Porous Surfaces

Description
Porous surfaces are either placed in lieu of a paved, impervious surface (resulting in a product referred to as porous pavement), or placed as an overlay on an impervious surface (resulting in a product referred to as porous overlay). Porous pavement allows stormwater to infiltrate into underlying soils, or in some cases storage basins. The primary constituents removed include total suspended solids (TSS), total nitrogen and phosphorus, pesticides, total and dissolved metals, microbiological constituents, biological oxygen demand (BOD), and total dissolved solids (TDS). Porous overlays are often placed atop a roadway surface to improve driver safety by reducing glare and eliminating tire spray and hydroplaning. Porous overlays also reduce pavement noise.

Stormwater drains through the porous overlay to the conventional road surface below and then travels along the boundary between pavement types until it emerges as runoff at the edge of the pavement. Preliminary findings in a recent study by the University of Texas at Austin (M. Barrett, Effects of a Permeable Friction Course on Highway Runoff, Journal of Irrigation and Drainage Engineering, September/October 2008) suggest that highways with a porous friction course overlay may provide some pollutant removal (such as total suspended solids) from stormwater runoff. The expected key treatment process is filtration. The expected primary constituents removed include total suspended solids (TSS), total phosphorus, and total metals.

Experience
Caltrans Open Graded Asphalt Pavement Pilot Study
The OGAP Pilot Study is a multi-year study conducted at various sites throughout the state to assess porous pavement overlays as a potential water quality Best Management Practice (BMP). Porous pavement overlays include Open Graded Friction Course (OGFC) and Rubberized Hot Mix Asphalt–Open Graded (RHMA-O). At each site, two systems were constructed to collect runoff from highway sections using (1) porous pavement, referred to as a test site, and (2) Conventional Dense Graded Hot Mix Asphalt (DG HMA), referred to as a control site. Water quality samples from the test sites were compared to those from the control sites.

OWP Tasks
  • Assisted in Study Planning
  • Reviewed Designs of Monitoring Collection Systems
  • Provided Monitoring Assistance
  • Reviewed Data Assessment and Reporting
OWP Contacts: David Alderete