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Permeable Pavement Research at the Edison Environmental Center
Citation:
OCONNOR, T. P. Permeable Pavement Research at the Edison Environmental Center. Presented at 2nd International Forum on Integrated Water Management, University of Sherbrooke, Quebec, QC, CANADA, October 23 - 25, 2011.
Impact/Purpose:
To inform the public.
Description:
There are few detailed studies of full-scale, replicated, actively-used permeable pavement systems. Practitioners need additional studies of permeable pavement systems in its 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 has been monitoring an instrumented pervious pavement parking lot. The parking lot design at the Edison Environmental Center (EEC) allows for statistical analysis of collected data. The lot is used by EPA personnel and visitors to the EEC. The parking lot opened in late October, 2009 and monitoring began in December, 2009. Each parking row is 43 m long with 14 spaces on each side of the parking row (28 spaces in all) allowing access to the regular asphalt driving lanes. Each parking space is 6 m long and 3 m wide separated by 10-cm wide striping. The placement of the permeable surfaces was chosen randomly by the architect. The monitored parking lot has three types of permeable surfaces: interlocking concrete pavers, porous concrete, and porous asphalt. Each of the three monitored rows of permeable pavement has nine equally divided sections. It is impossible to re-create a wet-weather flow event for statistical purposes, but the sub-divisions of the parking rows permits the reasonable assumption of replicates. Four subsections are underlain with an impermeable liner to collect the infiltrating water and drain to a dedicated HDPE collection tank. Five subsections allow the filtered effluent to infiltrate to the underlying soil. The unlined sections at the ends of row allow monitoring of the interaction of the infiltrated water with the subgrade soil. Access pipes and data loggers are accessible from the tree islands so they are out of the way of parked cars and the impermeable driving lanes. Permanent instrumentation installed in the porous parking rows during construction includes time domain reflectometers (TDRs), and thermistors. TDRs are being used to document the passing of the wetting front produced by both direct precipitation and stormwater runoff generated by the impervious areas of the lot. TDRs are in the storage layer below the permeable surfaces as well as in the underlying soil. The magnitude and the timing of the passing wetting front are quantifiable in both media types. Thermistors were installed at varying depths to monitor soil temperature differences among the layers: the wearing surface; the interface between the wearing surface and the aggregate (depth of which varies according to permeable surface type); 40 cm below the surface; 15 cm into the subgrade; and 90 cm into the subgrade. Conventional asphalt and unpaved soil are similarly instrumented with thermistors at the surface for temperature comparison purposes. Surface infiltration rates over the initial six months were comparable to those seen in the literature for each permeable surface type. One year later, some decreases in infiltration rates have been observed, predominantly on the near edge to the impermeable driving lane surface. Reduction in infiltration rates has not yet reached a point such that maintenance in the form of a regenerative-vacuum cleaning is needed. The parking lot endured the first winter without an operational or maintenance incident. A suite of water quality parameters on the infiltrate have been periodically measured and results on metals and nutrients are currently being analyzed. The parking lot is having an effect on the pH of the collected rainfall and runoff. The collected infiltrate water is alkaline while the pH of rainfall in Edison, NJ is acidic. The monitoring allows for the assessment of the long-term performance of permeable pavements as stormwater low impact development controls with regard to pollutant removal capability and runoff volume reduction.
