4.6 Permeable Pavement

Pavement for vehicular and pedestrian travel generates roughly twice the impervious surface cover of buildings. While essential for the movement of people, goods, and services, vehicular pavement generates significant levels of heavy metals and most hydrocarbon pollutants in stormwater (Ferguson, 2005). The concentration of pollutants (specifically metals and hydrocarbons) in vehicular pavement surface flow, in general, increases with traffic intensity (Ferguson, 2005 and Colandini et al., 1995).

Both pedestrian and vehicular pavements also contribute to increased peak flow, flow durations, and associated physical habitat degradation of streams and wetlands. Effective management of stormwater quality and quantity from paved surfaces is, therefore, critical for improving fresh water conditions in eastern Washington.

Properly designed, constructed, and maintained permeable pavement can be an effective design solution in cold weather climates. Permeable pavement use is geographically widespread throughout the United States and has been used in arid climates such as Tucson, Arizona, wet climates such as areas of western Washington and Florida, and areas with significant seasonal temperature variation such as Ohio and Minnesota.

Permeable paving surfaces are an important management practice within the LID approach and can be designed to accommodate pedestrian, bicycle, and auto traffic while allowing infiltration, treatment, and storage of stormwater. The general categories of permeable paving systems include:
  • Porous hot or warm-mix asphalt pavement, a flexible pavement similar to standard asphalt that uses a bituminous binder to adhere aggregate together. However, the fine material (sand and finer) is reduced or eliminated and, as a result, voids form between the aggregate in the pavement surface and allow water to infiltrate.
  • Pervious Portland cement concrete, a rigid pavement similar to conventional concrete that uses a cementitious material to bind aggregate together. However, the fine aggregate (sand) component is reduced or eliminated in the gradation and, as a result, voids form between the aggregate in the pavement surface and allow water to infiltrate.
  • Permeable interlocking concrete pavements (PICP) and aggregate pavers. PICPs are solid, precast, manufactured modular units. The solid pavers are impervious, high-strength Portland cement concrete manufactured with specialized production equipment. Pavements constructed with these units create joints that are filled with permeable aggregates and installed on an open-graded aggregate bedding course. Aggregate pavers (sometime called pervious pavers) are a different class of pavers from PICP. These include modular precast paving units made with similar-sized aggregates bound together with Portland cement concrete with high-strength epoxy or other adhesives. Like PICP, the joints or openings in the units are filled with open-graded aggregate and placed on an open-graded aggregate bedding course. Aggregate pavers are intended for pedestrian use only.
  • Grid systems made of concrete or plastic. Concrete units are precast in a manufacturing facility, packaged and shipped to the site for installation. Plastic grids typically are delivered to the site in rolls or sections. The openings in both grid types are filled with topsoil and grass or permeable aggregate. Plastic grid sections connect together and are pinned into a dense-graded base, or are eventually held in place by the grass root structure. Both systems can be installed on an open-graded aggregate base as well as a dense-graded aggregate base.

Nomenclature for permeable paving systems varies among designers, installers, and geographic regions. For this Manual, permeable pavement is used to describe the general category of pavements that are designed to allow infiltration through the pavement section. The following terms are used throughout this Manual and represent the major categories of permeable pavements that carry vehicular as well as pedestrian traffic: pervious concrete, porous asphalt, permeable interlocking concrete pavements, and concrete and plastic grid pavements.

Fig 4.6.1
Permeable pavement. Source: HDR Engineering