Impacts of Size Distribution and Storm Intensity on the Behavior of Suspended Particles and Their Associated Metals in a Bioswale Stormwater Control Measure

Abstract

Suspended solids in runoff were evaluated along the gradient of a bioswale stormwater control measure (SCM), considering storms of varying intensities. Total and size-fractionated suspended solids and their associated metals were used to investigate resuspension or deposition patterns and metal adsorption. Total suspended solids and their associated metal concentrations increased along the gradient of the SCM when average storm intensity was higher than 4.5 mm/h, suggesting resuspension was occurring. However, solids and their associated metals for fine size classes (D<10 μm) revealed that resuspension or ineffective deposition occurred along the SCM regardless of storm intensity, but the degree of resuspension was not related to average storm intensity. Adsorption coefficients derived from analysis of fine sizes were higher compared to coarser sizes by orders of magnitude (10 to 1,000 times), indicating a higher affinity for fine solids. Freundlich isotherm had the best goodness of fit in modeling metal adsorption onto fine solids. The observed resuspension and fine particle–associated metal transport highlight the importance of proper SCM design (e.g., employing forebays and weirs) and maintenance (e.g., vegetative cover and mulching) to address their corresponding challenges.