PERVIOUS ASPHALT: A CASE STUDY OF IMPACTS ON STORM WATER VOLUME AND POLLUTANT LOAD

Pervious pavement is a green storm water best management practice (BMP) whose effectiveness is not well documented. Wishing to evaluate the appropriateness of using pervious pavement on city-owned parking lots, the City of Milwaukee, in association with Symbiont, retrofitted one city-owned parking lot with pervious asphalt in the fall of 2006 and evaluated its effectiveness in the spring of 2007. The goal of the evaluation was to measure reductions in storm water flow rate and pollutant load and to assess the potential for groundwater contamination resulting from the use of the pervious pavement. Storm water discharge pollutant concentrations, discharge volume, and total discharged pollutant load were determined and compared for pervious (post- BMP) and conventional (pre-BMP) asphalt for 10 rainfall events. Statistical analyses determined verifiable increases and decreases in mean pollutant concentration from the pre-BMP to post- BMP condition for measured pollutants at a 5% significance level. No runoff was recorded from the pervious asphalt, suggesting that the pervious parking lot resulted in a 100 percent reduction in discharged pollutants for all of the wet weather events monitored. However, the water quality data raises questions about pervious pavement infiltrated water quality. These findings provide useful insight into the effectiveness of pervious pavement and the design of future pervious parking lots.