Assessment of Car Wash Runoff Treatment Using Bioretention Mesocosms

Abstract

Car wash runoff is known to be a pollution source to surface water bodies. Many groups hold car-washing fundraisers unaware of pollution issues associated with car wash runoff. This preliminary study investigated whether rain gardens are an appropriate management practice for reducing car wash pollutants, specifically surfactants. The concentrations of total phosphorus (TP), total suspended solids (TSS), and surfactants were measured in car wash runoff before and after treatment in three rain garden mesocosms. Mean TSS and surfactant effluent concentrations were significantly lower than the car wash runoff with TSS reductions ranging from 84 to 95% and surfactant reductions ranging from 89 to 96%. The removal efficiencies for surfactants were not enough to reduce concentrations below literature-based values for aquatic toxicity. Mean TP effluent concentrations were higher than the car wash runoff with increases ranging from 197 to 388%, although the increase was not statistically significant. This project demonstrates the potential for using bioretention to reduce pollutants associated with car wash runoff and using car wash events to educate the public about watershed protection.