Permeable Pavements Taking Industry by ‘Storm’
The U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) Rating System is the standard for determining a building’s degree of sustainability. At least two credits toward a LEED certification can be attained by using a permeable pavement stormwater system — one credit for managing rate and quantity of stormwater and another for managing water quality, Wible says. Both are achievable if they are designed and installed properly. There are many other credits available depending if concrete or asphalt surface is chosen including rainwater collected and used onsite, innovation in design, heat island reduction, and others. If a building or property receives enough credits, it is LEED-certified as a sustainable property, which is very attractive when property owners plan to sell or lease a building. Indirectly, this could lead to more properties using the pervious concrete in place of other materials.
Importance of water quality
Water quality is very important. The National Pollutant Discharge Elimination System (NPDES) requirements mandate criteria for a stormwater runoff quality. As mentioned earlier, the silty clay soil may drain slowly, but is better at filtering the water. The sandy loam soil drains quickly, but it is less effective at filtering out dissolved solids. The stormwater that percolates through the system will undergo natural filtering and purification so that the water reaching the groundwater table is close to the same quality as runoff soaking directly into the surface as long as the infiltrating runoff contains only the common, mostly biodegradable, materials. The purpose of naturally treating the water is to prevent pollutants from entering streams, lakes, rivers, or groundwater supplies. Some pollutant sources for parking lots include litter, spills, fertilizers, pesticides, and vehicle pollutants, such as greases and oils.
Permeable pavement and concrete both use a very deep sub-base of crushed aggregate uniformly graded with about 40 percent void space for stormwater storage and recharge.
A study on water quality is currently being conducted on porous asphalt and pervious concrete pavements right now at Villanova University, located outside Philadelphia. “It’s just a matter of waiting for Mother Nature to cooperate,” Kresge says. The project consists of side-by-side, 1,500-square-foot pavement sections divided by a concrete barrier with a waterproof membrane. The RMC Research & Education Foundation in partnership with Villanova University, the U.S. Environmental Protection Agency, and Prince George’s County, Md., is funding the study.
Patrick Jeffers, a Villanova graduate student participating in the study, says the next step is to wait for rain. The pavements must receive a minimum 1/4-inch rainfall to flush the system and calibrate the equipment. Following that, data can be gathered with each rainfall of at least 1/4 inch. The three-year study of water quantity and quality will focus on adjacent pervious concrete and porous asphalt surfaces and will measure both systems’ efficacy in treating polcyclic aromatic hydrocarbons (PAH), phosphorous, nitrogen, metals, total suspended solids (TSS), total dissolved solids (TSD), PH, and conductivity. Additionally, first flush samplers will be used to evaluate any runoff from both pavements.
For more information on pervious concrete or porous asphalt pavements systems, see the following publications:
Porous Asphalt Pavements — National Asphalt Pavement Association. Information Series 131.
Pervious Concrete — National Ready Mixed Concrete Association NRMCA/American Concrete Association ACI pub. ACI 522R-06 Pervious Concrete.
Milan Lipensky is the technical services manager for Pennsy Supply, Inc. in Harrisburg, Pa. Pennsy Supply is a supplier of aggregate, concrete, and asphalt in the Mid-Atlantic region. The company is part of the Mid-Atlantic Group of Oldcastle Materials, Inc.
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