A Field Study to Evaluate Permeable Pavement Surface Infiltration Rates, Runoff Quantity, Runoff Quality, and Exfiltrate Quality

Abstract

The surface infiltration rates of 48 permeable pavement sites were tested in North Carolina, Maryland, Virginia, and Delaware. Two surface infiltration tests (pre- and post-maintenance) were performed on 15 concrete grid paver (CGP) lots filled with sand. Maintenance consisted of removing the top layer of residual material (13 - 19 mm (0.5 — 0.75 in)). Maintenance significantly (p = 0.007) improved the surface infiltration rate. The median site surface infiltration rate increased from 4.9 cm/h (1.9 in/h) for existing conditions to 8.6 cm/h after simulated maintenance. Fourteen permeable interlocking concrete paver (PICP) and eleven porous concrete (PC) sites were also tested. PICP and PC sites built in close proximity to disturbed soil areas had surface infiltration rates that were significantly (p = 0.0014 and p = 0.0074, respectively) lower than stable landscape sites. Median PICP surface infiltration rates of for each condition were 80 cm/h (31 in/h) and 2000 cm/h (800 in/h), respectively. Median PC surface infiltration rates with and without fines were 13 cm/h (5.1 in/h) and 4000 cm/h (1600 in/h), respectively. This study showed that (1) the location of permeable pavements and (2) maintenance of permeable pavements were critical to maintaining high surface infiltration rates.

Three permeable interlocking concrete pavements (PICP) sites were monitored for runoff quality in North Carolina in Cary, Goldsboro, and Swansboro. The Cary site was located in clay loam soil; 15 samples of exfiltrate and rainfall were analyzed for pollutant concentrations from February 2004 to November 2004. NH4-N, PO4, and Bound Phosphorus (BP) concentrations were significantly (p < 0.05) lower in exfiltrate than collected rainfall. The Goldsboro site was constructed in 2002 to compare the water quality of asphalt runoff to exfiltrate of adjoining permeable pavement. Up to 14 samples of Zn, NH4-N, TKN, NO2+3-N, TP, and Cu were collected from the asphalt runoff and the permeable pavement exfiltrate from July 2003 to November 2004. The Swansboro site was constructed in 2003 and instrumented to monitor runoff flow, record rainfall rates, and collect water samples from PICP exfiltrate and runoff from March 2004, to December 2004; however, during the entire monitoring period, precipitation on the 740 m2 parking lot produced no runoff.

Permeable pavement surface infiltration rates presented herein were compared to grassed lawn infiltration rates from other studies. Ninety percent of permeable pavement surface infiltration rates in sandy soils were greater than 5.4 cm/h (2.1 in/h), compared to 6.4 cm/h (2.5 in/h) for grassed sandy loam lawns in urban soils. Rational coefficients and Curve Numbers were determined for monitored permeable pavement sites in eastern North Carolina and compared to those of grassed lawns. Comparable ratios of impermeable surface to grassed lawns were also determined. These comparisons were used to assign a suggested percent perviousness to be given to permeable pavements. A credit could then be developed for permeable pavements related to grassed lawns in sandy soils. The credit could be an equivalent ratio of grassed lawn area to impervious area for permeable pavements based on runoff volumes.