Pervious Concrete: the concrete that drinks!
The answer to many Phase II Stormwater Control Problems!
Pervious Concrete is concrete that allows water to flow through it, while still functioning as a conventional pavement.
EPA Approved Best Management Practice (BMP):
Use it as a parking lot to clean up 95% of “first-flush” pollutants. Place the Pervious Concrete parking lot on top of an open-graded stone base, and store the storm water runoff from the pavement surface, and from your roofs by directing your roof drains directly into this open graded stone layer.
The pervious concrete filters out the large sediments, and bacteria that naturally colonize the pavement will biologically breakdown most of the hydrocarbons that drip off of cars. The heavy metals settle out to the bottom layer of the system.
A filter fabric is placed between the sub-base and the open-graded stone layer in order to keep the sub-base from migrating into the storage layer. The storage layer should be designed to hold the locally mandated volume of stormwater. The amount of water that a stone layer will hold varies by location and supplier, but a 30% storage volume is average. Pervious concrete will have between 15 to 25% voids and storage volume.
For example, a 10 inch thick storage layer will hold 3 inches of rainfall, and 6 inches of Pervious concrete will hold 1 inch or more of rainfall.
An over-flow drain is recommended to allow the system to release water at the locally mandated rate, and to keep the system from becomingly completely full, and is mandatory if the sub-base does not perk well.