The three primary options available for addressing the PCBs in sediments are provided below. These options can be used alone or in combination.
- Natural recovery of the river through natural processes such as ongoing sedimentation. In this solution, natural processes such as burial by clean sediments that enter the river from upstream isolate contaminants from fish and other organisms. A routine monitoring program is established to measure changes in PCB levels in fish and other media over time.
- Capping of sediments which contain PCBs. In this method, clean material such as a sand and topsoil mixture is placed over the contaminated sediments, isolating contaminants from fish and other organisms in order to accelerate system recovery. The cap is designed and built to withstand various flow conditions specific to the river. Gravel and/or larger stones may be part of the cap depending on flow conditions. Long-term monitoring is conducted to ensure the cap is effective and remains in place.
- Removal (dredging) of sediments that contain PCBs. In this process, mechanical and/or hydraulic dredging equipment is used to remove sediments from the river. A containment system such as silt curtains is installed to help control resuspension to other areas of the river. The removed sediments and water are separated, and the water stream is treated and discharged. The contaminated sediments are typically stabilized and placed in a constructed onsite landfill or taken to a permitted offsite landfill. Under the sponsorship of EPA, the National Academy of Sciences (NAS) completed a study to evaluate the effectiveness of dredging as a remedial option. NAS reviewed a total of 26 environmental dredging projects through the United States, including two removal projects conducted in the Grasse River. This document entitled Sediment Dredging at Superfund Megasites: Assessing the Effectiveness was released in June 2007 and presents an analysis of available information regarding the effectiveness of dredging as a remedial option for the management of contaminated sediments.
Arconic (formerly Alcoa) has pilot tested these options at the Grasse River. These options were further evaluated in the Analysis of Alternatives, and EPA selected the cleanup for the river in the Record of Decision. See Project History for more information.