PROFILE

BMP Manual reference: BMP 6.4.1

Concept
Pervious pavement sometimes also called porous asphalt or porous pavement, consists of a permeable surface course underlain by a uniformly-graded stone bed. Stormwater drains through the surface, is temporarily held in the voids of the stone bed, and then slowly drains into the underlying, uncompacted soil mantle.

Stormwater Function
• Volume Reduction: Medium
• Recharge: Medium
• Peak Rate Control: Medium
• Water Quality: Medium

Potential Applications
• Residential: Limited
• Commercial: Yes
• Ultra Urban: Yes
• Industrial: Yes
• Retrofit: Yes
• Highway/Road: Limited

Special Maintenance Considerations:
• Prevent Clogging of Pavement Surface with Sediment
• Vacuum pavement 2 or 3 times per year
• Maintain planted areas adjacent to pavement
• Immediately clean any soil deposited on pavement
• Do not allow construction staging, soil/mulch storage, etc. on unprotected pavement surface
• Clean inlets draining to the subsurface bed twice per year

Site:
• Morris Arboretum
  Philadelphia County, PA

DETAILS

Description
Pervious pavement is a permeable pavement surface with a stone reservoir underneath. It is some times referred to as porous asphalt or porous pavement. The reservoir temporarily stores surface runoff before infiltrating it into the subsoil. Runoff is thereby infiltrated directly into the soil and receives some water quality treatment. Pervious pavement may consist of pervious / porous asphalt, pervious concrete, or pervious pavers. The pervious surface often appears the same as traditional asphalt or concrete but is manufactured without "fine" materials, and instead incorporates void spaces that allow for infiltration.

Uses
Pervious pavement is ideal for parking lots, walking paths, sidewalks, playgrounds, plazas, tennis courts, and other similar applications. It can be used on driveways where a homeowner is aware of its stormwater functions, limitations, and maintenance requirements. In extremely dense urban areas porous pavement has been used successfully in redevelopment projects, since it treats and stores stormwater without consuming extra land. Porous pavement can also be used on individual sites where a parking lot is being resurfaced.

Benefits
Since the reservoir area underneath pervious pavement stores and infiltrates surface runoff, its use can significantly reduce the amount of land needed for stormwater management measures. Studies have shown that pervious systems are very effective in reducing contaminants such as total suspended solids, metals, and oil and grease. When designed, constructed, and maintained properly, pervious pavement with underlying infiltration systems can dramatically reduce both the rate and volume of runoff, recharge groundwater, and improve water quality in nearby rivers and streams.

Properly installed and maintained pervious / porous pavement has a significant life-span: systems that are more than twenty years old continue to function.

Concerns
Pervious pavement is not recommended for high traffic areas because of the potential for clogging, nor is it a good idea for stormwater “hotspots” which generate highly contaminated runoff with a higher than usual concentration of pollutants. Areas of low soil permeability, seasonal high groundwater tables, and areas close to drinking water supply wells should also be avoided.

Pervious pavement can present some challenges in cold weather climates and requires planning when it comes to plowing, use of road salt, and other winter maintenance measures, but it is not adversely affected by freeze-thaw cycles. It also has less of a tendency to form black ice and can provide better traction in snow and rain conditions than traditional asphalt and concrete.

Pervious / porous pavement is most susceptible to failure because of problems that arise during construction, so it is important that care is taken during construction to prevent:

• Compaction of underlying soil
• Contamination of stone sub-base with sediment and fines
• Tracking of sediment onto pavement
• Drainage of sediment laden waters onto pervious surface or into constructed bed

Careful staging, construction practices, and erosion and sediment control must all be taken into consideration when using pervious pavements.

Maintenance
The overall maintenance goal is to prevent clogging of the void spaces within the surface material and the underlying infiltration bed. The surface of pervious pavement systems must not be sealed or repaved with non-porous materials if the system is to continue to function. Occasional (bi-annual) sweeping or vacuuming of debris is recommended to keep the system clean and prolong its life span. Pavement washing systems or compressed air units are not recommended.

Planted areas adjacent to pervious pavement should be well maintained to prevent soil washout onto the pavement. Superficial dirt does not necessarily clog the pavement voids, but dirt that is ground in repeatedly by tires can lead to clogging. Trucks and other heavy vehicles should be prevented from tracking dirt onto the pavement and construction or hazardous materials carriers should be prohibited from entering a pervious pavement lot.

Cost
Costs of porous pavement installation depends on the application method chosen. Materials costs are often higher for porous paving applications but this expense can usually be offset by the need for less land, piping and other materials that would otherwise be required for traditional stormwater management practices.

RESOURCES

PA DEP Manual BMP 6.4.1: Pervious Pavement with Infiltration Bed

NEMO Permeable Pavements Resource Center

Lake Superior Site Design Toolkit

From Stormwater Journal--Porous Pavement: New Findings about Functionality and Performance

Stormwater Manager’s Resource Center Fact Sheet