration, creating storm water runoff.
Permeable pavement, while more expensive to install, can be very cost effective in relation to traditional pavement. The savings in maintenance and stormwater management costs make up for higher per foot construction. For example, in Pennsylvania, permeable pavement costs about seven dollars per square foot to install, whereas asphalt alone costs about two dollars per square foot. But when considering the full construction costs including stormwater management, typical asphalt construction comes to more that fifteen dollars per square foot. The exact cost of installation depends on site conditions as well as the level of stormwater management needed.
Some limitations of permeable pavement reduce the spaces appropriate for installation. For example, permeable pavement is not as strong as traditional asphalt, so it is not recommended for areas with high volumes of traffic or heavy loads like highways and busy roads. Moreover, permeable pavement is not for “stormwater hot spots” with hazardous material, whether it is being loaded or unloaded, stored, or if there could be spills or leaks.
Permeable pavement can be used by businesses, government spaces, and homeowners to reduce the amount of storm water runoff. Before installing a permeable pavement, one must consider the type, area, and cost. While permeable pavement Is not suited for every location, it can be a cost-effective way to contribute to clean water practices.
Bureau of Watershed Management, “Pennsylvania Stormwater Best Management Practices Manual,” Department of Environmental Protection, 2022, http://www.stormwaterpa.org/bmp-manual-introduction.html
County Conservation District, “Using Smart Growth Techniques as Stormwater Best Management Practices,” United States Environmental Protection Agency, 2022, https://lancasterconservation.org/~lancatd6/wp-content/uploads/Stormwater-BMPs-smart-techniques-1.pdf.
National Pollutant Discharge Elimination System, “Permeable Pavement,” United States Environmental Protection Agency, 2022, https://www.epa.gov/system/files/documents/2021-11/bmp-permeable-pavements.pdf#:~:text=Description%20Permeable%20pavements%20are%20a%20stormwater%20control%20that,pervious%20concrete%20and%20permeable%20interlocking%20concrete%20pavement%20%28PICP%29
State Transportation Innovation Council, ”Pervious Pavement,” Pennsylvania Department of Transportation, 2022, https://www.penndot.pa.gov/about-us/StateTransportationInnovationCouncil/Innovations/Pages/Pervious-Pavement.aspx