Accumulated soft sediment of the lower Ashtabula River in Ashtabula, Ohio, was contaminated with organic chemicals such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), heavy metals and some low level radionuclides. The Ashtabula River Remediation, a two phase project which began in 2006 and was completed in 2008, utilized hydraulic dredging in conjunction with geotextile tube dewatering to remove, dewater and dispose of the unwanted sediment. Geotextile tube dewatering technology was very successfully applied in this project, providing an innovative, cost-effective dewatering and disposal option for heavily contaminated soft sediment.
The scale of the Ashtabula River Remediation, the largest Great Lakes Legacy Act funded project to date, was enormous. Over the course of the project, performed in two phases over three dredging seasons, about 640,000 cubic yards of contaminated sediment were removed from the river. Infrastructure Alternatives was contracted by the general contractors of both Phase I & II of the project to design, operate and maintain the sediment dewatering system and was additionally responsible for operation of chemical addition and water treatment processes during Phase II of the project.
Contaminated sediment was removed from the river utilizing a 12 inch diameter hydraulic cutter head dredge. (The dredging contractor was J.F. Brennan Company of LaCrosse, Wisconsin.) The sediment transfer pipeline delivered the sediment slurry from the dredge to the sediment Consolidation Facility (CF), where it was dewatered in geotextile tubes. The CF was a 12.5 acre landfill, permitted under the Toxic Substances Control Act (TSCA), and constructed specifically for the Ashtabula River Remediation project. The CF was designed not only to provide a dewatering site, but also a permanent disposal site for the dewatered sediment. At the conclusion of the project, the CF was prepared for capping and closure.
Geotextile tubes were used to dewater the dredged sediment slurry. As the slurry arrived at the CF, flowing at a rate of up to 5,000 gallons per minute, it was directed through a header system to geotextile tubes which were filled in place inside the CF. By project’s end, geotextile tubes had been filled and stacked in ten layers, forming a pyramid shape inside the CF. Weep water (clear water released from the geotextile tubes) drained by gravity to a sump in the CF floor and was processed in an on-site water treatment plant before being discharged back into the Ashtabula River.
Due to the contamination present in the dredged sediment, Infrastructure Alternatives’ entire project staff of approximately 50 personnel were OSHA 40-hour Hazardous Waste Operations and Emergency Response (HAZWOPER) certified and also received Radiation Worker II training on site.