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Dredging, Water Quality Monitoring, and Hydrographic and Geophysical Survey

Dredging, Water Quality Monitoring, and Hydrographic and Geophysical SurveyIntegral scientists characterized water quality and bathymetric variability as part of an EPA-led evaluation of the Ashtabula River Environmental Dredging Project. The dredging project was performed to remove PCB-contaminated sediments from the Ashtabula River, which is one of 43 contaminated sites on the Great Lakes in Ohio that has been a designated Great Lakes Area of Concern by the United States and Canada since 1987. Contamination from industrialization and unregulated discharges dates back to the 1940s and includes PCBs, PAHs, mercury, and other heavy metals. Dredging was selected as the remedy in the site’s remedial action plan.

In 2007, EPA implemented a research program to evaluate the efficacy of environmental dredging in removing large quantities of PCB-contaminated sediment. Integral personnel, working with Sea Engineering Inc. and Battelle, collected fixed and mobile current profiles and water quality measurements upstream and downstream of the hydraulic dredging operations. In addition, the team deployed water quality moorings upstream and downstream of the dredge region to measure background conditions at the project extents. The moorings also acted as boundary conditions for hydrodynamic and sediment flux modeling of river conditions during dredging.

The team performed initial, progressive, and final multibeam and side-scan sonar surveys during the project to locate dredge cuts and measure residual sediment depths. Daily multi-beam surveys identified dredge progression, allowing quantification of residual sediments. Notable submarine features and hazards, including dredge cut lines, and locations requiring additional dredging were identified from survey data.

This state-of-the-art approach was effective in plume monitoring, which can minimize work stoppage due to false plume detection. Bathymetric surveys conducted before, during, and after dredging helped to identify and minimize dredge residuals. In addition, the evaluation helped to quantify the magnitude and extent of dredge residuals due to resuspension.

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