In an effort to prevent polluted parking lot rain runoff from contaminating surrounding soil and underground water, the U.S. Environmental Protection Agency on Thursday said it has launched decadelong test of permeable materials to find one that can filter out impurities in rainwater before it flows to its final destination.

Parking lot pavement tends to collect grease, oil, antifreeze and other chemicals leaked from parked cars. When a heavy rain or snowstorm passes over this area it tends to wash these toxins toward the nearest porous surface. Sometimes this water rushes to a storm drain but other times storm drains are overwhelmed and runoff keeps flowing until it reaches the nearest patch of soil or body of water.

The EPA's first test site is its Edison, N.J., facility, where the agency has replaced a 3,995-square-meter section of parking lot with three different types of permeable pavement—interlocking concrete pavers, porous concrete and porous asphalt—and planted several rain gardens (pdf) with varying vegetation for the study. (Note: Interlocking concrete pavers are often called porous pavers, although the pavers themselves are not porous.) Researchers will over time evaluate the effectiveness of each pavement type and the rain gardens in removing pollutants from stormwater, and how they help water filter back into the ground, according to the agency.

This long-term porous pavement research is part of the agency's Green Infrastructure Research Program and expected to let the EPA document the performance and capabilities of three porous pavement systems simultaneously at the same site, according to an EPA document describing the study. Each of the monitored porous pavement parking rows has subsections lined with an impermeable geotextile fabric to collect the infiltrating water as well as sections that infiltrate into the underlying soil. Each impermeable section has a perforated pipe that drains the accumulated runoff through pipes under the roadway to a dedicated collection tank to the side of the lot.

Pollution runoff from hard surfaces remains a complicated problem, an EPA spokesman says. In urban areas, polluted runoff often flows from pavement into storm drains. "When heavy rain events occur, polluted water is often released into rivers, streams and oceans through events called combined sewer overflows," he says. "In rural areas, polluted runoff can flow off of paved areas directly into water bodies or onto land that may be used for farming."

Images courtesy of the U.S. Environmental Protection Agency