Standard paving materials (such as concrete and asphalt) used for driveways, patios, walkways, and parking lots are highly impervious and produce high rates of storm water runoff. Rainfall flows quickly across these paved surfaces, picking up accumulated surface pollutants and draining directly to gutters and storm drains and thence to local creeks and the Bay. The use of permeable paving materials allows rainfall to enter the pavement section and infiltrate into the underlying soils. The three primary permeable pavement technologies are porous asphalt, pervious concrete, and permeable interlocking concrete pavers. All permeable pavements have high initial surface infiltration rates and can immediately infiltrate and store rainfall from most storm events. Permeable pavements rely on the ability of open-graded aggregate in their surfaces and base to receive, store, and infiltrate runoff into the underlying soil. In many cases, storm water runoff from the pavement is completely eliminated.
Rebate Information Install a driveway, patio, walkway, or parking lot using an permeable pavement material and receive a rebate of $1.50 per square foot.
Porous asphalt Porous (or Open-graded) Asphalt pavement contains no fine aggregate particles, thereby creating void spaces between the large aggregate comprising the pavement. This allows water to collect within and drain through the pavement.
Pervious Concrete Pervious concrete is made from carefully controlled amounts of water and cementitious materials used to create a paste that forms a thick coating around large aggregate particles. Unlike conventional concrete, the mixture contains little or no sand, creating a substantial void content between 15% to 25% that allows water to flow through the pavement.
Links to additional information on pervious concrete
Permeable Interlocking Concrete Pavers (PICP) Permeable interlocking concrete pavement is comprised of a layer of specially-designed durable concrete pavers separated by joints filled with small stones and underlain by a base of open-graded large aggregate. The void spaces between the crushed stones store water and infiltrate it into the soil subgrade. Not all interlocking concrete pavements are permeable - there must be openings between the pavers and the openings must be filled with small aggregate (not sand) in order for the pavement to be effectively permeable.
Links to additional information on permeable interlocking concrete pavers
Flexible Porous Pavement Flexible porous pavement consists of a plastic grid structure filled with decorative gravel or planted with grass and underlain by a sandy gravel mixture of base material that promotes infiltration of stormwater.
Links to additional information on flexible porous pavement