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Bioretention Longevity Project


Very little information is available on the long-term performance of bioretention for treatment of stormwater runoff. Additionally, it is unknown what depth of bioretention is necessary to provide long-term treatment. This project is designed to assess chemical and biological performance of up to 5 depths of bioretention over 10 years.


Bioretention in experimental columns will be used to treat highway stormwater runoff over 2 years of compressed treatment representing 10 water years. Five depths will be tested during the first two water years (6”, 9”, 12”, 15”, 18”) after which two depths will be eliminated. Three replicates of each depth will be tested, plus an additional 3 replicates of the 18” depth that will receive clean water only. A full suite of chemicals will be measured in influent and effluent waters for the storm representing the end of a water year (approximately every 7th storm). Toxicology tests of acute impacts from influent and effluent water will be assessed for the storm ending each water year. These will include zebrafish embryo screens (every water year) and juvenile coho salmon exposure (first storm, end of water year 5 and 10).

Project Summary

Bioretention is a popular and effective method for treating stormwater runoff. This project addresses the need for long-term data on performance in terms of removing toxic chemicals and preventing acute toxic impacts. This study will be the first assessment of long-term performance of toxicity prevention.


Experimental treatment: 2 years (Oct 2019-Oct 2021)

Parameters measured

Fecal coliform

Total suspended solids

Dissolved organic carbon

Calcium, magnesium, sodium

Total and dissolved metals (As, Cd, Cu, Ni, Pb, Zn)

Polycyclic aromatic hydrocarbons (PAHs)



Nutrients (ortho-P, nitrate+nitrite)


USFWS Environmental Contaminants Division


SAM (Stormwater Action Monitoring)

Project Reports

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