Factors Influencing Dissolved Copper Concentrations in 1 Oregon Highway Stormwater Runoff

Highway stormwater runoff represents a significant source of dissolved copper to surface 4 waters. It is well established that even low concentrations of dissolved copper can be toxic to many 5 aquatic organisms. In the Pacific Northwest of the United States, recent research has focused on the 6 effects of low-level copper exposure to salmonids listed as threatened or endangered under the 7 Endangered Species Act (ESA). In light of these recent studies, increasingly stringent guidelines for the 8 discharge of highway stormwater runoff have been imposed as part of ESA assessments of 9 transportation projects. Assessing factors that may impact dissolved copper concentrations in 10 stormwater provides a practical framework for predicting when and where copper toxicity could be 11 problematic. A stormwater sampling effort was performed to examine the influence of site locale, 12 traffic density, storm hydrology, the “first-flush” effect, and water quality parameters on measured 13 dissolved copper concentrations in highway stormwater runoff. In general, runoff from urban/high 14 traffic sites and “first-flush” samples exhibited higher copper concentrations than other samples. 15 Increased dissolved copper concentrations were highly correlated with both dissolved organic carbon 16 (DOC) and alkalinity. However, multiple linear regression modeling suggests that only the correlation 17 1 Assistant Professor, School of Chemical, Biological, and Environmental Engineering, Oregon State University, 103 Gleeson Hall, Corvallis, OR 97331-2702 (corresponding author). E-mail: [email protected] 2 Water/Wastewater Engineer, URS Corporation, 8181 E. Tufts Avenue, Denver, CO 80237 3 Engineering Technician, City of Portland Water Bureau: Operations Division, 2010 N Interstate Ave, Portland, OR 97227 2 with DOC has the potential to be causative. These findings will help inform State and Federal 18 transportation and environmental protection agencies regarding the conditions under which elevated 19 copper concentrations (and potential copper toxicity) are most likely to occur. 20 CE Database subject headings: Runoff; Stormwater management; Heavy metals; Copper 2