Title page for ETD etd-06182007-110858

Type of Document

Master's Thesis

Author

Collins, Kelly Alyssa,

URN

etd-06182007-110858

Title

A field evaluation of four types of permeable pavement with respect to water quality improvement and flood control

Degree

Master of Science

Graduate Program

Biological and Agricultural Engineering

Advisory Committee

Advisor Name	Title
Dr. William F. Hunt	Committee Chair
Dr. Gregory D. Jennings	Committee Member
Dr. Robert C. Borden	Committee Member

Keywords

permeable pavement
runoff
stormwater
water quality
BMP

Date of Defense

2007-06-15

Availability

unrestricted

Abstract

In North Carolina and several other U.S. states, all permeable pavements are currently considered to have similar capabilities in reducing runoff, but are not credited for improving water quality. To further test the hydrologic and water quality responses of various permeable pavement designs, a 20-stall parking lot consisting of four different types of permeable pavements and standard asphalt was constructed in Kinston, NC. Each pavement section covered an area of 111.5 m2. The four permeable pavement sections consisted of porous concrete (PC), two types of permeable interlocking concrete pavers (PICP) with gravel fill, and concrete grid pavers (CGP) filled with sand. The void spaces of the PICP sections differed, at 12.9 % (PICP1) and 8.5 % (PICP2). All permeable sections were underlain by a gravel base layer. No liner was installed between the gravel base and the underlying sandy clay loam soils. Exfiltrate from the permeable pavements drained via underdrains in the gravel base layer. Hydrologic and water quality data were monitored and collected from April 2006 through April 2007.
Hydrologic differences among pavements were evaluated for surface runoff volume, total outflow volume, peak flow rate, and peak delays. The effects of rainfall depth, rainfall intensity, antecedent dry period, season, and lot age, were evaluated for all hydrologic responses. All permeable pavements significantly reduced surface runoff volumes and peak flow rates from those of asphalt (p<0.01). Of permeable pavements, CGP generated the highest surface runoff volumes (p<0.01). Large outflow volume reductions were observed for the PICP1 and CGP cells, which both generated significantly lower outflow volumes than asphalt and the other permeable pavement sections evaluated (p<0.01). The CGP cell displayed the greatest reductions in peak flow and time to peak, followed by the PICP1 cell. The response of the PICP1 cell was likely due to an increased base storage volume resulting from an elevated outlet pipe. Volume reductions in the CGP cell were attributed to water retention in the sand fill layer. Up to 6mm of rainfall was able to be stored in these sections, a volume accounting for roughly 30% of the median rainfall event that occurred throughout the study. Permeable pavement reductions in peak flow rate from those of asphalt appear to be more negatively correlated to rainfall depth than rainfall intensity. Peak delays were negatively correlated to rainfall intensity.
Rainfall and asphalt runoff water quality were compared to permeable pavement exfiltrate quality for pH and concentrations of total nitrogen (TN), nitrite-nitrate as nitrogen (NO2,3-N), total kjeldahl nitrogen (TKN), ammonia as nitrogen (NH4-N), organic nitrogen (ON), total phosphorus (TP), orthophosphate (OPO4), and total suspended solids (TSS). Due to problems with initial laboratory results, analyses of many parameters were limited to samples collected from January 2007 through April 2007. All pavements were effective in buffering rainfall pH (p<0.01). Permeable pavement?s pH was higher than that of asphalt (p<0.01) and the PC cell had the highest pH values of all pavement sections (p<0.01). Exfiltrate from all permeable pavement sections generated significantly lower NH4-N concentrations and significantly higher NO2,3-N concentrations (p<0.01) than asphalt and rain. The CGP cell exfiltrate had the lowest mean values of NO2,3-N and TN, and the highest mean concentrations of TP. TP increases were likely due to phosphorous leaching from the underlying soils or the sand fill media. The N reductions of the CGP cell were similar to sand filter research, not surprising considering CGP voids were filled with sand, essentially performing like a large, shallow sand filter. Additional monitoring is expected to clarify the effects of climate variables on the water quality responses of various pavement sections.
Overall, different permeable pavement sections performed similarly both with respect to hydrology and water quality. Subtle differences in the performance of CGP were noticed, due primarily to the characteristics of the sand fill media compared to gravel. Based upon this study, it is recommended to the State of North Carolina that:
(1) various permeable pavement types be treated similarly with respect to runoff reduction.
(2) no nitrogen or phosphorous concentration removal credit be assigned to permeable pavements at this time.

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