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Hydrologic and Pollutant Removal Performance of a Full-Scale, Fully Functional Permeable Pavement Parking Lot
BORST, M., T. P. OCONNOR, A. A. Rowe, AND E. K. Stander. Hydrologic and Pollutant Removal Performance of a Full-Scale, Fully Functional Permeable Pavement Parking Lot. Presented at 2011 AEESP Emerging Research Symposium at WEFTEC, Los Angeles Convention Center, Los Angeles, CA, October 17, 2011.
To inform the public.
In accordance with the need for full-scale, replicated studies of permeable pavement systems used in their intended application (parking lot, roadway, etc.) across a range of climatic events, daily usage conditions, and maintenance regimes to evaluate these systems, the EPA’s Urban Watershed Management Branch (UWMB) installed an instrumented, fully functional, 110-space pervious pavement parking lot to be used by EPA facility staff. The UWMB is monitoring water quantity and quality parameters in side-by-side pervious asphalt (PA), pervious concrete (PC), and permeable interlocking concrete paver (ICP) systems. The parking lot consists of three monitored permeable parking rows, each with a different surface separated by conventional asphalt driving lanes. The permeable pavement parking areas have subsections underlain with an impermeable liner to collect the infiltrating water. The remaining sections are lined with a permeable geotextile liner to allow the filtered effluent to infiltrate to the underlying soil. There are four impermeable and five permeable sections for each pervious pavement type, which allows for statistical analyses of collected data. The monitoring plan allows the EPA to document the performance of the three permeable pavements, identify environmental stressors in the exfiltrate, and reduce runoff volume. This site is equipped for long-term monitoring and the effect of regular maintenance will be investigated by examining changes in surface infiltration rates with time. Preliminary results indicate no significant changes in surface infiltration rates of the three permeable surfaces since the parking lot became fully functional in October 2009. Surface infiltration rates are significantly different among the three surfaces, with the PC having the largest measured rate and PA the lowest rate. However, mean rates for all three surfaces remain large enough to preclude maintenance through vacuuming accumulated solids. Anecdotally, researchers have observed discrete parking lot locations, typically immediately downslope of the impermeable driving lanes, where surface infiltration is noticeably slower during rain events, resulting in temporary ponding. This may be caused by disproportionately greater accumulation of solids immediately downgradient of the driving lanes in the permeable parking rows. Monitoring efforts have documented stressor removal performance across all three surfaces. Repeated measures ANOVA tests incorporating data from 19 sampling dates from January 2010 through April 2011 demonstrated significant differences in infiltrate suspended solids concentrations (SSC) among surfaces, with larger SSC concentrations in infiltrate from ICP than in infiltrate from PC and PA. PC and PA infiltrate SSC concentrations were not significantly different. This pattern may be explained by larger void spaces in the smaller aggregate (AASHTO #8 and #57) bedding and choking layers supporting the pavers compared to the larger aggregate (AASHTO #2) sub-base beneath the PC and PA surfaces. These void spaces may allow larger solids to pass through, thus increasing the SSC concentrations. Infiltrate heavy metals concentrations were measured across an unusually broad spectrum of heavy metals, with varied results.