Changes

===Geometry and Site Layout===

===Space===

[[File:Perforated concrete block alt.jpg|thumb|Parking lot with perforated pavers in stalls only, Singapore]]

[[File:Perforated concrete block alt.jpg|thumb|Parking lot with perforated pavers in stalls only, Singapore]]

Permeable paving can be used for entire parking lot areas or driveways and can be designed to receive runoff from adjacent impervious surfaces. For example, the parking spaces in a parking lot may be permeable pavers while the drive lanes themselves are impervious asphalt. In general, the impervious area should not exceed the area of the permeable paving which receives the runoff.  

Permeable pavements can be used for the entire parking lot, driveway or road surface, or be designed to to receive runoff from adjacent impervious surfaces. For example, the parking spaces of a parking lot or road can be permeable pavements while the drive lanes are conventional asphalt. The impervious area draining on to the permeable pavement should not exceed the area of the permeable pavement itself. Relatively clean drainage areas such as roofs may be up to 4 times the size of the pavement but should include filtration pretreatment to remove coarse debris prior to being conveyed directly to the storage reservoir.

A hybrid permeable paving/[[infiltration chambers|infiltration chamber]] design can feature connection of a roof [[downspout]] directly to the stone reservoir of the permeable paving system, which is sized to store runoff from both the pavement surface and the roof drainage area.

Permeable pavements should be located down-gradient from building foundations. If the pavement does not receive drainage from other surfaces, no setback is required. If the pavement receives drainage from other surfaces a minimum setback of four metres down-gradient is recommended. A smaller setback may be permissible where foundations are protected by a geomembrane.

In most designs, the surface acts as pretreatment to the stone reservoir below. Periodic vacuum sweeping and preventative measures like not storing snow or other materials on the pavement are critical to prevent clogging. Another pretreatment element is to have a [[choking layer]] above the coarse gravel storage reservoir.

===Landscaping===

 

Landscaped areas must drain away from permeable paving to prevent sediments from running onto the surface. Urban [[trees]] will benefit from being surrounded by permeable paving rather than impervious cover, because their roots receive more air and water. Interlocking pavers used around the base of a tree may be removed as the tree grows.

===Site Topography===

Permeable pavement surface slope should be at least 1% and no greater than 5%.  Steeper slopes may require additional features (see subgrade section below).  Pervious areas should not drain onto permeable pavements.

 

Maintaining a separation of one metre between the elevations of the base of the practice and the seasonally high water table, or top of bedrock is recommended. Lesser or greater values may be considered based on groundwater mounding analysis. See Groundwater page for further guidance and a spreadsheet tool.  

To protect groundwater from possible contamination, runoff from pollution hot spots should not be treated by permeable pavements designed for full or partial infiltration. Facilities designed with an impermeable liner (filtration-only) can be used.

 

Also see [[Site considerations]] page.  

===Risk of Groundwater Contamination===

===Risk of Groundwater Contamination===