United States
Environmental Protection Agency
 Office of Water (4203)
Washington, DC  20460
EPA-841-B-00-005B
     October 2000
Field  Evaluation  of

Permeable  Pavements  for

Stormwater Management
Olympia,  Washington

   Introduction

   This study demonstrates the potential of
   permeable pavement systems to restore soil
   infiltration functions in the urban landscape. It is
   based on the results of a project that included
   installing and monitoring several porous
   pavement systems in a parking area. The project's
   objectives were to

      -  Review existing information on permeable
         pavements

      -  Construct full-scale test sites
      -  Evaluate the long-term performance of
         these systems

   The report outlines the difficulties encountered,
   costs of installing and maintaining the systems,
   performance based on existing soil systems,
   special benefits of filling the open cells with grass
   as opposed to gravel, and other water quality
   benefits.

   Project Area
   The demonstration site was in an office
   parking lot in Olympia, Washington. Two
   adjacent parking stalls were constructed
   using four types of permeable  pavement
   systems that consisted of a combination of
   grass and gravel, as shown in Figure 1. The
   designs were

      1.  A flexible system consisting of a
         plastic network of cells with grass
         infill and virtually no impervious
         area coverage.
      2. A flexible system consisting of a
         plastic network of cells similar to
         design 1 but filled with gravel.
            Key Concepts:
            > Structural Controls
            > Volume Reduction
            > Space Savings
      LOW-IMPACT
      DEVELOPMENT
        CENTER
            Project Benefits:

            >  Elimination of Stormwater
                Ponds
            >  Demonstration of Water
                Quality Benefits
            >  Lower Maintenance

              3.  A system consisting of impervious blocks
                 with the space between the blocks filled
                 with grass. (Total surface area is 60
                 percent impervious).

              4.  A system consisting of impervious blocks
                 with the space between the blocks filled
                 with gravel. (Total surface area is 90
                 percent impervious).


           A control stall was constructed out of traditional
           asphalt. A system of pipes, gutters, and automatic
           sampling gauges was installed to collect and
           measure the quantity and chemistry of surface
           runoff and subsurface infiltrate. Figure 2 shows a
           schematic of the test facility.
      Figure 1. Different types of permeable pavement. From top
      left: reinforced gravel and grass pavement, reinforced grass
      pavement, 60% impervious concrete blocks with grass, 90%
      impervious blocks with gravel.

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     ASPHALT
     CONTROL
90% IMPERVIOUS BLOCK
    W/GRAVEL
60% IMPERVIOUS CONCRETE
   BLOCK W/GRASS
                                                         REINFORCED GRASS PAVEMENT
REINFORCED GRAVEL AND
  GRASS PAVEMENT
                                   TREATED 2x8 LUMBER BETWEEN
                                   •TRIAL PAVING SYSTEMS
                                        I 1/2 ROUND
                                        \Jf
      TIPPING BUCKET
      FLOW MEASUREMENT
      EQUIPMENT
 Figure 2. Schematic of the test facility showing treatments and runoff collection devices.
Project Summary and Benefits
The results of this study showed the following
relationships:

   -  The use of permeable pavement systems
       dramatically reduced surface runoff
       volume and attenuated the peak discharge,
       as shown in Figure 3.

   -  Although there were significant structural
       differences between the systems, the
       hydrologic benefits were consistent.

   -  Storm characteristics and weather
       conditions influenced the hydrologic
       responses of the systems.

   -  Permeable pavement system types vary
       widely in cost and are more expensive
       than typical asphalt pavements. Cost
       comparisons between permeable pavement
       installations and conventional ponds or
       underground vaults are limited. However,
       the elimination of conventional systems
       and reduced life cycle and maintenance
       costs can result in significant cost savings
       over the long term.

   -  A significant contribution of permeable
       pavements is  the ability to reduce effective
       impervious area, which has a direct
       connection with downstream drainage
                                        systems. This strategy of hydrologic and
                                        hydraulic disconnectivity can be used to
                                        control runoff timing, reduce runoff
                                        volume, and provide water quality
                                        benefits.

                                 Contact Information
                                 Derek Booth, Director
                                 Center for Urban Water Resources Management
                                 Box 3 52700
                                 Roberts Annex 100
                                 (206)543-7923
                                 dbooth@u.washington.edu
                                         ---  Asphalt
                                         —  60% impervious concrete
                                             block w/grass
                                                       Time (minutes)
                                  Figure 3. Runoff volumes from asphalt and permeable
                                  pavements.

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