Should you consider porous asphalt pavement for your development or redevelopment project? The case can certainly be made for it, especially in northern climates.
Porous asphalt pavement is the low impact development (LID) stormwater strategy best suited for cold climates, according to Dr. Robert Roseen of the University of New Hampshire Stormwater Center, who spoke at the 19th Annual Nonpoint Source Pollution Conference in Groton, CT. The conference, coordinated by the New England Interstate Water Pollution Control Commission, brought together representatives from federal and state governments, municipalities, and nonprofit organizations to discuss potential partnerships in watershed protection efforts.
Dr. Roseen's presentation focused on the benefits of using porous asphalt pavements in northern climates as a strategy to limit or reduce contaminant loading and to limit impervious covers. The use of standard pavement causes the accumulation of heavy metals, organics, and inorganic compounds in urban snow and rain runoff. Porous pavements, in comparison, have been shown to reduce contaminants, and reduce peak flow, lag time, and runoff volume. These pavements are also more resistant to freezing than standard pavements because of the disconnection to subsurface moisture and because porous pavements thaw much more rapidly.
Some conference attendees questioned the cost effectiveness of using porous asphalt pavement. Dr. Roseen agreed that the concern is justified material costs associated with using the porous materials can run 10 to 20 percent more than the conventional, impervious materials. However, he continued, total project costs may eventually equal those of conventional projects, as the need for infrastructure, such as curbing, catch basins, piping and ponds, is eliminated. In addition, routine weather-related costs associated with de-icing and anti-icing practices are also reduced.
Beyond cost, environmental benefits are realized through the use of porous asphalt pavement. Chlorine-contaminated stormwater runoff from winter treatment, associated with the routine salt application on standard pavement, is toxic to aquatic life, harms drinking water supplies, and is unable to be reduced by treatment but rather only through reduced application.
So why doesn't everyone use porous asphalt paving? First, there are those material costs that developers do not want to absorb. Second, porous asphalt pavement is a system that includes the asphalt at the surface, a stone layer, a finer filter materials (sand to gravel) layer, and a drainage layer, and requires maintenance just as all systems do. Third, there is a certain degree of maintenance sensitivity; the system can clog because it is essentially a filter. Further, during certain winter weather, the porous pavement may require minor salting and plowing to return the surface to high infiltration.
But, Dr. Roseen concluded, the benefits outweigh the disadvantages. In New Hampshire, where he conducted his research, the use of porous asphalt reduced the typical application of salt by 75 percent while still providing the friction required during winter weather. In addition, porous pavement systems require less space than other LID stormwater strategies such as retention ponds. In these systems, rainfall drains through the surface and infiltrates into the subsurface, reducing runoff volume, improving water quality, and eliminating impervious surface while requiring less space than standard pavement. The use of porous pavement also speeds the rate of snow and ice melt, which reduces the need for salt for winter maintenance.
