Date of Award

2023

Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Environmental Engineering (MS)

Administrative Home Department

Department of Civil, Environmental, and Geospatial Engineering

Advisor 1

Noel R. Urban

Advisor 2

Judith A. Perlinger

Committee Member 1

Gordon Paterson

Committee Member 2

Cory P. McDonald

Abstract

The Keweenaw area continues to be influenced by the century of copper mining that ended nearly 50 years ago. This project is focused on Torch Lake, an aquatic ecosystem that has been heavily impacted by mining waste disposal. The watershed has been impaired by mine discharge and tailings, smelter and smokestack plumes, and poor waste disposal practices. The lake is listed as a Great Lakes Area of Concern with beneficial use impairments of restrictions on fish consumption and a degraded benthic community. Polychlorinated biphenyl compounds (PCBs) and methylmercury (MeHg) are persistent, bioaccumulative, and toxic substances (PBTs). These contaminants pose threats to human and environmental health primarily via fish consumption. The use impairment of restricted fish consumption is a result of elevated concentrations of PCBs and MeHg in Torch Lake. In this research, kinetic bioaccumulation models were developed using MATLAB to estimate steady state concentrations in each trophic level of the Torch Lake food chain. The model links the contaminated environment to the bioaccumulation in a single organism. The model is most sensitive to the dietary uptake rate constants, and Monte Carlo simulations indicate that the uncertainty (95% confidence interval) is approximately 0.13 ng/g ww for PCBs and 0.02 mg/g ww for MeHg. Model-predicted concentrations agree with the steady-state model, AQUAWEB, and with concentrations measured in walleye (Sander vitreus). The kinetic model coupled with a mass balance model is used to predict the extent of recovery of the ecosystem following remediation actions, such as removal of local contaminant sources to the lake. Removal of contaminated sediments is predicted to reduce the PCB congener concentrations by a factor of 2-14, and elimination of in-lake methylation was predicted to reduce fish Hg concentrations by a factor of 2. Thus, the model suggests that the planned remediation under the Legacy Act will significantly reduce PCB concentrations in fish. The model indicates that adult fish entering Torch Lake from the Keweenaw Waterway could reach the observed PCB contaminant concentrations in fish within 62 days to over 10 years, but other studies have indicated that immigration of fish to Torch Lake is uncommon.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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