VELMA Model Green Infrastructure Applications for Reducing 6ppd-Quinone Concentrations in Puget Sound Urban Streams (Presentation)
This presentation focuses on applications of the U.S. EPA’s VELMA ecohydrological model for assessing the effectiveness green and gray infrastructure improvements for reducing stormwater contaminant loads to Seattle’s Longfellow Creek. This creek, like many other urban creeks draining to Puget Sound, experiences high rates of coho salmon prespawn mortality associated with lethal concentrations of 6PPD-quinone, a breakdown product of 6PPD contained in tire-wear particles (Tian et al. 2020). Details of the hydrological and biogeochemical processes controlling spatial and temporal dynamics of 6PPD-quinone fate and transport from points of deposition to stream and estuary are poorly understood. Here we present new VELMA model results to elucidate these processes for the upper Longfellow Creek watershed (730 ha). This presentation is an update of earlier work (McKane et al. 2021) and features higher-resolution (5-m vs. 10-m) watershed analyses and spatiotemporal animations that more clearly highlight the effectiveness of alternative green infrastructure treatments for limiting 6PPD-quinone fate and transport to Longfellow Creek. Key findings emphasize the importance of roadside raingardens and bioswales, and pervious pavements for diverting elevated first flush stormwater concentrations of 6PPD-quinone before reaching stormwater drains and pipes.