IMPACT OF A POROUS PAVEMENT PARKING LOT ON SUBSURFACE WATER QUALITY

Accidental or diffuse release of pollutants, for example from urban and industrial areas, including those resulting from widespread application of agrochemicals, clearly impinges on the quality of surface and ground water. A major contributor to the pollution problem is stormwater runoff. Many federal and state agencies are now calling for better-contained pavement drainage. Porous pavement has become a popular best management practice alternative for stormwater management. This presentation summarizes the results of an ongoing study that investigates the possible impact of organic and inorganic pollutants (including bacteria) originating from a porous parking lot on the water quality immediately beneath it. Four water sampling ports were installed inside and outside the parking lot. The locations of the sample ports were selected to represent high-traffic and low traffic areas. One sample port was installed outside the parking lot to serve as background test case. The sampling stations used a nested design to capture infiltrating water at 1 m and 1.5 m below the parking lot surface (total of 8 sample ports). This sampling network permitted not only the collection and analysis of water samples for organic and inorganic compounds, but it also allowed for spatial and temporal contaminant mass flux studies. Tracer tests indicate a good hydraulic connection of the permeable parking surface and the shallow ports. But, further vertical percolation to the deeper ports was hampered by a Geotextile layer at the base of the parking lot structure. Channelized infiltration (i.e., preferential infiltration at discrete points below Geotextile layer) basically converted the permeable parking lot from a “non-point” to a “point” source of pollution. Also, clogging of the permeable surface was evident at some locations. Water samples indicated that cars bring road salt and sand into the parking lot during winter. The sand was identified as the main cause for clogging in heavy traffic areas. Organic pollutants (PAH) were present at very low concentrations. No bacteria, BOD, lead and copper was found in the aqueous samples. There was some indication that nutrients (nitrate and phosphate) were leached into the ground via the permeable parking lot surface.