Study Tests Permeable Paver Potential

Photo: mass.govPhoto:

The U.S. Geological Survey (USGS) tested the abilities of permeable pavers.

The organization conducted a study in Wilmington, Massachusetts to determine how to reduce the quantity of stormwater runoff into a local lake.

The study started when the lake was being closed due to high bacteria counts that had occurred repeatedly for many years.

The lake was negatively impacted from nutrients, sediment and bacteria from the conventional stormwater system. 

The Purpose:

  • Reduce the quantity of stormwater runoff and nonpoint source pollution to Silver Lake and maximize infiltration to groundwater.
  • Demonstrate the use and performance of different types of permeable paving materials to infiltrate stormwater.
  • Demonstrate the use of bioretention cells to reduce runoff and pollutants from impermeable areas.
  • Assess and characterize any potential impacts to groundwater quality that might result from the use of permeable pavement.

The group installed seven wells in the parking lot. Four of the wells provided data on groundwater levels and three provided data on groundwater quality. USGS monitored the preconstruction conditions after five storms over four months. After construction, the group monitored groundwater levels and collected samples monthly.

This project incorporated three practices designed to reduce runoff volume, improve water quality and enhance groundwater recharge:

  • Permeable paving materials
  • Bioretention cells
  • Vegetated water quality swales

In the study, four types of permeable paving materials were used to repave about half of the parking lot. The parking spaces consisted of approximately 8,000 square feet and were paved with porous pavers.

The parking aisles, consisting of 16,600 square feet, were paved with porous asphalt. Underneath the porous pavers and asphalt is an infiltration bed of crushed stone that filters contaminants and allows water to slowly percolate into the underlying soil.

Additionally, a porous paving system called Gravelpave, consisting of interlocking plastic cells filled with gravel, was installed in a portion of the overflow parking area. Finally, a porous material called Flexi-Pave, made from recycled tires, was installed in another small section of the overflow parking lot.  For comparison purposes, one half of the existing main parking lot was resurfaced with standard asphalt. 

The results:

  • Infiltration tests of the permeable paving materials, conducted after construction, indicated that infiltration rates met or exceeded specifications; the average observed infiltration rates were:

Porous Asphalt

Permeable Pavers



69 in./hr.

49 in./hr.

1,492 in./hr.

exceeds 5,000 in./hr

  • Results of USGS monitoring show no indication of groundwater impairment beneath the areas with pervious paving.
  • Reports from the town Board of Health show no closures of the swimming beach as a result of E. coli bacteria in the four years following installation of the LID features. For eight years prior to installation, beach closures due to E. coli occurred one or more times each summer.
  • Since the installation of the LID features, the beach had one closure due to cyanobacteria, an algal bloom often associated with in influx of nutrients.
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