WDNR - Lower Fox River - Evaluation of the Effectiveness of Remediation Dredging

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Evaluation of the Effectiveness of Remediation Dredging:

The Fox River Deposit N Demonstration Project
November 1998 - January 1999
Fox River Remediation Advisory Team
Madison, Wisconsin

The Fox River Remediation Advisory Team (FRRAT) was established in April 1998 to review plans for monitoring the effectiveness of dredging at the Fox River Deposit N demonstration site, near Kimberly, Wisconsin.

Based on an agreement between the Wisconsin Department of Natural Resources and the Fox River Group (FRG) on January 31, 1997, it was agreed that FRG would perform the monitoring phase of the Deposit N dredging demonstration project. The Fox River Remediation Advisory Team (FRRAT) was formed at the request of the DNR to evaluate FRG monitoring plans that were developed by Blasland, Bouck and Lee, Inc. The FRG provided funding to the University of Wisconsin Water Resources Institute (UW-WRI) through the DNR

During Phase I of the project, approximately 17.1 kg of PCBs and 2.3 kg of mercury were removed from the west lobe of Deposit N. This represented 89% of the PCBs and 81% of the mercury in this lobe of the deposit. The press cake material that was trucked away from the site accounted for most of the contaminants removed from the deposit, representing 96% of the PCBs and 87% of the mercury. The concentrations of PCBs and mercury in treated waters discharged back to the Fox River were less than 0.01% of the concentrations in the sediment slurry transported to the shoreside treatment site.

Based on the results of Phase I activities, the advisory team reached the following conclusions regarding the effectiveness of dredging at Deposit N:

Environmental dredging is an effective mechanism for removal of contaminated sediments from Deposit N in the Lower Fox River;
A mass balance approach is the most scientifically defensible measure for assessing the effectiveness of a dredging operation;
Shoreside processing was an effective means of concentrating and permanently removing contaminated sediments from the river;
Dredging on the Fox River should be conducted during a period when monitoring is sufficient to determine losses from the activity;
Common techniques such as measurement of total suspended solids (TSS) and turbidity do not adequately describe riverine transport of PCBs;
Prior to dredging, Deposit N represented an active source of PCBs to the Lower Fox River and was not "naturally" capping with clean sediments;
The demonstration project at Deposit N provided information important for future shoreside processing design;
The demonstration project at Deposit N provided information important for water column sampling designs; and
The mass balance framework is a feasible and useful approach for future dredging activities.