Unnamed Tributary PCB Sediment Remediation
Date of Execution: January 1998
Significant Project Features:
- Excavation, stabilization, transportation, and disposal of PCB-contaminated soils and sediments.
- Construction of a permanent sheetpile cofferdam along the Ottawa River mouth to isolate the Unnamed Tributary.
- Construction of temporary sheetpile cutoff walls as protective shoring in excavation areas.
- Construction of a concrete headwall and permanent maintenance road.
History and Location of Project
In 1998, Sevenson Environmental Services, Inc., was contracted to perform a polychlorinated biphenyl (PCB) sediment remediation project at the Unnamed Tributary Site in Toledo, Ohio. The site is located within the city of Toledo, Ohio, north of U.S. 75 and between LaGrange and Stickney Avenues.
The Unnamed Tributary is bordered by a low-lying wetland area extending to the west. The east bank of the Unnamed Tributary is lined with steep, vegetated soil banks. The Unnamed Tributary was historically an oxbow in the main channel of the Ottawa River, which has since been rechannelized and the oxbow abandoned and partially filled. The remaining, unfilled portion of the old oxbow (the Unnamed Tributary) conveys storm water to the Ottawa River and is approximately 975 feet long and 90 feet wide at its mouth.
Description of Work
Remedial action at the Unnamed Tributary Site was preceded by site preparation work. Remediation was then conducted in two distinct phases, which were followed by site restoration. Sevenson's work in these tasks included:
Site Clearing and Preparation. Before starting remedial action work at the Unnamed Tributary Site, Sevenson implemented extensive site-preparation activities to minimize the potential for any disturbance or release of PCB-contaminated sediments during their removal. First, Sevenson constructed large earthen berms around sediment excavation areas to allow for site dewatering and prevent flooding from high water or lake seiche events. Sevenson utilized on-site borrow material to construct the berms and designed them to serve first as access roads and later as a source of grading and backfill material during site restoration. This multi-function design of the berms resulted in significant cost savings to the client. Sevenson then constructed a new storm-water drainage swale to redirect storm water and surface water flow directly to the Ottawa River from the existing 96-inch, 54-inch, 30-inch, and 12-inch storm sewer pipes on the site. Finally, Sevenson completed its site preparation work by constructing an excavated sediment and equipment staging area and installing a pug mill and on-site wastewater treatment plant.
Phase I: Water Diversion and Sediment Excavation, Handling, and Disposal. As a continuation of the site preparation work involving the storm sewer rerouting, Sevenson began Phase I work by removing approximately 2,000 cubic yards of sediment (adjacent to the 96-inch, 54-inch, and 30-inch storm sewer outfalls) containing the highest reported PCB concentrations, dewatering them, and disposing them off site in a permitted, secure landfill. Sediment excavation was conducted by first installing sheet piling and berms around a manageable reach of the Unnamed Tributary and dewatering this contained reach. Standing water was discharged to the Ottawa River and residual water routed to the on-site water treatment system.
Once dewatered, Sevenson removed the sediments to pre-established excavation limits. Water infiltration to the excavation areas was controlled, and the sediments were effectively dewatered in place, allowing their removal to occur essentially in a dry state. Due to the absence of standing water and the dense, cohesive nature of the sediments and underlying clay, distinct layers of sediment were effectively removed by Sevenson with little or no contamination of the cleaner, underlying material during removal. Phase I activities also included construction of a sheet pile dam at the mouth of the Unnamed Tributary to physically isolate it from the Ottawa River. Taken together, Phase I activities effectively prevented the Unnamed Tributary from acting as any sort of surface-water flow channel for contaminants during the sediment-removal process.
Phase II: Additional Remedial Activities. Sevenson's work during Phase II included the additional removal of PCB-containing materials from the remainder of the Unnamed Tributary and the adjacent low-lying area, with subsequent covering and restoration through the placement of clean fill. In total, Sevenson excavated 8,000 cubic yards of PCB-contaminated sediment, and 1,650 cubic yards of soil were excavated, segregated, stabilized in a pug mill, and transported off site for disposal in a secure landfill.
Restoration. Following completion of the Phase II sediment and soil excavation activities, Sevenson leveled the berms created during site preparation and used the berm material and additional on-site borrow material for placement into the Unnamed Tributary. This fill material was compacted to effectively eliminate the tributary as a flow channel to the Ottawa River. The site was then regraded, fenced, and shaped, and topsoil was placed and hydroseeded with a wetland seed mix to construct an on-site wetland.
Health and Safety Overview:
- Unique Characteristics: Personal protective equipment was required for employees on the Unnamed Tributary Site because PCB levels ranged up to 74,000 ppm.
- Health and Safety Measures: Workers utilized Modified Level C protection during hazardous waste removal operations.
- Health and Safety Staff: Paul J. Hitcho, PhD, CIH, was responsible for the development and oversight of the Unnamed Tributary Site health and safety plan. Ken Walters was Sevenson's on-site Health and Safety Officer and was responsible for the day-to-day implementation and enforcement of the plan.
- How 40-Hour Training Was Implemented: Sevenson performs both 40-hour and 8-hour Occupational Safety and Health Administration (OSHA) training in house for all company employees.