This report presents the results of an exploratory study conducted in water years (WY) 2023 and 2024 to characterize 6PPD-quinone (6PPDQ) in stormwater runoff from highways in the Pacific Northwest. The study also evaluated 6PPDQ removal by stormwater treatment technologies, how field sampling protocols and equipment may impact 6PPDQ recovery in stormwater samples, and differences in 6PPDQ quantification between two analytical laboratories. This project was funded by the Washington State Department of Ecology (Ecology).