Water quality performance of vegetated compost blankets for highway stormwater management: Particulate matter and trace metals

Abstract

Urban stormwater pollution poses serious risks to human and environmental health, including trace metals toxicity. To improve the performance of existing highway Vegetated Filter Strips (VFS), which have limited performance for volume reduction and pollutant removal, amendment with a Vegetated Compost Blanket (VCB), a layer of seeded compost, has been proposed. A novel VCB/VFS system was assessed as a Stormwater Control Measure (SCM) via particulate matter and trace metals removal performance. Field and greenhouse studies of the VCB/VFS system were conducted and concentrations of total suspended solids (TSS), filtered and total copper, and total zinc were analyzed. Thirty-three representative field storm events were sampled over a period of 2.25 years. Significant TSS removal was observed in both the field and greenhouse studies, with effluent particles likely flushing from the media itself and the majority of effluent concentrations below the water quality target of 25 mg/L. Particulate copper, and likely particulate zinc, were also largely concurrently removed. Dissolved trace metals performance was mixed, and differences in initial compost copper content was likely influential in observations of dissolved copper leaching in the field which was not observed in the greenhouse. Despite positive performance for particulate matter and associated trace metals removal from stormwater, potential detriment to downstream water bodies due to dissolved copper leaching is a concern. Before widespread implementation, compost composition and potential for dissolved trace metals release should be thoroughly considered, as well as the age and ability of the VFS to immobilize dissolved metals.