Dynamic Treatment of County Maintenance and Service Facility Stormwater by a Pump-Fed Bioswale System

Limited data exist on the stormwater characteristics and treatment of maintenance and services (M&S) facilities. Such facilities are generally dynamic in land use and support diverse operations. This study characterized stormwater from a M&S facility in Benton County, Oregon and evaluated the dynamic stormwater treatment performance of an on-site bioswale system. Over a period of 2 years, stormwater was characterized from 12 storm events, and the dynamic bioswale performance was characterized for four storm events. High variations in stormwater pollutant concentrations were observed, even when hydrological and meteorological conditions were similar. This indicated the critical role played by the diverse activities in the catchment on stormwater composition. Regarding the dynamic bioswale performance, bioswales consistently achieved high removal of particulate contaminants. However, regarding dissolved contaminants, bioswale performance was overall poor and highly variable. Effluent dissolved metal concentrations were often higher than influent concentrations, and the bioswale system itself appears to be a source of orthophosphate in the effluent stormwater. Field results demonstrate the importance of hydrologic controls and selecting the correct bioswale media for proper contaminant removal. (C) 2021 American Society of Civil Engineers.