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U.S. Department of the Interior U.S. Geological Survey
USGS  Water-Resources Investigations Report 00-4245 December 2000
   
Abstract

Introduction

Description of the study area

Sampling methods

Suspended-solids transport during dredging

PCB concentration changes during dredging

PCB loading in the Fox River due to the dredging operation

PCB transport back into the river from the onshore-processing operation

Postdredging PCB concentration and loads

Adjusting water-column PCB concentrations to allow comparison with onshore-sample PCB data

Lessons learned

References

Acknowledgments and Information

  

A Mass-Balance Approach for Assessing PCB Movement During Remediation of a PCB-Contaminated Deposit on the Fox River, Wisconsin

figure 2: Location of the Fox River Point-source dicharge sites

Introduction

Water quality and aquatic life in the Lower Fox River, which flows from Lake Winnebago to Green Bay (fig. 2), have been affected by contaminants that have accumulated in streambed sediments over the last several decades. The Wisconsin Department of Natural Resources (WDNR) has determined that contaminants released from Fox River sediment deposits cause exceedances of State water-quality standards and necessitate fish-consumption advisories. From the perspective of human health and ecological risk, polychlorinated biphenyls (PCBs) and mercury are the principal contaminants of concern. Sampling has confirmed that sediment-associated PCBs and mercury are accumulating within the aquatic food chain and are actively being transported within the river and out into Green Bay and Lake Michigan (Brazner and DeVita, 1998).

figure 3: Location of The Sediment Management Unit 56/57 (SMU 56/57)
The Sediment Management Unit 56/57 (SMU 56/57) remediation project was a joint effort between the State of Wisconsin and the Fox River Group (FRG), a coalition of paper companies. A primary purpose of the project was to remove PCB-contaminated sediment by dredging and thereby generate information relevant to the effectiveness of large-scale dredging and disposal of the sediments (in this case, 7­11 million cubic yards) from the Lower Fox River (ThermoRetec Consulting Corp., 1999; Blasland, Bouch, and Lee, Inc., 1999; Montgomery Watson, 2000). 

A hydraulic dredge was used to pipe a sediment slurry from the river bottom to a settling basin; the onshore operation consisted of filter-pressing the slurry, filtering the liquid effluent and returning it to the stream, and trucking away the solids. In support of the sampling plan designed by the FRG and WDNR, a mass-balance approach (a combined examination of concentration and flow) was used to determine the effectiveness of dredging in removing the PCBs from the river environment.

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