Challenges and Opportunities in Tracking Sediment-Associated Contaminants in Green Stormwater Infrastructure

Abstract:

Green stormwater infrastructure (GSI), such as rain gardens and bioswales, have been found to be effective in removing suspended sediments typically found in urban stormwater. Sediments of different sizes tend to be associated with a wide range of contaminants (including heavy metals, PFAS, etc.). These sediment-associated contaminants can, however, accumulate over time within the GSI in different locations and for different residence time. In this research, we present our findings in tracking sediment associated contaminants at a field-scale bioswale in a research facility, OSU-Benton County Green Stormwater Infrastructure Research (OGSIR), Corvallis, Oregon. The study also involves a novel magnetic tracer study approach to track the transport of sediments within the bioswale. In the tracer study, a series of experiments were conducted to track the movement of silt sized particles through the facility. The goals of these studies were to quantify, and develop models for, the transport of such particles under natural storm conditions and in natural vegetated soil. Laboratory studies were conducted to determine the rate of particle trapping by infiltration into idealized soil media. Results were then scaled to the field site, utilizing dual-signature fluorescent/magnetic tracer particles. These silt-sized tracer particles were introduced at the upstream end of the facility, and allowed to be transported over multiple storm cycles. During the experiment, spatially distributed sediment samples were analyzed for tracer concentration, to estimate rates and pathways of transport. In this presentation, recommendations will be also presented for stormwater treatment design based on the above studies. These include design considerations for reducing metal load in effluent, adjusting the residence time of sediments, and preventing undesired sediment effects such as clogging.