UDFCD position on the use of porous asphalt pavement

In April 2008, UDFCD worked with the Colorado Asphalt Pavement Association (CAPA) and several pavement contractors to install a porous asphalt demonstration pad in front of the City and County of Denver's Wastewater Management building.  This site has been monitored regularly to determine if porous asphalt can maintain the minimally acceptable infiltration rate for any permeable pavement in the UDFCD region, which we have determined to be:

For the UDFCD-recommended impervious tributary area/pavement area ratio of 2:1, this minimally acceptable infiltration rate is equal to 20 inches per hour.  Over a few years, the infiltration rate at this site and several other porous asphalt installations in the UDFCD region fell below this minimum standard and that cleaning with reasonably available methods and equipment were generally not successful in restoring infiltration rates to the minimum acceptable level. To properly clean porous asphalt on a commercial scale, regenerative air or vacuum sweepers are recommended.  More intensive cleaning with power washers and higher efficiency vacuums was performed at some of these sites by CAPA and they were generally able to restore infiltration rates via these more extreme methods.

UDFCD considers porous asphalt an adequate BMP for use in locations where clogging sources are minimal, traffic volume is low, and maintenance is regular and intensive, but our experience indicates that such locations are rare.  The intent of the USDCMV3 has always been to include only stormwater BMPs can be widely used throughout the UDFCD region and that have a good chance of success in capturing and treating the full design volume of stormwater over the life of the BMP with only reasonable maintenance practices and readily accessible equipment.

For this reason we will not at this time include porous asphalt pavement in the USDCMV3 and we further recommend both caution and realistic expectations in regard to performance and maintenance costs when implementing this particular permeable pavement.

This memorandum applies only to porous asphalt pavement.  UDFCD continues to monitor and to recommend the use of other permeable pavement technologies found in the USDCMV3 such as permeable interlocking concrete pavement (PICP), concrete grid pavement, porous gravel pavement, and reinforced grass pavement.  UDFCD will continue to monitor advances in porous asphalt composition, mixing and placing, and will update this position as appropriate.

Source: www.udfcd.org