Areas of Concern: Technical Guidance for Assessing Remedy Effectiveness, Restoration, and Revitalization at Great Lakes AOCs and Great Lake Legacy Act (GLLA) Sites

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Technical Guidance for Assessing Remedy Effectiveness, Restoration, and Revitalization at Great Lakes AOCs and Great Lake Legacy Act (GLLA) Sites

USGS scientists collaborated with the USEPA to provide guidance for assessing the effectiveness of environmental remediation projects in the Ottawa and Ashtabula rivers (tributaries to Lake Erie) and Thompson and Scanlon reservoirs in the St. Louis River (tributary to Lake Superior). USEPA employed environmental dredging in the Ottawa and Ashtabula Rivers designated Areas-of-Concern (AOCs) and is planning to cap contaminated sediments in some portions of the St. Louis River AOC. USGS designed and implemented monitoring strategies to assess effectiveness of these remedies.

Survey results from prior sediment, water, and biota along with environmental sampling in the St. Louis River AOC were summarized and used to characterize baseline conditions prior to remediation. Water, sediment, benthic invertebrates, fish and riparian spiders were collected from Thompson and Scanlon Reservoirs and analyzed for mercury and dioxins. In addition, samples from across the entire St. Louis River AOC, were analyzed for mercury, mercury stable isotopes, and carbon and nitrogen stable isotopes.

Micrograph of a long-jawed spider head

Scanning electron micrographic of a long-jawed spider head.

(Public domain.)

Environmental samples from the Ottawa and Ashtabula rivers were analyzed for polychlorinated biphenyl (PCB) contamination. Results were used in statistical models to better understand PCB sources and the effectiveness of dredging at these sites. One aspect of the PCB monitoring was to develop and implement the use of riparian riparian sentinels of aquatic contamination (spiders) for use in the Great Lakes and other aquatic systems (Walters, D.M.., R.R. Otter, J.M. Kraus, and M.A. Mills. 2018).

These field studies and data analyses provided critical information on the sources, fate, and transport of contaminants at multiple AOC that were integrated into planned remediations under the Great Lakes Legacy Act. The results of this work directly informed USEPA decision making in terms of site selection, remedy selection and design, and remedy effectiveness assessment. USGS has also provided guidance on targeting historic and planned restoration sites for restoration effectiveness assessments. USGS data was used to inform remedial planning and design for the Thompson and Scanlon Reservoirs in the St. Louis River AOC, and to plan additional monitoring efforts in the Ottawa River in 2020.


Briefings and Presentations:

Otter, R., D. Walters, Jim Lazorchak, K. Fritz, AND M. Mills. PCB export at the lower Ottawa River (Maumee River AOC): A pre- and post-dredging analysis of sediment, passive samplers, aquatic invertebrates, and riparian spiders. Presented at SETAC North American 39th Annual Meeting, Sacramento, CA, November 04 - 08, 2018. Available at:

Technical Reports and Journal Articles:

Otter, R.R., D.M. Walters, J. Lazorchak, K.M. Fritz, and M.A. Mills. In Review. Lower Ottawa River (Maumee AOC) 2009-2015: Relative trends in sediment, macroinvertebrates, and riparian spider PCB concentrations. Technical Memo Prepared for Site Managers at U.S. EPA GLNPO.

Walters, D.M.., R.R. Otter, J.M. Kraus, and M.A. Mills. 2018. Riparian spiders indicate the magnitude and sources of polychlorinated biphenyl (PCB) contamination at a large contaminated sediment site. Environmental Toxicology and Chemistry 37:2467-2474.

Walters, D.M., Otter, R.R., Kraus, J.M., and Mills, M.A., 2018, Polychlorinated biphenyl concentrations and lipid content in riparian spiders at the Ashtabula River Area of Concern, USA: U.S. Geological Survey data release,


U.S. EPA ORD (Office of Research and Development)

U.S. EPA GLNPO (Great Lakes National Program Office)

Other partners include Army Corp of Engineers, USFWS, and state agencies in MI, OH, MN, and WI.