What is porous pavement:
Porous pavement is a permeable pavement surface with a stone reservoir underneath. 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. Porous pavement often appears the same as traditional asphalt or concrete but is manufactured without "fine" materials, and instead incorporates void spaces that allow for infiltration.

Why consider porous pavement:
Traditional stormwater management practices significantly reduce groundwater recharge has led to a number of environmental concerns in recent years. As infiltration decreases, base flows in streams are decreased and previously flowing, small streams now often dry up between rains. Homeowners and public water suppliers often rely on wells that tap groundwater. Without recharge, the threat exists that these drinking water supplies could dry up rapidly.

Application:
The ideal location for porous pavement is in low traffic or overflow parking areas. 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. Newer applications of porous pavement include uses on some highways to reduce hydroplaning.

Concerns:
Porous pavement poses some challenges in cold weather climates, but is not impossible to use in these areas. Porous pavement should be avoided where activities generate highly contaminated runoff. Areas of low soil permeability, seasonal high groundwater tables, and areas close to drinking water supply wells should also be avoided.

Benefits:
Since the reservoir area underneath porous pavement stores and infiltrates surface runoff, using porous pavement will significantly reduce the amount of land needed for traditional stormwater management measures. Porous pavement increases groundwater recharge, reduces pollutants in stormwater runoff, and helps alleviate flooding and contamination to streams.

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.

Maintenance:
The overall maintenance goal for porous pavement is to prevent clogging of the void spaces within the surface material. The surface of porous pavements must not be sealed or repaved with non-porous materials if it is to continue to function. Areas where sand and salt are applied to roadways or parking lots should not be considered for porous pavements. Occasional sweeping or vacuuming of debris will be required to ensure the void spaces do not clog. Educational signage should be used wherever porous pavement is installed as a teaching tool for the public and as a reminder of maintenance obligations.