HEAVY-METAL POLLUTION RELATED TO THE INFILTRATION OF RUN-OFF WATER IN A PERVIOUS ROAD CONSTRUCTION

The fate of Pb, Cu, Cd, Zn and Ni, has been studied in a work located within a car-park associating a porous asphalt and a retention reservoir, and allowing the on-site infiltration of stormwater in the soil. The suspended matters from run-off water contain a large amount of Pb, Cu, Cd and Zn. The metallic pollutions are located in the porous asphalt and close to the infiltration pipes which distribute stormwater in the reservoir. No pollutant effects could be seen in the soil under the work. The porous road construction seems to filter the heavy metals contaminated suspended matter. The risk of heavy metals release from the structure has been studied. During normal conditions of use, the porous asphalt accumulates contaminated particles and, even with deicing salts, run-off water could only release small amounts of toxic metals. In presence of exchangeable ions, complexing agent or moreover acid solution, heavy metals could be easily mobilised from the construction. In order to limit pollution risks it seems to be necessary to clean the porous asphalt and to intercept suspended matters before their entry into the infiltration pipes.