Abstract

Introduction

Description

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

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

PCB aroclor analyses provided the foundation for the onshore-processing (slurry, trucked press cake) PCB concentrations (Blasland, Bouck, and Lee, Inc., 1999). However, to reduce the limits of detection, the 80-L water column samples were analyzed on a congener-specific basis. The congener-specific analysis approach is expensive ($835 per sample); thus, only a few onshore-processing samples were analyzed to this level of detail. Most samples collected onshore were examined with the less expensive Aroclor-basis PCB analysis. Therefore, to compare water-column results with the onshore-process PCB masses, a water-column PCB Aroclor concentration had to be estimated (Aroclor*1242) from the congener-specific data. This was done by an approach developed in a previous remediation assessment (Fox River Remediation Advisory Team, 2000). The conversion was based on the dissolved (35 percent) and particulate (65 percent) average phase distributions (figs. 8B and 8C) and the Aroclor/congener sum ratios as calculated in the previous assessment.

The congener sum PCB load of 16.9 kg was adjusted to an Aroclor*1242 basis as follows:

Aroclor *1242 PCB load =(0.35)(16.9kg)(0.88)+(0.65)(16.9kg)(0.85)=14.5kg ,
                             (Dissolved)                         (Particulate)

where 0.88 and 0.85 are the Aroclor/congener sum ratios for the dissolved and particulate phases. Thus, the net water-column load due to dredging is estimated to be 14.5 kilograms on an Aroclor*1242 basis. A similar conversion on the congener summation PCB load entering the deposit area from upstream (24.5 kg) resulted in 20.9 kg PCB mass on an Aroclor*1242 basis.

U.S. Department of the Interior, U.S. Geological Survey
http://wi.water.usgs.gov/
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Last Update: Mon 22 Dec 2001