|Bioretention Photo Courtesy of US Navy|
One such approach is to use green infrastructure techniques to remediate PAHs. It has long been known that a living and active plant-soil matrix can break down many PAHs. But how effective is it?This is what researchers at Washington State University intend to find out in an upcoming study as described by the university below.
One suggestion is the research should seek to understand not just removal, but also the fate of the PAHs. The last thing anyone wants is a proliferation of treatment devices that ultimately become waste repositories that are expensive to remediate later on. This is the lesson all should learn from the greater Minneapolis area's experience with detention pond remediation that has estimated cleanup costs of at least $1 billion dollars. See here for a related story The High Cost of Cheap Coal Tar.
Scientists at the WSU Puyallup Research and Extension Center are testing a method known as “soil bioretention” to eliminate the toxic effects from highway runoff. “Vehicle exhaust often contains dangerous levels of polycyclic aromatic hydrocarbons (PAHs), which are known to cause heart and cardiovascular defects in animals,” said Jen McIntyre, lead WSU Puyallup stormwater researcher. “We want to eliminate or lower the PAHs to create a healthier environment for aquatic life and the general population.”
The group is simulating brief rainstorms by using sprinklers on a 27-foot x 44-foot area of pavement. The plot, treated with coal tar sealcoat (CTSC) commonly used throughout much of the country–but not in Washington State–contains many of the same PAHs as urban highway runoff.
Traffic counters record the number of vehicles passing over the site during the test period since abrasion is a major source of contamination to runoff from seal-coated surfaces. “After the runoff is collected it will be transported to a greenhouse with large bioretention soil columns,” said McIntyre. “Half of the water will be kept as untreated runoff. The rest will be passed through the soil columns as a kind of biological filter that mimics what happens when runoff infiltrates the ground.”
During the six-week study, fish and aquatic invertebrates will be exposed to both raw runoff and that which has been run through the bioretention system to see if the toxicity is eliminated. Findings from the study, funded in part by EPA Region 10 and the NOAA Coastal Storms Program, will be published in a peer-reviewed scientific journal and presented at local and regional conferences to raise awareness of stormwater contamination and increase understanding about the role of PAHs in runoff toxicity and the benefits of bioretention to clean up urban runoff.
Find out more about the Puyallup stormwater research program at http://puyallup.wsu.edu/stormwater.