Evaluating the Effectiveness of Bioswales and Catch Basin Inserts for Treating Urban Stormwater Runoff in Detroit, Michigan

Bioswales and catch basin inserts are two current “buzz words” in the field of the environmental engineering. Bioswales are a “U” or “V” shaped depression in the landscape designed to: (1) reduce stormwater runoff volumes by increasing infiltration rates and (2) improve water quality by capturing sediment and sorbing contaminants. Catch basin inserts are runoff-filters with a sediment trap and various sorption media filters installed under an individual sewer grate with the goal of filtering particles and dissolved pollutants (both organic and inorganic) from stormwater before entering a sewer system. Both of these techniques improve the quality of stormwater runoff and these techniques have independently shown the potential to be effective. However, efficiencies of the processes are reduced in some situations due to poor management practices or insufficient design criteria. We first collected runoff samples from various locations around Detroit, MI, near the Wayne State University campus (parking lot runoff entering bioswales, street runoff entering storm sewers, etc.) to quantify appropriate concentrations of pollutants to use in our testing. We then tested various sorbent materials from commercial catch basin inserts and other promising sorbents (e.g., bonechar) with synthetic urban runoff to quantify the potential pollutant removal using inserts. Various amounts of sorbents were added to synthetic runoff solutions in 50 mL centrifuge tubes and measured for metal concentrations over time. We also evaluated some potential design flaws in bioswales and catch basin inserts and provided some recommendations to improve the efficiency of the processes and update best management practices.