Highway stormwater runoff represents a significant source of dissolved copper to surface
waters. It is well established that even low concentrations of dissolved copper can be toxic to many
aquatic organisms. In the Pacific Northwest of the United States, recent research has focused on the
effects of low-level copper exposure to salmonids listed as threatened or endangered under the
Endangered Species Act (ESA). In light of these recent studies, increasingly stringent guidelines for the
discharge of highway stormwater runoff have been imposed as part of ESA assessments of
transportation projects. Assessing factors that may impact dissolved copper concentrations in
stormwater provides a practical framework for predicting when and where copper toxicity could be
problematic. A stormwater sampling effort was performed to examine the influence of site locale,
traffic density, storm hydrology, the “first-flush” effect, and water quality parameters on measured
dissolved copper concentrations in highway stormwater runoff. In general, runoff from urban/high
traffic sites and “first-flush” samples exhibited higher copper concentrations than other samples.
Increased dissolved copper concentrations were highly correlated with both dissolved organic carbon
(DOC) and alkalinity. However, multiple linear regression modeling suggests that only the correlation
with DOC has the potential to be causative. These findings will h 18 elp inform State and Federal
transportation and environmental protection agencies regarding the conditions under which elevated
copper concentrations (and potential copper toxicity) are most likely to occur.Keywords: Copper, Runoff, Heavy metals, Stormwater managemen
