St.Lawrence River Remediation Project
United States Environmental Protection Agency (USEPA) issued the Explanation of Significant Differences (ESD) in December 2008 explaining the proposed activities for the St. Lawrence River adjacent to the Alcoa East Facility (formerly known as Reynolds) for the 2009 Remedial activities. In summary, this document pointed out the majority of the proposed river construction activities for 2009, which would include a large Capping component to complete the original 2001 St. Lawrence River Remediation Project (SLRRP) efforts.
In 2001, 268 cells were dredged to meet clean-up goals for PCBs, PAHs, and TDBFs (contaminants determined to pose a risk to the environment and/or human health). In 2001, post-monitoring sampling indicated that removal of PCBs had achieved a 98.6% reduction, and over 90% reduction in PAHs. Despite this successful removal action, 12 cells still had PCB concentrations above the clean-up goal of 1 mg/kg, and 76 cells above the PAH clean-up goal of 10 mg/kg (after additional sampling efforts in 2002-2006 to further delineate the PAH concentrations remaining). The USEPA December 2008 document changed the PAH clean-up trigger value from 10 mg/kg to 20 mg/kg for 2009 activities based on lines of scientific evidence of low-molecular weight polycyclic aromatic hydrocarbons (PAHs). Based on this change of trigger value, additional cells with PAH elevated levels were reduced to 53 cells that needed additional attention. See December 2008 USEPA ESD.(3.3 MB PDF File)
2009 St. Lawrence River activities include capping with clean material over 15 cells that had exceeded the PCB clean-up level and 53 cells which exceeded the PAH clean-up goal (3 of those cells to include nearshore excavation prior to cap). A cap design includes a layer of clean sand as an isolation layer and armor stone on top of that to protect the isolation layers from ice, wave, and water erosion. As a final addition, a 6-inch layer of “habitat” will be added on top of the armor layer to help facilitate re-rooting of vegetation in the area of the cap. A total of 3.5 acres will be “capped”, with an engineer designed cap to prevent distribution of underlying material.
In May 2009, Alcoa’s contractors mobilized to site with excavation and capping activities beginning in June 2009. A Mobile Capping Cell (MCC) was developed specifically for this project to facilitate placement of clean material with a “rolling hopper” to displace the cap material. The MCC also included turbidity control curtains surrounding the barges to help control suspended material. Capping placement was verified though electronics and manual surveys.
Although all material placed in the river was tested prior to river placement and determined to be “clean”, additional environmental monitoring activities were conducted to ensure excessive turbidity, total suspended solids, PCBs, and PAHs were not impacting the water quality in the river or nearby water intakes. Visible turbidity was noted almost daily from the capping activities, but water monitoring data indicated threshold levels were not exceeded, and contaminants were not displaced downstream.
An additional unit, the Habitat Capping Cell (HCC), was utilized to facilitate shallow-water capping and habitat material placement.
In-river activities are expected to be complete by October 2009. Please feel free to contact Jessica Jock, SRMT Superfund Project Coordinator for any questions regarding the St. Lawrence River Remediation Project (SLRRP). 518-358-5937 ext. 135.
- US EPA - Explanation of Significant Differences - Reynolds Metals Company Site- December 2008 - (3.3MB)
- Printer friendly version of this Article - (109 KB)
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