Quantifying Environmental Dredging Contaminant Losses with a Multimedia Chemodynamic Model

The process of extracting bottom sediments contaminated with metals and organic chemicals will result in significant losses to the adjoining media. A multimedia box model has been developed for environmental dredging in order to quantify and forecast the various losses. Prior to model development detailed mass balance studies quantifying the effectiveness of dredging and the collateral losses were completed at four sites. The sites were: Bayou Bonfouca, LA containing PAHs, Grasse River, NY containing PCBs, Manistique Harbor, MI and the Fox River, MI. At the latter two sites PCBs were the major concern. The objective of performing detailed studies at a limited number of sites that have been dredged was to gain specific knowledge about the various aspects of the dredging operations in order to develop quantitative chemodynamic process elements for each. The material presented will include brief descriptions of the Fox River site, the dredging technologies used, the monitoring results used for extraction efficiencies of the in-place mud and chemical masses, and the quantities lost by various chemodynamic processes. The development and structural elements of the multimedia model designed to estimate mud and chemical mass quantities extracted and the collateral losses to the surrounding environmental media will be reviewed. Data collected at the Fox River site was used to quantify both the solids and chemical mass balances. Comparison of the model predicted mass quantities and the reported field measured one of extracted and loss material will be made. The model predictions and reported quantities were in general agreement. For the PCBs in Deposit N the model and reported values were: 69% & 82% delivered to shore, 28% & 14% non-targeted, 3% & 4% advection down stream, 0.002% evaporated and 0.006% & 0.02% fall-back.