About Porous Asphalt
General Information Performance Data Water Quality Treatment Process Design




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System Performance

Water Quality Treatment
The water quality treatment performance of the porous asphalt lot generally has been excellent. It consistently exceeds EPA’s recommended level of removal of total suspended solids, and meets regional ambient water quality criteria for petroleum hydrocarbons and zinc. Researchers observed limited phosphorus treatment and none for nitrogen, which is consistent with other non-vegetated infiltration systems. The system did not remove chloride. However, since it drastically reduced the salt needed for winter maintenance, it may prove effective at reducing chloride pollution. The chart at top right reflects the system’s performance in removing total suspended solids, total petroleum hydrocarbons, dissolved inorganic nitrogen, total phosphorus, and total zinc. Values represent results recorded over a total of two years, with the data further divided into summer and winter components.

Water Quantity Control
The porous asphalt system’s ability to manage runoff was exceptional. It has outperformed all systems tested at UNHSC. No surface runoff has been observed from this lot since its installation in 2004; this includes the 100-year storm events that New Hampshire experienced in 2006 and 2007. Groundwater recharge has been achieved despite the system’s location over clay soils. The figure at bottom right illustrates effective peak flow reduction and long lag times for the range of seasons monitored.

Maintenance
Researchers performed no maintenance on this parking lot since it was installed in 2004. (Typical, annual maintenance calls for vacuuming two to four times.) After two winters, the pavement’s condition remains good, with no frost heaving or rutting. It does have scars from plowing, but these do not impact the asphalt structurally. Only moderate clogging has been observed. Once significant clogging occurs, researchers will vacuum the lot and assess the system’s ability to regenerate infiltration capacity.

Cold Climate
This system’s performance remained steady year round. Some of the highest infiltration rates were in the winter—on average more than 1,000 inches an hour. While researchers observed conditions conducive to frost penetration in the filter media, the pores remain open and drained year round. As a result, freezing and thawing did not limit infiltration. This ability to maintain drainage minimizes freeze thaw, which contributes to the porous asphalt’s durability. In practice, the lifespan of these lots can exceed impervious asphalt lots, which tend to lose structural integrity in northern climates due to frost heaving.

A substantial benefit of porous asphalt is the reduced need for sodium chloride for deicing in winter. Researchers observed that winter maintenance of porous asphalt requires between zero and 25 percent of the salt routinely applied to impervious asphalt to achieve equivalent, or better, deicing and traction.