Two-year Monitoring Study of Permeable Interlocking Concrete Pavement Completed by the University of New Hampshire Stormwater Center

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The study results confirmed that PICP eliminates stormwater runoff in cold climates and is an effective tool for removing sediment, nutrients and metals through infiltration even during winter months. The study also verified that PICP does not heave from winter freezing and thawing.

The University of New Hampshire Stormwater Center (UNHSC), well-known for evaluation of stormwater management practices in cold climates, issued the results of a two-year monitoring study of a permeable interlocking concrete pavement (PICP). Monitoring occurred from October 2010 through April 2012 on Hood House Drive in the center of the UNH campus in Durham. In summer 2010, the University retrofitted the drive and adjoining parking lot with 13,500 sf of PICP. The removed asphalt pavement included no stormwater control measures and conveyed surface runoff into the municipal storm sewer.

The PICP was designed over high infiltration soils (~3 in./hr). Excess stormwater exits through underdrains on the soil subgrade discharging subsurface flows to the municipal storm sewer system. Pollutant loads for the former asphalt pavement was estimated by monitoring runoff from an adjacent parking lot at Thompson Hall similar in size, use, and location.

Following two years of monitoring 18 storms, volume and pollutant load reductions were exceptional. Volume reduction and subsequently pollutant mass removal exceeds 95% for all contaminants measured including sediment measured as total suspended solids and suspended solids concentrations, metals, petroleum hydrocarbons, and nutrients (nitrogen and phosphorous forms). Effuent volumes in any single event didn’t exceed five gallons and peak flows were almost all less than one gallon per minute.

Decreasing surface infiltration rates were observed for PICP subject to run-on and sediment from impervious surfaces, yet it still retained a surface infiltration rate greater than 1,000 in./hr. Minimal maintenance was performed during the monitoring which included topping up the joints with permeable stone and vacuuming the surface. Thermal analyses were conducted in the summer comparing four pavement surface types at three different times. PICP surface temperatures were lower than that for porous asphalt, pervious concrete, and standard asphalt.

A 56-page project report and fact sheet are available on the UNHSC website at This report includes all of the monitoring data, surface infiltration rates, and thermal data as well as project plans/sections, site soils information, site vacuuming information, photos including plowed snow, the two-page project summary and test results on the concrete pavers.

The ICPI Foundation for Education & Research supported the monitoring project with the following companies contributing toward construction: Genest Concrete Works, Pavers by Ideal, Unilock, SF Concrete, Pavestone Company, Nicolock Paving Stone, Hanson, Oldcastle Architectural, Techo-Bloc, and the New England Concrete Masonry Association with support from the Northeast Cement Shippers Association.

About the ICPI Foundation: The ICPI Foundation for Education and Research positions the segmental concrete pavement industry for a stronger and more predictable future. The Foundation's mission is to provide educational and research programs designed to benefit the concrete paver industry and users. It accomplishes this by developing educational resources that optimize manufacturing, construction operations and maintenance, that demonstrate superior value, while encouraging acceptance by the design and construction communities; and, supporting, conducting and disseminating research and technical studies that enhance and improve knowledge.

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Jessica Chase, CAE
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