Pervious Concrete

Photo by Crag.org

Last summer the Philadelphia Water Department changed the way it bills commercial customers, separating stormwater charges from sewer bills and basing charges on the amount of impervious surface in a parcel. While the changes will help to reduce stormwater runoff, pollution to our water system, flooding and drought, they have also caused businesses to rethink the material used in designing roofs, pathways, sidewalks, parking lots and other normally impervious surfaces.

Because impervious surfaces do not allow water to soak into the ground as nature intends, this reduces the amount of water available for wells and springs and increases the amount of water above ground and the potential for flooding. Another downside is when water sits on a surface it collects pollutants from the air and cars, and during storms excess water that could not seep into the ground, flows across impervious surfaces and sweeps these pollutants into surrounding waters and farther downstream.

The Philadelphia's implementation of stormwater charges is hoped to serve in a catalyst for further green design, and acheive the city's goals laid out in Mayor Nutter's plan for sustainability, Greenworks, which began in 2009.


Here is the way the city calculates stormwater charges:

Stormwater Charge = (Gross Area Rate * Gross Area of Property) +

                                    (Impervious Area Rate * Impervious Area of Property)

By reducing the area of impervious property, business can see a reduction of their water bill, as well as reduction in overflow and flooding. Ways to reduce stormwater include impervious surfaces, such as using products like Empire Blended Pervious Concrete, a pre-blended permeable paving product. It looks just like concrete yet through small voids allow water and air to pass through. Another avenue to stormwater reduction, is installing a green roof. Colbond Enkadrain Mats and Rooflite lightweight.

For further information, check out the Stormwater Basic Information page.