October 2006 Update
During September 2006, work continued along the Bailey's Branch stream channel to remove impacted soil and sediment from the creek channel and floodplain. The upstream removal contractor has advanced removal of soil and sediment, along the creek channel and floodplain, to approximately 6,300 feet downstream of the Outfall 002 to Broomsage Road. The contractor for the cleanup in the downstream section (north of Broomsage Road), has advanced removal of soil and sediment, along the creek channel and floodplain, to approximately 5,300 feet north of Broomsage Road and will continue in a northerly and westerly direction. To date, more than 682,438 tons of soil, rock and sediment exceeding the cleanup criteria have been removed, tested, and disposed off-Site to permitted landfills, or transferred into the East Plant Area as part of the Interim Measure. Restoration activities will follow behind these removal activities as work progresses downstream. Excavation of impacted soil began on the Western Tributary on the west side of the plant. Excavation of impacted soil on the Norther Tributary is expected to begin soon.
GM is in the process of designing and implementing the Interim Measure (IM) for the GM property east of GM Drive (East Plant Area). The East Plant Area was historically used for plant waste management activities. Components of the IM include soil removal of areas with greater than 50 ppm PCBs (the soil to be placed in an on-Site vault), a cover system to prevent contact with the remaining soil materials and limit rain water infiltration, the use of low-level (less than 50 ppm) PCB soil from the off-Site creek removal work as grading soil below the low permeability cover system, a groundwater collection trench installed downgradient into the bedrock around the northern, eastern, and southern perimeter of this area, and a groundwater source removal system in the former process pond 4 area. Long-term maintenance and monitoring are also part of the selected remedy. Excavation and placement of greater than 50 ppm PCBs soil into the vault was initiated in May 2006 and should be completed in the fall.
GM also has been conducting additional on-Site investigations for the East Plant Area remedy. These investigations have involved further delineation of the fill materials, dye trace studies, and bedrock coring.
Groundwater sampling throughout the Plant property was conducted May through June 2006. Results of the analyses are pending. A dye trace test of the groundwater in the West Plant Area was started to determine potential contaminant migration pathways from the Plant area. Additional dye trace tests will be completed in the future as required, and the results will be incorporated into the final design of the groundwater collection trench. Additional soil testing was completed on the GM property west of GM drive (West Plant Area) to further delineate PCB concentrations.