Long-Term Effectiveness of a Bioretention System Treating Road Runoff in Northeastern Kansas

Recent studies have indicated that the use of ecologically-based methods for stormwater treatment, including bioretention systems, may provide increased pollutant removal and protection of downstream receiving waters. However, there is little data addressing the long-term performance of these systems in the field or the effects of contaminant accumulation over time on treatment effectiveness. In this study, we present results from an ongoing three-year study of bioretention performance and contaminant fate at a 0.1 acre bioretention cell located in northeastern Kansas. Samples of influent and treated stormwater from storm events during 2007 and 2008 were analyzed for a range of water quality parameters, including total suspended solids, nutrients and total and dissolved Cu and Zn. Results of this sampling show that the bioretention system successfully removes > 70% of suspended solids and more than half of influent total metals. Removal of dissolved constituents is much lower, with the exception of nitrate, which had removal rates of up to 50% during the study. Improvements to the mulch material and vegetative establishment could potentially increase system performance for these constituents.