Lake Superior/Duluth-Superior Harbor Toxics Loading Study

This study presents toxic contaminant concentration data for the water discharging into Lake Superior from the Duluth-Superior Harbor and water discharging into the Duluth-Superior Harbor from the St. Louis and Nemadji Rivers. The Duluth-Superior Harbor along with the lower St. Louis River and the lower Nemadji River have been designated as an Area of Concern (AOC) by the International Joint Commission due to impairment of beneficial uses, including fish consumption, swimming and aquatic community support (MPCA and WDNR, 1992). The data generated in this study were used to estimate contaminant loading rates to Lake Superior from the Duluth-Superior Harbor and to the Duluth Superior Harbor from the Nemadji and St. Louis Rivers. The U.S. Geological Service in Madison, WI performed the load computations using the Stratified Beal Ratio Estimator Model. These loading estimates may be used to prioritize watersheds for nonpoint pollution management activities. The contaminant data and loading estimates will serve as baseline data for monitoring progress in the Lake Superior Lakewide Management Plan and the St. Louis River Area of Concern Remedial Action Plan. The contaminant concentration data may also be used in the process of assessing waterbodies for listing on the Clean Water Act 303d list of impaired waters.