We’ve been involved in various types of permeable pavement over the years and recently learned of a new “tool” from the toolbox. Pervious Interlocking Concrete Paver Systems (PICP) can be a great asset for use in sidewalks and lower impact traffic areas.

According to this trade organization, a PICP system is comprised of a layer of concrete pavers separated by joints filled with small stones. Water enters joints between solid concrete pavers and flows through an “open-graded” base, with no small or fine particles. The void spaces among the crushed stones store water and infiltrate it back into the soil subgrade. These units are installed over compacted coarse bedding sand, interlocked or installed over compacted aggregate base, depending upon the impact of traffic.

A few specifics on design characteristics:

• A typical PICP paving section is 14” thick.
• Costs vary with size and method of installation, but a range of $6 to $10 per square foot is typical.
• PICP can be used in conjunction with groundwater harvesting systems.
• Maintenance of a system includes annual vacuum truck service.
• PICP does not work well in floodplain areas due to hydrostatic pressure and an overflow effect when overloaded.

Benefits:

• 90% of pollutants are captured and carried into a storm sewer or body of water in the first 1” of runoff.
• There is an elimination or reduction of need for a water detention pond or facility onsite.
• The water is retained under the pavers and recharges the underground aquifers in the natural location as opposed to re-routing runoff into a detention pond.
• Variations of colors in the paver system can yield different SRI values for LEED accreditation.

All in all, this surface makes certain types of paving permeable. PICP creates filtration of stormwater, provides a pretty good number in life cycle cost and has a positive impact on the environmental aspects. The results? Reduction in storm water pipe cost, reduction in storm water pollution and an attractive surface that  is aesthetically pleasing. All this for between $6 and $10 a sf.