Pervious Concrete/Porous Asphalt Comparison Site

Executive Summary

PAPC


Villanova University's Stormwater Research and Demonstration Park is home to a SCM- Pervious Concrete / Porous Asphalt Comparison Site. The site, formerly a standard asphalt paved area, is located behind Mendel Hall. The area was constructed in fall 2007. The site consists of an infiltration bed overlain by a 50' x 30' pervious concrete surface and an equally sized porous asphalt surface.  The site receives continuous use by faculty vehicles.

Pervious concrete has functionality and workability similar to that of regular concrete. However, the pervious concrete mix lacks the sand and other fine particles found in regular concrete. This creates a significant amount of void space which allows water to flow relatively unobstructed through the concrete. Additives are often used to increase the strength of the concrete.

Porous asphalt is similar to standard asphalt, with a few notable exceptions.  The fine aggregate of the mix is removed, resulting in greater void space and permeability. 

The site is designed to capture and infiltrate storms of up to two inches of rainfall. From these events there is no runoff from the site. Before the retrofit this rainwater would have runoff to the nearby first-order streams contributing to flooding problems which cause excessive stream bank erosion and sedimentation. Instead the rainwater now recharges the local groundwater and helps maintain baseflow in the same first-order streams. This recharge is especially crucial because Villanova University is located in the extreme headwaters of the watershed.

The pervious pavements receive water solely from parking areas.  The beds are level and range from 3 to 5 feet deep and are filled with washed stone, with approximately 40% void space. Here the rainwater is temporarily stored while it infiltrates back into the soil below the beds. In extreme events when the capacity of the storage beds is exceeded, flows are permitted to exit the site and flow out to the original storm sewer system. This overflow eventually makes its way to the stormwater wetland.

The Pervious Concrete / Porous Asphalt site is part of the Villanova University Stormwater SCM Park. It has been fully equipped with monitoring instrumentation. The site is instrumented to record rainfall using a standard tipping bucket rain gage. A pressure transducer measures the depth of water in the beds.

Another component of the research is water quality. First flush samplers are used to obtain water quality information of the stormwater as it enters the SCM. Samples can also be obtained from the modified manholes located at each end of the site to obtain water quality information of the water stored in the beds. Groundwater samplers called lysimeters have been installed beneath infiltration beds. These samplers allow the infiltrated rainwater to be extracted from the soil and taken to the lab for chemical analysis. The site is being monitored for temperature, various metals, hydrocarbons, nutrients and conventional water quality parameters such as pH and conductivity.