Factors Influencing Dissolved Copper Concentrations in Oregon Highway Storm Water Runoff

Abstract

Highway storm water 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 storm water runoff have been imposed as part of ESA assessments of transportation projects. Assessing factors that may affect dissolved copper concentrations in storm water provides a practical framework for predicting when and where copper toxicity could be problematic. A storm water 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 storm water 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 help 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.