February 2008 Update
- Creek soil excavations/restoration
- Groundwater migration controls & investigations
- On-site activities
Creek soil excavations/restoration
- Work continues along the Pleasant Run/Bailey's Branch stream channel to remove impacted soil and sediment from the creek channel and floodplain.
- Creek restoration is nearly complete from the facility to Broomsage Road.
- Restoration north of Broomsage Road to Peerless Road is partially completed and will continue in 2008.
- The culvert bridge over the creek at Broomsage Road has been removed, the creek in the area excavated, and the bridge replaced.
- Excavations are nearing completion downstream of Peerless Road and restoration plans are being finalized in consultation with the U.S. Fish & Wildlife Service, the Indiana Department of Environmental Management, and the Indiana Department of Natural Resources.
- Excavation of impacted soil was completed on the Western Tributary on the west side of the plant and those excavations have been restored.
- Excavation of impacted soil on the Northern Tributary (North of Breckenridge Road) has been completed and restoration as a ravine similar to original, pre-filling conditions is expected to begin soon.
- To date, more than 1.3 million tons of soil, rock and sediment exceeding the cleanup criteria have been removed, tested, and disposed off-Site to permitted landfills, or transferred into GM's East Plant Area as part of the Interim Measure.
Groundwater migration controls & investigations
GM currently samples approximately 40 spring locations on a quarterly basis. Groundwater seeps or springs where PCBs have been detected are being collected at 17 locations and treated at a newly constructed treatment facility on the GM property.
Locations of the monitored springs and control systems are in the Site Source Control Work Plan Addendum No. 6 (September 2007) (PDF) (41pp, 19.7MB, About PDF)
These individual groundwater collection systems were installed to collect impacted groundwater until a groundwater collection trench is cut into the competent bedrock surrounding the eastern portion of the facility. This groundwater collection trench will intercept bedrock groundwater flowing horizontally from the east portion of the facility.The design of the collection trench is in progress and GM is installing new bedrock cores along the southeast side of the GM property to guide trench installation in that area.
GM also continues to investigate a larger spring to the south of Broomsage Road (Spring 18 Area) and is developing a proposal to address this spring. The investigation work plan for Spring 18 are in the Site Source Control Work Plan Addendum No. 5 (November 2006) (PDF) (34pp, 9.6MB, About PDF)
GM is implementing the Interim Measure (IM) for the 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 placed in an on-Site double-lined vault with an underlying groundwater collection system)
- a multi-layer 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.
GM has started installing the multi-layer cover system at the East Plant Area. The clean clay layer has been placed over areas which are at final grade and will continue as remaining areas are completed.
A work plan to install a system of active groundwater source recovery wells in the former process pond 4 area is being developed. This area formerly held two cascading water ponds which collected the PCB hydraulic fluid from the plant. PCB oils have been found in a few bedrock cores in this area and the recovery wells will be installed to attempt to remove as much oil and affected groundwater as possible.
Additional soil testing was completed on the GM property west of GM drive (West Plant Area) to further delineate PCB concentrations. An IM for portions of the West Plant Area is being developed. Project progress reports, electronic documents and work plans can be found at the online document repository