The influence of urban pavements on water chemistry

We studied the influence of different pavement types on water chemistry using recirculating laboratory mesocosms. Pavement types range from roads to sidewalks to parking lots and driveways and are primarily constructed from asphalt concrete and portland cement concrete.  From an aquatic ecosystem perspective, pavements are of concern because water running off these surfaces may carry contaminants such as hydrocarbons, nutrients and metals which can negatively influence receiving waters.  We studied different pavement types by placing 1 m x 1 m pavement slabs into 10 L of water in recirculating laboratory mesocosms for a 2 week incubation followed by chemical analyses of recirculated water.  Pavement types tested were unsealed and sealed asphalt, portland cement concrete, portland cement with fly ash and portland cement with ground-granulated blast furnace slag as well as porous concrete pavement. Pavement types variably influenced pH, hydrocarbon, bromide, chloride, phosphate and sulfate concentrations relative to controls.  Interestingly, porous pavement yielded the highest concentration of mercury and phosphorus in recirculating water relative to the impervious pavement samples.  These data suggest pavement types can directly contribute to contamination of receiving waters.  Further, there is need for continued monitoring of chemicals originating from different pavement surfaces.