You are here:
DETERMINING THE EFFECTIVENESS OF DREDGING: FIELD STUDY FOR EVALUATING DREDGING RESIDUALS
Citation:
TIMBERLAKE, D. L., R. C. BRENNER, J. P. SCHUBAUER-BERIGAN, M. MILLS, P. J. CLARK, P. T. MCCAULEY, J. R. MEIER, J. M. LAZORCHAK, E. FOOTE, AND V. MAGAR. DETERMINING THE EFFECTIVENESS OF DREDGING: FIELD STUDY FOR EVALUATING DREDGING RESIDUALS. Presented at Fourth International Conference on Remediation of Contaminated Sediments, Savannah, GA, January 22 - 25, 2007.
Impact/Purpose:
To inform the public.
Description:
Dredging is a commonly selected remedy for the risk management of contaminated sediments. Even so, there are questions regarding both the short-term and long-term effectiveness of dredging. A significant aspect in the performance of dredging is dredging residuals. Post-dredging residuals may consist of material not captured by the dredge, sediment adjacent to the dredge cut that falls into the dredge footprint, suspended sediment that settles into the footprint, and suspended sediment that is transported downstream outside of the dredge footprint. Residuals are influenced by many variables including the type of dredge, the operator's level of experience, the geochemical nature of the contaminated sediment, the hydraulics of the waterway, the physical nature of the sediment bed (e.g., slope, bulk density, grain size distribution), and the presence of debris in/on the sediment bed. One of the current working hypotheses regarding post-dredge residuals is that the contaminant concentration associated with residuals in the dredge footprint will be approximately equal to the average contaminant concentration of the pre-dredge profile. However, limited field data exists to validate this hypothesis. Therefore, U.S. EPA's National Risk Management Research Laboratory (NRMRL) in cooperation with U.S. EPA's National Exposure Research Laboratory (NERL), and the U.S. EPA Great Lake National Program Office (GLNPO), initiated a field research project in the summer of 2006 to evaluate post-dredge residuals in the Ashtabula River, Ohio. Sediments in portions of the Ashtabula River are contaminated with polychlorinated biphenyls (PCBs) and approximately 600,000 cubic yards of contaminated sediments are scheduled to be removed from the river by the end of 2007 under the Great Lakes Legacy Act. An in-field research study is being conducted in parallel with active dredging and will incorporate monitoring before, during, and after dredging activities in the following two fields of interest: portions of the river where dredging will commence to bedrock and portions of the river where maximum dredge depth will be several meters above bedrock. Specific objectives of this investigation include determining (a) how estimates of volume and concentration of post-dredging residuals can be improved; (b) the bioavailability of contaminants in post-dredging residuals; and (c) if conventional characterization techniques can be used to measure residuals. The research described was initiated in 2006 and is ongoing. When completed, findings from this research will be used directly by the Office of Superfund Remediation and Technology Innovation (OSRTI) as well as Regional Remedial Project Managers (RPMs) to select the most effective and environmentally prudent remediation techniques at contaminated sediment sites around the country.