To determine the distribution of contaminants associated with different particle size fractions of the Ashtabula River sediments.
To determine the kinetics of contaminant release from the different sediment components during dewatering of these sediments.
To determine the limits of success that can be expected from the addition of admixtures to the Ashtabula River sediments.
To determine the optimal method for removal of pore water from the Ashtabula River sediments and treatment of the aqueous effluent.
PCB-contaminated sediments from the Ashtabula River will be used for this project. The results and recommendations are expected to be generally applicable to similar future cleanup efforts in the Great Lakes region.

Contaminated sediments are a serious problem in 42 of the 43 Great Lakes Areas of Concern (AOCs). In most cases, dredging and disposal is the most attractive remedial option, as opposed to a contaminant-specific cleanup method, due to the wide variety of contaminants in the sediments. A typical example is the two-mile stretch of the lower Ashtabula River and Harbor, designated as an AOC in 1985 due to heavily contaminated sediments. The main contaminants of concern are polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), and heavy metals (mercury, cadmium, lead, zinc). Most of the Ashtabula sediments are too contaminated for reuse or open-lake disposal. As such, confined disposal facilities (CDFs) are planned for sediment dewatering and final disposal. The Ashtabula River cleanup effort is representative of the many future similar actions that will be needed in the Great Lakes region.

The objective of this proposal is to perform experimental tests and numerical simulations to evaluate possible methods for dewatering of dredged sediments from the lower Ashtabula River in Ashtabula, Ohio. This information is needed to better and more economically remediate the Ashtabula River and similar contaminated sediment sites in the Great Lakes region. This information will also be useful for upcoming remediation work expected to result from the Great Lakes Legacy Act. The proposed research would, for the first time, quantitatively estimate contaminant releases that occur during sediment dewatering. The results from this project will allow project managers to make better decisions regarding the use of dredging, dewatering, and treatment for remediation of contaminated sediment sites.

The proposed research is intended to identify the most efficient and/or cost-effective means to dewater a large mass of high water sediment contaminated primarily with PCBs. In most cases, dredging and disposal is chosen for sediment cleanups in the Great Lakes region due to the wide variety of sediments in each system. The dredged sediments will typically have a high water content and must be dewatered to meet the legal requirements for no disposal of free liquids in a landfill. This research is important because sediment dewatering is expensive and typically represents one of the greatest technical challenges for a dredging and disposal operation. At the Ashtabula River site, sediment dewatering is expected to cost $4.9M of the total $37.2M in construction costs for the project. Little information is currently available on the best technology for sediment dewatering and treatment of the resulting aqueous effluent. This information is needed for the many future sediment dredging and disposal activities that will occur in the Great Lakes region.

Task 1: Determine baseline geotechnical and environmental properties of sediment and sediment pore water.

Task 2: Evaluate contaminant mass-transfer from sediment solids to pore water.

Task 3: Perform laboratory experiments to evaluate sediment dewatering properties and methods.

Task 4: Perform numerical simulations for dewatering methods.

Task 5: Analysis of results and final report.

In discussions with representatives from the Ohio Environmental Protection Agency (OEPA), Ohio Sea Grant, the U. S. Army Corps of Engineers (USACE), and the Ashtabula River Partnership (ARP), we have identified the following key questions that need to be answered to increase the likelihood for economic and successful dewatering of PCB-contaminated sediments within the Great Lakes region:

1. What is the most efficient and/or cost effective process to dewater a large mass of high water content contaminated sediment? *For a confined disposal facility (CDF), how long will the consolidation process take? *What CDF capacity ratio is needed, considering the consolidation of the sediments over time? *What is the best design for the CDF(s), including drainage provisions and filling procedures? *Is there a superior method of dewatering (centrifugation, filter press, vacuum, admixtures, etc.) instead of CDFs that would be more cost-effective?
2. What will be the fate of contaminants during the dewatering process? *Will contaminants remain sorbed to the solids or be released with the water effluent in either dissolved or colloidal form? *What is the best means to treat the aqueous effluent to meet project guidelines?

The research conducted for this project is intended to produce experimental data and numerical modeling results that will help to answer these questions.