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Region 2

Serving New Jersey, New York, Puerto Rico, US Virgin Islands and Eight Tribal Nations.

Green Parking Lot

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Much of New York and New Jersey rely on a combined sewer and stormwater system to move stormwater, waste and wastewater to treatment plants.  During dry weather, these systems often work properly.  However, impervious surfaces (such as roads, houses, sidewalks, driveways and parking lots) don’t allow rain to percolate into the ground; instead they channel rainwater to a storm drain.  A mere inch of rainfall running off these impervious surfaces adds up to a lot of water, overwhelms the system, and causes an overflow of water and waste called a Combined Sewer Overflow (CSO).  Stormwater runoff and CSOs not only impact our health by exposing us to pathogens and toxics in our waters but also negatively impact the habitat and living conditions of fish and other aquatic life. 

It is possible to design urban stormwater structures to mimic the natural processes of water filtration and percolation into the ground. To minimize the likelihood of CSOs, rain needs to slow down and to be soaked up by the soil.  How can we make that happen?  This challenge was the motivation behind the research and construction of a new “green” parking lot at the Edison, New Jersey facility.

What Makes the Parking Lot Green

The Edison, New Jersey, facility, including office and laboratory space, is the largest EPA-owned site.  The location is not easily accessible by public transportation.  Therefore, most visitors and employees need a place to park.  Parking lots can cover large areas and are generally impervious. Under EPA’s facility environmental management system, EPA Region 2 aims to minimize the stormwater runoff impacts associated with a traditional parking lot.  To achieve a “green” parking lot, much of the rainwater needs to be captured directly by the permeable pavement in the parking lot.  Any rainwater running off the parking lot and building roofs needs to be redirected into rain gardens where it can drain into the underlying soil instead of flowing into storm drains.  These processes reduce the volume of stormwater runoff and slow down the flow.

How EPA Is Building a Green Parking Lot

The concrete from the pre-existing parking lot was recovered, crushed and reused on-site to provide the drainage layer beneath the permeable pavement surfaces.  The demonstration parking lot includes three types of permeable pavement: pervious concrete, porous asphalt, and porous pavers. It also has three different sizes of rain gardens to infiltrate rainfall and stormwater from the traditional, impervious surfaces of the parking lot driving lanes and sidewalks. The rain gardens also receive runoff from the roof of the building adjacent to the parking lot. 

What EPA is Studying

Scientists from the Urban Watershed Management Branch of EPA’s Office of Research and Development are leading the research effort. Data will be collected and managed in situ over the next ten years. 

The primary focus of the research falls into the following categories:    

  • Monitoring infiltrated runoff for water volume, flow rates and stressor loadings
  • Infiltration rates of the different permeable surfaces and rain gardens 
  • Functionality and performance of the permeable surfaces and rain gardens with time
  • Heat island (temperature) reduction potential as related to climate change

What EPA Hopes to Learn

This long-term, ten-year project aims to address questions such as:

  • Do permeable pavement systems stand the test of time and perform as well as conventional, impervious pavement?
  • Are there differences between permeable pavement types in terms of infiltration capacities and stressor loads?
  • Can smaller rain gardens handle excess stormwater runoff from impervious pavement and roofs as effectively as larger rain gardens?  Is there an optimal size?
  • Can plants and soils in the rain gardens effectively remove stressors, such as heavy metals and nutrients, from the stormwater runoff and prevent them from contaminating surface and ground waters?
  • Do permeable pavement and rain gardens successfully and consistently lower surface temperatures, resulting in a decrease in the urban heat island effect?


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