Page 421 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

Low-Impact Development and Stormwater Issues 381

Permeable Pavements
Another novel group of LID practices includes the various permeable pavements.
Permeable pavements serve as a structured surface for vehicles, bicycles, or pedestrians,
while also aiding in stormwater management. There are various different types of
permeable pavements, but the four main categories are permeable pavers, permeable
grids, porous asphalt, and pervious concrete. Permeable paver placements are typically
made with traditional impermeable pavers such as brick or concrete precast pavers,
although there are some pervious pavers being marketed. With the traditional pavers,
the water infiltrates to the ground below through the interstitial spaces between the
pavers.
Permeable grid systems have a grid made up of various materials such as concrete
or plastic with open spaces filled with usually gravel or grass in between. The grass-
filled grid systems are usually placed where grass is desired, but occasional traffic will
be in that location such as for fire lanes around schools or for occasion parking for large
events at campuses or arenas. Both porous asphalt and pervious concrete are similar to
traditional asphalt or concrete placements, except that the materials are designed and
carefully placed with an interconnected void structure which allows water to pass
through the pavement. Both of these systems usually allow water to pass at a very rapid
rate and are frequently part of a layered system with an aggregate sub-layer for
additional below-ground water storage. These additional layers are used when placed
over poorly draining soils to allow time for the water to infiltrate and also for additional
loading capacity for the pavement system. Porous asphalt and pervious concrete are
becoming popular pavement alternatives in parking lots, for trails and for low volume
streets. Figure 10.1.14 is a photograph of a pervious concrete parking lot in Oregon.
It is important that standards, specifications, and testing methods are developed for
these novel pavements for municipalities to use in determining acceptance and also for

FIGURE 10.1.14 Pervious concrete parking lot in Salem, OR. (Photograph courtesy Scott
Erickson of Evolution Paving taken November 2009.)