Porous Pavement and Water Quality: Investigation of a Parking Lot and Its Potential Impact on Subsurface Water Final rept

摘要

A non-polymer modified porous pavement parking lot on the University of Rhode Island campus was recently constructed in an environmentally sensitive area, i.e., in close proximity to a drinking water well field. The objective of this study was to investigate possible impacts of organic and inorganic pollutants (including bacteria) originating from a permeable asphalt parking lot on the water quality immediately beneath it. Another aspect of this study was to evaluate the functioning of the permeable pavement, including clogging and restricted vertical percolation. Four nested sample ports (shallow and deep) were installed below low and high traffic areas, including one port outside the parking lot. At least initially there was a good hydraulic connection between the parking surface and the shallow sample ports. The percolation to the deeper ports, however, was hampered for two reasons: over-compaction of material covering the deep sample ports and the presence of a geotextile layer at the base of the parking lot structure that may have acted as a hydraulic barrier. Clogging of the permeable surface was most pronounced in heavy traffic areas and below snow pile storage areas. Sand brought in by cars during winter was identified as the principal cause for clogging, but at the same time may have provided sorption sites for metal contaminants. Cars also brought up to 65.23 g/m(sup 2) yr road salt (as chloride) into the parking lot. No bacteria, BOD, and lead were found in percolating water. Polycyclic aromatic hydrocarbons (PAH) were present at concentrations near detection limit. Nutrients (nitrate and phosphate) were being leached into the ground via the permeable parking lot surface at annual flux rates of 0.45 g/m(sup 2) yr to 0.84 g/m(sup 2) yr. A multi-species tracer test demonstrated a retention capacity of the permeable parking lot structure >90% for metals. About 27% and 52% of the released nutrients and salicylate were not recovered. Bio-consumption of these compounds of was identified as a possible explanation for the low tracer recoveries.