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. ------- 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. ------- |